1.

Introduction
ASD is a complex neurodevelopmental, biologically based condition with an estimated
prevalence of 1 in 44 people [1] that impacts all areas of child development — from
behaviour, problem solving abilities and self-care skills, to complex social communication
ability, language, and executive functioning skills. The range of symptoms and severity of
ASD vary greatly from child to child, and clinical manifestations depend on the individual’s
age, cognitive and language abilities, and co-occurring conditions.
The last revision of the Diagnostic and Statistical Manual (DSM-5) defines ASD as
impairments in two main domains:
(1) social communication and interaction, which comprises challenges in social-emotional
reciprocity, challenges in using nonverbal strategies during social interaction, and challenges
developing, maintaining and understanding relationships, and
(2) restricted, repetitive, and stereotyped patterns of behaviours, manifested by unusual
repetitive movements or behaviours, restricted interests, insistence on sameness and
inflexible adherence to routines, as well as sensory challenges ranging from seeking to
avoiding certain sensory stimuli [2–4].
Proposed DSM-5 ASD criteria include three severity classifications: Level 1 (“Requiring
support”), Level 2 (“Requiring substantial support”), and Level 3 (“Requiring very
substantial support”) [5]. Prescribers often describe or identify level 1 as mild ASD, level 2
as moderate ASD, and level 3 as the most severe form of ASD [6,7].
It is a group of neurodevelopment disorders known as pervasive developmental disorders
(PDD). These disorders are characterized by three core deficits: impaired communication,
impaired reciprocal social interaction and restricted, repetitive, and stereotyped patterns of
behaviours or interests. In 1943, the American psychiatrist Leo Kenner used the term “early
infantile autism” to describe children who lacked interest in other people.[8] In 1944, an
Austrian paediatrician, Hans Asperger, independently described another group of children
with similar behaviours, but with milder severity and higher intellectual abilities. Since then,
his name has become attached to a higher functioning form of autism, Asperger syndrome. It
was not until the 1980s that the term pervasive developmental disorders were first used [9].
Medical comorbidities are more common in children with ASD than in the general population
and can include epilepsy, macrocephaly, cerebral palsy, migraine/headaches, congenital
abnormalities of the nervous system, gastrointestinal disorders, sleep disorders, allergic
disorders, and persistent neuroinflammation [10]. According to the World Health
Organisation (WHO), approximately 1 in 100 children have ASD; however, these figures
could be substantially higher based on results from additional well-controlled studies and the
absence of ASD statistics in various low and middle-income countries [11]. In South Africa,
accurate local statistics for ASD are not available but it has been estimated that between 1%
and 2% of the population may be affected by ASD [12].

2.Epidemiology:
ASD occurs more often in boys than girls, with a 4:1 male-to-female ratio. [12] The reported
prevalence rates of autism and its related disorders have been increasing worldwide over the
past decades, from approximately 4 per 10 000 to 6 per 1000 children. [13-17] Globally,
autism is estimated to affect 24.8 million people as of 2015.[18] In the 2000s, the number of
people affected was estimated at 1–2 per 1, 000 people worldwide.[19]
3.Sign and symptoms:
➢ Behavior:
• Has inexplicable tantrums
• Has unusual interests or attachments
• Has unusual motor movements such as flapping hands or spinning
• Has extreme difficulty coping with change
➢ Sensory:
• Afraid of some everyday sounds
• Uses peripheral vision to look at objects
• Fascination with moving objects
• High tolerance of temperature and pain
➢ Communication:
• Not responding to his/her name by 12 months
• Not pointing or waving by 12 months
• Loss of words previously used
• Speech absent at 18 month
• No spontaneous phrases by 24 months
• Selective hearing – responding to certain sounds but ignoring the human voice
• Unusual language patterns (e.g. repetitive speech)

➢ Social skills:
• Looks away when you speak to him/her
• Does not return your smile
• Lack of interest in other children
• Often seems to be in his/her own world
• Does not seek to share interests with others
➢ Play:
• Prefers to play alone
• Very limited social play (e.g. “Peek-a-boo”)
• Play is limited to certain toys
• Plays with objects in unusual ways such as repetitive spinning or lining up
• Shows very strong interest in or attachment to a limited number of games or toys[20]

4.Causes of autism:
The exact cause of ASD is unknown. The most current research demonstrates that there’s no
single cause. Some of the suspected risk factors for autism include:
 having an immediate family member with autism
 genetic mutations
 fragile X syndrome and other genetic disorders
 being born to older parents
 low birth weight
 metabolic imbalances
 exposure to heavy metals and environmental toxins
 a history of viral infections
  fetal exposure to the medications valproic acid (Depakene) or thalidomide (Thalomid)
[21,22,23]

According to the National Institute of Neurological Disorders and Stroke (NINDS), both
genetics and environment may determine whether a person develops autism.
Types of ASD:
There are three different types of Autism Spectrum Disorders:
▪ Autistic Disorder: (also called "classic" autism) This is what most people think of when
hearing the word "autism." People with autistic disorder usually have significant language
delays, social and communication challenges, and unusual behaviors and interests. Many
people with autistic disorder also have intellectual disability.
▪ Asperger Syndrome: People with Asperger syndrome usually have some milder
symptoms of autistic disorder. They might have social challenges and unusual behaviors and
interests. However, they typically do not have problems with language or intellectual
disability.
▪ Pervasive Developmental Disorder: Not Otherwise Specified (PDD-NOS; also called
"atypical autism") People who meet some of the criteria for autistic disorder or Asperger
syndrome, but not all, may be diagnosed with PDD-NOS. People with PDD-NOS usually
have fewer and milder symptoms than those with autistic disorder. The symptoms might
cause only social and communication challenges. [24,25,26]

5.DIAGNOSIS:
Diagnosis is based on behavior, not cause or mechanism.[27,28] Under the DSM-5, autism is
characterized by persistent deficits in social communication and interaction across multiple
contexts, as well as restricted, repetitive patterns of behavior, interests, or activities. These
deficits are present in early childhood, typically before age three, and lead to clinically
significant functional impairment.[29] Sample symptoms include lack of social or emotional
reciprocity, stereotyped and repetitive use of language or idiosyncratic language, and
persistent preoccupation with unusual objects. Several diagnostic instruments are available.
Two are commonly used in autism research: the Autism Diagnostic Interview-Revised (ADI-
R) is a semi structured parent interview, and the Autism Diagnostic Observation Schedule
(ADOS)[30] uses observation and interaction with the child. The Childhood Autism Rating
Scale (CARS) is used widely in clinical environments to assess severity of autism based on
observation of children. [31] The Diagnostic interview for social and communication
disorders (DISCO) may also be used. [32] Although the symptoms of autism and ASD begin
early in childhood, they are sometimes missed; years later, adults may seek diagnoses to help
them or their friends and family understand themselves, to help their employers make
adjustments, or in some locations to claim disability living allowances or other benefits. Girls
are often diagnosed later than boys. [33]
6.Pathophysiology:
➢ Autism mechanism can be divided into two areas: the pathophysiology of brain structures
and processes associated with autism, and the neuropsychological linkages between brain
structures and behaviours.[34] The behaviours appear to have multiple pathophysiologies.
[35] How autism occurs is not well understood.
➢ A 2015 review proposed that immune dysregulation, gastrointestinal inflammation,
malfunction of the autonomic nervous system, gut flora alterations, and food metabolites may
cause brain neuroinflammation and dysfunction.[36] A 2016 review concludes that enteric
nervous system abnormalities might play a role in neurological disorders such as autism.
Neural connections and the immune system are a pathway that may allow diseases originated
in the intestine to spread to the brain.[37] Several lines of evidence point to synaptic
dysfunction as a cause of autism. Some rare mutations may lead to autism by disrupting some
synaptic pathways, such as those involved with cell adhesion. [38]
➢ All known teratogens (agents that cause birth defects) related to the risk of autism appear
to act during the first eight weeks from conception, and though this does not exclude the
possibility that autism can be initiated or affected later, there is strong evidence that autism
arises very early in development. [39]
➢ Autism affects the amygdala, cerebellum, and many other parts of the brain.[40]
7.STRATEGIES FOR ASD TREATMENT
Therapeutic interventions for a complex disorder like ASD need to be multi-directional.
Available treatment strategies were divided based on the species and the stage of research:
humans (clinical research and practice) and rodents (basic and translational research) (Fig. 1).
No single strategy claims to be a multifaceted solution to the diverse symptomatology of
ASD. As such, each one is used for single-target modifications in standalone issues
recognized in ASD pathogenesis.
It is suggested to divide treatment strategies in humans into three groups: current,
promising, and perspective (Table 1). Current/basic: These therapies were studied and
continue to be verified through expanding research efforts. Most of the strategies in this
group are safe and recommended for current clinical use. Promising: Strategies in this group
still need to be approved for clinical use but show good signs for the near future after ample
research evidence is published and verified. Perspective: Strategies here are considered the
cutting-edge of current scientific research. As such, they have a tempting quality to be
regarded as complete treatment strategies. However, as studies need to support their safety
and viability in clinical practice, they cannot be included in the current recommendations.
Research on treatment strategies that potentially improve the quality of life for people with
ASD is ongoing. Newer, safer, and potential aches are still under development. Treatment
must be initiated as soon as possible, and specific therapies must be chosen for each case.
Herein, treatment strategies undergoing rigorous testing and research are presented. Some are
still being tested in animal models to establish their safety levels; others are approved for
testing in human cohorts worldwide.
Table 1. Classification of suggested ASD treatment strategies in humans.
Improvement of E/I Imbalance
Risperidone
Glutamate modulators
NMDA-receptor modulators
GABA-receptor agonists
rTMS
Oxytocin
Improvement of Mitochondrial Dysfunction
Antioxidants
L-Carnosine
L-Carnitine
Butyrate
Resveratrol
Rapamycin
Regulation of Methylation
B12, B9
GI Regulation /Restoring Gut Microbiota
Current/basic strategies Microbiota Transfer Therapy (MTT)
Probiotics / Prebiotics
 PPA Corrections through Biofilm Treatment
Dietary Corrections (GFCFD, KD)
Chelation Therapy
DMSA
Anti-Inflammatory Treatment
NSAIDS
Vitamin D
HBOT
Vitamin and Mineral Supplementation
Zinc and Copper
Selenium
Magnesium and Calcium
Vitamin A, C, D, E, B1, B6, B9 and B12
Tryptophan and supplementation
Promising strategies Immunotherapy
IVIg
Treatment with cannabinoids
Prospective strategies Cellular therapy

8.Improvement of excitation and inhibition imbalances

Key Mechanisms of Excitation-Inhibition (E/I) Imbalance in Autism Spectrum Disorder

(ASD)

1. Genetic Mutations: Mutations in scaffolding proteins like SHANK-3 and synaptic

cell adhesion molecules such as NLGN3, NLGN4, and NRXN1 disrupt synaptic
function, contributing to E/I imbalance in ASD [41].
2. Disruptions in Neural Signalling Pathways: Impaired function of Parvalbumin
(PV)-positive inhibitory neurons reduces cortical plasticity and disrupts gamma
oscillations in the neocortex and hippocampus, further exacerbating imbalance [42].
3. Alterations in Neuronal Network Development: Disturbances in the GABAergic
pathway, critical for synaptic tuning and proper neuronal wiring, result in abnormal
neuronal network construction [43].
4. GABAergic and Glutamatergic Dysfunction: Evidence suggests a link between
ASD and disruptions in both GABAergic and glutamatergic receptors, which play
key roles in maintaining neuronal balance [44].

Strategies for Addressing E/I Imbalance

1. Direct Interventions: Utilizing agents that directly target GABA and glutamate
systems to restore balance.
2. Indirect Interventions: Approaches that address secondary issues such as:
• Mitochondrial dysfunction
• Impaired methylation
• Gut microbiota dysregulation

Zinc (Zn) and Copper (Cu) in Modulating E/I Balance

1. Zinc:
 • Approximately 10% of total brain Zn resides in synaptic vesicles of
glutamatergic neurons.
• Zinc plays a role in regulating GABAergic inhibition, reducing seizure
susceptibility, and maintaining anxiolytic effects.
• Zn deficiency has been shown to impair GABAergic function [45].

2. Copper:
o Copper is a strong inhibitor of GABA-evoked responses, particularly
affecting Purkinje cells.
o By interacting with Zn and the GABAA receptor complex, copper modulates
synaptic transmission [45].

Relevance for ASD Treatment: Due to their regulatory roles in the GABAergic and
glutamatergic systems, maintaining appropriate levels of Zn and Cu is crucial. Balancing
these metals may enhance synaptic function, improve neuronal communication, and
contribute to addressing E/I imbalances in ASD [45].

8.1. Dopamine and Serotonin Receptor Antagonist - Risperidone

The pharmacological management of autism spectrum disorder (ASD) has primarily aimed at
addressing behavioural symptoms such as aggression, self-injury, and hyperactivity.
Although typical antipsychotics are effective in alleviating repetitive behaviours, tantrums,
and hyperactivity while improving social interactions, their use is often limited due to the
presence of unwanted extrapyramidal effects (UEE). Atypical antipsychotics, however, show
similar efficacy in managing these symptoms while presenting a lower risk of UEEs [46].
Additionally, the evaluation of medications in ASD is complicated by movement disorders,
which may be intrinsic to the condition or arise because of treatment, making it difficult to
assess the effectiveness of therapies on unusual stereotypic behaviours [46].

Risperidone (Risperdal) is an FDA-approved atypical antipsychotic with significant potential

for behavioural management in ASD. It has demonstrated a high safety profile in conditions
such as bipolar I disorder, psychosis, depression with psychotic features, and acute or chronic
schizophrenia, as well as in autistic disorder [47]. Its chemical structure includes a
tetrahydropyrido[1,2-a]pyrimidin-4-one scaffold connected via a piperidine moiety to a
benzisoxazole nucleus. This design enables risperidone to act as a combined antagonist of
dopamine D2 and serotonin 5-HT2A receptors [48].

Risperidone is among the few FDA-approved medications specifically indicated for

managing irritability in children with ASD aged 5 to 16 [49]. The dosage is weight-
dependent, typically beginning with a lower starting dose that is gradually increased to the
target dose before tapering off after the prescribed course of therapy [49-51]. Some studies
recommend an additional four-week extension for patients showing continued improvement
and willing to proceed with treatment [52,53].

Clinical studies on risperidone have employed various ASD assessment tools, including the
Aberrant Behaviour Checklist (ABC), Clinical Global Impression-Severity (CGI-S), Clinical
Global Impression-Improvement (CGI-I), and Children’s Global Assessment Scale (C-GAS).
On average, risperidone has performed well across these parameters, with experimental
groups demonstrating noticeable and consistent improvements in behaviours and mannerisms
associated with ASD. However, dropout rates in both experimental and placebo groups were
observed across studies, which may contribute to the ongoing difficulty in reaching a
consensus on an optimal pharmacological treatment for ASD-related behavioural symptoms
[46, 49-53].

8.2. Glutamate Modulating Medications

Emerging treatments targeting glutamatergic neurotransmission are gaining attention as

research increasingly suggests a critical role of glutamatergic dysfunction in autism spectrum
disorder (ASD). Evidence from peripheral biomarkers, neuroimaging, protein expression
studies, genetics, and animal models supports the connection between glutamate
dysregulation and ASD. Medications that modulate glutamate, originally developed for other
disorders, are now being repurposed for ASD. For example, the valproic acid (VPA) animal
model of ASD demonstrates excitatory/inhibitory (E/I) imbalances caused by increased
differentiation of glutamatergic neurons and reduced GABAergic neuron populations [54].

Agmatine, an endogenous polyamine synthesized from arginine, is a promising candidate for

repurposing in ASD treatment. It has been implicated in the pathophysiology of several
disorders, including anxiety, depression, and schizophrenia [55, 56]. Agmatine exhibits
various therapeutic properties, including anticonvulsant, neuroprotective, antiapoptotic,
antioxidant, anxiolytic, and antidepressant effects [57]. It also inhibits the nitric oxide
synthase enzyme and acts as an antagonist at NMDA alpha-2 and imidazoline receptors [57].
Experimental studies suggest that agmatine can alleviate ASD-like symptoms by addressing
E/I imbalances. In the VPA animal model, a single regimen of agmatine treatment improved
impaired social behaviours and reduced hyperactivity and repetitive behaviours [57].
Notably, patients with ASD have significantly lower levels of agmatine, suggesting that its
deficiency may contribute to ASD pathogenesis and highlighting its potential as a therapeutic
target [55, 57].Another approach to reducing excitatory neurotransmission involves inhibiting
metabotropic glutamate 5 (mGlu5) receptors using negative allosteric modulators. For
instance, the mGlu5 receptor antagonist 2-methyl-6-(phenylethynyl)-pyridine (MPEP) has
been studied in the BTBR mouse model of ASD. Acute treatment with MPEP in this model
successfully decreased repetitive behaviours in BTBR mice, demonstrating its potential as a
therapeutic strategy (Silverman et al. 2012) [58].

8.3. NMDA Receptor Modulators

The N-methyl-D-aspartate (NMDA) receptor, a subtype of glutamate receptor, plays a vital
role in synaptic plasticity and is essential for learning and memory. Research suggests that
disruptions in NMDA receptor signaling may be involved in the development of ASD
(autism spectrum disorder) [59].
Memantine, an NMDA receptor modulator, has been explored as a potential treatment for
ASD. It functions by inhibiting excessive NMDA receptor activity, potentially helping to
restore the balance between excitatory and inhibitory signals in the brain. Clinical trials
assessing memantine's efficacy in treating ASD have yielded mixed outcomes [60–62].
Additionally, other NMDA receptor modulators are under investigation for their therapeutic
potential in ASD. For instance, d-cycloserine, a partial agonist of NMDA receptors, has
demonstrated improvements in social interactions and reductions in repetitive behaviors in
animal models of ASD [63–65]. However, further studies are necessary to confirm whether
these effects translate to human populations.
The exploration of NMDA receptor modulators as a treatment option for ASD remains
ongoing. More comprehensive research is required to fully assess their efficacy and safety in
individuals with ASD.
8.4. GABA Receptor Agonists
GABA receptor agonists are being studied as potential treatments for ASD [66]. Research
using Fragile X mouse models (Fmr1-knockout) has revealed a reduction in GABAergic
input across various brain regions, leading to diminished GABAergic activity.
The selective GABA-B receptor agonist R-baclofen has been shown to reverse social deficits
and reduce repetitive behaviors in a mouse model of Fragile X syndrome [67]. To further
evaluate R-baclofen in a broader range of ASD mouse models, the enantiomer was tested in
two inbred mouse strains exhibiting low sociability and/or pronounced repetitive or
stereotyped behaviors [68]. In BTBR mice, R-baclofen treatment reduced repetitive self-
grooming and high marble-burying scores. At non-sedating doses, it also decreased
stereotypical jumping behavior in C58/J (C58) mice [68].
Moreover, a randomized, double-blind, placebo-controlled study investigated the efficacy of
baclofen as an adjuvant to risperidone over a ten-week period [69]. Participants were assessed
three times, and the findings indicated that those in the baclofen adjuvant group experienced
greater improvements on the ABC-C scale compared to those receiving a placebo with
risperidone. The targeted ASD-related behaviors that improved included irritability, lethargy,
stereotypic behaviors, hyperactivity, and inappropriate speech. Overall, this clinical trial
supports the use of baclofen as an effective and safe adjuvant to risperidone for managing
ASD-associated symptoms [69].
8.5. Repetitive Transcranial Magnetic Stimulation
Repetitive transcranial magnetic stimulation (rTMS) is a non-invasive method that modulates
brain excitability and synaptic plasticity. Studies using animal models with autistic-like
behaviors induced by neonatal isolation showed that a two-week low-frequency rTMS
treatment significantly improved these behaviors in young adult rats. Additionally, rTMS
restored the excitation/inhibition (E/I) balance at the synaptic level by regulating GABA
transmission in synaptosomes [70].
In clinical practice, rTMS is increasingly utilized to enhance inhibitory mechanisms, resulting
in notable reductions in core ASD symptoms [71]. Protocols for multicenter randomized
controlled trials have been established, highlighting the growing importance of this
therapeutic approach [72].
8.6. Treatment with Oxytocin (OXT)
A central deficit in oxytocin (OXT) is considered a significant contributing factor to ASD,
potentially underlying impairments in social behavior [73]. To investigate this hypothesis,
studies using valproate (VPA) and fragile X rodent models of autism disrupted the
neuroprotective, oxytocin-driven shift in GABA signaling from excitatory to inhibitory
during delivery [73]. Recent research on the central OXT system in VPA-induced rat models
of autism further explores this connection. Research supports the hypothesis that oxytocin
(OXT) deficits contribute to ASD. Lower OXT levels were observed in the hypothalamic
mRNA of adolescent valproate (VPA) rats and the supraoptic nucleus (SON) of neonatal
VPA rats, both of which exhibited autistic-like behaviors [74]. Intranasal OXT administration
restored social preference in adolescent VPA rats, while early postnatal OXT treatment
showed long-term therapeutic effects on autistic-like behaviors in these models [74].
Findings in animal studies align with human research, showing that oxytocin is well-tolerated
and can significantly improve social behaviors in children with ASD [75]. A double-blind,
randomized, placebo-controlled trial involving intranasal OXT administered over four weeks
to 40 adult ASD patients showed no treatment-specific improvements but suggested positive
trends in secondary outcomes like repetitive behaviors and avoidance. This study
recommended further research on multi-dose regimens to evaluate long-term efficacy [76].
Another study aimed to clarify the mechanisms of intranasal oxytocin (IN-OXT) in 38 adult
ASD patients, addressing the recommendations of previous trials [77]. Oxytocin, a
neuropeptide, modulates social behavior by influencing cooperation, attachment, and
bonding. Anatomical effects were assessed using imaging of the amygdala and posterior
superior temporal sulci (pSTS). Reduced bilateral amygdala activity correlated with
improved social behavior, while increased pSTS activity was linked to enhanced social
engagement [77].
A single dose of IN-OXT showed variable effects on amygdala activity depending on
emotional states. It attenuated activity in happy states but increased it in angry states. In
contrast, multiple doses of IN-OXT reduced bilateral amygdala activity across both emotional
states compared to placebo, suggesting sustained improvement in social behavior through
consistent amygdala attenuation. Additionally, a single dose of IN-OXT significantly
improved social behavior by amplifying pSTS activity, regardless of hemisphere or emotional
state [77]. However, a generalized negative trend was observed with multiple-dose regimens.
Notably, the right pSTS demonstrated a stronger overall response to multiple-dose IN-OXT
therapy compared to the left pSTS.
Based on these findings, the study suggests exploring extended multiple-dose IN-OXT
treatment regimens to promote neural changes in ASD patients that persist beyond those
achieved with four-week treatments [77].
9. Mitochondrial Dysfunction Improvement
9.1. Antioxidant Therapy
Recent research on the pathophysiology of ASD has identified oxidative stress and
inflammation as contributing factors to its development [78,79]. Studies have reported
decreased levels of endogenous antioxidant enzymes and elevated oxidative stress biomarkers
in individuals with ASD. Consequently, antioxidant compounds have been proposed as
potential therapeutic agents to reduce or prevent the effects of free radical damage in ASD
patients [80,81].
Sulforaphane, an antioxidant found in vegetables such as broccoli, cauliflower, and cabbage,
has been extensively studied in individuals with ASD. Results from double-blind,
randomized, placebo-controlled clinical trials indicate that sulforaphane significantly
improves core behavioral and cognitive symptoms in patients with ASD [82].
9.2. L-Carnosine Supplementation
A meta-analysis of four double-blind, placebo-controlled randomized controlled trials (RCTs)
and one open-label trial evaluated the neuroprotective, antioxidant, and anti-convulsive
properties of L-carnosine. However, the findings were inconclusive due to the lack of well-
designed RCTs with larger sample sizes [83].
One study examined the effectiveness of L-carnosine as an adjunct to risperidone in 70
children with ASD [84]. While the treatment did not significantly affect irritability subscale
scores, it did lead to improvements in the hyperactivity/noncompliance subscales of the
Aberrant Behavior Checklist-Community (ABC-C) in these patients [84].
Additionally, a meta-analysis of three studies found no significant differences between the L-
carnosine-supplemented groups and placebo-controlled groups on the Gilliam Autism Rating
Scale [83].
9.3. L-Carnitine Supplementation
Carnitine plays a key role in transporting long-chain fatty acids into mitochondria for
oxidation and energy production. Some treatments for mitochondrial diseases have shown
improvements in core and associated ASD symptoms. Around 10%-20% of ASD patients
experience disorders in L-carnitine synthesis, making supplementation the treatment of
choice for them [85].
In one study, 30 children with ASD were divided into experimental (L-carnitine-
supplemented) and placebo-controlled groups. The experimental group showed significant
improvements in CARS scores, with notable differences in both free and total carnitine
levels, though no direct link between these changes was established. The study suggests a six-
month L-carnitine supplementation regimen to improve autism severity but calls for further
research to support this recommendation [86].
Systemic Primary Carnitine Deficiency (PCD) is associated with numerous clinical issues,
including hepatomegaly, muscle weakness, elevated transaminase levels, hyperammonemia,
and gastrointestinal motility changes [87]. Although neurodevelopmental disorders like ASD
have not been reliably linked to PCD, a case report described a 7-year-old girl with ASD
caused by systemic PCD. The report suggested that early PCD screening could detect
carnitine deficiencies and allow for early supplementation, potentially preventing brain
carnitine deficiencies that lead to functional brain changes later on. In this case, a delayed
diagnosis and supplementation resulted in only mild to moderate responses to treatment, with
no observed improvements in ASD features [87]. Thus, further studies are needed to explore
the potential connection between undiagnosed, worsening PCD and functional brain changes
linked to ASD.
Additionally, recent studies have explored the benefits of combined therapies. A randomized,
double-blind, placebo-controlled clinical trial showed that adding L-carnitine to risperidone
treatment in children and adolescents with ASD improved symptoms, including social
isolation, stereotypic behavior, and inappropriate speech [88].
9.4. Butyrate Treatment
Butyrate is a major metabolite produced by anaerobic microbes like Clostridium clusters IV
and XIVa in the gut microbiome [89], though Lactobacilli contribute indirectly by supporting
clostridia growth [90]. Butyrate plays several important regulatory roles, including improving
mitochondrial function during oxidative stress, maintaining gut barrier integrity, modulating
the microbiome-gut-brain axis, enhancing mucosal immunity with its anti-inflammatory
effects, and promoting the expression of genes linked to cognition and behavior (such as
CREB1 and CamKinase II) [91].
Studies have shown that butyrate treatment can improve ASD-related behaviors, including
regulating social behavior in autistic mice [92], acting on transporters and receptors to correct
gut-brain axis abnormalities [95], and suppressing Histone Deacetylase activity to improve
immune response [91].
9.5. Resveratrol Treatment
Resveratrol (RSV) is an antioxidant and anti-inflammatory compound that enhances
mitochondrial function and helps prevent social impairments in the VPA animal model of
autism [94]. Prenatal exposure to VPA in animals leads to sensory behavior changes, altered
localization of GABAergic parvalbumin (PV+) neurons in sensory brain regions, and
modifications in excitatory and inhibitory synapse protein expression. RSV treatment
prevents these pathological changes in the brains of experimental animals [95]. Additionally,
the role of RSV in regulating mitochondrial fatty acid oxidation (mt-FAO) and energy
homeostasis is being explored as a potential strategy for treating ASD [94].
9.6. Rapamycin Therapy
The mTOR signaling pathway plays a crucial role in regulating cell growth and metabolism
and is closely linked to intracellular oxidative stress when overactivated [96,97]. In mice with
tuberous sclerosis complex (TSC), treatment with rapamycin, a specific mTOR inhibitor,
resulted in recovery from social interaction deficits [98]. Therefore, regulating mitochondrial
dysfunction with antioxidants could improve ASD behavior by modulating the mTOR
pathway.
10. Regulation of Methylation: Administration of Vitamins B12 and B9
Some key metabolic pathways involved in redox regulation are disrupted in individuals
diagnosed with ASD. Glutathione (GSH), a primary redox buffer in all cells, is significantly
influenced by methylation processes (linked to vitamin B12) and folate metabolism (linked to
vitamin B9) [99].
Research has shown that individuals with ASD often have vitamin B12 deficiency [100-102].
Low B12 levels result in elevated homocysteine and reduced levels of S-Adenosylmethionine
(SAM), a critical co-substrate involved in methyl group transfers, which affects DNA and
histone methylation throughout the body, including in the brain. Depletion of SAM leads to a
decrease in GSH production, impairing the antioxidant defense system.
A clinical trial demonstrated that methyl B12 supplementation improved symptoms and
reduced oxidative stress in children with autism [103]. Further studies explored the
relationship between low cobalamin levels and the decreased GSH seen in both ASD and
schizophrenia. Specifically, both total cobalamin (vitamin B12) and methyl-cobalamin
(active B12) levels were found to be low in GCLM-KO mice, which exhibited reduced GSH
levels [104].
Folinic acid (vitamin B9), a folate analog, can pass through the blood-brain barrier even in
the presence of folate receptor (FRα) autoantibodies, which are commonly found in children
with ASD and their mothers [104,105]. These autoantibodies block folate activity, and folinic
acid has been shown to prevent behavioral deficits in rats. In humans, folate supplementation
during preconception and gestational periods may help prevent ASD by enabling the
methylation of B12, activating the methionine cycle, and producing GSH.
Studies have suggested that administering low-dose folic acid orally alongside
subcutaneously injected methyl-cobalamin can increase blood plasma levels of glutathione,
which may enhance antioxidant capacity and reduce oxidative stress in a subset of children
with autism [103,106].
A two-part study in China found that folic acid supplementation increased homocysteine
levels, supporting its potential role in improving ASD-related behaviors. Regulation of
Glutathione Metabolism and Folate Supplementation Recent studies suggest that
supplementation with folic acid can improve biochemical pathways related to glutathione
metabolism, leading to enhanced sociability, verbal and non-verbal communication, and
overall social interaction in children with autism compared to a control group [107,108].
However, a review analyzing the impact of folic acid supplementation during pregnancy on
the risk of ASD in offspring found conflicting results, mainly due to differences in study
designs. As a result, the review could not conclusively confirm that folic acid
supplementation during pregnancy increases the likelihood of ASD in unborn children [109].
11. Restoring Gut Microbiota in ASD
Alterations in gut microbiota have been proposed as potential pathways for the development
of ASD. Research has increasingly focused on characterizing the "fragile gut" in children
with autism, which is marked by low digestive enzyme activity and impaired gut barrier
integrity. This supports the hypothesis that dietary peptides and metabolites from microbial
activity in the gut entering the bloodstream might trigger an abnormal immune response
[110-112]. Interventions aimed at regulating the "fragile gut" through microbiota transfer
therapy, pre/probiotic treatment, fatty acid supplementation, and specific diets (e.g., gluten-
free/casein-free or ketogenic) have generally shown improvements in gastrointestinal (GI)
and behavioral symptoms.
11.1. Microbiota Transfer Therapy (MTT)
An open-label clinical trial examining the effects of Microbiota Transfer Therapy (MTT) on
gut microbiota composition, GI symptoms, and ASD behaviors found that GI symptoms
decreased by nearly 80% by the end of the study, with improvements persisting for eight
weeks. Behavioral improvements in ASD symptoms were also observed during and after
treatment. Analysis of bacterial and phage deep sequencing showed successful partial
engraftment of donor microbiota and beneficial changes in the gut environment, indicating
that MTT could be an effective method for improving both ASD and comorbid GI symptoms
by modifying the gut microbiome [110]. Thus, targeting the gut microbiome through
pre/probiotics, fecal microbiota transplantation, and biofilm eradication could be promising
treatments for ASD [113-115].
11.2. Probiotics and Prebiotics
Probiotics, beneficial microorganisms in the gut, support metabolism, immunity, and health,
influencing neuro-intestinal processes through the gut-brain axis. Prebiotics, non-digestible
carbohydrates that serve as food for probiotics, work synergistically with probiotics. In
individuals with ASD, altered gut microbiota has been observed, with a decrease in beneficial
strains like Alistipes and Parabacteroides, and an increase in others like Corynebacterium
and Lactobacillus [117]. This imbalance leads to common GI symptoms such as constipation,
abdominal pain, diarrhea, and flatulence. Animal studies have shown that probiotics may
have a lasting effect on neuroactive compounds like GABA and serotonin [116,118]. For
example, a study involving golden Syrian hamsters demonstrated that probiotics containing
Bifidobacteria and Lactobacilli restored gut microbiota, reduced glutamate, and increased
GABA and Mg2+ levels, suggesting their potential as a safe treatment for glutamate
excitotoxicity [119]. Additionally, probiotics have been shown to reduce the activity of the
HPA axis in depression cases [120].
Given these positive findings, several studies have examined whether restoring gut
microbiota in ASD patients could improve neurobehavioral symptoms. A 12-week
randomized, double-blind, controlled trial showed some improvements in GI symptoms but
no changes in adaptive or repetitive behaviors [121]. A second randomized, double-blind,
placebo-controlled study reported contrasting results when testing prebiotic monotherapy and
combination therapy. Monotherapy showed no GI improvements, while combination therapy,
along with gluten and casein-free diets, resulted in reduced anti-sociability scores [122].
Another study with 40 Egyptian children with ASD (aged 2-5) found that after three months
of daily probiotic supplementation, Bifidobacterium and Lactobacillus levels in stool samples
significantly increased. Additionally, 80% of the children exhibited reduced anxiety and
improved sleep patterns [123].
A crossover-design pilot study investigated the effects of bovine colostrum product (BCP)
supplementation in children with ASD and chronic GI symptoms, using both BCP alone and
a combination of BCP and Bifidobacterium (B.). The study included a washout period
between the different regimens [124,125]. The researchers observed significant
improvements in GI symptoms and stool quality, along with notable reductions in aberrant
behaviors. However, due to several limitations of the study, such as the lack of a control
group, the short study duration, and the continuation of concurrent ASD treatments, the
authors suggest that further, more rigorous studies are necessary to verify the reliability of
these findings.

11.3. Propionic Acid (PPA) Adjustments through Biofilm Treatment

Propionic acid (PPA), along with other short-chain fatty acids produced in the gut, is found in
elevated amounts in individuals with autism, and it is associated with behavioral impairments
due to its ability to easily cross the blood-brain barrier [126]. In rats, PPA administration
causes abnormal neural cell organization and induces several electrophysiological,
behavioral, and neuropathological changes characteristic of ASD [127]. The harmful effects
of PPA are primarily linked to its concentration in the body. PPA is produced by gut bacteria,
particularly Clostridia, which generate PPA and exotoxins [128]. Interestingly, children with
ASD exhibit differences in gut microbiota compared to neurotypical individuals, with a
decrease in Bacteroidetes and an increase in Candida [117, 129, 130]. This imbalance
disrupts the cycle of PPA production and degradation, leading to elevated PPA levels that
contribute to behavioral deficits.
Several clinicians using biofilm eradication protocols have been successful in balancing PPA
concentrations. This approach involves a stepwise, nutrition-based method aimed at restoring
gut microbiome integrity. Initially, proteolytic enzymes such as nattokinase, streptokinase,
and other mucolytics break down the biofilm, exposing the underlying microbial colonies
[131,132]. Next, antimicrobial therapies (antibiotics and antifungals) target these dense
populations. Then, binders like EDTA, chitosan, and citrus pectin are used to remove the
remnants [133]. Finally, probiotics and prebiotics are introduced to restore a normal
physiological environment [134].
12. Proposed Dietary Corrections
12.1. Gluten-Free and/or Casein-Free (GFCF) Diet in Children with ASD
In 1979, Panksepp suggested that autism might be caused by endogenous overactivity in the
brain's opioid system, proposing what is known as the "opioid excess theory" of autism. He
hypothesized that proteins like gluten from wheat and casein from milk could be potential
contributors to ASD development. These proteins are broken down into peptides
(gluteomorphine from gluten and casomorphins from casein), which can bind to opiate
receptors in the central nervous system (CNS), mimicking the effects of opioids and
potentially leading to symptoms associated with autism [135-138].
The updated version of this theory suggests that children with ASD, often having a "leaky
gut," may metabolize gluten and casein incompletely. This allows these peptides to pass
through a compromised intestinal barrier, enter the bloodstream, and penetrate the blood-
brain barrier, affecting brain function and neurotransmission [139]. The benefits of a GFCF
diet are thus thought to stem from both the "opioid excess theory" and its updated version.
Children with celiac disease, who are sensitive to gluten, exhibit an immune response where
their intestinal T cells react to gluten, producing interferon-γ, which impairs gluten digestion
and damages the intestinal lining [140,141]. Both gluten and casein are also common
allergens, triggering immune responses that produce IgA and IgG antibodies [142].
The GFCF diet as an ASD treatment option has been debated. Some studies report
improvements in ASD behaviors in children with comorbid gastrointestinal (GI) symptoms
when following the GFCF diet, as observed by their parents. However, other studies find no
statistically significant differences between experimental and control groups [143-145]. Some
researchers criticize the GFCF diet findings as methodologically flawed, recommending its
use only if gluten or casein intolerance or allergy is diagnosed [146].
12.2. Ketogenic Diet (KD)
Behavioral assessments of the ketogenic diet (KD) in ASD models have shown positive
changes in social behaviors, including higher sociability and increased social novelty scores
[147,148]. Recent studies suggest that a low-carbohydrate, moderate-protein, high-fat diet
can significantly improve core autism features in both animals and humans, with these effects
lasting over extended periods [149-152].
In one case-control study, participants were divided into three groups [150]. The first group
followed a modified version of the ketogenic diet called the Modified Atkins Diet (MAD),
which is less restrictive than the standard KD. The second group adhered to the
gluten-free/casein-free (GFCF) diet, and the third group served as the control. All participants
were assessed using the Childhood Autism Rating Scale (CARS) and the Autism Treatment
Evaluation Checklist (ATEC). The study found that both MAD and GFCF diets led to a
reduction in CARS and ATEC scores, indicating improvements in autism-related behaviors.
Notably, MAD participants showed significant improvements in speech, social interaction,
and cognition as measured by the ATEC. The study concluded that both diets showed
beneficial effects, although these improvements were more pronounced in different
behavioral areas depending on the diet [150].
A six-month pilot study with 30 participants aged 4 to 10 years used the John Radcliffe keto
diet [151]. Of the 18 participants who completed the study, varying levels of psychosomatic
improvements were observed. The researchers hypothesized that autistic children have
impaired glucose oxidation and that ketone bodies could serve as an alternative energy source
for their brains. The study acknowledged several limitations, including the heterogeneity of
the participants' biochemical responses, difficulties for some children (especially those with
severe ASD) in adhering to the diet, and uncertainty about the optimal duration and method
of applying the diet.
13. Chelation Therapy
Chelation therapy is a medical treatment that uses chelating agents to remove toxic metals
from the body [153-155]. Its application in children with ASD remains controversial due to
mixed results from various studies. The choice of chelating agent depends on the type and
severity of metal toxicity and the patient's overall health. One clinical study found that meso-
2,3-dimercaptosuccinic acid (DMSA) was effective in reducing lead and mercury levels and
improving autistic symptoms in children with high levels of these metals [156].
Metallothioneins (MTs) are proteins that bind to metals to prevent their harmful effects, but
toxic metals like mercury (Hg) can displace zinc (Zn) and copper (Cu) from MTs, potentially
causing negative health effects. Chelation therapy increases the excretion of essential trace
elements like Cu and Zn, which can lead to deficiencies, so monitoring these levels is critical.
Excess Cu in the body can interfere with Zn absorption, affecting MT gene transcription and
the elimination of toxic metals, emphasizing the importance of careful monitoring of metal
toxicity and the patient's health status [155].
Chelation therapy should only be conducted under medical supervision, after assessing the
potential risks and benefits. A review of available data identified serious adverse events
associated with chelation therapy in ASD, including hypocalcemia, renal impairment, and
even deaths, leading to the conclusion that the risks currently outweigh any proven benefits
[157].
14. ANTI-INFLAMMATORIES
14.1. Non-steroidal Anti-inflammatories (NSAIDs)
Non-steroidal anti-inflammatory drugs (NSAIDs), such as Ibuprofen (a non-selective COX-1
and COX-2 inhibitor) and Acetaminophen (a COX-3 inhibitor), have been investigated for
their potential anti-inflammatory effects during fever in children with ASD. Studies found
that Ibuprofen was less associated with the development of ASD in children compared to
Acetaminophen. Additionally, the use of Acetaminophen in children aged 12 to 18 months
was associated with an eightfold increased risk of developing ASD compared to control
children [158].
14.2. Vitamin D Supplementation
Among all the vitamins linked to ASD pathology, Vitamin D has the strongest and most
extensively researched correlation. Several studies have found a connection between Vitamin
D deficiency in pregnant mothers and an increased likelihood of their children developing
ASD [159, 160]. This led to research exploring how low Vitamin D levels might contribute to
ASD and how supplementation might alleviate related symptoms. Vitamin D's anti-
inflammatory effects are seen in its ability to counteract inflammation induced by
Lipopolysaccharide (LPS) by inhibiting MAPK pathways and the production of inflammatory
molecules [161]. Additionally, Vitamin D has a synergistic effect with serotonin. Calcitriol
activates Tryptophan Hydroxylase 2 and suppresses Tryptophan Hydroxylase 1 transcription,
which increases serotonin in the brain, leading to prosocial behaviors. However, this effect is
absent in children with autism who exhibit antisocial behaviors [162]. A randomized
controlled trial demonstrated that Vitamin D supplementation led to better retention of its
precursor, 25(OH)D, and resulted in significantly improved scores across various behavioral
assessments after four months of supplementation [163].
14.3. Hyperbaric Chamber Therapy
Hyperbaric oxygen therapy (HBOT) is an emerging treatment for ASD that may improve
inflammatory responses in children with cerebral hypoperfusion. HBOT involves placing
patients in a chamber with 100% oxygen at pressures greater than one atmosphere, promoting
tissue recovery and improved physiological function due to increased oxygen availability.
Neuroimaging studies have shown cerebral hypoperfusion in children with ASD [164].
HBOT has been suggested to counteract this condition, and while it is effective for treating
conditions like carbon monoxide poisoning, there is still limited evidence supporting its use
in ASD. A single randomized controlled trial reported positive changes in Aberrant Behavior
Checklist-Community (ABC), Autism Treatment Evaluation Checklist (ATEC), and Clinical
Global Impression-Improvement (CGI) scores [165], but another study found no significant
differences between HBOT and placebo groups in terms of social reciprocity,
communication, or repetitive behaviors [166]. These results have not been consistently
replicated, and researchers emphasize the need for further large-scale studies to clarify
HBOT's effectiveness in treating ASD symptoms. The FDA has not endorsed the use of
HBOT for children with ASD due to insufficient evidence.
15. Mineral Imbalances
15.1. Zinc and Copper
Zinc is an essential trace element critical for maintaining optimal brain function [167, 168]. A
deficiency in zinc can lead to neuropsychological changes such as emotional instability,
irritability, and depression [169, 170]. Zinc is also vital for cognitive performance and plays a
role in glutamatergic transmission, influencing both short-term and long-term mental effects
[45]. Zinc acts by blocking NMDA receptors and serving as a signal factor in various cellular
processes, and its deficiency may impair neurotransmission [171]. Moreover, zinc acts as a
co-transmitter with glutamate, helping to prevent excitotoxicity and providing essential
nutrients for enzymes involved in synaptic functions related to learning and memory
processes [45].
Copper toxicity can have a significant impact on the brain, leading to symptoms such as
depression, irritability, anxiety, nervousness, as well as learning and behavioral issues [45,
170]. Copper serves as a cofactor for dopamine-β-hydroxylase (DBH), an enzyme that
converts dopamine into norepinephrine [172]. Excess copper can elevate norepinephrine
levels, which have been observed in individuals with ASD. Additionally, excess copper
inhibits the enzyme hydroxytryptophan decarboxylase, which results in reduced serotonin
production. Hypercupremia, or copper excess, may be linked to depression. Furthermore, an
overabundance of Cu/Zn-dependent superoxide dismutase can heighten oxidative stress,
causing redox imbalances through reactions with hydrogen peroxide (H₂O₂) and
peroxynitrite [45]
Zinc (Zn) and copper (Cu) are essential trace elements with an inverse relationship, and their
levels in the body are crucial for various biological processes. Cytokines play a role in
regulating this balance by facilitating Zn uptake and the production of ceruloplasmin in the
liver. In neurotypical individuals, the normal Zn-to-Cu ratio is approximately 1:1 [45]. The
plasma zinc/serum copper ratio can be used to quickly assess the functional state of
metallothioneins (MTs). Studies have shown that children with ASD tend to have lower
Zn/Cu ratios compared to neurotypical children, suggesting either a deficiency in Zn or an
accumulation of toxic metals that antagonize Zn [45, 169, 170]. Mercury toxicity, in
particular, may significantly disrupt MT function in children with ASD, potentially reflected
in the altered Zn/Cu ratio [45].
Toxic metals such as cadmium (Cd) and mercury (Hg) can have opposing effects on Zn and
Cu metabolism. MT induction in the liver may influence Cu excretion more significantly than
its mobilization into the bloodstream, while Zn's mobilization to the blood is more affected.
Increased MT induction due to oxidative stress may also lead to the retention of toxic metals
like Cd and Hg in organs such as the liver and kidneys, explaining the higher levels of these
metals found in ASD patients. Once accumulated, these metals may further impair Zn
metabolism, worsening the patient's condition [45].
Patients with ASD may have a reduced tolerance to toxic metal exposure. Enhanced MT
induction due to oxidative stress may also disrupt Cu excretion through the bile, leading to
Cu accumulation in the liver and potential toxicity. This buildup could interfere with Zn
metabolism and reduce tolerance to additional toxic metal exposure. The opposing effects of
MT induction on Cu and Zn metabolism may worsen both Zn deficiency and Cu toxicity
simultaneously in ASD patients [45].
15.2. Selenium
Research suggests that disruptions in selenium (Se) metabolism may play a role in the
development of ASD [173, 174]. Oxidative stress, which is commonly observed in ASD, is
linked to mitochondrial dysfunction, immune dysfunction, and inflammation [78, 79, 174].
Selenium has been shown to help alleviate these conditions, prompting several studies to
explore its potential role in managing ASD [175, 176]. However, the exact mechanisms
remain unclear, as some studies have reported altered selenoprotein expression in ASD, while
others have found no significant changes [175].
Selenium may offer protection against the harmful effects of mercury [177, 178] and may
also protect against heavy metal toxicity, which has been hypothesized as a contributing
factor in ASD development [179]. The complex interaction between selenium and mercury
may have implications for ASD and other neurological disorders, though further research is
needed to better understand this relationship and its clinical significance.
Alterations in the gut microbiota have also been associated with ASD, and selenium
deficiency has been shown to cause changes in bacterial populations that promote
lipopolysaccharide (LPS) overproduction and translocation. Selenium may influence LPS-
induced inflammation by modulating p38 MAPK and NF-κB signaling pathways to protect
against endotoxemia [175]. Although the evidence regarding selenium’s role in ASD is
limited and sometimes contradictory, it is an essential micronutrient that may provide
benefits for alleviating some ASD symptoms. More research is required to identify the
optimal dosage and duration for selenium supplementation and to clarify its role in ASD
treatment.
15.3. Calcium and Magnesium
Calcium (Ca) and magnesium (Mg) are essential minerals that are vital for various bodily
functions, including neurological development and function [180]. Imbalances or deficiencies
in these minerals have been implicated in the pathogenesis of ASD [181].
Calcium is the most abundant mineral in the body, playing essential roles in muscle
contraction, blood clotting, nerve function, and regulating neuronal communication, which is
crucial for proper brain function [182]. Studies suggest that calcium dysregulation may
contribute to ASD development, with research showing that children with ASD have lower
serum Ca levels compared to neurotypical children [184]. Calcium dysregulation is also
linked to oxidative stress, inflammation, and mitochondrial dysfunction, which are common
in individuals with ASD [183]. Calcium channel blockers, which regulate Ca influx into cells,
have been shown to improve social behavior in ASD mouse models.
Magnesium is another crucial mineral involved in muscle and nerve function, energy
production, and protein synthesis. It plays a key role in regulating calcium levels in the body
[185], and its dysregulation has also been associated with oxidative stress, inflammation, and
mitochondrial dysfunction in ASD [186]. Some studies have indicated that children with
ASD have lower serum Mg levels compared to neurotypical children [187, 188].
The interaction between calcium and magnesium is critical for proper body function.
Magnesium regulates calcium levels by activating vitamin D, which is necessary for calcium
absorption in the intestines [189]. Magnesium also controls the influx of calcium into cells,
essential for neurological function, and helps inhibit glutamate release, a neurotransmitter
that can lead to excessive calcium influx and oxidative stress [190]. Studies have shown that
children with ASD have a higher calcium-to-magnesium ratio compared to neurotypical
children, and this ratio correlates with autism severity. Additionally, children with both ASD
and ADHD exhibit more significant changes in magnesium levels in their hair and urine
compared to neurotypical children [188]. Magnesium may help protect against the harmful
effects of calcium dysregulation and has anti-inflammatory properties that could help
mitigate mitochondrial dysfunction, commonly observed in children with ASD.
The role of calcium and magnesium in ASD is complex, and further research is needed to
clarify their exact mechanisms. However, evidence suggests that dysregulation of these
minerals may contribute to ASD pathogenesis, and supplementation with calcium and
magnesium may alleviate some ASD symptoms [192]. The optimal doses and duration for
supplementation still require further investigation.
16. Vitamins
Vitamin supplementation is a common adjunct therapy for individuals with ASD due to the
links between certain vitamins and ASD pathology [193-195]. Vitamins A, C, and E are
known to enhance antioxidant capabilities, while vitamin D plays roles in anti-inflammatory
processes and serotonin regulation [162, 196, 197]. Vitamin B1 is involved in energy
regulation [198], and vitamin B6 helps balance excitation and inhibition in the brain through
neurotransmitter synthesis, particularly in regulating GABA [199, 200]. Vitamins B9 and
B12 contribute to methylation processes [201].
Individuals with ASD often experience metabolic and nutritional abnormalities, including
issues with sulfation, methylation, glutathione redox imbalances, oxidative stress, and
mitochondrial dysfunction [202-204]. Vitamin supplementation may support these
physiological processes. A non-randomized double-blind study involving 16 children with
ASD, who received high doses of B6 and magnesium, found significant behavioral
improvements [205]. However, the role of B6 supplementation in ASD remains unclear.
Vitamin D supplementation may also benefit individuals with ASD due to its immune-
modulating and inflammation-reducing properties [206].
The optimal dosages and duration of vitamin supplementation for individuals with ASD are
still unclear. Moreover, vitamin supplementation may not be effective for all individuals with
ASD and should be tailored on a case-by-case basis [194].
17. Tryptophan
Tryptophan, an essential amino acid and precursor to serotonin, may benefit individuals with
ASD by improving social behavior, reducing repetitive behaviors, and increasing cognitive
flexibility [207, 208]. While its exact mechanism in ASD is not fully understood, it may
enhance serotonin levels in the brain and exert anti-inflammatory effects. However,
tryptophan supplementation should be approached cautiously due to potential side effects and
the risk of serotonin syndrome when combined with certain medications. While tryptophan
may be deficient in some individuals with ASD, supplementation with B vitamins and
magnesium may influence tryptophan metabolism [207]. More research is necessary to better
understand the benefits and risks of tryptophan supplementation in ASD.
18. Immunotherapy
Individuals with ASD often exhibit immune system dysregulation, which includes alterations
in T cells, B cells, monocytes, natural killer cells, dendritic cells, and elevated cytokine levels
leading to neuroinflammation. Immune dysfunction and inflammation are key aspects of
ASD diagnosis and treatment [209]. Understanding immune dysregulation and inflammation
in ASD can significantly improve diagnostic and therapeutic approaches. Immunotherapy,
such as intravenous immunoglobulin (IVIG) injections, has shown promise in improving
ASD symptoms [210]. However, further research is needed to identify additional immune
biomarkers and explore the long-term risks and effects of such treatments.
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