KENYATTA UNIVERSITY

NAME: AGOI CONSOLATA

REG NO: E37/CE/17576/2012

UNIT TITLE: GENERAL GENETICS

UNIT CODE: SBT 401

DEPARTMENT: PLANT SCIENCES

LECTURER NAME: DR. LYDIA ASANDE

SUBMISSION DATE: 7/3/2024

ASSIGNMENT 1

Discuss the genetic disorders in man that arise from variations in chromosome
structure. (30 marks)

A chromosome structure can be altered in several ways including:

i. Deletions – A portion of the chromosome is missing or deleted.

ii. Duplication – A portion of the chromosome is duplicated, resulting in extra genetic
material.
iii. Translations – A portion of one chromosome is transferred to another chromosome.

These variations in chromosome structure results to different genetic disorders in man.

A genetic disorder is a health problem caused by one or more abnormalities in the genome. They
include:

i. Cri du chat (cry of the cat)

ii. Fragile X
iii. Acute Myelogenous Leukemia
iv. Trisomy 13 (Patau Syndrome)
v. Trisomy 18 (Edwards Syndrome)
vi. Trisomy 21 (Down Syndrome)

SEX CHROMOSOME ANEUPLOIDIES

i. Turner syndrome
ii. Down syndrome
iii. Cri du chat syndrome
iv. Klinefelter syndrome
I. Turner syndrome

It is a female – only genetic disorder that affects about 1 in every 2000 baby girls.
A girl with turner syndrome only has one normal X sex chromosome, rather than the usual two.
This chromosome variations happens randomly when the baby is conceived in the womb. It is
not linked to the mother’s age.

Characteristics of Turner syndrome

✓ Females with Turner syndrome often have a wide range of symptoms and some
distinctive characteristics.
✓ Almost all girls with turner syndrome.
• Are shorter than average.
• Have underdeveloped ovaries, resulting in a lack of monthly periods and
infertility.
✓ As height and sexual development are the two main things affected, Turner syndrome
may not be diagnosed until a girl fails to show sexual development associated with
puberty, usually the ages of 8 and 14 years.
✓ Other characteristics of Turner syndrome can vary significantly between individuals.

Treating Turner syndrome

There’s no cure for turner syndrome but many of the associated symptoms can be treated.

Girls and women with turner syndrome will need to have their heart, kidney and reproductive
system checked regularly throughout their lives.

However, it’s usually possible to lead a relatively normal and healthy life.

Life expectancy is slightly reduced, but it can be improved with regular health checks to identify
and treat potential problems at an early age.

II. Down syndrome

It is a condition in which a person has an extra chromosome.

Down syndrome remains the most common chromosomal condition diagnosed in the world.
Each year, about 6000 babies born in United States have down syndrome. This means that down
syndrome occurs in about 1 in every 700 babies.
Types of down syndrome

There are three types of down syndrome. People often can’t tell the difference between each type
without looking at the chromosomes because the physical features and behaviors are similar.
They include;

i. Trisomy 21 – About 95% of people with down syndrome have Trisomy 21. With these
types of down syndrome, each cell in the body has three separate copies of chromosome
21 instead of the usual 2 copies.
ii. Translocation down syndrome – This type accounts for a small percentage of people with
down syndrome (about 3%). This occurs when an extra part of a whole extra
chromosome 21 is present, but it is attached or “trans-located” to a different chromosome
rather than being a separate chromosome 21.
iii. Mosaic down syndrome – This type affects about 2% of the down syndrome. Mosaic
means mixture or combination. For children with mosaic down syndrome, some of their
cells have 3 copies of chromosome 21, but after cells have the typical two copies of
chromosome 21. Children with down syndrome may have features as other children with
down syndrome. However, they may have fewer features of the condition due to the
presence of some (or many) cells with a typical number of chromosomes.

People with down syndrome usually have an IQ (a measure of intelligence) in the mildly to
moderately low range and are slower to speak than other children.

Some common physical features of down syndrome include:

• A flattened face, especially the bridge of the nose

• Almond-shaped eyes that slant up
• A short neck
• Small ears
• A tongue that tends to stick out of the mouth
• Tiny white spots on the iris of the eye
• Small hands and feet
• A single line across the palm of the hand
• Small pinky fingers that sometimes curve towards the thumb
 • Poor muscle tone or loose joints
• Shorter in height as children and adults

Diagnosis

There are two basic types of tests available to detect down syndrome during pregnancy:

i. Screening tests – This can tell a woman and her healthcare provider whether her
pregnancy has a lower or higher chance of having down syndrome. They do not provide
an absolute diagnosis but they are safer for the mother and the developing baby.
ii. Diagnostic tests – This can typically detect whether or not a baby will have down
syndrome, but they can be riskier for the mother and the developing baby

Treatments

Down syndrome is a lifelong condition. Services early in life will often help babies and children
with down syndrome to improve their physical and intellectual abilities.

Most of the services focus on helping children with down syndrome develop to their full
potential. These services include speech, occupational and physical therapy, and they are
typically offered through early interventions programs in each stage.

Children with down syndrome may also need extra help or attention in school, although many
children are included in regular classes.

III. Cri Du Chat Syndrome

It is a group of symptoms that result from missing a piece of chromosome numbers 5.

The syndrome’s name is based on the infant’s cry, which in high pitch and sounds like a cat.

Causes

Cri du chat syndrome is rare. It is caused by a missing piece or chromosome 5.

Most cases are believed to occur during the development of the egg or sperm. A small number of
cases occur when a parent passes a different, rearranged form of a chromosome to their child.
Symptoms

They include:

• Cry that is high-pitched and may sound like a cat.

• Downward slant to the eyes.
• Epicanthal folds, an extra fold or skin over the inner corner of the eye.
• Low birth weight and slow growth
• Low set or abnormally shaped ears.
• Hearing loss.
• Heart defects.
• Intellectual disability.
• Partial webbing or fusing of fingers or toes.
• Curvature of the spine (scoliosis)
• Single line in the palm of the hand.
• Skin tags just in front of the ear.
• Slow or incomplete development of motor skills.
• Small head.
• Small jaws.
• Wide set eyes.
IV. Klinefelter’s syndrome

This is where boys and men are born with an extra X chromosome.

Symptoms of Klinefelter’s syndrome

Does not usually cause any obvious symptoms early in childhood, and even later symptoms may
be difficult to spot.

Many boys and men do not realize they have it. Possible features which are not always present
may include:

In babies and toddlers – Weak muscles and very flexible joints, learning to sit up, crawl, walk
and later that usual, being quitter and more possible than usual, having undescended testicles,
only one testicle or a smaller penis.
In childhood – Shyness and low self-confidence, problems with reading, writing, spelling and
paying attention, mild dyslexia or dyspraxia, low energy levels and difficulty socializing or
expressing feelings.

In teenagers – growing taller than expected for the family (with long arms and legs), broad hips,
poor muscle tone ad slower that usual muscle growth, reduced facial and body hair that starts
growing later than usual, small firm testes and enlarged breasts.

In adulthood – Inability to have children naturally (infertility), low sex drive, small, firm testes
and erection problems.

Diagnosis

See your GP if you have concerns about your son’s development or you notice any symptoms of
Klinefelter’s syndrome in yourself or your son.

Early diagnosis and treatment can help prevent health problems in the future.

Treatment of Klinefelter’s syndrome

There’s no cure for Klinefelter’s syndrome, but some of the problems associated with the
conditions can be treated if necessary.

Possible treatments include;

• Testosterone replacement therapy.

• Speech and language therapy during childhood to help with speech development.
• Educational and behavioral support at school to help with any learning difficulties or
behavior problems.
• Psychological support for any mental health issues.

Conclusion

In conclusion, the syndromes Turner syndrome, Down syndrome, Cri du chat syndrome, and
Klinefelter syndrome represent complex genetic conditions with distinct characteristics, causes,
symptoms, diagnostic approaches, and treatment modalities.
Turner syndrome, stemming from missing or incomplete X chromosomes in females, manifests
in various physical features and health complications, including short stature and reproductive
issues. Timely diagnosis through karyotyping facilitates tailored interventions such as hormone
replacement therapy and growth hormone treatment, aiming to mitigate associated health
concerns and optimize growth potential.

Down syndrome, resulting from an extra copy of chromosome 21, presents with intellectual
disabilities, distinct facial features, and congenital heart defects. Although there is no cure, early
intervention programs encompassing education, therapy, and medical management play pivotal
roles in addressing developmental needs and enhancing overall well-being.

Cri du chat syndrome, arising from a deletion on chromosome 5, manifests in distinctive features
like a high-pitched cry in infancy, along with developmental delays and speech impairments.
Early intervention services, including speech therapy and educational support, are instrumental
in promoting communication skills and fostering developmental progress.

Klinefelter syndrome, characterized by an extra X chromosome in males, leads to

hypogonadism, infertility, and potential developmental delays. Diagnosis typically occurs later in
life, prompting interventions such as testosterone replacement therapy and psychosocial support
to manage symptoms and improve quality of life.

While advancements in genetic testing and medical management have significantly enhanced
outcomes for individuals with these syndromes, ongoing research and awareness efforts are
crucial to further understanding and addressing the multifaceted needs of affected individuals
and their families. By adopting a holistic approach that integrates medical, educational, and
social support systems, we can strive to empower individuals living with these syndromes and
promote inclusivity and acceptance within our communities.
 References

National Human Genome Research Institute Chromosome Abnormalities Fact Sheet.

Shin M, Siffel C, Correa A survival of children with Mosaic Down Syndrome, Am J Med Genet
A.

U.S National Library of Medicine (2019). Chromosome Y Health conditions related to

chromosomal changes