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Alkaptonuria

Alkaptonuria is a rare autosomal recessive metabolic disorder caused by a deficiency of the enzyme homogentisate oxidase, leading to the accumulation of homogentisic acid in the body. Clinical features include darkening of urine, bluish-black pigmentation of connective tissues (ochronosis), and arthritis. Diagnosis is confirmed through urine tests and genetic testing, while treatment focuses on managing symptoms with dietary changes and pain relief measures.

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12 views3 pages

Alkaptonuria

Alkaptonuria is a rare autosomal recessive metabolic disorder caused by a deficiency of the enzyme homogentisate oxidase, leading to the accumulation of homogentisic acid in the body. Clinical features include darkening of urine, bluish-black pigmentation of connective tissues (ochronosis), and arthritis. Diagnosis is confirmed through urine tests and genetic testing, while treatment focuses on managing symptoms with dietary changes and pain relief measures.

Uploaded by

akshayvardhan025
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as DOCX, PDF, TXT or read online on Scribd
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Alkaptonuria

Definition:

Alkaptonuria is a rare autosomal recessive inborn error of


metabolism caused by a deficiency of the enzyme homogentisate
oxidase, leading to the accumulation of homogentisic acid (HGA)
in the body.
---
Biochemical Basis:

It is a disorder of tyrosine metabolism.

Normal pathway:
Tyrosine → p-hydroxyphenylpyruvate → Homogentisic acid →
Maleylacetoacetic acid
(via homogentisate oxidase)

In Alkaptonuria:
❌ Deficiency of homogentisate oxidase →
✅ Accumulation of homogentisic acid (HGA) in tissues and urine
---

Key Metabolic Block:

Tyrosine metabolism → Homogentisate oxidase enzyme defect


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Clinical Features:

1. Urine darkens on standing (due to oxidation of homogentisic


acid)

2. Ochronosis – bluish-black pigmentation of connective tissues,


especially:

Cartilage (ears, nose)

Sclera

Skin
3. Arthritis (especially of spine and large joints) – due to HGA
deposition in cartilage

4. Stiffness and pain in joints

5. Pigmented sweat and earwax


---
Diagnosis:

Urine turns black on standing

Ferric chloride test – green/black color

Gas chromatography/mass spectrometry – to detect homogentisic


acid

Genetic testing
---

Treatment:

No complete cure, but symptoms can be managed:

Low-protein diet (↓ phenylalanine & tyrosine)

Vitamin C – may slow ochronosis

Analgesics and physiotherapy for joint pain

In severe arthritis – joint replacement surgery


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Inheritance:

Autosomal recessive
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Viva Questions Quick Recap:

Question Answer

Enzyme deficient? Homogentisate oxidase


Urine color change? Turns black on standing
Disease type? Inborn error of tyrosine metabolism
Pigmentation name? Ochronosis
Mode of inheritance? Autosomal recessive
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Extra Tip:

Alkaptonuria is the first human metabolic disorder discovered (by


Sir Archibald Garrod – “inborn error of metabolism”).

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