Medical Wikipedia : The Medical Encyclopedia
Disorder of Metabolism
Homocystinuria is inherited disorder of the metabolism of the amino acid methionine due to a deficiency of - cystathionine beta synthase or methionine synthase
These are a series of inborn errors of metabolism that are characterized by
increased homocysteine levels in blood and urine.
These are autosomal recessive disorders and are seen in 1 in 200,000 births.
Normal homocysteine level in blood is 5–15 micromol/L. It can rise to 50-100
times the normal level in diseases. Moderate increase is seen in aged people,
vitamin B12 or B6 deficiency, smokers and alcoholics and also in
Elevated homocysteine levels in blood is associated with increased risk of
coronary artery disease through increased oxidant stress, impaired endothelial
function, and induction of thrombosis.
Causes of homocystinuria
1. Cystathionine beta synthase deficiency (defective CBS gene)
2. Deficient N 5 ,N 10 -Methyl THFA reductase (defective MTHFR gene)
3. Cobalamin (B12) deficiency.
1. Mental Retardation
2. Charlie Chaplin gait - Bilateral extorsion of the tibia .
3. Involvement in the eye: Ectopia Lentis (Subluxation of lens) and severe Myopia are seen.
4. Increased platelet adhesiveness and increased risk of intravascular
thrombosis due to activation of Hagemann’s factor (clotting factor XII).
Cyanide-Nitroprusside test is positive in urine. Urinary homocysteine exceeds
300 mg/24 hours.
Diet low in methionine and vitamin B6 therapy along with folate and B12
supplements. Betaine therapy is usually added to the therapeutic regimen.
- Homocystinuria - disorder of the metabolism of the amino acid methionine
Which enzyme deficiency causes Homocystinuria?
Deficiency of cystathionine beta synthase or methionine synthase
Which Vitamin deficiency can cause symptoms of homocysteinuria?
Symptoms of homocystinuria can also be caused by a deficiency of vitamins B6, B12, or folate
How the Ectopia Lentis of homocystinuria differs from Ectopia lentis of Marfan syndrome?
Ectopia lentis –
|Marfan syndrome||Ectopia lentis- Upward dislocation|
|Homocystinuria||Ectopia lentis- Downward dislocation|
What is the cause of homocystinuria?
Homocystinuria is caused by the deficiency of :
|Deficiency of Enzymes-||1. Cystathionine beta synthase||2. Methionine synthase|
|Deficiency of Vitamins-||1. Folic acid
||2. Vitamin B12
||3. Pyridoxine (vitamin B6)|
What are the types of homocystinuria?
Due to the deficiency of cystathionine ß synthase, Most common inborn error of methionine metabolism.
homocystinuria type-II -
Homocystinuria due to defect in methylcobalamin formation, Characterized by the triad of megaloblastic anemia, Homocystinuria and hypomethionemia.
Deficiency of the enzyme methyltetrahydrofolate reductase, Characterized by homocystinemia,homocystinuria, Low-low normal levels of methionine
|Homocystinuria type-I||Due to the deficiency of cystathionine ß synthase,|
Most common inborn error of methionine metabolism.
|Homocystinuria type-II||Homocystinuria due to defect in methylcobalamin formation, |
Characterized by the triad of megaloblastic anemia,
Homocystinuria and hypomethionemia.
|Homocystinuria type-III||Deficiency of the enzyme methyltetrahydrofolate reductase.|
Characterized by homocystinemia and homocystinuria,
Low-low normal levels of methionine