Homocystinuria
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Ayokunle Olubaniyi, M.B,B.S [2]
Synonyms and keywords: CBS deficiency; cystathionine beta-synthase deficiency
Overview
Homocystinuria, also known as cystathionine beta synthase deficiency, is an inherited disorder of the metabolism of the amino acid methionine, often involving cystathionine beta synthase. It is an inherited autosomal recessive trait, which means a child needs to inherit the defective gene from both parents to be affected.
Presentation
This defect leads to a multisystemic disorder of the connective tissue, muscles, CNS, and cardiovascular system. Homocystinuria represents a group of hereditary metabolic disorders characterized by an accumulation of homocysteine in the serum and an increased excretion of homocysteine in the urine. Infants appear to be normal and early symptoms, if any are present, are vague.
Symptoms
- A family history of homocystinuria
- Nearsightedness
- Flush across the cheeks
- Tall, thin build
- Long limbs
- High-arched feet (pes cavus)
- Knock-knees (genu valgum)
- Pectus excavatum
- Pectus carinatum
- Mental retardation
- Psychiatric disease
- Eye anomalies:
- 90% have ectopia lentis
- Myopia
- Glaucoma
- Optic atrophy
- Seizure
- extensive atheroma formation at young age which affects many arteries but not the coronary arteries [1] [2]
Mortality/morbidity
The life expectancy of patients with homocystinuria is reduced only if untreated. It is known that before the age of 30, almost one fourth of patients die as a result of thrombotic complications (e.g. heart attack).
Treatment
No specific cure has been discovered for homocystinuria; however, many people are treated using high doses of vitamin B6 (also known as pyridoxine). Slightly less than 50% respond to this treatment and need to intake supplemental vitamin B6 for the rest of their lives. Those who do not respond require a low methionine diet, and most will need treatment with trimethylglycine. A normal dose of folic acid supplement and occasionally added cysteine in the diet is helpful.
Recommended diet
Low-protein food is recommended for this disorder, which requires food products low in particular types of amino-acid (i.e. methonine).