Homocystinuria, also known as Cystathionine beta synthase deficiency, is inherited disorder of the metabolism of the amino acid methionine. It is inherited an autosomal recessive trait, which means the child is to inherit the defective gene from both parents. 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 normals and early symptoms, if any are present, are vague.

The life expectancy of patients with homocystinuria is reduced. 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).

No specific cure has been discovered for homocystinuria. However, many people are treated to high doses of vitamin B6(also known as pyridoxine). Slightly less than 50% respond to this treatment and are needed to intake supplemental vitamin B6 for the rest of their lives. Those that 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 cysteinein the diet is helpful.

Low-protein food is recommended for these disorder requires food products which are low in particular types of amino-acid (i.e. methonine).