Homocystinuria is a condition that leads to high levels of homocysteine in the body. This happens because of a missing enzyme called cystathionine beta-synthase.
Babies with homocystinuria might have trouble growing and gaining weight. They could also face eye issues like nearsightedness and lens dislocation. People with this condition might have curved spines, fragile bones, and abnormal blood clots, which can be dangerous if they reach vital organs. Some individuals with homocystinuria might respond to vitamin B6 treatment, but others might not. Treatment aims to keep homocysteine levels low. Doctors often suggest a lifelong diet low in methionine (which turns into homocysteine). Vitamin B6, betaine, vitamin B12, and vitamin B9 supplements can be helpful. It’s a lifetime commitment, and people with this condition need to avoid unnecessary surgeries and certain medications like oral contraceptives. Pregnant women with homocystinuria should work closely with their doctors to manage clotting risks. In some cases, surgery might be needed to fix dislocated eye lenses.
This form of homocytinuria is caused by pathogenic (disease-causing) variants in the CBS gene and exhibits autosomal recessive inheritance. This means that both parents must be carriers to have a 25% chance to have a child with the condition. The risk of being a carrier is based on a person’s ancestry or ethnic background. For example, individuals of Ashkenazi Jewish descent have a 1 in 330 chance to be a carrier.
Carriers may be at risk for symptoms related to hyperinsulinism. If you are found to be a carrier, a genetic counselor can talk to you in more detail about this risk and what it means.
Other names for this condition are cystathionine beta synthase deficiency and homocysteinemia.
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Revised October 2023
