What Your Test Results Mean:

Carriers typically show no symptoms of homocystinuria; however, carriers are at an increased risk of having a child with homocystinuria. Risk for the current or future pregnancies is dependent on your partner’s carrier status. Carrier testing of your partner is recommended in addition to consultation with a genetic counselor for more detailed risk assessment.

Disease Explained:

Homocystinuria is an inherited metabolic disorder characterized by nearsightedness, dislocation of the lens at the front of the eye, an increased risk of abnormal blood clotting, and osteoporosis or other skeletal abnormalities. It is caused by a deficient level of the enzyme cystathionine beta-synthase. Without this enyme, the body cannot convert homocysteine to cystathionine. As a result, homocysteine builds up in the blood. Some affected individuals experience developmental delay and intellectual disability. Symptoms of homocystinuria typically develop during the first year of life and are managed by metabolic physician and dietician.

How the Genetics Works:

Homocystinuria is an autosomal recessive disorder caused by pathogenic variants in the CBS gene. In general, individuals have two copies of the CBS gene. Carriers of homocystinuria have a single variant in one copy of the CBS gene, while individuals with homocystinuria have variants in both copies of the CBS gene, one inherited from each parent. Risk for two carriers to have a child with the disorder is 25%.