Classical Homocystinuria (HCU)

Classical homocystinuria (HCU), also known as homocystinuria due to CBS deficiency, is a rare genetic metabolic disorder caused by a deficiency in the enzyme cystathionine beta synthase (CBS). Without enough CBS, the amino acids homocysteine (Hcy) and methionine build up in the blood.

Classical HCU leads to toxic levels of homocysteine that can result in life-threatening thrombotic events such as stroke, pulmonary embolism and deep vein thrombosis, ophthalmologic and skeletal complications, as well as developmental delay.

Current treatment options include significant dietary restrictions and use of vitamin B6 and betaine. For many individuals with classical HCU, homocysteine levels remain elevated despite the availability of these treatments.

The disorder is inherited in an autosomal recessive genetic manner, meaning that a child is affected when each parent passes on one copy of the mutated gene.


Learn About our Development Efforts for classical HCU


Patient Advocacy Organizations

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