Which of the following is caused by a deficiency in cystathionine synthase?

The condition caused by a deficiency in cystathionine synthase is homocystinuria. This enzyme is critical in the metabolism of the amino acid methionine, where it catalyzes the conversion of homocysteine and serine into cystathionine. A deficiency in this enzyme leads to an accumulation of homocysteine in the body, which can result in various clinical manifestations, including developmental delays, ocular abnormalities (such as lens dislocation), skeletal abnormalities, and a significantly increased risk of thromboembolic events.

The pathway that cystathionine synthase is involved in is also linked to vitamin B6 deficiency, as this vitamin is a cofactor for the reaction. Therefore, correcting B6 levels can sometimes improve symptoms in patients with cystathionine synthase deficiency.

Homocystinuria is distinct from the other conditions listed. Alkaptonuria results from a deficiency of homogentisate oxidase, affecting the breakdown of phenylalanine and tyrosine; maple syrup urine disease is due to a deficiency in branched-chain alpha-keto acid dehydrogenase, which metabolizes branched-chain amino acids; and phenylketonuria arises from a defect in phenylalan