Which enzyme is deficient in patients with homocystinuria, leading to elevated levels of homocysteine in the blood?

A Cystathionine beta-synthase ✓
B Methionine synthase
C Homocysteine methyltransferase
D Betaine-homocysteine methyltransferase

Explanation

Cystathionine beta-synthase is an enzyme that converts homocysteine to cystathionine. A deficiency in this enzyme leads to elevated levels of homocysteine, causing homocystinuria.

Mnemonic

'CBS' (cystathionine beta-synthase) = 'see' the problem with homocysteine

Source

NCBI (National Center for Biotechnology Information)
Enzymes in Disease Amino Acid Metabolism Disorders Homocystinuria Hard MEDICAL Confidence: high