Which of the following conditions is characterized by an inability to convert methionine to cysteine due to a deficiency in cystathionine beta-synthase?

A Homocystinuria type I ✓
B Homocystinuria type II
C Cystinuria
D Methioninuria

Explanation

Homocystinuria type I is caused by a deficiency in cystathionine beta-synthase, leading to an accumulation of homocysteine and an inability to convert methionine to cysteine.

Source

Scriver's The Metabolic and Molecular Bases of Inherited Disease
Metabolic and Nutritional Disorders Amino Acid Metabolism Sulfur Amino Acid Metabolism Hard MEDICAL Confidence: high