What is the primary cause of Homocystinuria, a metabolic disorder characterized by elevated levels of homocysteine in the blood?

A Deficiency of vitamin B12
B Deficiency of cystathionine beta-synthase ✓
C Excess of methionine
D Deficiency of folate

Explanation

Homocystinuria is primarily caused by a deficiency of the enzyme cystathionine beta-synthase, which is necessary for the conversion of homocysteine to cystathionine.

Source

Harper's Biochemistry
Metabolic and Nutritional Disorders Biochemistry Amino Acid Metabolism Medium MEDICAL Confidence: high