Homocystinuria results from a deficiency of which amino acid's metabolism?

Homocystinuria results from a deficiency of which amino acid's metabolism?

• A. Phenylalanine
• B. Tyrosine
• C. Methionine
• D. Leucine

Answer: (C)

Homocystinuria is a metabolic disorder characterized by the accumulation of homocysteine in the urine and is primarily linked to a deficiency in the metabolism of methionine. Methionine is an essential amino acid that serves as a precursor to homocysteine. When there is a deficiency in the enzymes responsible for converting homocysteine to other non-toxic substances, such as cystathionine through transsulfuration pathways, it results in an accumulation of homocysteine.

In patients with homocystinuria, methionine may be processed adequately in the initial steps of metabolism, but the failure to convert homocysteine leads to its elevated levels. This excessive accumulation can cause various health issues, including developmental delays, skeletal abnormalities, and an increased risk of thrombosis. In summary, the condition directly stems from disturbances in the metabolism of methionine, making this amino acid the key player in the disorder's pathology.