Question:medium
Branched chain ketoacid decarboxylation is defective in:
Branched chain ketoacid decarboxylation is defective in:
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Defective branched chain alpha ketoacid dehydrogenase gives urine that smells of maple syrup.
Updated On: Jun 24, 2026
- Maple syrup urine disease
- Hartnup disease
- Alkaptonuria
- GM1 gangliosidosis
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The Correct Option is A
Solution and Explanation
Start from the enzyme named in the question. Decarboxylation of branched chain ketoacids is the job of the branched chain alpha ketoacid dehydrogenase complex, a mitochondrial enzyme similar in design to pyruvate dehydrogenase. When this complex fails, the alpha ketoacids derived from leucine, isoleucine and valine pile up, and so do the parent amino acids. The classic clinical clue is urine that smells like maple syrup, hence the disease name Maple syrup urine disease.
Now eliminate the alternatives by their actual defects. Hartnup disease is a membrane transporter problem affecting absorption of neutral amino acids, with a pellagra like picture; it has nothing to do with ketoacid decarboxylation. Alkaptonuria comes from a block at homogentisate oxidase during tyrosine breakdown, producing urine that darkens on standing. GM1 gangliosidosis is a lysosomal disorder caused by deficient beta galactosidase, leading to ganglioside storage, again unrelated to branched chain ketoacids.
Only one option matches a defective decarboxylation of branched chain ketoacids.
\[\boxed{\text{Maple syrup urine disease}}\]
Now eliminate the alternatives by their actual defects. Hartnup disease is a membrane transporter problem affecting absorption of neutral amino acids, with a pellagra like picture; it has nothing to do with ketoacid decarboxylation. Alkaptonuria comes from a block at homogentisate oxidase during tyrosine breakdown, producing urine that darkens on standing. GM1 gangliosidosis is a lysosomal disorder caused by deficient beta galactosidase, leading to ganglioside storage, again unrelated to branched chain ketoacids.
Only one option matches a defective decarboxylation of branched chain ketoacids.
\[\boxed{\text{Maple syrup urine disease}}\]
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