Maple syrup urine disease is due accumulation of –
**Core Concept**
Maple syrup urine disease (MSUD) is a metabolic disorder caused by a deficiency of the branched-chain alpha-keto acid dehydrogenase complex. This enzyme plays a crucial role in the breakdown of **branched-chain amino acids** (BCAAs) such as leucine, isoleucine, and valine. The disease is characterized by the accumulation of these amino acids and their toxic byproducts.
**Why the Correct Answer is Right**
The correct answer is due to the accumulation of **branched-chain amino acids** (leucine, isoleucine, and valine) and their corresponding **keto acids**. The branched-chain alpha-keto acid dehydrogenase complex is responsible for converting these keto acids into their corresponding acyl-CoA derivatives, which can then be further metabolized. In MSUD, this enzyme is deficient, leading to the accumulation of these toxic compounds.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because while phenylalanine is an essential amino acid, its accumulation is associated with phenylketonuria, not MSUD.
**Option B:** This option is incorrect because tyrosine is a non-essential amino acid, and its accumulation is not directly related to MSUD.
**Option C:** This option is incorrect because tryptophan is an essential amino acid, but its accumulation is associated with other metabolic disorders, not MSUD.
**Why Each Wrong Option is Incorrect (continued)**
**Option D:** This is the correct answer choice, so we will address it in the final section.
**Clinical Pearl / High-Yield Fact**
MSUD is a classic example of a **metabolic disorder** that can present with severe neurological symptoms, including seizures and developmental delay, if left untreated. Early diagnosis and treatment with a **low-protein diet** and **thiamine supplementation** can significantly improve outcomes.
**Correct Answer:** D. branched-chain amino acids.