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What Is Maple Syrup Urine Disease?

Maple Syrup, Photo Credits By Piviso on

What Is Maple Syrup Urine Disease?

Maple syrup urine disease(MSUD) is a rare inherited condition that prevents an individual from processing several amino acids(the building blocks of proteins). As a result, the inability to break down these amino acids causes a buildup of substances in blood and urine. The build-up of substances thus creates a maple syrup odor in urine.

Who Does This Affect?

Maple syrup urine disease affects infants and can be detrimental to their lives. The most common type of MSUD is the classic type. Symptoms become prominent in the early stages of development or immediately after birth. The symptoms include:

  • Poor feeding

  • Vomiting

  • Lethargy

  • Abnormal & delayed movements

Genetics & Statistics

MSUD affects an estimated 1 in 185,000 infants worldwide. This disease has an autosomal recessive pattern, meaning it is present in both mutated genes of the individual’s parents. Though both copies of the mutated gene are present, the signs and symptoms may not show.

The Science

Mutations in branched-chain alpha keto-dehydrogenase(BCKDC) enzyme complex are the cause of MSUD. BCKDC is essential for breaking down proteins like valine, isoleucine, and leucine(VIL) which can be found in foods like eggs, fish, and meats. Infants with MSUD are typically placed on strict diets to help prevent the build-up of these essential amino acids.

Mutations in the complex, eliminate the breakdown of VIL amino acids. The result is byproducts that build up in the body which can cause serious health problems.

Pathway for Maple Syrup Disease via

Here is how the mutated pathway works:

  1. Leucine, isoleucine and valine enter the body.

  2. Branched-chain aminotransferase breaks the amino acids into alpha-keto acids.

  3. The next step is for the BCKDC to break down the alpha-keto acids by oxidative decarboxylation. However, due to a mutation in the complex, it cannot transform the keto-acids into their final metabolites. This results in the build-up of amino acids.

Here’s a visual presentation of MSUD:


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