Maple syrup urine disease

Maple syrup urine disease is an inherited metabolic disorder in which impaired breakdown of branched-chain amino acids causes toxic metabolites to accumulate, especially in the brain.

Branched-chain amino acids: Leucine, isoleucine, and valine are essential amino acids with branched carbon side chains. Their impaired breakdown initiates the characteristic metabolite buildup.
Newborn screening: Testing performed shortly after birth to detect serious conditions before symptoms appear. Screening can identify affected infants before a first metabolic crisis.
Classic maple syrup urine disease: The severe form of maple syrup urine disease, usually presenting in newborns with markedly reduced enzyme activity. This form illustrates the rapid neurological danger of untreated metabolite accumulation.
Autosomal recessive inheritance: An inheritance pattern in which disease usually occurs when both copies of a gene carry pathogenic variants. Affected children typically inherit one disease-causing variant from each carrier parent.
Isovaleric acidemia: An inherited metabolic disorder caused by impaired leucine degradation due to isovaleryl-CoA dehydrogenase deficiency. It affects another step in leucine metabolism and can also cause acute metabolic illness.
Branched-chain alpha-ketoacid dehydrogenase complex: A mitochondrial enzyme complex that oxidatively decarboxylates branched-chain amino-acid breakdown products. Reduced activity of this complex creates the central metabolic block.
Tandem mass spectrometry: An analytical method that identifies and quantifies molecules by their mass-to-charge ratios in successive stages. It measures elevated branched-chain amino acids in newborn screening and diagnostic samples.
Intermediate maple syrup urine disease: A form of maple syrup urine disease with partial enzyme activity and less severe baseline biochemical abnormalities. Its symptoms may emerge later, yet illness can still trigger acute decompensation.
BCKDHA: A gene encoding the E1 alpha subunit of the branched-chain alpha-ketoacid dehydrogenase complex. Pathogenic variants in this gene account for one genetic cause of the enzyme deficiency.
Propionic acidemia: An inherited organic acid disorder caused by deficiency of propionyl-CoA carboxylase. It can resemble branched-chain amino-acid disorders during crises but produces a distinct metabolic profile.

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