Table 2.

Clinical Phenotypes of Maple Syrup Urine Disease

TypeAge of Onset 1Clinical FeaturesBiochemical Signs 2% with Normal BCKD Activity 3
Classic Neonatal
  • Maple syrup odor of cerumen
  • Poor feeding
  • Irritability, lethargy
  • Opisthotonus
  • Focal dystonia
  • "Fencing," "bicycling"
  • Obtundation, coma
  • Central respiratory failure
  • ↑ BCAAs in plasma
  • ↑ plasma alloisoleucine
  • ↑ BCKAs in urine
  • Ketonuria
0%-2%
Intermediate Variable
  • Maple syrup odor of cerumen
  • Poor growth
  • Poor feeding
  • Irritability
  • Developmental delays
  • Encephalopathy during illness
Similar to classic phenotype, though quantitatively less severe3%-30%
Intermittent Variable
  • Normal early growth & development
  • Episodic decompensations that can be severe
  • Normal BCAAs when well
  • Similar to classic biochemical profile during illness
5%-20%
Thiamine-responsive VariableSimilar to intermediate phenotypeImprovement of leucine tolerance & biochemical profile w/thiamine therapy2%-40%

BCAAs = branched-chain amino acids; BCKAs = branched-chain alpha-ketoacids

1.

All infants with classic MSUD present during the neonatal period. For other forms, age of presentation depends on several variables, including dietary protein and calorie intake, growth rate, number and severity of infectious illnesses, and rarely, dietary thiamine intake.

2.

Biochemical signs should always be interpreted in the context of dietary leucine tolerance and prevailing clinical circumstances. Dietary leucine tolerance (in mg/kg/day) is defined as the steady-state leucine intake that permits normal growth and maintains plasma leucine concentration within the normal range.

3.

The authors do not rely on tissue measurements of decarboxylation activity but classify affected individuals based on their leucine tolerance and metabolic response to illness. Decarboxylation data are from Chuang & Shih [2001].

From: Maple Syrup Urine Disease

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