The major clinical features of maple syrup urine disease are mental and physical retardation, feeding problems, and a maple syrup odor to the urine. The keto acids of the branched-chain amino acids are present in the urine, resulting from a block in oxidative decarboxylation. There are 5 clinical subtypes of MSUD: the 'classic' neonatal severe form, an 'intermediate' form, an 'intermittent' form, a 'thiamine-responsive' form, and an 'E3-deficient with lactic acidosis' form (246900). All of these subtypes can be caused by mutations in any of the 4 genes mentioned above, except for the E3-deficient form, which is caused only by mutation in the E3 gene.
Confirmation of a clinical diagnosis, Carrier testing in unaffected family members