| maple syrup urine d. |
an autosomal recessive aminoacidopathy due to a defect in the second step in branched-chain amino acid catabolism; the decarboxylation of the corresponding α-keto acids by the branched-chain α-keto acid dehydrogenase complex. Branched-chain amino acids and their keto acid analogues accumulate in blood and urine, causing severe ketoacidosis, seizures, coma, physical and mental retardation, and a characteristic smell of maple syrup in the urine and on the body. The disease can be divided into four clinical phenotypes: classic, the most severe, with neonatal onset and usually rapid death; intermediate, of lessened severity and usually later onset; intermittent, with normal periods punctuated by periods of ataxia and ketoacidosis; and thiamine-responsive, caused by decreased affinity of the dehydrogenase complex for the cofactor thiamine pyrophosphate. In at least some cases, MSUD is due to deficiency of one of the enzymes of the branched-chain α-keto acid dehydrogenase complex (see under complex). See also lipoamide dehydrogenase deficiency. Called also branched-chain ketoaciduria.
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