Maple Syrup Urine Disease (MSUD) is due to an inability to metabolize branched chain amino acids. The intermittent form may be symptomatic only when the patient is under physiologic stress. The patient may develop clinical findings unexplained by the precipitating cause, presenting a diagnostic challenge.
Intermittent MSUD is associated with decreased activity of the BCKAD complex (branched-chain alpha-ketoacid dehydrogenase complex) compared to normal. Enzyme activity in fibroblasts range from 5 to 20% of normal (versus less than 3% in the classic form).
Onset: may not be evident until submitted to physiologic stress
General findings:
(1) normal growth
(2) normal development
Clinical findings when under physiological stress (acutely ill, dehydrated, fasting):
(1) anorexia with poor feeding
(2) encephalopathy and clinical deterioration
(3) respiratory failure
(4) focal dystonia
Laboratory findings when under physiologic stress:
(1) ketonuria
(2) elevated plasma leucine concentration
(3) maple syrup smell to urine and cerumen due to the presence of sotolone (4,5-dimethyl-3-hydroxy-2[5h]-furanone)
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