Maple Syrup Urine Disease (MSUD) is due to an inability to metabolize branched chain amino acids. Some forms of MSUD are associated with symptoms less severe than classic MSUD. Some patients with MSUD of intermediate severity appear to respond to dietary thiamine.
Some investigators do not believe that thiamine-responsiveness is a true phenotype but rather an expression of other factors.
Intermediate MSUD is associated with decreased but present activity of the BCKAD complex (branched-chain alpha-ketoacid dehydrogenase complex). Enzyme activity in fibroblasts range from 2 to 40% of normal (versus less than 3% in the classic form).
Onset: variable
General findings:
(1) anorexia with poor feeding
(2) normal to poor growth
(3) variable developmental delay
(4) variable irritability
(5) encephalopathy and clinical deterioration if acutely ill, dehydrated or fasting
Laboratory findings:
(1) ketonuria when sick
(2) elevated plasma leucine concentration when sick
(3) maple syrup smell to urine and cerumen due to the presence of sotolone (4,5-dimethyl-3-hydroxy-2[5h]-furanone)
Administration of oral thiamine (10 to 1000 mg per day) results in:
(1) improved leucine tolerance
(2) improved biochemical profile
In addition the patient is placed on dietary restriction of branched chain amino acids.
