This is characterized by progressively poorer feeding, vomiting , seizures , lethargy , and finally coma . Untreated infants die in the first few weeks of life. MSUD also occurs in an intermittent form and a mild form. Even the mildest form, MSUD results in retardation and bouts of acidosis precipitated by stresses such as illness. Infection or high protein intake may precede episodes of acidosis.
Untreated acidosis progresses to coma followed by death.
Large doses of vitamin B12 may be given during acute attacks. A low-protein diet must be maintained . Recurrent attacks of acidosis are expected. There are elevated levels of histidine in blood and urine. Mental retardation is common but not ubiquitous.