The classic, neonatal onset form appears in the first week of life, with impaired consciousness, refusal to drink, neurological signs and abnormal pedalling movements.

In a person who does not have MSUD, the level of leucine in the blood is between 1 and 5 mg/100mL, valine 1.5-5 mg/100mL and isolucine 0.5-3 mg/100mL.

In a person with this disease, the leucine level is over 26 mg/100mL, with valine levels of 8-10 mg/100mL and isoleucine levels at 3-7 mg/100mL.

Without treatment, the disease will progress to deep coma. Death can follow in

10-15 days.

There are also &lquot;intermediate&rquot; forms which appear later and present as encephalopathy with mental retardation or in the form of repeated coma.

The diagnosis : concentration of leucine, isoleucine and valine in the blood, the increase of keto acids excreted in the urine, characteristic smell of the urine. The coma back to the normal when the quantity of leucine, isoleucine and valine are reduced.