Early development may be normal. The pediatric
patient develops progressive dystonia and choreoathetosis. Acute encephalopathy often
develops between 6 to 18 months of age, causing striatal damage with severe neuronal
loss. Spongiform changes restricted to brainstem white matter and mild lymphocytic
infiltrates have been described.
Acute exacerbation may occur
after a minor infection, presenting with vomiting, ketosis, seizures, and coma. Death
commonly occurs during one of these episodes. A low-protein diet and high doses of
riboflavin may result in clinical improvement in some patients.