... after childhood illness. Treatment includes a low-protein diet. Propionic acidemia (>1 in 75,000). Defect in processing four amino acids leading to ill-ness in newborns, including brain damage, ... DisordersIsovaleric acidemia (<1 in 100,000). Inability to process the amino acid leucine. Can cause coma, brain damage, or death in infancy, or emerge later in childhood after infectious ill-ness. ... special diet, continued indefinitely.Homocystinuria (<1 in 100,000). Lack of an enzyme that converts the amino acid homo-cysteine into cystathionine, needed for normal brain development....