Autosomal recessive metabolic disorder caused by mutations in PROPIONYL-COA CARBOXYLASE genes that result in dysfunction of branch chain amino acids and of the metabolism of certain fatty acids. Neonatal clinical onset is characterized by severe metabolic acidemia accompanied by hyperammonemia, hyperglycemia, lethargy, vomiting, HYPOTONIA; and hepatomegaly. survivors of the neonatal onset propionic acidemia often show developmental retardation, and intolerance to dietary proteins. Late-onset form of the disease shows mild mental and/or developmental retardation, sometimes without metabolic acidemia.