Propionic acidemia is an autosomal recessive metabolic disorder caused by defective functioning in the mitochondrial enzyme propionyl CoA carboxylase (PCC), resulting in the accumulation of propionic acid metabolites, and dysfunction in the respiratory chain and urea cycle pathways. The disorder is clinically heterogeneous. A neonatal-onset form is characterized by poor feeding, vomiting, and fatigue in the first days of life in a previously healthy infant, and if untreated, may be followed by lethargy, seizures, coma, and death. The neonatal form is frequently accompanied by metabolic acidosis with anion gap, ketonuria, hypoglycemia, hyperammonemia, and cytopenia. A late-onset form in older children and adults has a milder phenotype, is less common, and may present with developmental regression, chronic vomiting, protein intolerance, failure to thrive, hypotonia, and occasionally basal ganglia infarction, which may result in dystonia and choreoathetosis, and cardiomyopathy. Metabolically unstable individuals can have an acute decompensation that resembles the neonatal presentation, often precipitated by a catabolic stress such as infection, injury, or surgery, or an excessive intake of intact (i.e., complete, dietary, or natural) protein. Long-term manifestations of neonatal and late onset of propionic acidemia can include growth impairment, intellectual disability, seizures, basal ganglia lesions, pancreatitis, and cardiomyopathy. Other less common manifestations include optic atrophy, hearing loss, premature ovarian insufficiency, and chronic renal failure (summary by Jurecki et al., 2019). [from
OMIM]