Propionic acidemia (PA) is a rare but severe recessive autosomal disease caused by a deficiency of propionyl-CoA carboxylase (PCC) alpha or beta subunits, respectively encoded by PCCA and PCCB. PCC catalyzes the conversion of propionyl-CoA to methylmalonyl-CoA, upon the catabolism of valine, isoleucine, threonine, methionine, odd-chain fatty acid, and cholesterol. The gene discussed is CRYGD; the disease is propionic acidemia.