Propionic acidemia (PA) is a rare inherited disorder caused by deficiency of the enzyme propionyl-CoA carboxylase. Deficiency of the propionyl-CoA carboxylase enzyme results in a buildup of potentially harmful compounds. High levels of these compounds are toxic to the body and damage the brain and nervous system. Children affected by neonatal-onset PA appear normal at birth but soon develop lethargy, seizures, coma, and possibly death in the first week of life. As they continue to grow, these individuals will have growth deficits, intellectual disability, seizures, brain abnormalities, heart manifestations, and pancreatitis. Individuals affected by late-onset PA have developmental regression, chronic vomiting, low muscle tone, and heart defects. These symptoms may become more pronounced during times of stress caused by illness, injury or long periods without food and are accompanied by breathing problems, seizures, and irritability. Movement disorders are common. Rarely, individuals present only with heart defects and arrhythmia. Currently there is no cure for PA; however initiation of a low-protein diet and medical formula as soon as a diagnosis is made, as well as careful management in times of illness or injury and avoidance of going a long time without food can help to minimize the stress and damage to the brain. Liver transplant is an option for some individuals with PA to treat some symptoms, but there are risks associated with this procedure. PA is caused by pathogenic variants in the PCCA or PCCB genes.