pediatrics
Branched Chain Amino Acid Metabolism Disorders
Propionic acidemia
Deficiency of propionyl CoA carboxylase, the enzyme responsible for metabolizing propionic acid to methylmalonate, causes propionic acid accumulation. Illness begins in the first days or weeks of life with poor feeding, vomiting, and respiratory distress due to profound High anion gap acidosis , hypoglycemia, and hyperammonemia. Seizures may occur, and bone marrow suppression is common. Physiologic stresses may trigger recurrent attacks. Survivors may have conjugates in blood and urine, and confirmed by measuring propionyl CoA carboxylase activity in white blood cells or cultured fibroblasts and/or genetic testing. (Also see Initial testing .) Acute treatment of propionic acidemia is with IV hydration (including high-dosedextrose), nutrition, and protein restriction; carnitine may be helpful. If these measures are insufficient, peritoneal dialysis or hemodialysis may be needed. Long-term propionic acidemia treatment is dietary restriction of precursor amino acids and odd-chain fatty acids and possibly continuation of carnitine supplementation. A few patients respond to high-dosebiotinbecause it is a cofactor for propionyl CoA and other carboxylases. Intermittent courses of antibiotics should be considered for reducing a propionic acid load resulting from intestinal bacteria. An emergency plan for how to manage acute illness, which may provoke a metabolic crisis, should be in place. 