Branched-chain organic acidurias.

Branched chain organic acidurias are a group of disorders that result from an abnormality of specific enzymes involving the catabolism of branched chain amino acids (leucine, isoleucine, valine). Maple syrup urine disease (MSUD), isovaleric acidaemia (IVA), propionic aciduria (PA) and methylmalonic aciduria (MMA) represent the most commonly encountered abnormal organic acidurias. All these four disorders present in neonates as a neurologic distress of the intoxication type with either ketosis or ketoacidosis and hyperammonaemia. There is a free interval between birth and clinical symptoms. MMA, PA and IVA present with a severe dehydration, leuconeutropenia and thrombopenia which can mimic sepsis. All these disorders can be diagnosed by identifying acylcarnitine and other organic acid compounds in plasma and urine by gas chromatography mass spectrometry or tandem MS-MS. These disorders are amenable to treatment by removing toxic compounds and by using special diets and carnitine.