Diagnosis of Methylmalonic Acidemia from Dried Blood Spots by HPLC and Intramolecular-Excimer Flu-

Methylmalonic acidemias, a group of heterogeneous dis-orders, are characterized by accumulation of methylma-lonic acid (MMA) and its byproducts in biological fluids (1, 2). Methylmalonic acidemia is now included in all tandem mass spectrometry (MS/MS)-based newborn screening programs (3–5). Detection is based on the finding of increased propionylcarnitine and/or increased propionylcarnitine-to-acetylcarnitine ratio in dried blood spots (DBS) by MS/MS. These markers, however, are not specific because they are increased in propionic acidemia and, possibly, in multiple carboxylase deficiency (3). In most programs, newborns or patients with initial positive results are recalled for a second blood spot, and a urine sample is collected for organic acids analysis to differen-tiate among the three disorders