Newborn screening for maple syrup urine disease (branched-chain ketoaciduria).

Routine newborn screening for maple syrup urine disease (MSUD) has been conducted since 1964, and more than 9 1/2 million newborns throughout the world have been tested with use of a bacterial inhibition assay (BIA) for leucine on dried filter paper blood specimens. Forty-three confirmed cases of the "classical" and the "intermediate" variant forms have been detected. The frequency of MSUD, based on these data, is approximately one in 224,000 newborns. The sensitivity and the specificity of the leucine BIA are demonstrated. There are several problems in routine screening for MSUD, including the fact that the "intermittent" variant form will be missed. A brief summary of the clinical course of the 13 cases detected by our collaborative laboratories is presented.