Because of high variance, however, it was impossible to reliably discriminate between classic and variant MSUD by NBS results.

Total leucine concentrations in newborns suffering from classic MSUD (subjects C1–C10) were significantly higher than concentrations in newborns who were later attributed to a variant form (subjects V1–V9). MSUD was suspected by detecting increased total leucine concentrations in dried blood spots collected between the second and eighth day of life. In Table 1, we present laboratory data of 19 newborns who screened positive for MSUD in Germany and Austria from 1999 to 2005. P < 0.05 was considered statistically significant. The Wilcoxon rank sum test (Mann–Whitney U-test) was used to compare differences between the 2 groups of patients. Data analysis was performed by SPSS-12 (SPSS Inc). Data are presented as ranges and/or mean (SD). Data on the patients with classic MSUD have been published recently( 2). We compared total leucine concentrations in dried blood and leucine concentrations in plasma during confirmation diagnosis between subjects attributed retrospectively to classic or variant MSUD.

About 75% of MSUD patients have the severe classic form (1.5 million newborns in the Bavarian and Berlin screening laboratory). Deficiency of the branched-chain 2-keto acid dehydrogenase leads to the accumulation of branched-chain amino acids (BCAA) leucine, valine, isoleucine, and alloisoleucine. Maple syrup urine disease (MSUD) 1 (OMIM 248600) is an inborn error of metabolism detectable by newborn screening (NBS).

Maple syrup urine disease animation