Carrier detection and rapid newborn diagnostic test for the common Y393N maple syrup urine disease allele by PCR-RFLP: Culturally permissible testingin the Mennonite community

The turnaround time for diagnosis of maple syrup urine disease (MSUD) by cl assic serum amino acid analyses often requires 3-4 days. This is due to the need for branched-chain amino acids (BCAA) to accumulate in the serum of t he newborn before testing. The accumulation of BCAAs in infants with MSUD d uring this time increases the risk of the infant becoming clinically sympto matic. We have developed a noninvasive DNA-based mismatch PCR-RFLP assay fo r the Y393N BCKDHA allele (E1 alpha gene of the branched chain alpha -keto acid dehydrogenase complex), the primary cause of MSUD in Old Order Mennoni te communities. The homozygosity and high frequency of this mutation in the Mennonite community and its prevalence in compound heterozygote non-Mennon ite MSUD patients is of significance. We describe carrier testing, present the results of nine newborns diagnostically evaluated for the Y393N BCKDHA allele, and demonstrate the efficacy of this PCR-RFLP assay for determining clinical status within 24 h after birth. Analyses within the first 24h of life allow for immediate diagnosis and treatment of infants homozygous for the Y393N MSUD defect. This is a significant improvement over the time requ ired by current serum amino acid analysis methods.