DMPK and myotonic dystrophy type 1: When we performed a previously reported modified TP-PCR assay for DM1 (Kakourou et al., 2010), which involves simultaneous 5′ TP-PCR and standard PCR of the DMPK CTG locus and PCR of a linked microsatellite marker, D19S112, on two DM1 samples GM04567 and GM3989, we observed several challenges.