Supplemental material from: A population-based prevalence of myotonic dystrophy type 1

Objective: To determine whether the genetic prevalence of the CTG expansion in the DMPK gene associated with myotonic dystrophy (DM1) in an unbiased cohort is higher than previously reported population estimates, ranging from 5-20 per 100,000 individuals. Methods: This study used a cross-sectional cohort of de-identified dried blood spots (DBS) from the newborn screening program in the state of New York, taken from consecutive births from 2013-2014. Blood spots were screened for the CTG repeat expansion in the DMPK gene using triplet-repeat primed PCR and melt curve analysis. Melt curve morphology was assessed by four blinded reviewers to identify samples with possible CTG expansion. Expansion of the CTG repeat was validated by PCR fragment sizing using capillary electrophoresis for samples classified as positive or premutation to confirm the result. Prevalence was calculated as the number of samples with CTG repeat size ≥50 repeats compared to the overall cohort.  Results: Out o...