Results from an external proficiency testing program: 11 years of molecular genetics testing for myotonic dystrophy type 1

Carolyn (Sue) Richards, Glenn E. Palomaki, Madhuri Hegde

Research output: Contribution to journalArticle

3 Scopus citations


Purpose:The aim of this study was to examine the performance of laboratories offering assessment for myotonic dystrophy type 1 (DM1) using external proficiency testing samples. DM1, a dominant disorder, has a prevalence of 1:20,000 due to the expansion of CTG trinucleotide repeats in the DMPK gene.Methods:External proficiency testing administered by the College of American Pathologists/American College of Medical Genetics and Genomics distributes three samples twice yearly. Responses from 2003 through the first distribution of 2013 were analyzed after stratification by location (United States/international). Both the repeat sizes (analytic validity) and clinical interpretations were assessed.Results:Over the 21 distributions, 45 US and 29 international laboratories participated. Analytic sensitivity for detecting and reporting expanded repeats (≥50) was 99.2% (382/385 challenges) and 97.1% (133/137 challenges), respectively. Analytic specificity (to within two repeats of the consensus) was 99.2% (1,790/1,805 alleles) and 98.6% (702/712 alleles), respectively. Clinical interpretations were correct for 99.3% (450/453) and 98.2% (224/228) of positive challenges and in 99.9% (936/937) and 99.6% (455/457) of negative challenges, respectively. Of four incorrect interpretations made in the United States, two were probably due to sample mix-up.Conclusion:This review of laboratory performance regarding laboratory-developed genetic tests indicates very high performance for both the analytic and interpretative challenges for DM1.

Original languageEnglish (US)
Pages (from-to)1290-1294
Number of pages5
JournalGenetics in Medicine
Issue number12
Publication statusPublished - Dec 1 2016



  • External proficiency testing
  • myotonic dystrophy type 1
  • trinucleotide repeats

ASJC Scopus subject areas

  • Genetics(clinical)

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