Myotonic Dystrophy Type 1 Clinical, Electrophysiological and Molecular Characterization: Experience at Tertiary Care...

Myotonic dystrophy type 1 (DM1) is the most common myotonic disorder. Molecular genetic testing of the Dystrophia Myotonica-Protein Kinase DMPK gene to detect expansion of CTG repeats is confirmatory. TP-PCR (Triplet Primed-Polymerase Chain Reaction) is rapid and effective screening for the CTG repeat expansions in myotonic dystrophy. Indian data regarding clinical and genetic evaluation of DM1 are sparse.

This was a prospective observational study at a tertiary neurology centre. It included subjects having clinical and electrophysiological evidence of myotonia with CTG repeat expansion of DMPK gene demonstrated by TP-PCR. Diagnostic molecular assessment was done by two-step procedure; conventional PCR and Fragment length analysis followed by TP-PCR.

Seventeen patients fulfilled the inclusion criteria. There were fifteen males and two females, with age ranging from 19 to 53 years (mean age 33years). In the phenotype, large calves were seen in three patients and ophthalmoparesis and scapular winging were seen in one patient each. Screening of patients by PCR-Fragment analysis identified all 17 cases to be of DM1. Further confirmatory test by TP-PCR also successfully identified the cases to be of DM1. TP-PCR technique using forward combination primers was used successfully in detecting expansion of CTG repeats in 13 cases whereas in remaining 4 cases reverse primer combination was used successfully.

This series establishes that a combination of PCR- Fragment analysis and TP-PCR is simple and cost effective in determining the diagnosis of Myotonic dystrophy type 1. This study also documents a new clinical observation of calf hypertrophy in genetically confirmed patients with DM1.