Myotonic dystrophy type 1 or Steinert’s disease is currently the most common form of muscular dystrophy in adults. Based on clinical ascertainment, worldwide prevalence is estimated to be 12.5/100000, but it can be higher as many patients in older generation remain undiagnosed. Inheritance of this multisystem disease is autosomal dominant, and phenotypic expression is highly variable due to an unstable expansion CTG trinucleotide repeats in the 3´ untranslated region (3´UTR) of the dystrophia myotonica protein kinase gene (DMPK, MIM*605377) located in the long arm of chromosome 19 (19q.21.3). The expanded DMPK gene produces a toxic RNA transcript that does not exit the nucleus.
Reference ranges for allele sizes were established by the Second International Myotonic Dystrophy Consortium (IDMC) in 1999 for technical standards and guidelines for testing. Normal alleles: 5-34 CTG repeats; Mutable normal (premutation) alleles: 35-49 CTG repeats. Individuals with CTG expansions in the premutation range have not been reported to have symptoms, but their children are at increased risk of inheriting a larger repeat size and thus having symptoms. Full penetrance alleles >50 CTG repeats are associated with disease manifestations.
Clinical findings in myotonic dystrophy type 1 (DM1) span a continuum from mild to severe and provide an excellent overview of all aspects of DM1. The clinical findings have been categorized into three somewhat overlapping phenotypes, mild, classic, and congenital, that generally correlate with CTG repeat size.
Adellgene® Myotonic Dystrophy Screening is a kit which detects the number of repetitions of CTG of 3´UTR region of the DMPK gene located in chromosome 19 resulting in Myotonic Dystrophy disease. The technology is based on the polymerase chain reaction (PCR) of genomic DNA extracted and purified from peripheral blood followed by fluorescence analysis of the size of the PCR fragments obtained by genetic analyzer and conversion of that size in the number of CTG repeats.