An expansion of an unstable (CTG)n trinucleotide repeat in the 3' UTR of a gene encoding a putative serine/threonine protein kinase (DMPK) on human chromosome 19q13.3 has been shown to be specific for the myotonic dystrophy (DM) disease phenotype.
The genetic basis of myotonic dystrophy is an unstable expansion of CTG repeats located in a gene on chromosome 19 that encodes a putative serine/threonine protein kinase.
The mutation causing myotonic dystrophy (DM) has recently been identified as an unstable CTG trinucleotide repeat located in the 3' untranslated region of a gene encoding for a protein with putative serine-threonine protein kinase activity.