Myotonic dystrophy (DM) is an autosomal dominant disorder, characterized mainly by myotonia and progressive muscle weakness, although central nervous system, cardiovascular and ocular manifestations also occur fre­quently [1]. The disease results from expansions of an unstable (CTG)n repeat, located in the 3' untranslated region (3'UTR) of the DM protein kinase (DMPK) gene on chromosome 19q13.3 [2,3]. Although the DM mutation was identified a decade ago, the pathogenic mechanisms underlying this neuromuscular disease remain elusive. Previous expression studies of the DMPK gene show con­tradictory results, indicating both increase and decrease of mRNA levels in DM patients compared to normal controls [4-11]. This may be due to different experimental ap­proaches. On the other hand, there is in vitro evidence that supports a nucleosome stabilization effect of the elongated trinucleotide repeat [12-15]. In turn, this may affect the expression of a number of genes, such as the 3' flanking DM adjacent homeobox protein (DMAHP) gene, which is expressed in myoblasts, muscle, brain, testes and other tissues often affected in DM patients [16].

In order to simultaneously monitor the effect of the (CTG)n expansion on transcription of the DMPK and DMAHP genes, we performed quantitative expression studies of both genes [using reverse transcription-polymerase chain reaction (RT-PCR)] in muscle biopsies and blood samples of DM patients and control subjects.