Reduced expression of DMAHP/SIX5 gene in myotonic dystrophy muscle

In myotonic dystrophy (DM), the expansion of CTG triplet repeats in the 3'- untranslated region of DM-protein kinase (DMPK) is a causal gene mutation. However, the pathogenic molecular mechanism of CTG repeat expansion for DM phenotypic expression is unclear. To investigate this issue, we examined th e influence of CTG repeat expansion on the expression levels of DMPK gene a nd 3'-flanking DM locus-associated homeodomain protein (DMAHP)/SIX5 gene in the muscles of DM patients. We isolated RNA from muscle tissues of six DM patients and six controls, and performed a competitive reverse transcriptio nal polymerase chain reaction (RT-PCR) assay. The total mRNA level of DMAHP /SIX5 was significantly lower in DM than in controls, but the DMPK mRNA lev el was unchanged. Our results suggest that CTG repeat expansion influences the expression of genes other than DMPK to cause the DM phenotype. (C) 2000 John Wiley & Sons, Inc.