Real-Time RT-PCR for CTG Repeat-Containing Genes

Myotonic dystrophy (DM1) is a neuromuscular disorder caused by a CTG_n expansion in the 3′-untranslated region (UTR) of myotonic dystrophy protein kinase (DMPK ). SIX5 is a homeodomain gene located just downstream of the repeat, and myotonic dystrophy WD protein (DMWD ) is located close upstream of DMPK . It has been hypothesized that the expansion might influence the expression of the three myotonic dystrophy locus genes (DM1-locus), contributing to the complex and varied phenotype in this disorder. Real-time quantitative reverse transcription-polymerase chain reaction, or TaqMan, is a very sensitive method that enables quantification of expression levels of genes from small amounts of tissue and lowly expressed genes. Because data are collected during the assay, the quantification is possible over a wide range of expression levels. By the use of a standard curve and an endogenous control, we have applied the TaqMan system for absolute quantification of the expression levels of the three genes (DMPK , DMWD , and SIX5 ) in the same tissue sample.