ANALYSIS OF DYSTROPHIN EXPRESSION AFTER ACTIVATION OF MYOGENESIS IN AMNIOCYTES, CHORIONIC-VILLUS CELLS, AND FIBROBLASTS - A NEW METHOD FOR DIAGNOSING DUCHENNE MUSCULAR-DYSTROPHY

Background. DNA analysis of peripheral-blood leukocytes is routinely u sed to demonstrate mutations in the dystrophin gene in patients with D uchenne's or Becker's muscular dystrophy. In approximately 35 percent of patients, DNA studies are not informative; in these patients immuno chemical analysis of a muscle-biopsy specimen can determine whether dy strophin, the protein product of the gene for Duchenne's dystrophy, is present at reduced levels or absent. DNA analysis can be performed in amniocytes or chorionic-villus cells to identify mutations of the dys trophic gene prenatally, but immunochemical testing for dystrophin can not be performed because the protein is not expressed in these cells. Methods. To circumvent this limitation in prenatal diagnosis, we induc ed myogenesis in 21 cultures of skin fibroblasts, 49 amniocyte culture s, and 6 chorionic-villus cell cultures by infecting the cells with a retrovirus vector containing MyoD, a gene regulating myogenesis. Trans fection of MyoD into cells that do not normally develop into muscle ce lls results in the production of a protein that switches on myogenesis . We performed immunocytochemical analysis for dystrophin in the MyoD- converted muscle cells. Results. We found that 60 of 61 myotube cultur es from subjects with no family history of Duchenne's dystrophy expres sed dystrophin. Both myotube cultures from the two patients with Becke r's dystrophy also expressed dystrophin, but all cultures from nine pa tients and two fetuses with Duchenne's dystrophy were dystrophin-defic ient. Conclusions. Immunocytochemical analysis of dystrophin in geneti cally altered non-muscle cells is feasible and may be applicable to th e prenatal and postnatal diagnosis of Duchenne's muscular dystrophy wh en conventional DNA analysis is not informative.