What causes progressive muscular dystrophy? 1, There is a gene called DMD on the human X chromosome, which encodes a protein that acts on the myocyte membrane to protect it from damage caused by exercise. 2, when the DMD gene is mutated, the protein produced by it also loses its function, so the myocyte membrane is not protected and breaks down continuously with exercise. 3, Myocytes are non-renewable cells, and one is one less if one is broken, so the child has fewer and fewer myocytes and less and less strength, thus showing a series of symptoms of weakness. DMD gene mutation → loss of Dystrophy protein function → whole body muscle cell damage → progressive weakness.