Study reveals a new form of muscular dystrophy associated with pathogenic changes in JAG2 gene In about a quarter of patients with hereditary diseases, the cause of the disease remains unclear even after extensive genetic testing. One reason is that we still do not know enough about the function of many genes. Of the 30,000 known genes, just a little more than 4,000 have been found to be associated with hereditary diseases. At the Department of Clinical Genetics of the University of Tartu Institute of Clinical Medicine, under the leadership of Professor Katrin Õunap, patients with hereditary diseases of unclear cause have been studied in various research projects since 2016.