Credit: University of Tartu 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. In collaboration with the Broad Institute of MIT and Harvard, these patients have undergone extensive genome-wide sequencing analyses at the level of the exome (the sequence of all genes), genome (whole DNA sequence), and transcriptome (RNA transcribed from the genome).