“…Gregg AR, Aarabi M, Klugman S, et al 2021 W hile affecting relatively few people, rare diseases are collectively common, occurring in an estimated 25 to 30 million people in the U.S. Many of these diseases have a genetic cause and, although causal genetic variants have been identified for thousands of Mendelian diseases, approximately half of the ~4,000 known rare genetic diseases remain of unclear etiology, despite the advent of increasingly inexpensive and accurate sequencing technologies (Mukherjee et al, 2021). In 2014, the National Institutes of Health established the Undiagnosed Diseases Network (UDN), comprising teams of researchers and clinicians from 12 sites in the country.…”