In addition to inherited breast and ovarian cancers, a variety of inherited diseases, including familial adenomatous polyposis (APC) [7], hereditary non-polyposis colon cancer (MSH2/MLH1) [8], polycystic kidney disease (PKD1) [9], neurofibromatosis (NF1 and NF2) [10,11], and Duchenne muscular dystrophy (DMD) [12], are caused by chain truncations as the primary mode. The gene discussed is PKD1; the disease is Duchenne muscular dystrophy.