EXT1 or EXT2 loss of function mutations results in the autosomal dominant disease multiple osteochondromas (MO, OMIM No. 133700 and 133,701), previously also known as hereditary multiple exostoses (HME) and multiple hereditary multiple exostoses (MHE) (Wuyts and Hul 2000). This evidence concerns the gene EXT1 and hereditary multiple exostoses.