Germline heterozygous loss-of-function mutations in the EXT1 (exostosin-1, located on chromosome 8q23-q24) or EXT2 (exostosin-2, located on chromosome 11p11-p12) tumor suppressor genes are responsible for over 70–95% of HME cases [5, 6]. The gene discussed is EXT2; the disease is neoplasm.