EXT1 and trichorhinophalangeal syndrome: In humans, EXT1 has been linked to tricho-rhino-phalangeal syndrome (TRPS) and multiple osteochondromas (MO) [38,39]; TRPS is characterized by skeletal and craniofacial abnormalities, and MO is characterized by multiple cartilage-capped bony outgrowths of the long bones, resulting in a variety of complications such as skeletal deformity.