Dysplasia of the long bones of the hands and feet is a bone growth disorder. Affected people usually have excessive shortness of the long bones of the arms and legs, which is also called mesomelia. As a result of the short leg bones, people with this disease have a very short stature. A bone in the forearm called the ulna and a bone in the leg called the fibula often do not develop or are absent, while other bones in the forearm (radius) and in the leg (tibia) They are abnormally short, thick and bent. Dysplasia of the long bones of the hands and feet originates from changes in the SHOX gene. The protein produced from this gene plays a role in bone development and is especially necessary for the growth and maturation of the bones of the arms and legs. The most common cause of this type of dysplasia is the complete deletion of the SHOX gene. Some people with this type of dysplasia have an anomaly of the wrist and forearm bones called Madelong deformity, which may lead to pain and limited wrist movement. In addition, some affected people have mild underdevelopment of the lower jaw bone (mandible).