Metachondromatosis is an autosomal dominant, incompletely penetrant genetic disease affecting the growth of bones, leading to exostoses primarily in the hands and feet as well as enchondromas of long bone metaphyses and iliac crests. This syndrome affects mainly tubular bones, though it can also involve the vertebrae, small joints, and flat bones. The disease is thought to affect exon 4 of the PTPN11 gene. Metachondromatosis is believed to be caused by an 11 base pair deletion resulting in a frameshift and nonsense mutation. The disease was discovered and named in 1971 by Pierre Maroteaux, a French physician, when he observed two families with skeletal radiologic features with exostoses and Ollier disease. The observation of one family with five affected people led to the identification of the disease as autosomal dominant. There have been less than 40 cases of the disease reported to date. Signs and Symptoms
Metachondromatosis is identified by the presence of both multiple enchondromas and osteochondromas in the patient, although other less characteristic symptoms are often associated with the disease. The symptoms usually become apparent in the first 10 years of life and disappear later in life. The symptoms of Metachondromatosis are seen as follows:

Enchondromas
Enchondromas are benign tumors present on the inside of bones. In Metachondromatosis, enchondromas involves the iliac crests and metaphyses of long bones, often the proximal femur. Usually, these tumors are painless; however, when present in the hands or feet, or in multiple lesions, as typically seen, bone deformity can occur.
Osteochondromas
Osteochondromas are benign tumors located on the surface of bone near growth plates. These tumors also often in the hands and feet, primarily affecting the digits of fingers and toes. These tumors tend to subside after 10-20 years of life. These tumors can become painful if they pressure sensitive tissue or nerves. Metachondromatosis is differentiated from hereditary multiple osteochondromas by the location of the location of Osteochondromas tumors as well as the lack of bone-shortening. Abnormality of epiphysis morphology
The epiphysis is the rounded end part of bone. The structure of the epiphysis can be abnormal in metachondromatosis. Abnormality of the metaphysis
The metaphysis is wide portion of a long bone, and also has abnormal structure in the disease. Avascular necrosis
Avascular necrosis is the death of bone due to a decreased blood supply. Bone pain
People with metachondromatosis often experience bone pain due to abnormal bone shapes. Cranial nerve paralysis
Cranial nerve paralysis can affect the functions associated with the cranial nerve. Genetics
Metachondromatosis is inherited in an autosomal dominant manner, needing only one copy of the defective gene to cause the disorder. The cause of the disorder has been linked to an 11 base pair deletion in exon four of the PTPN11 gene  (12q24.13). This deletion causes a frameshift, resulting in a nonsense mutation with a premature stop codon. This causes severe truncation and loss of function in the gene’s protein product, tyrosine phosphatase SHP-2.