Hereditary multiple exostoses

Hereditary multiple osteochondromas
Other names	Hereditary multiple exostoses
Photograph of the legs of a 26-year-old male showing multiple lumps leading to deformity.
Specialty	Medical genetics

Hereditary multiple osteochondromas (HMO), also known as hereditary multiple exostoses, is a disorder characterized by the development of multiple benign osteocartilaginous masses (exostoses) in relation to the ends of long bones of the lower limbs such as the femurs and tibias and of the upper limbs such as the humeri and forearm bones. They are also known as osteochondromas. Additional sites of occurrence include on flat bones such as the pelvic bone and scapula. The distribution and number of these exostoses show a wide diversity among affected individuals. Exostoses usually present during childhood. The vast majority of affected individuals become clinically manifest by the time they reach adolescence.^[1][2] The incidence of hereditary multiple exostoses is around 1 in 50,000 individuals.^[3] Hereditary multiple osteochondromas is the preferred term used by the World Health Organization. A small percentage of affected individuals are at risk for development of sarcomas as a result of malignant transformation. The risk that people with hereditary multiple osteochondromas have a 1 in 20 to 1 in 200 lifetime risk of developing sarcomas.^[4]