the purpose of the present registry is to describe the epidemiology of forearm deformities in patients with Hereditary Multiple Exostoses and to identify, independent predictors of severity of the disease and potential association with genotypic patterns

Hereditary Multiple Exostoses (HME) is a rare pediatric autosomal dominant disorder caused by loss-of-function mutations in the genes encoding the heparan sulfate (HS)-synthesizing enzymes EXT1 or EXT2. HME affects 1 in 50,000 people and has 100% penetrance but great variability in phenotypic expression. HME is characterized by formation of cartilaginous outgrowths, called osteochondromas or exostoses, next to the growth plates of many axial and appendicular skeletal elements, causing multiple, painful disfiguring and disabling skeletal deformities, and potential malignant transformation into peripherral chondrosarcoma.

The involvement of upper-limb bones by HME is associated with greater loss of function than elsewhere in the body, but even here the loss of function may be limited. Moreover, the constant relationship between height and ulnar length has long been recognized in forensic medicine and has been recently analyzed also in HME, in order to predict the clinical and functional outcomes of the upper limb.

the present registry aims to collect demographic, clinical, functional and radiographic information from patients with HME in order to establish phenotypic predictors of severity of the disease and potential association with genotypic patterns

Inclusion Criteria:

- patients with HME (> 2 exostoses)

Exclusion Criteria:

• Patients with solitary exostoses
• Patients, adults or minors, who are unable to give their timely informed consent.

Children and adults Patients with HME.