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.

Hereditary multiple osteochondromas (HMO) — formerly known as multiple hereditary exostoses — is a genetic condition caused by a change, or mutation, in one of your genes. This change causes many noncancerous (benign) tumors, known as osteochondromas, to form in certain bones.

What is hereditary multiple exostosis? Hereditary multiple exostosis, also known as diaphyseal aclasis, is a genetic condition often passed down to a child by one parent, but it can also be caused by a genetic mutation, meaning it can occur on its own by a change.