Multiple Hereditary Exostoses (MHE) is a benign condition characterized by the growth of many bony protrusions, known as osteochondromas, on the surface of bones. These growths occur frequently near where tendons attach to bones. MHE is an autosomal dominant genetic disorder primarily affecting the EXT1 and EXT2 genes. It is a rare condition that occurs in about 1 in 50,000 births.

MHE can lead to progressive skeletal abnormalities in the extremities, including unilateral or bilateral side shortening. This can result in a discrepancy in limb length and low height. Individuals with MHE are also at an increased risk of experiencing complications due to changes in bone growth. For example, if one bone grows faster or slower than the other, or osteochondromas develop on one or both bones, it can lead to difficulties. Osteochondromas can also put pressure on the opposite side of a joint, causing it to dislocate or become misaligned. In some cases, the growths can also influence on the joint itself, affecting joint motion.

Diagnosing MHE involves a combination of X-rays, clinical examinations, and genetic testing. However, based on current technology, around 15% of patients with MHE may have “normal” genetics.