Melorheostosis is a rare bone disease. It causes the abnormal growth of new bone tissue on the surface of existing bones. The new bone has a characteristic appearance on x-rays, often described as "flowing" or like dripping candle wax. The excess bone growth typically occurs on the bones in one arm or leg, although it can also affect the pelvis, breastbone (sternum), ribs, or other bones. (The term "melorheostosis" is derived from the Greek words "melos," which means limb; "rheos," which means flow; and "ostosis," which refers to bone formation.) The abnormal bone growth associated with melorheostosis is noncancerous (benign), and it does not spread from one bone to another.

Mutations in the MAP2K1 gene are estimated to cause about half of all cases of melorheostosis. The MAP2K1 gene provides instructions for making a protein called MEK1 protein kinase. This protein is active in many kinds of cells, including bone cells. It is part of a signaling pathway called RAS/MAPK. This signaling pathway helps control the growth and division (proliferation) of cells, the process by which cells mature to carry out specific functions (differentiation), and cell movement (migration). RAS/MAPK signaling is critical for normal development, including the formation of bones.

Melorheostosis affects about 1 in 1 million people. Approximately 400 cases have been reported worldwide.

This condition is not inherited from a parent, and it cannot be passed down to children. It arises from somatic mutations in bone cells that occur during an individual's lifetime.

Published Date: May 01, 2018
Published By: National Institutes of Health