Skeletal dysplasias with increased bone density: evolution of molecular pathogenesis in the last century.

Skeletal dysplasias (SKD) with increased bone density form a discrete group of SKDs as per the Nosology and Classification of Genetic Skeletal Disorders, 2010 Revision. This group, with the prototype disorder being osteopetrosis, has evolved over the last century, with new entities being described & their molecular basis being increasingly elucidated. Osteopetrosis, which remained an enigma in the early part of its description, is now known to be genetically heterogenous. Other disorders in this group, which were initially described as variant forms of osteopetrosis, are now recognised to be distinct conditions. However, all these SKDs with increased bone density share their molecular pathogenesis as majority arise due to mutations in the genes governing osteoclast formation and function.