Hide and seek: Somatic SMAD3 mutations in melorheostosis

In the current issue of JEM, Kang et al. (https://doi.org/10.1084/jem.20191499) describe somatic mutations in the SMAD3 gene causing endosteal melorheostosis. Using osteoblast models, the identified mutations are demonstrated to exert a gain-of-function mechanism, augmenting transforming growth factor (TGF) β signaling. These findings provide further insights into the genetic etiology of melorheostosis and consolidate the importance of the TGFβ pathway in skeletal disorders.