CLCN7 and osteosclerosis: Moreover, mutations of CLC‐7, which provides a Cl− countercurrent to allow acidification of the osteoclast resorption lacuna [Bollerslev et al., 2013], cause ADO type 2 (OPTA2), also called Albers–Schonberg disease, which is characterized by osteosclerosis predominantly affecting the spine, pelvis and skull base and resulting in bone fragility, fractures, and dental abscesses [Bollerslev et al., 2013].