Chloride channel 7 comprises H+/Cl- exchange transporter 7 (CLCN7) and osteopetrosis-associated transmembrane protein 1 (OSTM1) (Leisle et al. 2011). This complex localises to the lysosomal membrane where it mediates the exchange of Cl- and H+ ions, perhaps playing a role in the acidification of the lysosome (Graves et al. 2008).<br><br>Defects in CLCN7 cause osteopetrosis autosomal recessive types 2 and 4 (OPTB2, MIM:166600 and OPTB4, MIM:611490) (Frattini et al. 2003, Pangrazio et al. 2010). Defects in OSTM1 cause osteopetrosis autosomal recessive type 5 (OPTB5, MIM:259720) (Pangrazio et al. 2006).