ClC-7 KO mice show severe osteopetrosis without changes in lysosomal acidification (Kornak et al., 2001; Kasper, 2005) but with a reduction in luminal [Cl−] (Weinert et al., 2010), and lysosomal storage disease, associated with retinal degeneration and severe neurodegeneration (Kornak et al., 2001; Kasper, 2005). The gene discussed is CLCN7; the disease is osteopetrosis.