OSTM1 and osteopetrosis: In addition, there is the carbonic anhydrase II gene (CA2; MIM# 259730), responsible for osteopetrosis with renal acidosis [17], the CLCN7 gene (MIM# 602727), coding for a putative chloride channel, and the GL gene (OSTM1; MIM# 607649), the human homolog of the grey lethal (gL/gL) mouse mutant, that also account for a small proportion of ARO [18,19,20,21].