Marble bone disease, characterized by increased bone density is due to mutation in the gene encoding
Osteopetrosis  (marble  bone  disease),  characterized  by increased bone density, is a rare condition characterized by  inability  to  resorb  bone.  One  form  occurs  along  with  renal tubular acidosis and cerebral calcification. It is due to mutations  in  the  gene  (located  on  chromosome  8q22) encoding carbonic anhydrase II (CA II), one of four isozymes of carbonic anhydrase present in human tissues. In osteoclasts involved in bone resorption, CA II apparently provides protons to neutralize the OH−  ions left inside the cell when H+  ions are pumped across their ruffled borders.
Thus, if CA II is deficient in activity in osteoclasts, normal bone resorption does not occur, and osteopetrosis results. The mechanism of the cerebral calcification is not clear, whereas the renal tubular acidosis reflects deficient activity of CA II in the renal tubules.
Harper, Ed 30, Pg No 642, 643
Carbonic anhydrase I
Carbonic anhydrase II
Carbonic anhydrase III
Carbonic anhydrase IV