Of particular interest in this study is a specific intermediate recessive osteopetrosis (IRO) type which comprises a group of OP patients who present with renal tubular acidosis or carbonic anhydrase type II (CAII) deficiency, constituting a rare autosomal recessive disorder manifested clinically by renal tubular acidosis (RTA) and cerebral calcification. This evidence concerns the gene CA2 and renal tubular acidosis.