Carbonic Anhydrase II Deficiency Syndrome (osteopetrosis with Renal Tubular Acidosis and Brain Calcification): Novel Mutations in CA2 Identified by Direct Sequencing Expand the Opportunity for Genotype-phenotype Correlation

The carbonic anhydrase II (CA II) deficiency syndrome is an autosomal recessive disorder that produces osteopetrosis, renal tubular acidosis, and cerebral calcification. Other features include developmental delay, short stature, cognitive defects, and a history of multiple fractures by adolescence. With one exception, all patients with osteopetrosis and renal tubular acidosis examined have proven to have CA II deficiency. All CA II-deficient patients analyzed have been found to have mutations in the CA2 gene. Previously, we used single strand conformational (SSCP) analysis to identify exons to be sequenced from CA II-deficient patients. In this report, we amplified all seven exons by PCR from genomic DNA and directly sequenced the amplified products. Application of this method allowed identification of eleven new mutations in 21 patients referred for confirmation of the diagnosis of CA II deficiency. These mutations were scattered over the genome from exon 2 to 7. In two opportunities for prenatal diagnosis, one from cultured amniocytes and one from chorionic villus biopsy, we demonstrated the general utility of the direct sequencing method for prenatal DNA diagnosis. These studies expand our knowledge of the heterogeneity in mutations underlying the CA II deficiency syndrome.