Original investigation

Human Genetics

, Volume 99, Issue 5, pp 634-637

First online:

Carbonic anhydrase II (CA II) deficiency in Maghrebian patients: evidence for founder effect and genomic recombination at the CA II locus

  • D. M. FathallahAffiliated withHuman Molecular Genetics Group, Laboratory of Immunology, Institute Pasteur of Tunis, P.O. Box 74-1002 le Belvedere, Tunis, Tunisia Tel.: + 216-1-789 608; Fax: + 216-1-791 833
  • , Mohamed BejaouiAffiliated withDepartment of Pediatrics, Charles Nicolle Hospital, Tunis, Tunisia
  • , Denis LepaslierAffiliated withCentre d’Etude du Polymorphisme Humain CEPH, Paris, France
  • , Khelifa ChaterAffiliated withDepartment of History, Faculty of Arts and Literature, University of Tunis, Tunisia
  • , William S. SlyAffiliated withDepartment of Genetics and Molecular Biology, Saint Louis University, St. Louis, USA
  • , Koussay DellagiAffiliated withHuman Molecular Genetics Group, Laboratory of Immunology, Institute Pasteur of Tunis, P.O. Box 74-1002 le Belvedere, Tunis, Tunisia Tel.: + 216-1-789 608; Fax: + 216-1-791 833

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Abstract

A splice junction mutation at the exon 2 – intron 2 boundary of the carbonic anhydrase II (CA II) gene was previously shown to be the unique mutation underlying the CA II deficiency syndrome in patients of Arab descent. Fourteen Tunisian (Maghrebian) families with a history of osteopetrosis, renal tubular acidosis, mental retardation, and CA II deficiency were studied to test the hypothesis that the mutation, found in all 24 patients, derived from a common ancestor originating in the Arabic Peninsula. A filiation study permitted us to trace these families back to a common Arabic tribe that settled in the Maghreb in the tenth century, indicating a common ethnic origin for these families. Segregation of the mutation with a TaqI biallelic restriction site polymorphism upstream of the CA II gene was studied by sequence-tagged site analysis in all the family members. These studies showed cosegregation of the Taq (-) allele with the mutation in 12 families out of 14. This observation supports a founder effect to explain the common CA II deficiency allele in this population. In the remaining two families, a genomic recombination or gene conversion occurred between the TaqI restriction marker and the mutation causing the disease. The relatively high recombination frequency suggests the presence of a hot spot for recombination or gene conversion at the CA II locus.