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Blood, 15 September 2006, Vol. 108, No. 6, pp. 1925-1931. Prepublished online as a Blood First Edition Paper on May 23, 2006; DOI 10.1182/blood-2005-12-010660.
HEMOSTASIS, THROMBOSIS, AND VASCULAR BIOLOGY Compound heterozygosity of novel missense mutations in the gamma-glutamyl-carboxylase gene causes hereditary combined vitamin K–dependent coagulation factor deficiencyFrom the Laboratory of Hemostasis and Thrombosis, U689 Institut National de la Santé et de la Recherche Médicale, Institut Fédératif de Recherche 139, University Paris 7, Hôpital Lariboisière, France; Departments of Molecular Cardiology and Molecular Genetics, Lerner Research Institute, Cleveland Clinic Foundation, OH; Laboratory of Hematology, Hôpital Habib Thameur, Tunis, Tunisia; and Department of Pediatrics, Hôpital Mongi Slim, La Marsa, Tunisia.
Hereditary combined vitamin K–dependent (VKD) coagulation factor deficiency is an autosomal recessive bleeding disorder associated with defects in either the
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| Copyright © 2006 by American Society of Hematology Online ISSN: 1528-0020 | |||||||||
-carboxylase, which carboxylates VKD proteins to render them active, or the vitamin K epoxide reductase (VKORC1), which supplies the reduced vitamin K cofactor required for carboxylation. Such deficiencies are rare, and we report the fourth case resulting from mutations in the carboxylase gene, identified in a Tunisian girl who exhibited impaired function in hemostatic VKD factors that was not restored by vitamin K administration. Sequence analysis of the proposita did not identify any mutations in the VKORC1 gene but, remarkably, revealed 3 heterozygous mutations in the carboxylase gene that caused the substitutions Asp31Asn, Trp157Arg, and Thr591Lys. None of these mutations have previously been reported. Family analysis showed that Asp31Asn and Thr591Lys were coallelic and maternally transmitted while Trp157Arg was transmitted by the father, and a genomic screen of 100 healthy individuals ruled out frequent polymorphisms. Mutational analysis indicated wild-type activity for the Asp31Asn carboxylase. In contrast, the respective Trp157Arg and Thr591Lys activities were 8% and 0% that of wild-type carboxylase, and their compound heterozygosity can therefore account for functional VKD factor deficiency. The implications for carboxylase mechanism are discussed. 
