RESUMO
Hereditary combined vitamin K-dependent (VKD) coagulation factor deficiency is an autosomal recessive bleeding disorder associated with defects in either the gamma-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.
Assuntos
Carbono-Carbono Ligases/deficiência , Carbono-Carbono Ligases/genética , Transtornos de Proteínas de Coagulação/enzimologia , Transtornos de Proteínas de Coagulação/genética , Vitamina K/metabolismo , Alelos , Sequência de Aminoácidos , Substituição de Aminoácidos , Sequência de Bases , Transtornos Herdados da Coagulação Sanguínea/enzimologia , Transtornos Herdados da Coagulação Sanguínea/genética , Criança , Sequência Conservada , Análise Mutacional de DNA , Primers do DNA/genética , Evolução Molecular , Feminino , Heterozigoto , Humanos , Lactente , Masculino , Oxigenases de Função Mista/genética , Dados de Sequência Molecular , Mutação de Sentido Incorreto , Linhagem , Reação em Cadeia da Polimerase , Homologia de Sequência de Aminoácidos , Vitamina K Epóxido RedutasesAssuntos
Transtornos de Proteínas de Coagulação/genética , Oxigenases de Função Mista/genética , Animais , Anticoagulantes/farmacologia , Mapeamento Cromossômico , Cromossomos Humanos Par 16/genética , Transtornos de Proteínas de Coagulação/enzimologia , Resistência a Medicamentos/genética , Humanos , Camundongos , Oxigenases de Função Mista/antagonistas & inibidores , Oxigenases de Função Mista/química , Oxigenases de Função Mista/metabolismo , Mutação de Sentido Incorreto/genética , Ratos , Vitamina K/metabolismo , Vitamina K Epóxido RedutasesRESUMO
Coumarin derivatives such as warfarin represent the therapy of choice for the long-term treatment and prevention of thromboembolic events. Coumarins target blood coagulation by inhibiting the vitamin K epoxide reductase multiprotein complex (VKOR). This complex recycles vitamin K 2,3-epoxide to vitamin K hydroquinone, a cofactor that is essential for the post-translational gamma-carboxylation of several blood coagulation factors. Despite extensive efforts, the components of the VKOR complex have not been identified. The complex has been proposed to be involved in two heritable human diseases: combined deficiency of vitamin-K-dependent clotting factors type 2 (VKCFD2; Online Mendelian Inheritance in Man (OMIM) 607473), and resistance to coumarin-type anticoagulant drugs (warfarin resistance, WR; OMIM 122700). Here we identify, by using linkage information from three species, the gene vitamin K epoxide reductase complex subunit 1 (VKORC1), which encodes a small transmembrane protein of the endoplasmic reticulum. VKORC1 contains missense mutations in both human disorders and in a warfarin-resistant rat strain. Overexpression of wild-type VKORC1, but not VKORC1 carrying the VKCFD2 mutation, leads to a marked increase in VKOR activity, which is sensitive to warfarin inhibition.
