Informativeness of a novel multiallelic marker-set comprising an F8 intron 21 and three tightly linked loci for haemophilia A carriership analysis

Authors

  • F. B. MACHADO,

    1. Núcleo de Diagnóstico e Investigação Molecular, Universidade Estadual do Norte Fluminense Darcy Ribeiro, Campos dos Goytacazes, RJ, Brazil
    2. Hospital Escola Álvaro Alvim, Campos dos Goytacazes, RJ, Brazil
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    • Present address: Departamento de Genética, Faculdade de Medicina de Ribeirão Preto, Universidade de São Paulo, Avenida Bandeirantes, 3900, Monte Alegre, CEP 14049-900, Ribeirão Preto, SP, Brazil.

  • A. F. ALVES DA SILVA,

    1. Núcleo de Diagnóstico e Investigação Molecular, Universidade Estadual do Norte Fluminense Darcy Ribeiro, Campos dos Goytacazes, RJ, Brazil
    2. Hospital Escola Álvaro Alvim, Campos dos Goytacazes, RJ, Brazil
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  • L. C. ROSSETTI,

    1. Sección Genética Molecular de la Hemofilia, Departamento de Genética, Academia Nacional de Medicina de Buenos Aires, Buenos Aires, Argentina
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  • C. D. DE BRASI,

    1. Sección Genética Molecular de la Hemofilia, Departamento de Genética, Academia Nacional de Medicina de Buenos Aires, Buenos Aires, Argentina
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  • E. MEDINA-ACOSTA

    1. Núcleo de Diagnóstico e Investigação Molecular, Universidade Estadual do Norte Fluminense Darcy Ribeiro, Campos dos Goytacazes, RJ, Brazil
    2. Laboratório de Biotecnologia, Centro de Biociências e Biotecnologia, Universidade Estadual do Norte Fluminense Darcy Ribeiro, Campos dos Goytacazes, RJ, Brazil
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Enrique Medina-Acosta, Laboratório de Biotecnologia, Centro de Biociências e Biotecnologia, Universidade Estadual do Norte Fluminense Darcy Ribeiro, Avenida Alberto Lamego 2000, Parque Califórnia, Campos dos Goytacazes, RJ, CEP 28013-602, Brazil.
Tel./fax: +55 22 273 97086; e-mail: quique@uenf.br

Abstract

Summary.  The extraordinary heterogeneous nature of the deleterious mutations in the F8 gene that lead to functional deficiency of clotting factor VIII in haemophilia A makes routine direct mutation profiling difficult. When direct mutation analysis cannot be performed or a causative/candidate mutation is not found, a second-line approach to track the defective F8 gene within at-risk families is linkage genetic analysis with, tried-and-tested, F8-intragenic and/or extragenic non-recombining multiallelic short tandem repeats (STR). Although several typing STR loci within and around F8 have been described, there is need for improving assessment, because the combined informativeness of available assays rarely reaches 100%. Here, we characterized a newly identified 0.28 cM-resolution marker-set, consisting of a dinucleotide STR located on F8 intron 21 (F8Int21; [AC]n) and three extragenic tetranucleotide STR located on GAB3 intron 1 (GAB3Int1; [TAAA]n) and TMLHE intron 1 (TMLHEInt1.1; [GAAA]n and TMLHEInt1.3; [ATTC]n). Heterozygosity rates determined in 100 unrelated females ranged from 0.25 (GAB3Int1) to 0.63 (F8Int21). The set rendered a combined informativeness of 0.91 for at least one marker and 0.60 for a minimum of two loci, with at least one F8-intragenic. Multiallelic interlocus non-random association analysis revealed that GAB3Int1 is not in significant gametic disequilibrium (GD) with F8Int21, F8Int9.2, TMLHEInt1.3 or TMLHEInt1.1. Gametic disequilibrium breakdown attests historical recombination between GAB3Int1 and the F8 gene. Through computational analysis of reference assembly sequence data, we note in the GD breakdown region and in the F8 gene a higher than average density of the 13-mer CCNCCNTNNCCNC consensus motif, commonly associated with recombination hotspots.

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