High-resolution combined linkage physical map of short tandem repeat loci on human chromosome band Xq28 for indirect haemophilia A carrier detection.
Haemophilia A, the most common severe hereditary bleeding disorder in humans, is chiefly caused by mutations in the coagulation factor VIII F8 gene, which maps on chromosome band Xq28. Linkage analysis with F8 intragenic and/or closely located extragenic short tandem repeat (STR) elements is an effective method for indirect tracing of F8 pathogenic allelic variants in at-risk families. STR profiling is currently limited to 14 markers, 11 of which are dinucleotide elements. The aim of this study was to define novel polymorphic STR loci for haemophilia A carrier screening. The combined linkage physical map was restricted to a 2.4-Mb region on Xq28 that hosts 81 annotated genes, F8 inclusive. The inventory was in silico through comparative analyses with three X chromosome reference sequences, using microsatellite mining and validation computer software. Genetic distances for unmapped markers were interpolated on the Rutgers map of the human genome. The effort yielded 94 STR loci: 53 extragenic and 41 intragenic (14 STR elements map on the F8 gene; the other 27 on 19 further genes). The distribution per repeat period size was 61.7% di-, 5.3% tri-, 26.6% tetra- and 6.4% pentanucleotide loci. The success rate of validation of polymorphism for the new STR loci was 56.3%. For STR elements 0.78 Mb equidistant of the F8 gene, the interpolated downstream genetic length is 3.27 times the upstream genetic length. The inventory represents a 5.7-fold increase in polymorphic STR loci useful in carrier detection. Genotyping with the upstream extragenic tetra- and pentanucleotide markers is thus apprized.
Machado
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Hospital Escola Alvaro Alvim, Pelinca, Campos dos Goytacazes, RJ, Brazil.
Medina-Acosta
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