Molecular analyses of germ line methylation patterns and of the common intron 22 inversion mutation in the factor VIII gene

Abstract

The factor VIII gene includes two major mutation hotspots: the intron 22 inversion and transitions at CpG dinucleotides, both of which have been examined in the context of this thesis. A non-radioactive southern blot approach was implemented for the detection of the inversion, that allowed an accurate diagnosis for about 1/4 of the Turkish hemophilia A families. About 45 % of all point mutations in the factor VIII gene occur at CpG sites. Previous studies had pointed to a bias in paternal origin for transition mutation at CpG dinucleotides. This was believed to be a direct reflection of the hypomethylation in the female germ cells. However, to date there was no direct proof for a differential level of methylation in the germ cells, at human disease causing codons. In this study, an original investigation was undertaken to determine the methylation status of mature germ cells at selected sites in the human factor VIII and the FGFR3 genes. An equally high level of methylation, at non-cluster CpG sites, was observed in mature eggs, spermatocytes and polar bodies. This result shows that the higher mutation rate in the male germ line is apparently not a simple reflection of sex specific methylation differences.