Description of a Large Duplication in F8 Gene Responsible for Severe Hemophilia A.

Hemophilia A is a common inherited bleeding disorder, caused by factor VIII (FVIII) deficiency as a result of mutations in the factor VIII gene (F8 gene). Intron 1 and 22 inversions, small insertions/deletions and point mutations are the most common genetic defects responsible for severe hemophilia A. However, a F8 gene mutation is not found in 2–5% of patients with severe hemophilia A (FVIII:C<1IU/dL). Large rearrangements are frequent in other genetic disorders and only one case of exon 13 duplication was described in a patient with mild hemophilia (Casula et al, Blood 1990). We described here a large duplication in F8 gene in a CRM⁻ patient with severe hemophilia A: (FVIII:C < 1 UI/dL, FVIII:Ag < 1%) who developed a high-titer inhibitor (peak 10 BU). A previous investigation did not find intron 1 and 22 inversion or exons /splice sites sequencing abnormalities. The promoter region was also sequenced, but no genetic mutation was then characterized. The duplication was detected by MP/LC (Multiplex PCR/Liquid chromatography) which is a quantitative method able to detect large rearrangements. Initially described by Dehainault et al (Nucl Acids Res 2004) in retinoblastoma patients, this method showed that a duplication affected a large part of F8 gene, e.g. the 3′ part of intron 10, exons 11 to 14 and a part of intron 14. To our knowledge, this is the first duplication responsible for severe hemophila A described so far. This finding suggests that the detection of large rearrangements with quantitative method as MP/LC, QMPSF or MLPA would be useful in hemophilic patients where the screening for inversions or genetic events in the coding regions are unsuccessful. This kind of large gene modifications may indeed account for at least some of the 2–5% cases where the coding sequence does not appeared to be altered. In this case, the truncation of the primary polypeptide sequence did not result in any secretion of the FVIII protein, that may have increased the risk of inhibitor development.