The intron 22 inversion is caused by intrachromosomal homologous recombination of the Int22h (intron 22 homologous region) repeats in opposite orientation, accounting for almost 45%-50% of all cases of severe hemophilia A. By contrast, recombinations between similarly oriented int22h repeats in the same chromosome, homologous chromosomes or chromatids may cause deletion or duplication of the intermediate region between the two int22h copies, resulting in false-positive or false-negative possibility that obscure the characterization of intron 22 inversion. The modified long distance PCR(LD-PCR) and inverse shifting PCR(IS-PCR) would distinguish all the possible int22h-mediated rearrangements.