Figure 9.

Detection of the intron 22 inversion of the factor VIII gene using long distance PCR (LD-PCR).⁹⁷ Primers P and Q hybridise specifically to sequences within the factor VIII gene and flank int22h-1. Primers A and B hybridise specifically to sequences flanking int22h-2 and int22h-3. The normal factor VIII gene therefore gives the LD-PCR products P + Q (12 kb) and A + B (10 kb). The intron 22 inversion results in the hybridisation site for primer Q being displaced towards the telomere, whereas the hybridisation site for primer B from the distal or proximal int22h homologue (depending on which was involved in the homologous recombination leading to the inversion, distal shown here) is brought into context with primer P. The inverted gene therefore gives the LD-PCR products P + B (11 kb), A + B (10 kb), and Q + A (11 kb). An A + B product is always obtained because one copy of the int22h homologues is unaffected by the inversion.