Rearrangement of the PAX5 gene detected by FISH. FISH with PAX5 probes on both patients. (Ai-ii) FISH with PAX5 probe A: the RP11-243F8 BAC probe corresponds to the entire sequence of PAX5 gene. The signal of this probe is split between derived chromosomes 7 and 9 (arrows). (Bi-ii) FISH with PAX5 probe B: the BAC RP11-297B17 and RP11-344B23 correspond respectively to the 5′ part of the PAX5 gene up to intron 7 and the 3′ part of PAX5 from intron 7. FISH only shows a split of the RP11-344B23 probe. Thus, PAX5 is rearranged in both patients between exons 7 and 10.