Figure 4 Altered RAD51 foci kinetics in MSH2‐deficient primary fibroblasts after irradiation. Imunohistochemical examination of RAD51. Primary skin fibroblasts from an 18‐month‐old boy (A,B) and 16‐month‐old girl (C,D), where transfected for 96 hours with MSH2 or control siRNA (OnTarget; Dharmacon, Lafayette, Colorado, USA), according to the manufacturers' instructions. These cells, together with fibroblasts from child 3 (E), were then exposed to irradiation (10 Gy) and recovered for the time shown. They were then fixed in 4% paraformal‐dehyde, permeablised in 0.1% Triton‐X and incubated with anti‐MSH2 or anti‐RAD51 antibodies, appropriate secondary flourophore‐conjugated antibodies and stained for DNA with Hoechst‐33342 (shown in blue). All bars are 10 μm.