Clonogenic survival assay and VH gene usage. (A) Clonogenic survival after ionizing radiation showed hypersensitivity of the XLF-deficient patients (XLF5 and XLFP2) compared with control, ARTEMIS-deficient (n = 7), LIG4-deficient (n = 1), and XRCC4-deficient (n = 1) fibroblasts. (B) Median VH gene location according to the relative position in the locus starting from the first functional VH gene (VH4-74), in base pairs (bp). (C) Box-and-whisker representation of VH gene location.