Accelerated induction of mt mutations in UVA-irradiated CSA- and CSB-deficient cells. Primary human fibroblasts of two and three patients suffering from CSA and CSB, respectively, one XP patient (XP-D), and three normal individuals were irradiated with UVA and the relative amount of common deletion was assessed by quantitative real-time PCR. Levels of the common deletion are given in 2^−ΔΔCt as mean ± SD of at least three separate experiments. Levels above one indicate a higher amount of common deletion in UVA-treated cells relative to untreated control cells. Premature UVA-mediated induction of common deletion in CSA cells can be attenuated by treatment with the radical scavenger vitamin E. Expression of HA-tagged CSB protein in CSB-deficient cells lead to normalization of mitochondrial mutagenesis.