Generation of XpdTTD (XPDR722W) and XpdTTD/KO mice has been described previously [21,22]. A detailed description of the generation of targeting constructs for Xpd†XPCS and Xpd †XP alleles carrying mutations encoding the G602D and R683W alterations will be provided upon request. Chimeric mice and mouse embryonic fibroblasts were generated according to standard procedures. Haematoxylin and eosin staining was performed according to standard procedures. Amino acid analysis was conducted as described in [21]. Blood values were analysed using Animal Blood Counter Vet (ABX Diagnostix, Montpellier, France). Radiographs were taken, and relative bone mineral density was calculated as described in [15]. Mice used in this study were in a 129Ola/C57BL6 mixed background unless noted differently. All experiments involving mice were judged and approved by the national committee for genetic identification of organisms and the animal ethical committee, and were conducted according to national and international guidelines.