TP53BP1 and Hutchinson-Gilford progeria syndrome: We used two strains of fibroblasts derived from individuals with HGPS, AG11513 and AG11498, both carrying a typical C to T base-change mutation at nucleotide 1824 in the lamin A gene, and measured the number of DSB repair foci (53BP1 and γH2AX foci) at various times after irradiation with 1 Gy.