CLDN4 and Werner syndrome: To assess WS-region gene transcript levels, we isolated mRNA and performed quantitative RT-PCR on FZD9, BAZ1B, STX1A, CLDN3, CLDN4, RFC2, CLIP2, GTF2IRD1 (exon 2–3), GTF2IRD1 (exon 10–11), and GTF2I for 107 WS subjects (see map of deleted genes in WS in Fig. 1a).