ATM and ataxia telangiectasia: The best-studied PSs are Werner Syndrome (WS), Ataxia Telangiectasia (AT) and Hutchinson Gilford Progeria (HGPS), which carry causal mutations in the WRN RecQ helicase, ataxia telangiectasia checkpoint kinase ATM, and lamin A/C respectively (Hofer et al. 2005).