Various human topoisomerase homologs have also been shown to regulate cellular senescence [66], [67], promote telomere stability [68], and interact with the RecQ helicases encoded by WRN (MIM 604611) [69] and BLM (MIM 604610) [70], in which mutations cause the progeroid disorders Werner syndrome [71] and Bloom syndrome [72], respectively. Here, BLM is linked to Bloom syndrome.