BLM, WRN, and RTS syndromes are recessive genetic disorders of humans caused by loss of function by BLM (Ellis et al., 1995), WRN (Yu et al., 1996), and RTS helicases (Kitao et al., 1998, 1999, 2002; Lindor et al., 2000), respectively, and are characterized by genomic instability in patient cells, predisposition to various cancers and accelerated onset of aging phenotypes. Here, BLM is linked to hereditary disease.