Nevertheless, using conditional alleles, it has been demonstrated that CNS-specific loss of Nbs1 leads to microcephaly, defects in the development of the cerebellum and ataxia, in contrast to ATM-deficient mice or hypomorphic Nbs1 alleles that do not exhibit ataxia (Kang et al., 2002; Williams et al., 2002; Frappart et al., 2005; Stracker and Petrini, 2011). This evidence concerns the gene ATM and cerebellar ataxia.