To determine if Atm heterozygosity extends healthspan in Ercc1-/∆ mice, age-related symptoms, including kyphosis, tremor, ataxia, gait disorder, hind limb muscle wasting, forelimb grip strength and, in particular, dystonia were measured weekly in Ercc1-/∆ and Ercc1-/∆Atm+/- mice. The gene discussed is ATM; the disease is Ataxia.