Perturbation of RCAN1 levels early during aging, as shown using young Rcan1 KO and RCAN1 TG mice or Rcan1 triplication in Dp16 mice, disrupted light-entrained diurnal as well as circadian wheel running behavior in manners partly reminiscent of DS, AD, and aging. The gene discussed is RCAN1; the disease is Alzheimer disease.