Previous studies provide conflicting results on the relationship between repeat length and cognitive decline; one found longer CAG repeats (indicating less AR activity) associated with poorer cognitive performance (Yaffe et al., 2003), another found that shorter alleles associated with increased risk of AD (Lehmann et al., 2003), and a third found no relationship between repeat length and AD risk (Ferrari et al., 2013). The gene discussed is AR; the disease is Mental deterioration.