APOE and dementia: Previous studies reported a faster decline in cognitive performance only in APOE ε4 carriers.38,39 However, controlling for prediagnostic dementia, some studies showed a modifying effect of the ε4 allele on cognitive function,40 while others did not.41 Nevertheless, the magnitude of influence of the ε4 allele on cognition in nondemented populations is typically very small, compared to its influence on AD processes.