The association between APOE ɛ4 and cognitive ability may be modified by other genetic variables that exert independent effects.4 The TOMM40 523 poly-T repeat locus has recently been significantly associated with brain-related phenotypes (for example, cognitive decline), independent of APOE genotype.5 The independent effects of this locus on older-age cognitive ability have been examined in three studies. This evidence concerns the gene APOE and Mental deterioration.