A study of APP and PSEN1 mutation carriers from six families found no overall effect of APOE e4 on cognitive decline, but in a direct comparison of age-related cognitive decline of APOE e4+ APP and PSEN1 carriers, the APOE e4+ PSEN1 carriers had a steeper decline than the APOE e4+ APP carriers7. This evidence concerns the gene APOE and Mental deterioration.