Together these results suggest that any individual with a family history of dementia affecting a large number of relatives and with an onset in the mid-60s should be considered for mutation screening not only of the AD genes (APP, PSEN1 and 2), but also MAPT and GRN. Our study also indicates that mutations in these genes can be present in 1 to 3% of the sporadic cases. This evidence concerns the gene MAPT and Alzheimer disease.