Three common isoforms of APOE have been recognized: APOE2 (cys112, cys158), APOE3 (cys112, arg158) and APOE4 (arg112, arg158) and the presence of the alleles coding for the APOE4 isoform are associated with an increased risk (up to tenfold in homozygous cases1) of late onset AD when compared to the most common APOE3 allele or APOE2, a rarer allele, that appears to have, instead, a protective effect2, 3. Here, APOE is linked to Alzheimer disease.