People with the APOE4 allele, known to raise the risk of Alzheimer’s disease, may be protected if they are heterozygous for a particular genetic variant that has been linked to longevity, US researchers say.

California’s Stanford University researchers investigated the possible association of carrying one copy of a variant of the Klotho gene known to be associated with longevity (Klotho-VS) and Alzheimer disease risk in their study of 22 late-onset Alzheimer’s disease cohorts with genotype data.

Klotho-VS heterozygosity was associated with 25% lower odds of Alzheimer disease in participants who carried APOE4, a significant reduction, but there was no association between heterozygosity for the variant and Alzheimer’s disease risk in any APOE4-negative group, the researchers report in JAMA Neurology.

The association was only seen in 60- to 80-year-olds, however, and was not seen in people aged 80 and older.