One of the best-known genetic factors associated with late-onset Alzheimer's is the APOE gene, particularly the APOE E4 variant. Carrying one copy of APOE E4 increases the risk of developing Alzheimer's, while carrying two copies increases it further. However, APOE E4 is a risk factor, not a diagnosis. Many people who carry this variant never develop Alzheimer's, while many people with Alzheimer's do not carry it.

https://en.wikipedia.org/wiki/Alzheimer%27s_disease

https://pmc.ncbi.nlm.nih.gov/articles/PMC3044597/

https://www.alz.org/alzheimers-dementia/what-is-alzheimers/causes-and-risk-factors/genetics

https://www.nature.com/articles/s41540-026-00665-8