Final answer:
The most common genetic risk factor for Alzheimer's disease is the apolipoprotein E (APOE) gene variant E4.
Step-by-step explanation:
The most common genetic risk factor for Alzheimer's disease is the apolipoprotein E (APOE) gene variant E4. This particular variant increases an individual's likelihood of developing the disease. While there are other genes that may also be involved in the pathology of Alzheimer's, APOE E4 is the most well-known genetic risk factor.