Sporadic Alzheimer's disease accounts for more than 90 per cent of cases. Most cases occur in people over the age of 65 and the cause is unknown. Having a close family member with the condition increases risk by a small amount.
Although there are no known genetic changes to specific genes, having one or two copies of a gene called apolipoprotein E4 (ApoE4) can increase your risk of contracting Alzheimer's, although this gene does not make it certain that you will contract Alzheimer's disease. Some people with ApoE4 never develop Alzheimer's disease.