First of all, it is important to remember that the majority of cases of Alzheimer's disease are not hereditary. In fact, less than one percent of all cases of Alzheimer's disease are due to an identified gene change. In the vast majority of cases, it is likely to be a combination of heritage and environment and lifestyle factors.
Hereditary form of Alzheimer's disease means that at least three close relatives from three generations have had the disease. In about half of these cases (with close relatives for three generations), a gene mutation can be found, that is, a damaged gene that can be inherited and which is the direct cause of the disease. The research has found more than 200 gene changes/mutations in three different genes that lead to Alzheimer's disease. In the world there are a total of about 600 known families/families with hereditary Alzheimer's. In Sweden we only know about 10-15 families. In people who have early onset cognitive disorder (under 65 years) it is said that the risk of hereditary forms is somewhere between 7-12 percent.
Overall, Alzheimer's disease has only a hereditary explanation in rare cases.