article_snippet: In some of these cases, it is caused by mutations in one of three genes.
article_snippet: People with any of these extremely rare mutations tend to develop Alzheimer's disease in People with any of these extremely rare mutations 30s or 40s.
article_snippet: These genes, and the prevalence of their defective versions  is as follows: .
article_snippet: These genes, and the prevalence of their defective versions   are extremely rare and account for fewer than one in 1,000 cases of Alzheimer's disease.
article_snippet: It is likely that all of those who inherit faulty versions of any of these three genes will develop Alzheimer's disease at a comparatively early age.
article_snippet: On average, half of the children of a person with one of these rare genetic mutations will inherit Alzheimer's disease.
article_snippet: People who do not inherit the mutation cannot pass the mutation on.