Scientists think that a variety of factors determine how Alzheimer’s disease develops. Increasingly, research has found that genes are a key player in the onset of the degenerative brain disease. But Alzheimer’s can manifest at different stages in life. Whether the disease is early-onset or late-onset can dictate how it is passed down.
Early-onset Alzheimer’s typically takes place between the ages of 30 and 60, and is fairly rare — it afflicts less than 10 percent of everyone with the disease. But Alzheimer's is strongly linked to genetics. Scientists have found three genes where mutations can cause early-onset familial Alzheimer’s, or FAD. If either your (biological) mother or father harbors one of the mutated genes, you have a chance of inheriting it as well. However, not everyone with early-onset Alzheimer’s has mutations in those three genes.
For most people with Alzheimer’s, symptoms start to crop up around the age of 65 or later. While researchers are still working to understood what, exactly, leads to late-onset Alzheimer’s, they think a cocktail of genetic and environmental factors shape someone’s risk for getting the disease. So, if a relative has Alzheimer’s, that doesn’t necessarily mean you’ll inherit the disease. But you may be more susceptible than others.