When we consider early onset Alzheimer's disease (where symptoms appear before the age of 60) and late onset, there is a tendency to categorize early onset as familial, meaning that it has a strong hereditary component, and late onset as sporadic, meaning that it is much more random.
However, based on what researchers are learning, we may need to rethink this. A recent study discovered similar gene mutations in cases of both early and late onset Alzheimer's disease. This indicates that there may be a higher amount of heredity in late onset Alzheimer's disease than we have traditionally thought. These researchers also point to evidence that people with Alzheimer's often have multiple relatives who have Alzheimer's, other kinds of dementia, or a neurological disorder such as Parkinson's.
Additionally, the study, published in PLoS One, found evidence that some people who were diagnosed with Alzheimer's actually had gene mutations more consistent with frontotemporal dementia (FTD). FTD is an umbrella term that encompasses several disorders including behavioral variant FTD, primary progressive aphasia, progressive supranuclear palsy and corticobasal degeneration. These disorders affect people's behavior, mobility, and communication. Often it's not until the later stages of FTD that memory is impaired.
As we learn more about how to treat these disorders, being able to distinguish between them will become increasingly important.