Alzheimer’s disease (AD) is the most common type of dementia, currently affecting over 5 million Americans. Warning signs and symptoms of AD include memory loss, challenges in planning or solving problems, confusion with time or place, decreased or poor judgment, and changes in mood and personality. Given its prevalence, research on AD has soared, with investigators trying to better understand its cause and how best to treat it. Studies specifically looking at the risk factors for AD have found a significant family history effect, leaving those of us with an affected loved one worried about our own risks.
In order to truly understand our risks, however, it’s important to first understand the genetics of AD. AD is divided into two types: late-onset and early onset, with the age of 65 years old marking the separation between the two groups. Less than 5% of affected individuals have early-onset AD. A significant proportion of early-onset AD is due to an autosomal dominant genetic mutation that is inherited through the family. Autosomal dominant indicates that a mutation in only one copy of the gene is sufficient to cause disease, and therefore children of an individual with genetically confirmed autosomal dominant AD have a 50% risk of inheriting the mutation. This form of AD is what many would call ‘genetic’–inheriting one of these mutations virtually guarantees that an individual with develop AD and most often at a young age compared to the average affected individual. It is important to remember that autosomal dominant AD is very rare and represents less than 5% of all AD cases.
In addition to autosomal dominant AD, there also exists familial AD, where there is family history of AD but it does not appear to fit a strictly ‘genetic’ pattern of inheritance. This type accounts for approximately 15-25% of affected individuals and can often be seen in individuals with a specific form of a susceptibility gene called APOE. This APOE variant is typically associated with an increased risk for late-onset AD. APOE testing aside, if the average individual has a 10-12% lifetime risk for AD, an individual with an affected first-degree relative has a 15-39% lifetime risk for AD.
The remaining AD cases are considered sporadic, meaning there is very distant or no family history. The fact that approximately 75% of individuals with AD have no family history indicates that while family history is important to understand and may present an increased risk for unaffected family members, there are plenty of other factors that are just as important to consider. Studies suggest that cardiovascular risks such as smoking, obesity, diabetes, high cholesterol, and hypertension are all risk factors for AD–indicating that a healthy diet and exercise regimen can not only protect your heart but also your brain. Furthermore, studies also suggest that both social and cognitive engagement may reduce the risk for AD and other dementias.