Alzheimer’s disease is a shockingly common condition in older adults, particular those with dementia. Early-onset Alzheimer’s disease, which occurs in patients between age 30 and 64, can sometimes be caused by an inherited change in one of three specific genes, resulting in early onset familial Alzheimer’s disease, also known as FAD. There are specific variations that cause Alzheimer’s disease in the gene coding for three specific proteins: amyloid precursor protein (APP), presenilin-1 (PS-1) and presenilin-2 (PS-2). Also called autosomal dominant Alzheimer’s disease (ADAD), FAD accounts for less than one percent of all cases of Alzheimer’s. Other cases of early-onset Alzheimer’s may also have a genetic component.
While most Alzheimer’s cases have no genetic component and there is usually no specific cause for this devastating disease, several risk factors have become clear.
What are the Risk Factors for Developing Alzheimer’s?
- Age. The biggest known risk factor for developing Alzheimer’s is age. Your risk begins to increase after age 65, as the majority of patients who have the disease are age 65 or older. Once you reach 65, your risk of developing Alzheimer’s doubles approximately every five years. For those over age 85, the risk is almost 50 percent.
- Gender. Women are known to suffer from Alzheimer’s disease far more often than men. In fact, at age 65 women have a 1 out of 6 chance of developing Alzheimer’s disease, compared to a 1 out of 11 chance in men. These numbers may partly reflect the fact that women generally have a longer life expectancy than men, as well as the fact that after menopause their levels of estrogen drop.
- Race. Research studies have found that African Americans have the highest risk of developing Alzheimer’s disease, followed closely by American Indians, Alaskan Natives, and Latinos. Those with the lowest risk of developing Alzheimer’s are Pacific Islanders, followed by Asian Americans and Caucasians.
- Genetics. Those with an immediate family member (mother, father, brother, or sister) with Alzheimer’s are up to 3 times more likely to develop the disease. There is also a specific genetic risk factor dependent on which form, or allele, of the apolipoprotein E (APOE) gene is present on chromosome 19.
- APOE ɛ4 increases the risk for Alzheimer’s disease and is also associated with an earlier onset of the disease. A person may have zero, one, or two APOE ɛ4 alleles. The more APOE ɛ4 alleles a person has, the greater the risk of developing Alzheimer’s.
- APOE ɛ2 is rare and may actually provide some protection against developing the disease. Although some who develop Alzheimer’s disease do have this allele, it is more likely to develop later in life.
- APOE ɛ3 is the most common allele and is believed to play a neutral role in the disease, meaning it does not decrease or increase a person’s risk.
- Down syndrome. Those with Down Syndrome have a higher likelihood of developing Alzheimer’s disease during their 30s or 40s. These people are born with an extra copy of chromosome 21, which carries the APP gene, responsible for producing the APP, or amyloid precursor protein. Too much APP leads to a buildup of the clumps of beta-amyloid plaques in the brain. By age 40, almost all people with Down syndrome have these plaques, along with tau tangles – two characteristics of Alzheimer’s disease.
- Head trauma. Some studies have indicated that there may be a link between Alzheimer’s disease and a major head injury. Early adulthood head injury has a strong association with developing Alzheimer’s disease later in life, and injuries causing skull fractures and prolonged periods of amnesia increase the risk even more.
- Heart health. Factors that affect the heart, such as high cholesterol levels, high blood pressure, stroke, and diabetes all appear to increase the risk of getting Alzheimer’s disease.
There is ongoing research into understanding the causes and risk factors for developing Alzheimer’s. Hopefully, we will continue to gain better insights into the causes and risk factors associated with the disease – and eventually find a cure.