by National Institute on Aging

Many people wonder if Alzheimer’s disease runs in their family. Is it in your genes? This question isn’t easy to answer. Researchers have identified several genetic variants that are associated with Alzheimer’s and may increase or decrease a person’s risk of developing the disease. What does that mean? Let’s first learn about the role of genes.

Human cells contain the instructions needed for a cell to do its job. These instructions are made up of DNA, which is packed tightly into structures called chromosomes. Each chromosome has thousands of segments called genes.

Genes are passed down from a person’s biological parents. They carry information that defines traits such as eye color and height. Genes also play a role in keeping the body’s cells healthy.

Variations in genes — even small changes to a gene — can affect the likelihood of a person developing a disease such as Alzheimer’s.

Do genes cause diseases?

Permanent changes in one or more specific genes are called genetic variants. Some of these variants are quite common in the human population. While most genetic variants don’t cause diseases, some do. In some cases, a person inherits a genetic variant that will almost certainly lead to that individual developing a disease. Sickle cell anemia, cystic fibrosis, and some cases of early-onset Alzheimer’s are examples of inherited genetic disorders. However, other variants may simply increase, or even decrease, a person’s risk of developing that disease. Identifying genetic variants and their effects can help researchers uncover the most effective ways to treat or prevent diseases in an individual.

Additionally, factors such as exercise, diet, chemicals, or smoking can have positive or negative effects by changing the way certain genes work. In the field of epigenetics, researchers are studying how such factors can alter a cell’s DNA in ways that affect gene activity.

Genetic research is a component of precision medicine, an emerging approach that considers individual variability in genes, environment, and lifestyle. Precision medicine will enable researchers and doctors to predict more accurately which treatment and prevention strategies will work in particular groups of people.

In most cases, Alzheimer’s does not have a single genetic cause. Instead, it can be influenced by multiple genes in combination with lifestyle and environmental factors. Consequently, a person may carry more than one gene or group of genes that can either increase or reduce the risk of Alzheimer’s.

Importantly, people who develop Alzheimer’s do not always have a history of the disease in their families. Still, those who have a parent or sibling diagnosed with the disease have a higher risk of developing Alzheimer’s than those without that association.

Genetic variants that affect Alzheimer’s disease risk

Ten years ago, researchers knew of only 10 genes linked with Alzheimer’s. Today, scientists have identified more than 70 genetic regions associated with Alzheimer’s. Understanding which genes play a role — and what role they play — may help identify new methods to prevent, delay, or treat dementia.

Hospitalization due to infection may increase a person’s likelihood of developing dementia, according to a large NIA-funded observational study. The researchers found people hospitalized with an infection were more likely to be diagnosed with dementia years later than those who were not hospitalized with infections. The results, published in JAMA Network Open, suggest measures taken to prevent infection may also contribute to dementia prevention.

Previous findings have suggested an association between dementia and certain types of infections, such as systemic and central nervous system infections. Additionally, hospitalization for any reason, but notably for infection and critical illness, has been linked to cognitive decline. Building on these findings, a team led by researchers at the University of Minnesota and an NIA scientist explored the association between hospitalization for infection and dementia by looking at data from the Atherosclerosis Risk in Communities (ARIC) study, an observational study that has followed participants for up to 32 years.

Using data from 15,688 participants who did not have dementia when they entered the ARIC study, the scientists determined whether participants were hospitalized for an infection, and how many subsequently developed dementia three to 20 years later. The research team also investigated whether different types of infections were associated with varying dementia risk.

During the maximum follow-up period of 32 years, 19% of participants were diagnosed with dementia, and 38% were hospitalized with an infection. The researchers determined people who were hospitalized with an infection were 70% more likely to be diagnosed with dementia than those who were not. The types of infections most associated with dementia were blood and circulatory, urinary, and hospital-acquired infections, such as catheter-associated urinary tract infections.

The study’s findings provide evidence that hospitalization with an infection increases one’s risk of developing dementia, underscoring the importance of infection prevention when and if possible. More research on the links between infection and cognition could also lead to improved dementia screening practices.

This research was supported in part by NIA grants K76AG057020 and RF1AG072387 and the Intramural Research Program at NIA (ZIAAG000348).