Genetics definitely plays a role in diabetes. But in most cases, it isn’t the whole story.
Usually genetics affect how likely it is that someone will get diabetes. But whether they get it or not depends on what happens to them and/or what they do. Nature and nurture are both involved.
Before getting too far into what causes diabetes, let’s back up and talk about what diabetes is. Diabetes is a disease where sugar builds up in the blood. If untreated, this extra sugar can cause damage to eyes, nerves, blood vessels, and kidneys.
Where does this sugar come from?
After you eat, your body breaks down food into a sugar called glucose. The glucose is then released into the blood to feed your cells. Normally, a protein called insulin helps to get the glucose into the cells and turned into energy.
In people with diabetes, something in this process goes wrong. People with Type 1 diabetes don’t make enough insulin. People with Type 2 diabetes don’t use their insulin correctly.
In both cases, people inherit differences in their DNA that increase their risk of getting diabetes.
So what differences lead to Type 1 diabetes? One obvious difference would be one in or around the insulin gene itself*. This isn’t that common, though. Most people with Type 1 diabetes have a normal insulin gene.
Other DNA differences can lead to an increased risk of getting Type 1 diabetes. For example, some people with Type 1 diabetes have differences in genes called HLA genes that normally help the immune system to work. In addition, there are probably at least 16 other areas of DNA where differences can increase your risk of getting Type 1 diabetes. Scientists are still trying to figure out what these are and how they work.
With Type 2 diabetes, the story is even less clear. In most cases, you need more than one DNA difference to get Type 2 diabetes. There are at least 12 genes that have been shown to be involved in Type 2 diabetes, and there are probably more that scientists know nothing about yet.