When it comes to diabetes, genes are only part of the story.

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Experts have identified some of the gene mutations that contribute to type 1 diabetes, but there are certainly more waiting to be discovered. But the genes are only part of the story. Most experts believe that specific gene mutations only predispose you to develop type 1 diabetes while additional environmental factors are needed to activate those genes.

"There's a really strong genetic component but it's not the only thing going on," Leann Olansky, MD, an endocrinologist at the Cleveland Clinic tells Health. "There are environmental conditions that trigger the process."

Here's what we know about the complicated genetic portrait of type 1 diabetes.

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Credit: Getty Images

What is type 1 diabetes?

Type 1 diabetes is an autoimmune disease which interferes with one of biology's most fundamental processes: making sure sugar is available to fuel our bodies.

In a nutshell, a rogue immune system mistakenly destroys the pancreatic beta cells which produce insulin. We need insulin to move sugar from food out of our blood and into cells where it is stored for energy. Without insulin, sugar levels rise to stratospheric levels and can lead to coma and even death.

Type 1 diabetes is a lifelong disease which requires lifelong insulin replacement therapy to manage it.

Is there a "diabetes gene"?

Scientists have not identified one gene which causes type 1 diabetes. Instead, they've discovered mutations in a tribe of genes called the human leukocyte antigen (HLA) complex. Specific combinations of these mutations (called a haplotype) seem to confer a higher risk of developing type 1 diabetes.

"These mutations are associated with changes in one's immune system which stimulates an autoimmune destruction of the insulin-producing cells of the pancreas leading to type 1 diabetes," Deena Adimoolam, MD, a specialist in endocrinology and preventative medicine in New Jersey tells Health.

Specifically, these genes, which are located on chromosome 6, help the immune system identify which compounds are natural to the body and which shouldn't be there. Without this ability, the immune system has no way to tell which compounds are friend and which are foe.

This same gene complex is also involved in other autoimmune diseases, which may explain another feature of type 1 diabetes.

"Patients with type 1 diabetes can have other autoimmune diseases," says Dr. Olansky. "They probably have a similar pathway."

But the changes in HLA genes only explain about 40% of the genetic risk for type 1 diabetes. There are other genes that can not only increase the risk but also lower the risk. "There are a lot of other genes that modify that risk and make it greater or lesser," says Dr. Olansky.

The genes are most often present in Caucasian people, which makes sense because type 1 diabetes cases are overwhelmingly among white people. A specific gene mutation (HLA-DR7) may raise the risk for African Americans, while HLA-DR9 may heighten the risk for Japanese individuals.

One form of diabetes, called MODY (maturity-onset diabetes of the young), is clearly caused by variations in certain genes. Although MODY has many features of type 1 diabetes, it is not identical.

Is type 1 diabetes hereditary in families?

The gene variations responsible for type 1 diabetes are passed down in families. "The lifetime risk of developing T1DM is significantly increased if one has a family history of type 1 diabetes," says Dr. Adimoolam. "One study suggests that the risk of developing T1DM with no family history is 0.4%. If there is one parent with T1DM, the risk off their child developing T1DM increases to 3%-4%."

If your mother or father has type 1 diabetes, your risk of getting it is about 5%, versus only 1% in the general population, says Dr. Olansky.

But even among identical twins, the risk isn't equal. If one twin develops type 1 diabetes, then the other twin has a 50% chance of also developing the condition.

That means other issues are at play. "You can have the gene and be relatively protected until circumstances arise that trigger it," says Dr. Olansky.

Are there environmental triggers for type 1 diabetes?

About 25% of Caucasians have HLA types that are clearly associated with the risk of type 1 diabetes, but only about 1% of the total population actually develops type 1, says Dr. Olansky. What's more, only about 5% of those who have the actual mutations develop the condition.

So why do these gene mutations raise the risk for some folks and not for others?

Again, experts' knowledge is still in its infancy, but there seem to be environmental triggers that set the genes in motion. No one knows exactly what those triggers are but there are a number of candidates.

Certain pregnancy-related factors that have been associated with type 1 diabetes include having a mother older than 25 years, preeclampsia, neonatal respiratory disease, and jaundice, says Dr. Dr. Adimoolam.

Certain viruses have also been implicated, namely rubella and coxsackievirus, as has vitamin D deficiency and even exposure to cold weather. 

But just as no one gene explains type 1 diabetes, likely no one environmental trigger will either.

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