What is the Role of Genes in Diabetes?

Type 1 Diabetes, Type 2 Diabetes, and Gestational Diabetes all have different causes, but they all have a mix of genetic, environmental, and lifestyle risk factors that lead to their development. 

If you have any of these conditions, you inherited a genetic predisposition (increased liability or likelihood) which was then triggered by environmental factors. This results in the development of Type 1, Type 2, or Gestational Diabetes.

Researchers have identified several genes that can affect the release of insulin, uptake of glucose (sugar) into your cells, and the breakdown of glucose in your body, thus regulating your blood glucose levels. 

Any mutations in these genes can lead to an abnormality in the glucose metabolism in your body, which can lead to the development of diabetes. Though genes play a vital role in the development of this condition, environmental factors often play a deciding role in whether you develop diabetes. 

This is can be seen in the case of identical twins, where if one twin has Type 1 or Type 2 Diabetes, the other twin does not always have the condition, even though they are at an increased risk (50% likelier for Type 1 Diabetes, 75% likelier for Type 2 Diabetes) of developing it.

Is Diabetes Genetic?

Diabetes mellitus is a multifactorial disease, i.e. its development is likely to be connected to the effect of multiple genes and environmental risk factors. Though genes play a key role in diabetes, the environmental and lifestyle factors are the main culprits that trigger the development of the condition or make it “active”.

Let us understand the genetic and environmental risk factors for the three main types of diabetes mellitus.

Is Type 1 Diabetes Genetic?

Type 1 Diabetes is an autoimmune condition that occurs when your immune system mistakenly attacks your pancreatic beta cells (responsible for insulin production). This results in little to no insulin production in your body, leading to high blood glucose levels. 

Some people are born with a genetic predisposition to developing Type 1 Diabetes, though not all of these people develop it. Though genetic predisposition is a significant contributor, the condition develops only when triggered by an environmental factor. 

Some of these triggers may include:

• Exposure to viruses
• Exposure to harmful chemicals
• Not being breastfed as a child
• Living in cold climates

People who have siblings with Type 1 Diabetes are much likelier to develop the condition when compared to people whose parents have the condition. If both parents have Type 1 diabetes, the chances of the child developing the condition are between 10% and 25%.

According to the American Diabetes Association (ADA), you are much likelier to develop Type 1 Diabetes if your father has the condition (1 in 17 chance), compared to if your mother has the condition (1 in 25 chance). 

Also, children of women with Type 1 Diabetes are much likelier to develop the condition if they were born before their mother was 25 years of age (1 in 25 chance), compared to if they were born after their mother was 25 years of age (1 in 100 chance).

Is Type 2 Diabetes Genetic?

Type 2 Diabetes is a chronic lifestyle disorder characterised by increased insulin resistance in your cells, along with a gradual decline in pancreatic beta cell function and insulin production. Insulin resistance is the major cause of high blood sugar levels in Type 2 Diabetes.

Type 2 Diabetes is more strongly connected to family history than Type 1 Diabetes, as it tends to run in families. This can be due to heredity and genes, but may also be caused by lifestyle habits that are commonly shared among family members. 

People with Type 2 Diabetes are also more likely to have other underlying conditions like high blood pressure, high cholesterol levels, obesity, accumulation of fat in the abdominal area, etc. which also have a genetic component.

Though genetics play a role in the development of Type 2 Diabetes, poor lifestyle habits and other underlying conditions are the major contributors. Some of these triggers or risk factors are listed below:

• Being overweight or obese (Body Mass Index > 25 kg/m2 ), especially having excess visceral fat
• Lack of physical activity or exercise
• Poor or unhealthy dietary habits
• High blood pressure
• High or abnormal cholesterol and triglyceride levels
• Having a heart disease
• Chronic stress
• Smoking
• Excessive alcohol consumption

Your risk of developing Type 2 Diabetes is around 40% if you have one parent with the condition. This number shoots up to 70% if both your parents have Type 2 Diabetes.

Is Gestational Diabetes Genetic?

Gestational diabetes is a condition that is characterised by high blood sugar levels in a pregnant woman who did not have diabetes previously. These high blood sugar levels are caused by insulin resistance and a reduction in insulin production in pregnant women. 

Gestational diabetes generally develops around the 24th week of pregnancy, and usually resolves after delivery.

The ADA states that even though Type 2 Diabetes has a stronger genetic link than Type 1 Diabetes, it is possible to delay or prevent the condition with appropriate lifestyle changes. So even if you do have a family history of Type 2 Diabetes, it does not guarantee that you will develop the condition as well.

Similar to Type 2 Diabetes, genetics, environmental factors, and lifestyle factors all play a role in the development of gestational diabetes. Some of these risk factors include:

• Being overweight or obese (BMI > 25 kg/m2 )
• Being older than 25 years of age
• Having had gestational diabetes during a previous pregnancy
• Having a family history of Type 2 Diabetes or gestational diabetes
• Having previously given birth to a child who weighed over 4 kgs 
• Having hormone disorders like Polycystic Ovary Syndrome (PCOS)
• Having a sedentary lifestyle
• Having poor dietary habits
• Smoking

Having an immediate family member like a parent or sibling with gestational or Type 2 Diabetes increases your chance of developing this condition. Children born to mothers who had gestational diabetes are more likely to develop Type 2 Diabetes later in life.

Genetic Testing for Diabetes

Genetic testing is a medical testing process through which any changes or mutations in your genes can be determined by studying your DNA. The effectiveness of genetic testing for identifying diabetes depends on the form of diabetes you may have. Diabetes can be classified into monogenic and polygenic based on the number of genes involved in the development of the condition.

• Monogenic conditions

Monogenic disorders are conditions in which the mutation occurs in a single gene. So by performing genetic testing for that particular gene, it is possible to diagnose whether an individual may have the given condition. The most common forms of monogenic diabetes include maturity-onset diabetes in the young (MODY) and neonatal diabetes mellitus (NDM) (diabetes that occurs in children younger than 6 months of age). These conditions are rare and are primarily caused by genetic mutations.

Genetic testing can help in the accurate diagnosis and treatment of these conditions, as they may often be mistaken for other types of diabetes. Genetic testing can also be used to monitor the close family members of the affected individuals, as both MODY and NDM are conditions that can be inherited.

• Polygenic conditions

Conditions like Type 1, Type 2, and gestational diabetes can be classified as polygenic disorders as they are caused by mutations in several genes, along with other environmental risk factors.

In Type 1 Diabetes, researchers have noted mutations in the HLA genes. These genes make proteins that your immune system requires to fight infections. Mutations in these genes can be linked to the autoimmune response seen in Type 1 Diabetes.

In Type 2 Diabetes and gestational diabetes, genetic mutations can cause your cells or proteins to function improperly, resulting in an abnormal response of your cells to insulin (insulin resistance) or a decrease in insulin production.

Genetic testing is not an effective tool in diagnosing these types of diabetes, as these conditions are caused by mutations in several genes. Blood glucose tests like glycosylated haemoglobin (HbA1c) and fasting blood sugar (FBS) tests are much more reliable in the diagnosis of polygenic forms of diabetes.

Is it Possible to Lower the Risk of Passing on Diabetes?

Though there is nothing the parents can do to prevent the passing down of genes related to diabetes, it is possible to lower your child’s chances of developing these conditions. Depending on the type of diabetes, you can take the following measures to reduce your child’s risk of developing diabetes.

Type 1 Diabetes

Unfortunately, Type 1 Diabetes is not currently preventable. However, you can take the following measures to lower your child’s likelihood of developing this condition:

• Breastfeed your child till the age of 6 months.
• Try to minimise your child’s exposure to infections by ensuring good hygiene and staying up to date with their vaccinations.

Type 2 Diabetes

Type 2 Diabetes is a lifestyle disease that is largely preventable through the following measures:

• Ensure your child is in a healthy weight range for their age.
• Make sure they are physically active on a regular basis.
• Feed them a balanced and nutritious diet that is rich in fresh fruits, vegetables, whole grains, dairy products, etc.
• Limit their consumption of sugary drinks, sweets, deep-fried foods, refined carbohydrates, etc.

Gestational Diabetes

If you have gestational diabetes, helping your child formulate healthy lifestyle habits early in life can reduce their risk of developing Type 2 Diabetes and/or gestational diabetes (in the case of a female child) in the future. 

Also, taking the following precautions while you are pregnant can lower the chances of complications during birth:

• Stay active throughout your pregnancy and follow the exercise plan recommended by your doctor.
• Consume a healthy, diabetic-friendly diet.
• Strictly follow the treatment plan prescribed by your doctor and take all your medications as recommended.
• Keep all your doctor’s appointments and get regular checkups to monitor the growth of your child.
• Regularly monitor your blood sugar and blood pressure levels at home and report any abnormalities to your doctor.