Which type of diabetes is genetic?

Both Type 1 and Type 2 diabetes have genetic components, but inherited genes do not fully determine if someone will have diabetes. According to the American Diabetes Association, a person inherits the predisposition to diabetes, but something in the environment ultimately triggers the disease.

Impact of genetics on Type 1 diabetes

Type 1 diabetes is an autoimmune disease in which the body’s immune cells destroy the insulin-making cells of the pancreas. It is often diagnosed in childhood between the ages of 5 and 6 and then again between 11 and 13. 90% of kids who develop type 1 diabetes have no family members with Type 1 diabetes, precluding a solely genetic cause of the condition. In twin studies, one may get type 1 diabetes but not the other, even though they have identical genes. However, broad inheritance patterns indicate that some genetic factors are at play.

For parents with type 1 diabetes, the following inheritance patterns are noted:

• Fathers with type 1 diabetes have a 1 in 17 chance of passing the disease on to each child.
• Mothers with type 1 diabetes who are under 25 years of age have a 1 in 25 chance of passing on Type 1 diabetes to each child. After 25, they have a 1 in 100 chance of passing the disease to each child.
• If the parent got type 1 diabetes before the age of 11, the chances of each child inheriting the disease double.

Genetic factors that increase the risk of type 1 diabetes include HLA genes. The human genome has thousands of versions of HLA genes. Some versions increase the chances of type 1 diabetes, while others can help prevent it. Different HLA genes that increase the risk have been identified in different racial groups. Caucasian people with Type 1 diabetes often have genes HLA-DR3 or HLA-DR4. HLA-DR3 is frequently associated with non-organ specific autoimmune disease. HLA-DR4 is often associated with organ-specific autoimmune disease. In African Americans, HLA-DR7 may increase the risk of type 1 diabetes, whereas HLA-DR9 may increase the risk in people of Japanese descent.

Impact of genetics on Type 2 diabetes

Type 2 diabetes occurs when cells in the body gradually lose insulin sensitivity. Type 2 diabetes has a stronger link to genetics than type 1 diabetes. Genetics can predispose an individual to have issues with insulin sensitivity. However, no particular genes are known to guarantee the disease. Lifestyle factors such as obesity, how much exercise someone gets, and their eating habits often trigger or prevent type 2 diabetes. In some cases, weight loss and reverting to a low-carb diet can reverse the development of type 2 diabetes. Therefore, the development of type-2 diabetes depends on both environmental and genetic factors.

Many genes that encode proteins for insulin release and signaling are associated with type 2 diabetes. Genes responsible for regulating the division of pancreatic cells, and genes affecting the viability of pancreatic cells are also sometimes mutated in people with type 2 diabetes. Mutations may also be noted in genes that affect glucose metabolism and transport. Zinc is needed by pancreatic cells to regulate the release of insulin. Mutation in a key gene (SLC30A8) that interrupts the transport of zinc into the cells is also associated with type 2 diabetes.

Exceptions

• While Type 1 and type 2 diabetes are polygenic requiring an interplay of many different genetic factors can set the stage for diabetes, some rare forms of diabetes are caused by the malfunctioning of a single gene. These are called monogenic diabetes, and they represent about 1-4% of all diabetes cases. The two main types of monogenic diabetes are neonatal diabetes mellitus (NDM) and maturity-onset diabetes of the young (MODY). With only one parent with monogenic diabetes, each child has a 50% chance of inheriting the disease.
• When Type 1 diabetes occurs in addition to another condition called type 2 polyglandular autoimmune syndrome, it increases the chances of Type 1 diabetes being inherited to 50%.