During a genetic counseling session, a genetic counselor will often ask you questions about the health of your family members- parents, grandparents, children, and sometimes cousins, aunts, and uncles. It is very common for a person to tell a genetic counselor that they have a family history of diabetes. There has been a lot of research to determine the cause of diabetes. We know that typically diabetes is a combination of genetics and environment and that if someone has a first-degree relative diagnosed with diabetes, they have an increased risk to develop diabetes in comparison to the general population. 

There are two types of diabetes: type 1 and type 2. Type 1 diabetes is also known as juvenile or insulin-dependent diabetes and is a chronic condition where the pancreas produces little to no insulin. It’s typically diagnosed in childhood and currently has no cure. Type 2 diabetes occurs when your body changes the way your body metabolizes sugar and resists the effects of insulin, which regulates the amount of sugar in your body. Type 2 diabetes is known as adult-onset diabetes and often occurs due to weight gain, eating poorly, and not exercising. Fortunately, a healthy lifestyle can help manage type 2 diabetes. 

As discussed previously, we know that the majority of cases of diabetes are typically caused by a combination of genetics and environment. However, there are certain types of diabetes that have a known gene mutation and can have up to a 50% risk of passing on to a child. Maturity-onset diabetes of the young (MODY) occurs due to abnormally high blood sugar levels and is typically diagnosed before the age of 30. Blood sugar rises due to a reduced production of insulin. In 50-70% of cases, MODY is caused by a gene mutation in a gene called HNF1A and is referred to as MODY3. In 30-50% of cases, MODY2 is caused by a gene mutation in the GCK gene. There is also a less frequent type called renal cysts and diabetes syndrome, which accounts for 5-10% of cases of MODY. 

If you are diagnosed with MODY, your family members are also at risk to have the same gene mutation that causes MODY as you. It is important to let your family members know and encourage them to pursue genetic testing. If you plan to have children, there are options to test the pregnancy to see if the pregnancy has inherited the gene mutation as well. MODY is inherited in an autosomal dominant pattern, which means that each family member is at a 50% risk to inherit the gene mutation. MODY is only estimated to account for 1-3% of all cases of diabetes. 

In infants, there is a type of diabetes that can be diagnosed within the first 6 months of life called Permanent Neonatal Diabetes Mellitus. This type of diabetes can cause intrauterine growth, hyperglycemia, severe dehydration, and failure to thrive. Therapy with insulin can help with dramatic catch up in growth and development in infants. This type of diabetes is caused by a gene mutation in KCNJ11, which has a 50% risk of being passed on to a child. There are also gene mutations that are inherited in an autosomal recessive pattern, which means each parent would have to be a carrier of the gene mutation in order for a pregnancy to have a 25% chance of being affected. 

If you have a family history of diabetes and are interested in knowing if a genetic cause is responsible, or if you have a diagnosis of an inherited form of diabetes, please contact AT-GC to meet with a genetic counselor to discuss your options. 

Resources: 

https://www.mayoclinic.org/diseases-conditions/type-2-diabetes/symptoms-causes/syc-20351193

https://www.mayoclinic.org/diseases-conditions/type-1-diabetes/symptoms-causes/syc-20353011

https://medlineplus.gov/genetics/condition/maturity-onset-diabetes-of-the-young/#frequency

https://www.ncbi.nlm.nih.gov/books/NBK1447/

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