It’s easy to think that there are only two types of diabetes: Type 1 and Type 2. These forms of diabetes are polygenic, meaning a change or mutation in multiple genes causes them. Type 1 diabetes is caused by an autoimmune reaction, which destroys the cells in the pancreas that make insulin. Type 2 diabetes can be caused by weight, diet, and exercise, but it can also be caused by family history and ethnicity. Polygenic diabetes is found by testing the blood glucose levels of an individual. Even though these are the most common types of diabetes, affecting about 98% of those with diabetes, there is a rare form that is often misdiagnosed and therefore mistreated.
Monogenic diabetes is a rare form of diabetes that affects a mutation in a single gene instead of multiple genes. Monogenic diabetes is much more likely to be inherited from one or both of an individual’s parents. Sometimes, but even more rarely, the gene mutation can develop spontaneously, which means neither individual’s parents carry the mutation. The two types of monogenic diabetes are maturity-onset diabetes of the young (MODY) and neonatal diabetes mellitus (NDM).
MODY is the more common monogenic diabetes that first occurs in adolescence or early adulthood. A few gene mutations have been shown to cause MODY, but all limit the ability of the pancreas to produce insulin. This causes high blood glucose levels and can ultimately damage body tissues. MODY can often be misdiagnosed as type 1 because both conditions can cause high blood sugar levels and both are often diagnosed in children and young adults. Some mutations that cause MODY to allow the person to have only a slightly elevated blood sugar level that remains steady throughout life. In this case, no specific treatment is needed. In other mutations, specific treatments with insulin of sulfonylureas are needed to allow the individual to maintain relatively normal blood sugar levels. It can be dangerous to misdiagnose MODY as type 1 or type 2 diabetes because certain factors cause these forms to affect the body very differently. Only with an accurate diagnosis of MODY can individuals receive the correct treatment. In addition, there are important implications for other family members because of the strongly inheritable pattern of MODY.
Neonatal diabetes (NDM) is a monogenic form of diabetes that occurs within the first 6 to 12 months of life. This form is very rare as it only affects every 1 in 400,000 infants in the United States. Diabetes in the first six months of life almost always has a genetic cause. In about half of those diagnosed with NDM, the condition is permanent. In the other half of individuals, the condition is transient, meaning this form of diabetes disappears during infancy but can reappear later in life. It is essential for doctors to look for signs of NDM because NDM can be life-threatening if not treated properly. NDM can be diagnosed by finding elevated blood glucose levels. The lack of insulin in the infant can produce chemicals called ketones, which may lead to diabetic ketoacidosis, which is life-threatening.
It is so important to be properly tested and diagnosed for diabetes as the rare monogenic forms may call for much different treatment than polygenic forms. Treatment varies based on the specific genetic mutation that has caused monogenic diabetes. A correct diagnosis requires genetic testing, and the overlapping symptoms of monogenic diabetes with polygenic diabetes have caused misdiagnosis. Misdiagnosis can lead to inappropriate treatment so it is vital that the exact type of diabetes is diagnosed. Monogenic diabetes is important to understand because, although it is rare, about 2% of those with diabetes have it.
