Who Should Be Tested?

There are certain unique features associated with different forms of monogenic diabetes. When one or more of these features are present, there may be an indication for monogenic diabetes testing. Typical features include: 

Diabetes diagnosed less than 6 months of age usually has an identifiable monogenic cause (around 75-80%). Those diagnosed between 6-12 months have a much smaller chance of having a monogenic cause (around 5%). We suggest all those diagnosed under 6 months of age be tested and encourage families to contact us if they were diagnosed under 1 year.

One form of monogenic diabetes (GCK-MODY) has a distinctive glucose pattern. Family members affected have chronically raised morning blood sugars throughout their lives. Some may be described as having type 2 diabetes, pre-diabetes or impaired fasting glucose. Multiple members and generations of a family with this pattern alert us to the possibility of this form of diabetes.

Antibodies associated with diabetes are usually seen in the first few years after diagnosis with Type 1. The absence of antibodies can suggest a non-autoimmune cause for diabetes. The antibodies associated with type 1 include GAD, IAA, IA2, ZnT8.

MODY typically runs in families. The pattern of inheritance is described as linear, a mutation is passed from parent to child. Families affected by MODY usually have multiple generations affected. While type 1 diabetes can also be seen in multiple family members, the inheritance pattern is not as dramatic.

Most patients with type 1 diabetes will stop producing their own insulin within a few months or years after their diagnosis. It is difficult to distinguish insulin given by injection from any insulin made by the pancreas. Therefore, c-peptide is usually used as a proxy for measuring insulin production. C-peptide is made by beta cells simultaneously with insulin and it is rare to find c-peptide detectable in patients 3-5 years after diagnosis in patients with true type 1 diabetes. 

 

For information and helpful tips on genetic testing options for monogenic diabetes, please explore our Monogenic Diabetes Genetic Testing Info Sheet

Who should not get genetic testing? 

Genetic testing, although getting cheaper, remains an expensive test and is not indicated in most people with diabetes. Those diagnosed after 6 months of age with positive diabetes antibody testing are likely to have type 1 diabetes. Also, genetic forms of diabetes usually present in early life (rarely over 30 years of age). We encourage families to talk to their doctor if they are uncertain about their antibody results.