Insurance and monogenic diabetes

We learnt in Week 1 that family history is a major risk factor for developing diabetes. But once a genetic diagnosis of monogenic diabetes has been made, unaffected family members can decide whether to have a predictive genetic test to get a very accurate estimate of their own risk of developing diabetes. If they have not inherited the familial mutation then their risk of diabetes reduces to that of the population. Inheritance of a HNF1A or HNF4A mutation predicts a high risk of developing MODY and regular blood glucose monitoring is advised. But could this knowledge also have implications for obtaining life insurance or a mortgage?

In the UK, the answer is no. The existing voluntary agreement (or ‘moratorium’) between the Government and the Association of British Insurers (ABI) has been extended again until November 2019 and ensures fair rights of access to insurance for individuals who choose to undertake predictive tests. Since the number of policies affected is predicted to be low, this allows customers who have had adverse predictive genetic tests to obtain significant level of cover while protecting other customers from increased premiums resulting from high claims and supports the principle that insurers should not treat customers who have had adverse predictive genetic test less favourably than those who have chosen not to be tested at all.

For patients with mild fasting hyperglycaemia caused by a heterozygous GCK mutation, a genetic diagnosis can be beneficial for insurance purposes as well as allowing them to stop unnecessary treatment. The life insurance premiums for an individual previously misdiagnosed as having type 1 or type 2 diabetes, would have been weighted according to that diagnosis. Mutations in the GCK gene result in a very unusual form of hyperglycaemia in that the fasting blood glucose is raised mildly from birth and remains persistently raised throughout life. In contrast to type 1 or type 2 diabetes, there is no deterioration other than that seen in fasting glucose in the non-diabetic population. In addition the blood glucose is regulated at this higher level such that when patients ingest food they typically, as non-diabetic subjects do, bring their blood glucose back to normal levels. Fasting blood glucose is normally in the range of 5.5-8.5mmol/l and HbA1c is typically at or just above the upper limit of normal (40-60mmol/mol or 5.8-7.6%). Unlike in type 2 diabetes there is no increase in triglycerides or reduction in HDL cholesterol and no associated increased risk of hypertension. Patients with type 1 or 2 diabetes have an increased risk of both microvascular and macrovascular disease (stroke and heart disease), but in a study of 99 patients with GCK mutations we found no more significant microvascular or macrovascular disease than in unaffected family members of a similar age.

So the key point when considering insurance/mortgage risk weighting is that the mortality and morbidity risks associated with a GCK MODY mutation are considerably less than for a person diagnosed with type 1 or type 2 diabetes at the same age. It is completely inappropriate for the insurance weighting to be the same as for the common forms of diabetes and this case has been argued successfully for many patients.

Find out more about the UK insurance moratorium on the Association of British Insurers (ABI) website.

You can also read the JAMA article that describes a study demonstrating the evidence of reduced morbidity/mortality in GCK MODY vs type 1 or 2 diabetes:

• Prevalence of Vascular Complications Among Patients With Glucokinase Mutations and Prolonged, Mild Hyperglycemia, Steele et al, JAMA 2014.