The value of genetic testing for diabetes

26 February 2014

With news that 6% of the UK population is registered as diabetic and that over ¾ of a million more people may have diabetes without knowing it, diabetes is clearly a major public health concern.

Obesity and lack of exercise are known risk factors and consequently health prevention and management efforts have focused on promoting healthy lifestyle choices. The contribution of genetics to diabetes risk is well known, but specific genetic variants that influence risk of diabetes development and progression have only recently begun to be identified.

A new briefing from the PHG Foundation examines the case for genetic testing for diabetes as a way of identifying those at risk and ensuring appropriate treatments for those already presenting with diabetes.

The paper sets out the current state of knowledge regarding Type 1 and Type 2 diabetes (T1D and T2D respectively). These are by far the most common forms, with T2D accounting for approximately 90% of all cases.

It also considers two much rarer, monogenic forms of diabetes – neonatal and MODY (Maturity Onset Diabetes of the Young). These forms have a single genetic variant strongly linked to their onset and potentially require different treatment from common forms.

In both T1D and T2D, many genetic variants have been identified that mildly increase the risk of developing the disease. If present in combination, these mutations confer higher risk - approximately 10% higher for T2D - no practical application of this knowledge has yet been identified for prevention of disease, and there would be little utility in introducing genetic testing into population screening programmes.

From a population perspective, promoting a healthy lifestyle should continue as the focus for public health efforts; however, at an individual level, consideration of family history is a valuable tool in identifying those most at risk.

Similarly, at a population level, screening for neonatal diabetes and MODY is not advisable, but these monogenic forms of diabetes are often misdiagnosed as T1D or T2D diabetes in babies and young people. Genetic testing therefore does have clinical utility for patients presenting with diabetes in the first six months of life, since it can identify rare forms of the disease for which different therapies are recommended.

The PHG Foundation briefing also suggests considering MODY as a differential diagnosis in those under 25 diagnosed with diabetes, to ensure they are offered the most appropriate treatment.