This information leaflet has been produced by Gateshead Health NHS Foundation Trust Maternity Unit to provide information to pregnant people who have been diagnosed with Gestational Diabetes and are eligible for glucokinase gene variation testing.
What is glucokinase (GCK)?
Glucokinase (GCK) is a gene* that plays an important role in recognising how high blood sugar (glucose) is in the body. It acts as the ‘glucose sensor’ for the pancreas, so that when blood glucose rises, the amount of insulin produced by the pancreas increases in response.
You have been diagnosed with gestational diabetes (GDM) because you have been found to have a higher blood glucose level in pregnancy. Fewer than 2 in 100 people originally diagnosed with GDM will actually have a change in their GCK gene; it is this gene change that causes their raised blood glucose level and NOT gestational diabetes.
*Genes provide instructions to help our bodies develop, grow and work; genes are inherited from our parents.
What does it mean if there is a change or variation in the GCK gene?
If there is a change (‘spelling mistake’) in the GCK gene, fasting blood glucose is ‘reset’ at a higher level in comparison to people without this change. This is called glucokinase hyperglycaemia and is typically present from birth. Glucokinase hyperglycaemia is a subtype of maturity-onset diabetes of the young, often abbreviated to GCK-MODY; it very rarely leads to complications, and does not usually require any treatment.
Outside of pregnancy, people with GCK-MODY do not need specialist care or monitoring. They have no greater risk of developing Type 2 diabetes than other members of the general population.
A change in the GCK gene is more likely if you have:
- A raised fasting glucose tolerance test (GTT) result
AND
- A Body Mass Index (BMI) of under 30 kg/m2 (or under 27 kg/m2 for ethnic populations with a high risk of Type 2 diabetes).
Pregnant people who fulfil both of these criteria are eligible for a blood test to look for a change in the GCK gene. This is available via the NHS and is free of charge.
How is a change in the GCK gene diagnosed?
A sample of blood is taken from a vein in your arm and sent for genetic testing in Exeter to see if there is a change in the GCK gene.
It takes approximately 4-6 weeks to receive the results. During this wait, you will continue to receive routine gestational diabetes care.
What are the possible results from a GCK genetic test?
There are 3 possible results to genetic testing for GCK-MODY:
- GCK gene variant not identified (a negative result) – in most cases a change in the GCK gene will not be found and you will continue with routine gestational diabetes care.
- GCK gene variant identified (a positive result) – this is known to cause a raised blood glucose level and you will be offered additional testing (explained below) to guide the rest of your pregnancy care.
- Variant of unknown significance (VUS) – in an extremely small number of cases, a change in the GCK gene is identified but it is unclear if it is connected to the raised blood glucose level. If this happens, Exeter testing centre may ask for more information about other family members to help understand if this gene change is the cause or not.
Why is it important to test for a change in the GCK gene during pregnancy?
It is important to know if a pregnant person has GCK-MODY because it is managed slightly differently to gestational diabetes. If a parent is affected, the baby has a 50% chance of inheriting the same condition.
If a pregnant person is found to have GCK-MODY, the diabetes care team may be able to arrange a special blood test to determine if the baby has also inherited this gene change. This is possible as, when a person is pregnant, there is a small amount of the baby’s DNA in their bloodstream that can be extracted and analysed in a specialist laboratory.
Knowing whether the baby has inherited the same gene variation will guide how blood glucose is monitored and managed for the rest of the pregnancy. If your baby has inherited GCK-MODY you may be able to stop monitoring your blood glucose and any diabetes treatment that has been commenced, as there is no increased chance of the baby growing larger than their genetic potential. If your baby has NOT inherited GCK-MODY, then there is an increased chance of your baby growing larger than expected (in a similar way to having gestational diabetes). You will therefore need to continue monitoring your blood glucose levels and the diabetes team will carefully consider whether any diabetes treatment should be started or adjusted to reduce this risk.
If you choose to decline testing for this condition, it will not affect the routine care you receive throughout pregnancy from the antenatal diabetes team. In this case, we will assume that you have gestational diabetes and manage your care accordingly. Declining testing should not significantly increase the chance of pregnancy complications; however, if you do have undiagnosed GCK-MODY, this approach may not provide the most appropriate treatment for your condition.
Useful sources of information
https://www.diabetesgenes.org/what-is-mody/what-is-glucokinase-gck
At the Queen Elizabeth Hospital Maternity Unit, we advocate a shared decision making approach to all decisions made by our patients. This leaflet aims to give you additional information and to act as a point of reference following a discussion with your obstetrician or midwife. If you are asked to make a decision about your care please make sure you have asked all the questions you need to ask and are given the appropriate time to do so. Some questions you might want to ask could be:
- Benefits – what are the benefits of making this decision?
- Risks – what are the risks associated with this decision?
- Alternatives – are there any alternatives?
- Intuition – how do I feel?
- Nothing – what if I decide to do nothing? What would happen next?
- Second opinion – who else could I talk to about this?
Contact numbers
If you have any additional queries please contact:
