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Primary Care

Presentation: Patient with incidental finding of raised blood glucose

Raised blood glucose may indicate glucokinase maturity onset diabetes of the young. This condition is characterised by a mild, stable hyperglycaemia, which is often detected during routine screening and requires no treatment, monitoring or ongoing testing for diabetes-related complications.

At a glance:

  • Glucokinase maturity onset diabetes of the young (GCK MODY) is characterised by a mild, stable hyperglycaemia, which is often detected during routine screening (for example, pregnancy screening in women or routine medicals in men). It is estimated to affect around one in every 2,000 people in the general population.
  • GCK MODY follows an autosomal dominant inheritance pattern, meaning that first-degree relatives have a 50% chance of being affected.
  • GCK MODY needs no treatment or follow up. Individuals are not at increased risk of developing micro- and macrovascular complications associated with diabetes.
  • Alert! Those with GCK MODY will typically have haemoglobin A1C (HbA1c) levels between 40-60 millimoles per mole (mmol/mol) throughout life, and diabetes treatment will typically make no difference to their blood glucose levels due to counter-regulation.

Example clinical scenario

A 28-year-old woman presents during the first trimester of pregnancy with an HbA1c of 56mmol/mol. She is otherwise fit and healthy, with a pre-pregnancy BMI of 22. She mentions that her mother was also diagnosed with diabetes during her own first pregnancy and was treated with insulin,  but was told that she had ‘borderline’ diabetes later in life. Her maternal grandfather was diagnosed at the age of 22 during an army medical, and was subsequently given oral diabetes medication. He remains well, with no diabetes complications.

Identifying those at risk of a genetic condition

  • In this scenario, the incidental finding of a raised HbA1c in a slim patient during the first trimester of pregnancy in combination with the autosomal dominant family history raises the possibility of a monogenic cause.
  • GCK MODY typically results in mild, stable hyperglycaemia with fasting glucose of 5.5mmol/L to 8mmol/L and HbA1c 40mmol/mol to 60mmol/mol.
  • Glucokinase is an enzyme critical for glucose sensing by the beta cell. Pathogenic loss-of-function variants in GCK increase the set point around which glucose is regulated (from 4mmol to 6mmol or 7mmol), resulting in mild persistent hyperglycaemia from birth but with preserved glucose regulation.
  • GCK MODY follows an autosomal dominant inheritance pattern, meaning that first-degree relatives have a 50% chance of being affected, but other affected family members (including parents) may not be identified unless they have been tested already due to the mildness of the hyperglycaemia.
  • Flags for an underlying genetic diagnosis of GCK MODY include:
    • stable HbA1c of 40mmol/mol to 60mmol/mol throughout life in slim individuals with a raised fasting glucose of between 5.5mmol/L and 8mmol/L;
    • diagnosis of diabetes below the age of 25, which may have been picked up incidentally such as through routine screening, in an individual who may have a parent or child with a diagnosis of diabetes; and
    • family members diagnosed young who do not require treatment or have little to no change in glycaemia despite treatment.

What do you need to do?

  • Enquire about family history, including whether diabetes was diagnosed incidentally in other family members and what their HbA1c levels were, if known.
  • Enter the details into the MODY probability calculator.
  • Refer the patient to their local diabetes team for genomic testing.
  • If or when molecular genomic testing confirms a diagnosis of GCK MODY, arrange genomic testing for other family members via the local diabetes team and follow up. This may enable them to stop treatment.
  • GCK MODY requires no treatment, monitoring or screening for diabetes-related complications. Specialist advice can be given during pregnancy and cell-free fetal DNA testing may be possible to aid management in these cases.
  • Those with GCK MODY have a low prevalence of microvascular and macrovascular complications, and do not need follow up. They can be considered to not have diabetes, and a GCK MODY diagnosis should not affect insurance or employment.
  • Information about patient eligibility and test indications were correct at the time of writing. When requesting a test, please refer to the National Genomic Test Directory to confirm the right test for your patient.

Resources

For clinicians

References:

For patients

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  • Last reviewed: 19/06/2023
  • Next review due: 19/06/2024
  • Authors: Professor Maggie Shepherd
  • Reviewers: Dr Amy Frost, Dr Asma Hamad, Professor Kevin Colclough

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