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Endocrinology

Presentation: Pregnant patient with a genetic diagnosis of maturity onset diabetes of the young, subtype glucokinase

For pregnancies at risk of maternally-inherited glucokinase maturity onset diabetes of the young (GCK-MODY, also known as monogenic diabetes, subtype glucokinase and GCK monogenic diabetes, a form of monogenic diabetes) where knowledge of fetal genotype will impact pregnancy management, delivery and immediate postnatal care, it may be possible to design a bespoke non-invasive prenatal diagnosis (NIPD) assay.

Example clinical scenario

A 32 year old woman is diagnosed with diabetes in her second pregnancy following a glucose tolerance test. She is tested early because she had gestational diabetes in her first pregnancy. Despite difficulty in achieving glucose targets with insulin treatment, her first baby had a birthweight of 2.9kg at 38 weeks’ gestation (~25th percentile). Her BMI is 20 and her father had type 2 diabetes, managed well with metformin. Her diabetes specialist nurse suspects GCK-MODY, which is confirmed with a diagnostic genetic test at 24 weeks’ gestation. She is eligible for non-invasive prenatal diagnosis (NIPD) to help guide the management of this pregnancy.

When to consider genomic testing

  • Pregnancies at 50% risk of maternally inherited monogenic diabetes, subtype glucokinase.
  • Patients will have undergone genetic testing for monogenic diabetes (National Genomic Test Directory indications R141 Monogenic Diabetes or R142 Glucokinase-related fasting hyperglycaemia) and have a confirmed genetic diagnosis of GCK monogenic diabetes.
  • Patients who are pregnant or considering pregnancy with a family history of GCK-MODY, should be referred for R142 Glucokinase-related fasting hyperglycaemia testing (familial testing) first, and, if a genetic diagnosis is confirmed, then referred for R433 NIPD for Monogenic diabetes, subtype glucokinase testing.

What do you need to do?

  • Consult the National Genomic Test Directory. From here you can access the rare and inherited disease eligibility criteria, which provide information about individual tests and their associated eligibility criteria. You can also access a spreadsheet containing details of all available tests.
  • To find out which genes are included on different gene panels, see the NHS Genomic Medicine Service (GMS) Signed Off Panels Resource.
  • Testing should be discussed with the specialist diabetes team at Royal Devon University Healthcare NHS Foundation Trust, Exeter, as soon as pregnancy is confirmed to enable confirmation that non-invasive prenatal testing (NIPT) is possible and to allow timely delivery in pregnancy.
  • For R433 NIPD for Monogenic diabetes, subtype glucokinase testing, both maternal and paternal samples are required. Paternal samples are essential to accurately identify fetal DNA in maternal blood.
  • Three maternal venous blood samples collected in specialised cell-free DNA stabilising Streck tubes are required.
  • A fingerprick capillary blood sample is required from the father of the baby.
  • Sample collection kits and request forms will be sent out by the Exeter team.
  • A cord blood sample is required form the baby when born to confirm the diagnosis.
  • Further guidance about R433 NIPD for Monogenic diabetes, subtype glucokinase testing is available via the specialist diabetes team at the Royal Devon University Hospital NHS Foundation Trust.
  • 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: 02/12/2024
  • Next review due: 02/12/2025
  • Authors: Dr Jayne Houghton, Dr Alice Hughes
  • Reviewers: Dr Danielle Bogue, Dr Shailesh Gohil, Dr Louise Izatt