Series 3 episode 1. Mary Humphries, The doctor didn’t listen! A delayed diagnosis of MODY

Released 1 October 2024

Mary Humphries tells how her son Dan was diagnosed with diabetes aged 16 and it was assumed he had type 1 diabetes and treated with insulin. On insulin he had terrible problems with low blood sugars frequently losing consciousness and not managing to concentrate at school or at home.

Dan Humphries

Mary was very worried that he was getting worse on the insulin and asked about genetic tests because she had recently been diagnosed with Type 2 diabetes and there was diabetes in all generations of her family. She was not listened to; the insulin was continued, and Dan got worse. Searching the internet for answers she found the Exeter diabetesgenes.org website which led her to talking to Andrew and Maggie. They were able to rapidly diagnose that this was Maturity-onset Diabetes of the Young (MODY), subtype HNF1A with a genetic test. Maggie helped Dan to stop his insulin and get excellent control on a quarter of the sulphonylurea tablet called gliclazide. Dan rapidly improved off the insulin and passed his A levels with flying colours going to Bristol where he achieved his life’s ambition to become a large animal vet.

Maturity-onset diabetes of the young (MODY) is hard to diagnose as it only affects about 2% of all children diagnosed with diabetes with the vast majority having Type 1 diabetes. Key characteristics that suggest MODY are:

1, One parent is diagnosed with diabetes and often other relatives are diagnosed with diabetes passing from one generation to the next through an affected person.

2, the first measured HbA1c is low typically less than 7.5% or 58 mmol/mol

3, If on insulin treatment, there are not test features of Type 1 diabetes so none of the islet autoantibodies (GAD, IA2, or ZNF808) are detected at a high level. Patients are sill producing their own insulin shown by a C peptide of 200 pmol/l or above even many years after diagnosis of diabetes,

4, If not on insulin treatment there are not features of Type 2 diabetes so BMI <30kg/m2 adult (child BMI <95th centile) and a parent with diabetes (if White) or BMI <27kg/m2 (child BMI <95th centile) and a parent with diabetes (if high prevalence type 2 diabetes ethnic group) such as South Asian or Black.

Details about maturity-onset diabetes of the young (MODY) can be found on the www,diabetesgenes.org website here

https://www.diabetesgenes.org/what-is-mody/

The criteria for NHS testing can be found here

https://www.diabetesgenes.org/tests-for-diabetes-subtypes/guidelines-for-genetic-testing-in-mody/