Paediatric diabetes — which children can gain insulin independence?

The increase in type 1 and type 2 diabetes in childhood has been well documented worldwide and in Australia. In addition, the separate entity of monogenic diabetes is increasingly recognised in paediatric diabetes, and now encompasses neonatal diabetes mellitus and maturity onset diabetes of the young (MODY). Monogenic diabetes is defined as diabetes caused by a single gene defect. A diagnosis of monogenic diabetes should be considered in a child who is diabetes-associated-autoantibody negative, is diagnosed with diabetes in the first 6 months of life, has a parent with diabetes, and/or is not markedly obese.

Although uncommon — its frequency is estimated to be 1%–3% of all childhood diabetes — the clinical relevance of this condition is that at least some of those affected (in particular, those with MODY1 and MODY3) can achieve very good diabetes control with sulfonylurea rather than insulin therapy.

Neonatal diabetes mellitus presents in the first 6 months of life with signs of hyperglycaemia — polyuria, dehydration, failure to thrive and, in many, frank diabetic ketoacidosis. Diabetic ketoacidosis is an important diagnosis to consider in an infant who presents critically unwell because the clinical picture may mimic sepsis. While the reported incidence of neonatal diabetes mellitus is one in 500 000 newborns,4 the estimated incidence is thought to be a lot higher, and it may be the cause of some unexplained infant deaths. About half of affected patients will have transient neonatal diabetes mellitus, where insulin treatment can be discontinued within a median of 3 months (although diabetes mellitus may recur in the second or third decade of life). In contrast, patients with permanent neonatal diabetes mellitus have, until recently, required insulin therapy for life. The revolution in patient management we describe here is due to molecular genetic analysis of the ATP-sensitive potassium (KATP) channel of the pancreatic beta cell.

Sulfonylureas have traditionally been used to treat type 2 diabetes mellitus. They act by binding the sulfonylurea receptor (SUR1), which closes KATP channels, thereby stimulating endogenous insulin production from the pancreatic beta cell. Gloyn et al demonstrated that some patients with Kir6.2 potassium channel activating mutations secreted insulin in response to the intravenous sulfonylurea tolbutamide. Subsequently, the Neonatal Diabetes International Collaborative Group conducted a trial of glibenclamide, an oral sulfonylurea, in 49 patients with Kir6.2 mutations. This trial included two Australian centres, with three children — one white and two of Middle Eastern ethnicity. An impressive 90% of the trial patients were successfully switched from insulin to glibenclamide. Importantly, the responsiveness in vitro of mutant ATP channels to tolbutamide was proportionate to the patient’s response to glibenclamide. This enables a degree of predictability of whether a patient is likely to successfully switch from insulin to oral therapy.

Not only was oral therapy welcomed by families of patients, but the switch from insulin resulted in significant improvement of metabolic control, with glycated haemoglobin levels dropping from 8.1% to 6.4% after 12 weeks of treatment. Insulin response to oral glucose load was increased in those tested. Continuous glucose monitoring has also shown fewer fluctuations in postprandial glucose, which families report improves the child’s general wellbeing.