Monogenic diabetes and type 1 diabetes mellitus: a challenging combination

The co-existence of maturity onset diabetes of the young (MODY) due to a glucokinase gene (GCK) mutation and type 1 diabetes mellitus (T1DM) is rarely diagnosed. We present a family with GCK mutation, where one member also has T1DM. We highlight the challenges faced in the management of a child with dual diagnosis, due to the higher threshold for activation of counter-regulatory hormones in GCK mutations. Fluctuations in blood glucose (BG) levels and significant hypoglycaemia on attempts at normalising BG levels complicate management in these patients. Resetting the threshold for hypoglycaemia and target BG, combined with insulin pump therapy, enabled us to significantly reduce hypoglycaemia and improve quality of life. The population prevalence of GCK-MODY is 1.1 in 1000. T1DM neither predisposes to nor protects from GCK-MODY; one would therefore expect the prevalence of GCK-MODY to be the same in T1DM patients. In conclusion, it is important to recognise the co-existence of T1DM and GCK-MODY as symptoms of hypoglycaemia at BG levels usually considered ‘within target’ pose management challenges. A combined diagnosis warrants careful consideration of BG target