Neonatal Diabetes Mellitus May Offer the Missing Link to Monogenic Diabetes in Family Members: A Case Report

Neonatal diabetes mellitus (NDM) is a rare type of monogenic diabetes. It is predominantly described as insulin-requiring hyperglycemia before the age of 6 months. Diagnosis of NDM can be difficult due to its varying clinical presentation. Prompt genetic testing is paramount to determine the appropriate management. In this report, we demonstrate a case where genetic testing has led to an accurate diagnosis of NDM in a 7-month-old infant who was successfully switched from subcutaneous insulin to oral anti-diabetics. Identification of the infant's genetic diagnosis led to the correction of the father's misdiagnosis of type 1 diabetes mellitus to monogenic diabetes. Reclassification of the father's diabetes allowed the replacement of his long-lasting insulin therapy with oral anti-diabetics and the improvement of glycemic control. This report highlights the value of genetic testing in NDM diagnosis beyond the first six months of life and how NDM diagnosis in an index case could help with the correct diagnosis, classification, and treatment of other family members with diabetes even after several years of insulin treatment.