KCNJ11 (p.Arg192Cys)–associated MODY13 with coexisting autoimmunity in a child, a case report

Maturity-onset diabetes of the young type 13 (MODY13) is a rare autosomal dominant monogenic diabetes caused by mutations in the potassium inwardly rectifying channel subfamily J member 11 (KCNJ11) gene. It can mimic both type 1 and type 2 diabetes mellitus (T1DM and T2DM), making accurate diagnosis challenging. We describe the case of a five-year-old boy with overlapping features of T1DM and T2DM. He presented with hyperglycemia, obesity, and acanthosis nigricans. These symptoms improved after losing 11 kg owing to lifestyle modifications. His hemoglobin A1c (HbA1c) level decreased from 9.6% to 5.8%, and the continuous glucose monitoring system (CGMS) showed 91% time in range (TIR). Eighteen months later, he developed postprandial hyperglycemia and tested positive for T1DM antibodies, prompting the administration of insulin at 0.7 U/kg/day. His glucose levels continued to fluctuate. Whole-exome sequencing identified a likely pathogenic KCNJ11 variant (NM_000525.3, c.574 C > T, p.Arg192Cys), confirming the diagnosis of heterozygous autosomal dominant MODY13. He was then started on oral glibenclamide at 0.2 mg/kg/day, which lowered his HbA1c level to 7.5% and raised his CGMS TIR readings to 70%; however, insulin dependence persisted because of ongoing autoimmune β‑cell destruction. This case demonstrates the diagnostic challenge in pediatric diabetes when the features of T1DM, T2DM, and MODY overlap. Prompt genetic testing can lead to precise therapy. The simultaneous appearance of MODY13 and autoimmunity suggests possible interactions between the gene and the immune system.