Abstract
SUMMARY: We identified an adolescent young woman with new-onset diabetes. Due to suspicious family history, she underwent genetic testing for common monogenic diabetes (MODY) genes. We discovered that she and her father carry a novel variant of uncertain significance in the HNF1A gene. She was successfully transitioned from insulin to a sulfonylurea with excellent glycemic control. Based on her family history and successful response to sulfonylurea, we propose that this is a novel pathogenic variant in HNF1A. This case highlights the utility of genetic testing for MODY, which has the potential to help affected patients control their diabetes without insulin. LEARNING POINTS: HNF1A mutations are a common cause of monogenic diabetes in patients presenting with early-onset diabetes and significant family history. Genetic testing in suspected patients allows for the identification of mutations causing monogenic diabetes. First-degree relatives of the affected individual should be considered for genetic testing. The use of sulfonylurea agents in patients with HNF1A-MODY can reduce dependence on insulin therapy and provide successful glycemic control.