A case of maturity-onset diabetes of the young type 4 in Korea.

Maturity-onset diabetes of the young (MODY) is a rare, autosomal dominant disease characterized by non-ketogenic diabetes mellitus (DM). MODY type 4, caused by PDX1 mutation, is a very rare subtype of MODY, especially in Korea. We report a case of a 10-year-old, nonobese girl with a family history of type 2 DM. After diagnosis, the patient's serum glucose level was well controlled using metformin monotherapy; however, the glycated hemoglobin level increased to 9.0% approximately 2 years after treatment. No obesity or lifestyle problems were observed, and serum fasting C-peptide level was within the normal range. Furthermore, no islet-related autoantibodies were detected. A genetic screening for MODY using a next-generation sequencing panel was performed, and a likely heterozygous pathogenic PDX1 mutation (p.Gly246ArgfsTer21) was identified. The PDX1 variant was not detected in her mother, implying that the mutation had arisen de novo in the proband. She was prescribed insulin degludec in addition to metformin therapy, which improved her hyperglycemia. This report presents a novel MODY type 4 phenotype and highlights the importance of genetic screening in patients with MODY characteristics.