A synonymous variant leading to MODY13: A case report and literature review.

Background: Maturity-onset diabetes of the young, type 13 (MODY13) is a specific subclass of monogenic diabetes mellitus that does not exhibit the typical clinical manifestations of diabetes, necessitating the use of genetic testing for accurate diagnosis. With the progression of monogenic diabetes and MODY, the number of reported MODY13 cases has reached a minimum of 22. Nevertheless, there remains a dearth of information regarding patients diagnosed with MODY13 presenting synonymous variants.

Case Presentation: This study presents a description of the clinical and genetic features of a 9-year-old male patient diagnosed with MODY13. A noteworthy finding in this case was the occurrence of a "separation phenomenon" between C-peptide and insulin during the standard meal test. Whole exome sequencing (WES) identified a KCNJ11 c.843C > T (p.L281=) mutation in exon 1, which contradicted the previously reported phenotype. Following the onset of ketosis, the patient underwent insulin therapy for a duration of one month, during which the insulin dosage was gradually modified based on blood glucose levels. In order to maintain normoglycemia, he adhered to a diabetic dietary regimen and participated in 1-2 h of moderate exercise daily.

Conclusion: The study implies that patient with variant shows a "separation phenomenon" between C-peptide and insulin in standard meal test. Our report also enriched the genotype and phenotype spectrums of MODY13 and highlighted the importance of genetic testing in patients without characteristic clinical symptoms of diabetes.