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Objectives. There could be an overlap of monogenic diabetes and early onset type 2 diabetes mellitus. Precise diagnosis of early onset diabetes has proven valuable for understanding mechanism of diabetes and selecting optimal therapy. The majority of maturity onset diabetes of the young(MODY) pathogenic genes in China is still unknown. Methods. A family with suspected MODY were enrolled in this study.Whole exome sequencing(WES) was used to analyze the variants of the proband.Variants were filtered according to their frequency, location, functional consequences and bioinformatics software. Candidate pathogenic variants were validated by Sanger sequencing and tested for co-segreation in other members of the family and non-related healthy controls. KEGG(Kyoto Encyclopedia of Genes and Genomes)and protein-protein interaction(PPI) analysis were conducted using the DAVID(Database for Annotation, Visualization and Integrated Discovery) and the STRING online analysis tools for candidate pathogenic gene. Results. A total of 123291 variants including 105344 SNPs and 17947 InDels were found in WES. A likely pathogenic rare missense heterozygous mutation in diabetes genes(p.H713 Y in IRS1) was identified, which was co-segreate in his family and the non-related healthy controls. The position of the mutation in the aminoacid sequence of the gene is highly conserved among species. 2 significantly enriched KEGG pathways were identified including bta04930:Type II diabetes mellitus(GCK, INS, PDX1, ABCC8 and IRS1) and bta04910:Insulin signaling pathway(GCK, INS and IRS1). PPI analysis displayed that IRS1 interacts with 3 known pathogenic proteins including INS, KCNJ11 and GCK. Conclusions.WES could be an initial option for genetic testing in patients with early onset diabetes. Our data suggest IRS1 p.H713 Y as a possible pathogenic mutation in monogenic diabetes, which might require further validation, and the precise molecular mechanism underlying the influence of IRS1 p.H713 Y on the development of diabetes remains to be determined in the further prospective studies.