Abstract: 　Objective　To explore the etiology of unclassified diabetes mellitus in infancy and early childhood. Methods Clinical data of insulin-dependent type 1 diabetes mellitus (T1DM) patients with pancreatic islet autoantibody-negative with onset age less than 3 years old admitted to our hospital from 2013 to 2016 were retrospectively analyzed. Results　A total of 19 patients (12 boys and 7 girls) diagnosed with diabetes mellitus with onset age from on 8 months old to 3 years old. The main symptoms are fatigue, weight loss, polydipsia, and polyuria. HbA1C 8.6%～12%. Fourteen (14) patients were combined with ketoacidosis at diagnosis. Islet cell antibody, glutamate decarboxylase antibody, and insulin antibody were all negative in 19 patients. Insulin levels are normally low. Next-generation sequencing and methylation MLPA technology were used to analyze 28 diabetes mellitus relevant genes. Gene mutations were found in two patients: A c.1699G>A heterozygous mutation in HNF1A gene was identified in patient 1, and Sanger sequencing showed that the mutation was inherited from her mother who’s glucose was normal; a novel heterozygous deletion mutation of c.2214delT in CEL gene was identified in patient 2, and Sanger sequencing showed that the mutation was inherited from the father who’s fasting glucose was normal. Conclusion　This study demonstrated genetic overlap between autoantibody negative T1DM and monogenic diabetes. The next-generation sequencing assay has an important significance for helping early diagnosis of DM.

Key words: diabetes mellitus;　infancy;　gene mutation;　monogenic diabetes mellitus