ABSTRACT
Objective To screen the variation in NeuroD1 gene and to study its function in vitro and its clinical phenotypes and genetic characteristics in Chinese early-onset type 2 diabetic probands. Methods PCR-direct sequencing of NeuroD1 gene was performed in 85 early-onset type 2 diabetic probands, 95 late-onset type 2 diabetics with strong diabetic history and 87 non-diabetic control subjects. Distributions of the identified variation were calculated and compared among the three groups. Expression vectors with mouse NeuroD1 (mND1)cDNA wild type or mutant type and reporter vectors with human insulin promotor-linked luciferase were constructed. Then the above vectors were co-transfected into rat INS-1 cells. Relative luciferase activities were measured to compare transcriptional activities of insulin gene between WT and MT. Results S159P (T→C), a new mutation was identified in a proband, which was co-segregated with diabetes in 4 carriers from the paternal side. The functional study showed that the S159P mutant exhibited a 25% reduction in transcriptional activity of insulin gene as compared with the wild type. A45T (G→A), a common variation was identified. The AA + GA genotypic frequencies were markedly increased in early-onset type 2 diabetic probands as compared with late-onset type 2 diabetic probands and non-diabetic control subjects (P=0.006 and P=0.014, respectively). Conclusion The novel S159P mutation in the NeuroDl gene seems to contribute to the development of diabetes in the Chinese early-onset type 2 diabetic family. The A45T variation may increase susceptibility to or be in disequilibrium with early-onset type 2 diabetes mellitus in Chinese population. In addition, the A45T variation may affect the onset pattern of type 2 diabetes mellitns, such as early-onset but not late-onset type 2 diabetes mellitus.