In vitro studies showed that the transcriptional repressor capacity on human insulin and glucagon promoters was reduced in cell lineages transfected with PAX4 R192H plasmid when compared to those of wild-type PAX4, suggesting that PAX4 R192H polymorphism generated a protein with a defect in transcriptional repressor activities on its target genes, leading to β-cell dysfunction associated with MODY and the early onset-age of T2D. This evidence concerns the gene PAX4 and MODY.