The aim of our study is to elucidate the impact of the MODY3 disease-linked rSNP rs35126805 located in the non-coding DNA region, in the HNF-1α gene promotor -58 (upstream), on the binding of the transcription factor HNF-4α, and the regulation of HNF-1α gene expression. This evidence concerns the gene HNF1A and maturity-onset diabetes of the young type 3.