Because dimerization is required for members of the HNF1 homeoprotein family of transcription factors to bind DNA [44, 45], the alteration of the heterodimerization between HNF1A and HNF1B and the abolition of the DNA-binding activity of HNF1B have essentially the same impact on transcriptional regulation; hence both lead to MODY. The gene discussed is HNF1A; the disease is MODY.