HNF1B and diabetes mellitus: Thus, the identification of an HNF1B mutation provides molecular confirmation of a clinical diagnosis, raises the possibility of coexisting malformations, which should be investigated, facilitates the correct choice of treatment (unlike some types of MODY, diabetes of HNF1B carriers is not sensitive to sulfonylurea medication, and early insulin therapy is required),6 and provides information about recurrence risks for patients and family members.