HNF1B-MODY Masquerading as Type 1 Diabetes: A Pitfall in the Etiological Diagnosis of Diabetes.

Hepatocyte nuclear factor-1B (HNF1B) maturity-onset diabetes of the young (MODY), also referred to as "renal cysts and diabetes syndrome" or MODY-5, is a rare form of monogenic diabetes that is caused by a deletion or a point mutation in the HNF1B gene, a developmental gene that plays a key role in regulating urogenital and pancreatic development. HNF1B-MODY has been characterized by its association with renal, hepatic and other extrapancreatic features. We present the case of a 39-year-old female patient who was first diagnosed with type 1 diabetes, but then, owing to the absence of anti-islet autoantibodies and to the disease's progression, was labeled later on as having atypical type 2 diabetes.