An Unusual Form of Type 1 Diabetes With an Elevated Proinsulin Level

Introduction: Diabetes is one of the most prevalent diseases in the world. We recognize the three most common types of diabetes: type1, type2 and gestational diabetes. It is estimated that around 425 million of people worldwide have diabetes and about 90% of those represent type 2 diabetes. The most common types of diabetes are polygenic -- they are caused by a defect in multiple genes. Monogenic diabetes is caused by a mutation in a single gene. We currently have over 10 different types of monogenic diabetes called MODY (Maturity Onset Diabetes of the Young). Sun et al. states that over the past few years, 30 different insulin gene mutations were reported to cause a new syndrome called MIDY (Mutant INS-gene-induced Diabetes of Youth). Most of these mutations lead to proinsulin misfolding in the endoplasmic reticulum. We present a rare case of a young obese female with an elevated proinsulin level and low C-peptide level diagnosed with type 1 diabetes requiring therapy with insulin. Case Description: A 21 year old female with past medical history of chronic diarrhea initially presented with a complaint of dry mouth, dizziness, excessive urination, and thirst. She was found to have hyperglycemia of 203 mg/dL, A1C 8.3, and negative ketones. Patient had a strong family history of diabetes. She had a family history of: father with type 1 diabetes; mother with a past medical history of gestational diabetes who became diabetic postpartum; and three of the patient’s grandparents with a history of diabetes. Patient was started on the oral hypoglycemic agents metformin and glipizide, but she only had partial response to these medications. Because of her strong family history and incomplete response to oral hypoglycemic agents, additional testing was performed. Patient was found to have a low C-peptide level (1.6 ng/mL), elevated proinsulin (72.9 pmol/L), positive GAD antibody (10.3 units/mL) and negative islet cell autoantibody. Patient had a very good response to insulin and subsequently became insulin dependent. She is currently on an insulin pump. Conclusion: Sun et al. reports that proinsulin misfolding causes beta cell failure. Increased misfolding occurs under certain pathological conditions that are currently unknown. We think that there might be some increased proinsulin misfolding abnormality that might be occurring in this patient. There are most likely many epigenetic modifiers that would trigger certain individuals to be more prone to this phenomena of misfolded proinsulin. Future research in diabetes may one day yield antibodies that would specifically recognize misfolded proinsulin in the plasma. Further research is required to elucidate how defective proinsulin folding may lead to beta cell dysfunction and subsequent evolution of diabetes mellitus.