Adult-Onset Atypical (Type 1) Diabetes

Abstract

OBJECTIVE—In 1997, the American Diabetes Association proposed two subcategories for type 1 diabetes: type 1A or immunomediated diabetes and type 1B or idiopathic diabetes characterized by negative β-cell autoimmunity markers, lack of association with HLA, and fluctuating insulinopenia. The aim of this study was to examine clinical characteristics, β-cell function, HLA typing, and mutations in maturity-onset diabetes of the young (MODY) genes in patients with atypical type 1 diabetes (type 1 diabetes diagnosed at onset, without pancreatic autoantibodies and fluctuating insulinopenia). RESEARCH DESIGN AND METHODS—Eight patients with atypical type 1 diabetes (all men, 30.7 ± 7.6 years) and 16 newly diagnosed age- and sex-matched patients with type 1A diabetes were studied retrospectively. Islet cell, GAD, tyrosine phosphatase and insulin antibodies, and basal and stimulated plasma C-peptide were measured at onset and after 1 year. HLA-DRB1-DQA1-DQB1 typing and screening for mutations in the HNF-1α and HNF-4α genes were performed from genomic DNA. RESULTS—Atypical patients displayed significantly higher BMI and better β-cell function at onset and after 12 months. Three patients carried protective or neutral type 1 diabetes haplotypes, five patients displayed heterozygosity for susceptible and protective haplotypes, and seven patients showed Aspβ57. We found a nondescribed variant Pro436Ser in exon 10 of the HNF-4α gene in one atypical patient without susceptible haplotypes. CONCLUSIONS—In our population, there are atypical forms of young adult-onset ketosis-prone diabetes initially diagnosed as type 1 diabetes, differing from type 1 diabetes in the absence of β-cell autoimmunity, persistent β-cell function capacity, fluctuating insulin requirements and ketosis-prone episodes, as well as clinical features of type 2 diabetes. Only one subgroup could be strictly classified as having type 1B diabetes. Additional information is still needed to improve our understanding of the mechanisms that finally lead to the disease.