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Adult-Onset Atypical (Type 1) Diabetes

Additional insights and differences with type 1A diabetes in a European Mediterranean population

¹ Endocrinology and Diabetes Unit, IDIBAPS (Institut d’Investigacions Biomèdiques August Pi i Sunyer), Hospital Clínic i Universitari, Barcelona, Spain
² Hormonal Unit, IDIBAPS (Institut d’Investigacions Biomèdiques August Pi i Sunyer), Hospital Clínic i Universitari, Barcelona, Spain
³ Immunology Unit, IDIBAPS (Institut d’Investigacions Biomèdiques August Pi i Sunyer), Hospital Clínic i Universitari, Barcelona, Spain

Address correspondence and reprint requests to Dr. I. Conget, Endocrinology and Diabetes Unit, Villarroel 170, 08036 Barcelona, Spain. E-mail: iconget{at}clinic.ub.es

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 ß-cell autoimmunity markers, lack of association with HLA, and fluctuating insulinopenia. The aim of this study was to examine clinical characteristics, ß-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-1 and HNF-4 genes were performed from genomic DNA.

RESULTS—Atypical patients displayed significantly higher BMI and better ß-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 Asp^ß57. We found a nondescribed variant Pro436Ser in exon 10 of the HNF-4 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 ß-cell autoimmunity, persistent ß-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.

Abbreviations: GADAb, GAD antibody • IAAb, insulin autoantibody • IA2Ab, tyrosine phosphatase antibody • MODY, maturity-onset diabetes of the young • SSO, specific-sequence oligonucleoprobe

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