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OBJECTIVE--Previous studies have indicated that the latent autoimmune diabetes in adults (LADA) phenotype is heterogeneous and that LADA patients share features of type 1 and type 2 diabetes in various proportions. We tested for association of known type 1 and type 2 diabetes susceptibility genes in LADA subjects and analyzed relationships to a marker of autoimmune activity (titers of anti-GAD) and a phenotypic risk factor of type 2 diabetes (BMI). RESEARCH DESIGN AND METHODS--Data were assembled from the Nord-Trondelag Health Study (HUNT) study, which comprises the adult population of an entire county in Norway. We genotyped 60 single nucleotide polymorphisms (SNPs) known to be associated with type 1 or type 2 diabetes, including 14 tag SNPs used for HLA haplotyping in 120 type 1 diabetic, 126 LADA, and 1,090 type 2 diabetic patients and 1,503 age- and sex-matched nondiabetic subjects. RESULTS--The majority of the strongly associated HLA haplotypes for type 1 diabetes were significantly associated with LADA in general, but mainly with high anti-GAD LADA patients. Two distinct HLA haplotypes were associated only with LADA and mainly in low anti-GAD LADA patients. There were no associations of non-HLA type 1 diabetes loci with LADA. Of type 2 diabetes-associated genes, the CC/CT genotypes of rs7961581 (TSPAN8) and the obesity-linked AA/AC genotypes of rs8050136 (FTO) were associated with LADA in general, but mainly in low anti-GAD LADA patients (P = 0.004 and P = 0.004, respectively). CONCLUSIONS--Genetic heterogeneity in LADA is linked to various degrees of autoimmune activity and may be partly distinct from both type 1 and type 2 diabetes., Latent autoimmune diabetes in adults (LADA) is a slowly progressive form of autoimmune-associated diabetes (1). It is a common form of diabetes; for example, in the second Nord-Trondelag Health Study [...]