Homozygosity of the Polymorphism MICA5.1 Identifies Extreme Risk of Progression to Overt Adrenal Insufficiency among 21-Hydroxylase Antibody-Positive Patients with Type 1 Diabetes

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Abstract
Context: Autoimmunity associated with Addison’s disease (AD) can be detected by measuring 21-hydroxylase (21OH) autoantibodies. Subjects with type 1 diabetes (T1D) are at increased risk for AD. Genetic factors including HLA-DRB1*0404 and MICA have been associated with AD in populations with and without T1D. Objective: The objective of the study was to examine the effect of the MICA5.1 allele in subjects with 21OH autoantibodies on progression to AD. Design: Two components were used: 1) a cross-sectional study with subjects with AD identified and enrolled from September 1993 to November 2008 and 2) a cohort study prospectively following up patients with T1D who screened positive for 21OH autoantibodies. Setting: Subjects were identified from the Barbara Davis Center and through the National Adrenal Diseases Foundation. Patients: Sixty-three subjects with AD were referred through the National Adrenal Diseases Foundation (AD referrals). Sixty-three subjects with positive 21OH antibodies from the Barbara Davis Center were followed up for progression to AD, and 11 were diagnosed with AD (progressors). Results: Seventy-three percent of progressors (eight of 11) and 57% of AD referrals (36 of 63) were MICA5.1 homozygous (P = ns). Overall, 59% of patients with AD (44 of 74) were MICA5.1/5.1 compared with 17% of nonprogressors (nine of 52) (P < 0.0001) and 19% of normal DR3/4-DQB1*0302 controls (64 of 336) (P < 0.0001). Conclusions: Identifying extreme risk should facilitate monitoring of progression from 21OH antibody positivity to overt AD. The HLA-DR3/0404 genotype defines high-risk subjects for adrenal autoimmunity. MICA5.1/5.1 may define those at highest risk for progression to overt AD, a feature unique to AD and distinct from T1D. MICA5.1 homozygosity is associated with an increased risk for Addison’s disease in subjects positive for 21-hydroxylase autoantibodies.

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