Faculty Bibliography

OBJECTIVE: Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by autoantibody production and altered type I interferon expression. Genetic surveys and genome-wide association studies have identified >30 SLE susceptibility genes. One of these genes, TNIP1, encodes the ABIN1 protein. ABIN1 functions in the immune system by restricting NF-kappaB signaling. The present study was undertaken to investigate the genetic factors that influence association with SLE in genes that regulate the NF-kappaB pathway. METHODS: We analyzed a dense set of genetic markers spanning TNIP1 and TAX1BP1, as well as the TNIP1 homolog TNIP2, in case-control populations of diverse ethnic origins. TNIP1, TNIP2, and TAX1BP1 were fine-mapped in a total of 8,372 SLE cases and 7,492 healthy controls from European-ancestry, African American, Hispanic, East Asian, and African American Gullah populations. Levels of TNIP1 messenger RNA (mRNA) and ABIN1 protein in Epstein-Barr virus-transformed human B cell lines were analyzed by quantitative reverse transcription-polymerase chain reaction and Western blotting, respectively. RESULTS: We found significant associations between SLE and genetic variants within TNIP1, but not in TNIP2 or TAX1BP1. After resequencing and imputation, we identified 2 independent risk haplotypes within TNIP1 in individuals of European ancestry that were also present in African American and Hispanic populations. Levels of TNIP1 mRNA and ABIN1 protein were reduced among subjects with these haplotypes, suggesting that they harbor hypomorphic functional variants that influence susceptibility to SLE by restricting ABIN1 expression. CONCLUSION: Our results confirm the association signals between SLE and TNIP1 variants in multiple populations and provide new insight into the mechanism by which TNIP1 variants may contribute to SLE pathogenesis.

OBJECTIVE: American Indian-Europeans, Asians, and African Americans have an excess morbidity from systemic lupus erythematosus (SLE) and a higher prevalence of lupus nephritis than do Caucasians. The aim of this study was to analyze the relationship between genetic ancestry and sociodemographic characteristics and clinical features in a large cohort of American Indian-European SLE patients. METHODS: A total of 2,116 SLE patients of American Indian-European origin and 4,001 SLE patients of European descent for whom we had clinical data were included in the study. Genotyping of 253 continental ancestry-informative markers was performed on the Illumina platform. Structure and Admixture software were used to determine genetic ancestry proportions of each individual. Logistic regression was used to test the association between genetic ancestry and sociodemographic and clinical characteristics. Odds ratios (ORs) were calculated with 95% confidence intervals (95% CIs). RESULTS: The average American Indian genetic ancestry of 2,116 SLE patients was 40.7%. American Indian genetic ancestry conferred increased risks of renal involvement (P < 0.0001, OR 3.50 [95% CI 2.63- 4.63]) and early age at onset (P < 0.0001). American Indian ancestry protected against photosensitivity (P < 0.0001, OR 0.58 [95% CI 0.44-0.76]), oral ulcers (P < 0.0001, OR 0.55 [95% CI 0.42-0.72]), and serositis (P < 0.0001, OR 0.56 [95% CI 0.41-0.75]) after adjustment for age, sex, and age at onset. However, age and sex had stronger effects than genetic ancestry on malar rash, discoid rash, arthritis, and neurologic involvement. CONCLUSION: In general, American Indian genetic ancestry correlates with lower sociodemographic status and increases the risk of developing renal involvement and SLE at an earlier age.

OBJECTIVE: To evaluate the safety profile of long-term belimumab therapy combined with standard therapy for systemic lupus erythematosus (SLE) in patients with active disease. METHODS: Patients who were randomized to receive intravenous placebo or belimumab 1, 4, or 10 mg/kg, plus standard therapy, and completed the initial 52-week double-blind treatment period were then allowed to enter a 24-week open-label extension phase. During the extension period, patients in the belimumab group either received the same dose or were switched to 10 mg/kg and patients in the placebo group were switched to belimumab 10 mg/kg. Patients who achieved a satisfactory response during the 24-week extension period were allowed to participate in the long-term continuation study of monthly belimumab 10 mg/kg. Adverse events (AEs) and abnormal laboratory results were analyzed per 100 patient-years in 1-year intervals. RESULTS: Of the 364 patients who completed the 52-week double-blind treatment period, 345 entered the 24-week extension, and 296 continued treatment with belimumab in the long-term continuation study. Safety data through 4 years of belimumab exposure (1,165 cumulative patient-years) are reported. Incidence rates of AEs, severe/serious AEs, infusion reactions, infections, malignancies, grades 3/4 laboratory abnormalities, and discontinuations due to AEs were stable or declined during 4-year belimumab exposure. The most common AEs included arthralgia, upper respiratory tract infection, headache, fatigue, and nausea. Serious infusion reactions were rare: only 1 occurred during the 4-year followup period. Rates of serious infection decreased from 5.9/100 patient-years to 3.4/100 patient-years, and no specific type of infection predominated. CONCLUSION: Belimumab added to standard therapy was generally well-tolerated over the 4-year treatment period in patients with SLE, which suggests that belimumab can be administered long term with an acceptable safety profile.