Food groups associated with immune-mediated inflammatory diseases: a Mendelian randomization and disease severity study

BACKGROUND/OBJECTIVES

Immune-mediated inflammatory diseases (IMIDs) are prevalent diseases. There is, however, a lack of understanding of the link between diet and IMIDs, how much dietary patterns vary between them and if there are food groups associated with a worsening of the disease.

SUBJECTS/METHODS

To answer these questions we analyzed a nation-wide cohort of n = 11,308 patients from six prevalent IMIDs and 2050 healthy controls. We compared their weekly intake of the major food categories, and used a Mendelian randomization approach to determine which dietary changes are caused by disease. Within each IMID, we analyzed the association between food frequency and disease severity.

RESULTS

After quality control, n = 11,230 recruited individuals were used in this study. We found that diet is profoundly altered in all IMIDs: at least three food categories are significantly altered in each disease (P < 0.05). Inflammatory bowel diseases showed the largest differences compared to controls (n ≥ 8 categories, P < 0.05). Mendelian randomization analysis supported that some of these dietary changes, like vegetable reduction in Crohn's Disease (P = 2.5 × 10^-10, OR(95% CI) = 0.73(0.65, 0.80)), are caused by the disease. Except for Psoriatic Arthritis and Systemic Lupus Erythematosus, we have found ≥2 food groups significantly associated with disease severity in the other IMIDs (P < 0.05).

CONCLUSIONS

This cross-disease study demonstrates that prevalent IMIDs are associated to a significant change in the normal dietary patterns. This variation is highly disease-specific and, in some cases, it is caused by the disease itself. Severity in IMIDs is also associated with specific food groups. The results of this study underscore the importance of studying diet in IMIDs.

Genetic variation at the glycosaminoglycan metabolism pathway contributes to the risk of psoriatic arthritis but not psoriasis

OBJECTIVE

Psoriatic arthritis (PsA) is a chronic inflammatory arthritis affecting up to 30% of patients with psoriasis (Ps). To date, most of the known risk loci for PsA are shared with Ps, and identifying disease-specific variation has proven very challenging. The objective of the present study was to identify genetic variation specific for PsA.

METHODS

We performed a genome-wide association study in a cohort of 835 patients with PsA and 1558 controls from Spain. Genetic association was tested at the single marker level and at the pathway level. Meta-analysis was performed with a case-control cohort of 2847 individuals from North America. To confirm the specificity of the genetic associations with PsA, we tested the associated variation using a purely cutaneous psoriasis cohort (PsC, n=614) and a rheumatoid arthritis cohort (RA, n=1191). Using network and drug-repurposing analyses, we further investigated the potential of the PsA-specific associations to guide the development of new drugs in PsA.

RESULTS

We identified a new PsA risk single-nucleotide polymorphism at B3GNT2 locus (p=1.10e-08). At the pathway level, we found 14 genetic pathways significantly associated with PsA (p_FDR<0.05). From these, the glycosaminoglycan (GAG) metabolism pathway was confirmed to be disease-specific after comparing the PsA cohort with the cohorts of patients with PsC and RA. Finally, we identified candidate drug targets in the GAG metabolism pathway as well as new PsA indications for approved drugs.

CONCLUSION

These findings provide insights into the biological mechanisms that are specific for PsA and could contribute to develop more effective therapies.

A deletion at ADAMTS9-MAGI1 locus is associated with psoriatic arthritis risk

OBJECTIVE

Copy number variants (CNVs) have been associated with the risk to develop multiple autoimmune diseases. Our objective was to identify CNVs associated with the risk to develop psoriatic arthritis (PsA) using a genome-wide analysis approach.

METHODS

A total of 835 patients with PsA and 1498 healthy controls were genotyped for CNVs using the Illumina HumanHap610 BeadChip genotyping platform. Genomic CNVs were characterised using CNstream analysis software and analysed for association using the χ(2) test. The most significant genomic CNV associations with PsA risk were independently tested in a validation sample of 1133 patients with PsA and 1831 healthy controls. In order to test for the specificity of the variants with PsA aetiology, we also analysed the association to a cohort of 822 patients with purely cutaneous psoriasis (PsC).

RESULTS

A total of 165 common CNVs were identified in the genome-wide analysis. We found a highly significant association of an intergenic deletion between ADAMTS9 and MAGI1 genes on chromosome 3p14.1 (p=0.00014). Using the independent patient and control cohort, we validated the association between ADAMTS9-MAGI1 deletion and PsA risk (p=0.032). Using next-generation sequencing, we characterised the 26 kb associated deletion. Finally, analysing the PsC cohort we found a lower frequency of the deletion compared with the PsA cohort (p=0.0088) and a similar frequency to that of healthy controls (p>0.3).

CONCLUSIONS

The present genome-wide scan for CNVs associated with PsA risk has identified a new deletion associated with disease risk and which is also differential from PsC risk.

PDE3A-SLCO1C1 locus is associated with response to anti-tumor necrosis factor therapy in psoriatic arthritis

Aim: Variation at PDE3A-SLCO1C1 locus has been recently associated with the response to anti-TNF therapy in rheumatoid arthritis. We undertook the present study to determine whether PDE3A-SLCO1C1 is also associated with the response to anti-TNF therapy in psoriatic arthritis. Patients & methods: Genomic DNA was obtained from 81 psoriatic arthritis patients that had been treated with anti-TNF therapy. PDE3A-SLCO1C1 SNP rs3794271 was genotyped using Taqman realt-time PCR. The clinical response to anti-TNF therapy was measured as the change from baseline in the level of disease activity according to the DAS28 score. Results: A significant association between rs3794271 and anti-TNF response in psoriatic arthritis was found (beta = -0.71; p = 0.0036). Conclusion: PDE3A-SLCO1C1 locus is also associated with response to anti-TNF therapy in psoriatic arthritis.

Original submitted 12 May 2014; Revision submitted 18 August 2014

Risk variants for psoriasis vulgaris in a large case-control collection and association with clinical subphenotypes

Recent genome-wide association studies (GWASs) have identified >20 new loci associated with the susceptibility to psoriasis vulgaris (PsV) risk. We investigated the association of PsV and its main clinical subphenotypes with 32 loci having previous genome-wide evidence of association with PsV (P < 5e-8) or strong GWAS evidence (P < 5e-5 in discovery and P < 0.05 in replication sample) in a large cohort of PsV patients (n = 2005) and controls (n = 1497). We provide the first independent replication for COG6 (P = 0.00079) and SERPINB8 (P = 0.048) loci with PsV. In those patients having developed psoriatic arthritis (n = 955), we found, for the first time, a strong association with IFIH1 (P = 0.013). Analyses of clinically relevant PsV subtypes yielded a significant association of severity of cutaneous disease with variation at LCE3D locus (P = 0.0005) in PsV and nail involvement with IL1RN in purely cutaneous psoriasis (PsC, P = 0.007). In an exploratory analysis of epistasis, we replicated the previously described HLA-C-ERAP1 interaction with PsC. Our findings show that common genetic variants associated with a complex phenotype like PsV influence different subphenotypes of high clinical relevance.

An unexpectedly high frequency of MEFV mutations in patients with anti-citrullinated protein antibody-negative palindromic rheumatism

OBJECTIVE

To investigate whether the MEFV gene, which is involved in the regulation of the inflammatory response and has been associated with familial Mediterranean fever (FMF) and intermittent hydrarthrosis, is implicated in the pathogenesis of palindromic rheumatism (PR) and to examine its clinical presentation and its evolution in a Spanish cohort of PR patients.

METHODS

Family histories, demographic clinical data, and laboratory characteristics of 75 patients diagnosed as having PR were collected from medical records and personal interviews. The healthy control group included 325 blood bank donors. The FMF control group was made up of 84 Spanish FMF patients. Genomic DNA was isolated, and MEFV gene mutation analysis was performed by polymerase chain reaction amplification and sequence analysis.

RESULTS

Sixty-five unrelated PR patients were finally included in the study. MEFV gene mutation analysis identified 8 of these 65 patients (12.3%) as carriers of at least 1 mutated MEFV allele. Patients with MEFV mutations had higher mean age and age at disease onset, but lower mean serum levels of anti-citrullinated protein antibodies (ACPAs). No other significant differences were observed between patients with and those without mutations. The frequency of MEFV mutations in ACPA-negative PR patients was 22.2%, compared with 5.3% in ACPA-positive PR patients (P = 0.058).

CONCLUSION

This study shows a previously unreported high prevalence of mutations of the MEFV gene in patients with ACPA-negative PR. This supports the hypothesis that it might be a susceptibility gene. Our findings also support the hypothesis that the MEFV gene might participate in the pathogenesis of other undifferentiated relapsing inflammatory rheumatic disorders.