Background/Purpose: Periodic fever, aphthous stomatitis, pharyngitis, cervical adenitis (PFAPA) syndrome is the most common periodic fever syndrome of childhood. Although familial clustering of the disease has been noted, associated genetic variants have not yet been identified and replicated in multiple cohorts. We aimed to identify common genetic variants associated with PFAPA and understand the functional consequences of these variants.

Methods: We genotyped 2 cohorts of European-American and one cohort of Turkish individuals with PFAPA (total N=231) for common genetic variants previously associated with two other ulcerative diseases, Behçet’s disease and recurrent aphthous stomatitis. We compared the genotypes of these variants among PFAPA patients to the frequencies reported in large databases (gnomAD, ALSPAC). We also imputed HLA alleles from genotyping data in the MHC region and compared the frequency of these alleles to those among European-American and Turkish controls. In order to understand the functional significance of these variants, we obtained tonsils from children undergoing tonsillectomy with PFAPA syndrome (N=12) and with structural oropharyngeal disorders (N=10). Mononuclear cells from the tonsils were separated by standard methods and cells were analyzed by flow cytometry and gene expression with Nanostring. Cytokine production by isolated tonsillar mononuclear cells was measured by flow cytometry following phorbol 12-myristate 13-acetate (PMA) and ionomycin stimulation for 4 hours ex vivo. We obtained peripheral blood from individuals from the National Institutes of Health Blood Bank and The Genomic Ascertainment Cohort with and without the IL12A risk variant, isolated CD14+ monocytes by magnetic-activated cell sorting, and measured IL-12p70 production by ELISA after stimulation with IFNγ and LPS for 8 hours. 

Results: We found that the rs17753641 variant upstream of IL12A is strongly associated with PFAPA in all three cohorts (OR_meta of 2.13, p_meta=6×10^-9) and is associated with elevated IL-12p70 production by CD14+ monocytes upon stimulation with IFNγ and LPS. We also found that variants near STAT4, IL10, and CCR1-CCR3 were significant susceptibility loci for PFAPA. In addition, we identified class I and class II HLA risk alleles for PFAPA including HLA-DRB1*1301, HLA-DQA1*0103, HLA-DQB1*0603, HLA-B*1501, and HLA-B*3502. In the tonsils, we found that CD4+ T cells of patients with PFAPA have increased expression of Th1 and Th17-related genes. Moreover, upon stimulation with PMA and ionomycin, CD4+ effector T cells in PFAPA tonsils produce more IFNγ and IL-17 than controls.

Conclusion: We identify genetic risk variants and HLA risk alleles for PFAPA that replicate in multiple cohorts. Because the non-HLA risk variants are also associated with Behçet’s disease and recurrent aphthous ulcers, we propose to group these three diseases as a family called Behçet’s spectrum disorders (BSD) to highlight the overlap in their pathogenesis. HLA may be a factor that influences phenotype along this spectrum. The genetic variants and tonsil CD4+ T cell profile we found suggest that PFAPA is a disorder of dysregulated antigen-presenting cell function and heightened Th1 and Th17 cell activation.

« Back to 2020 Pediatric Rheumatology Symposium

ACR Meeting Abstracts - https://acrabstracts.org/abstract/genetic-susceptibility-loci-for-periodic-fever-aphthous-stomatitis-pharyngitis-and-cervical-adenitis-pfapa-syndrome/