Genetics, Pathophysiology, and Treatment of Dominant Autoinflammatory Diseases

National Human Genome Research Institute

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Abstract

During the current reporting period we focused on two areas of investigation: 1) Retinal dystrophy, optic nerve edema, splenomegaly, and headache (ROSAH) syndrome ROSAH syndrome was first described by another research team in 2019. In their initial manuscript, these investigators reported five families with the cardinal clinical manifestations denoted in the ROSAH acronym, who shared the p.Thr237Met mutation in the ALPK1 gene, which encodes a novel kinase. Shortly before the description of ROSAH, another group discovered that ALPK1 is a cytosolic innate immune receptor for bacterial 7-carbon sugars, but the team that described ROSAH did not consider the possibility that ROSAH might be an autoinflammatory disease caused by constitutive activation of this intracellular receptor. In the current project we recruited 27 subjects with ROSAH syndrome, the largest cohort described to date, and performed careful clinical, immunologic, and molecular phenotyping to test the hypothesis that ROSAH is an autoinflammatory disease. This cohort study systematically evaluated 27 patients with ROSAH syndrome for inflammatory features and investigated the effect of ALPK1 mutations on immune signaling. Clinical, immunologic, and radiographical examinations were performed, and 10 patients were empirically initiated on anticytokine therapy and monitored. Exome sequencing was used to identify a new pathogenic variant. Cytokine profiling, transcriptomics, immunoblotting, and knock-in mice were used to assess the impact of ALPK1 mutations on protein function and immune signaling. The majority of the cohort carried the p.Thr237Met mutation, but we also identified a new ROSAH-associated mutation, p.Tyr254Cys. Nearly all patients exhibited at least one feature consistent with inflammation including recurrent fever, headaches with meningeal enhancement and premature basal ganglia/brainstem mineralization on MRI, deforming arthritis, and AA amyloidosis. However, there was significant phenotypic variation, even within families, and some adults lacked functional visual defects. While anti-TNF and anti-IL-1 therapies suppressed systemic inflammation and improved quality of life, anti-IL-6 (tocilizumab) was the only anticytokine therapy that improved intraocular inflammation (two of two patients). Patients primary samples and in vitro assays with mutated ALPK1 constructs showed immune activation with increased NF-kappaB signalling, STAT1 phosphorylation, and interferon gene expression signature. Knock-in mice with the Alpk1 T237M mutation exhibited subclinical inflammation. Clinical features not conventionally attributed to inflammation were also common in the cohort and included short dental roots, enamel defects, and decreased salivary flow. We concluded that ROSAH syndrome is an autoinflammatory disease caused by gain-of-function mutations in ALPK1 and that some features of disease are amenable to immunomodulatory therapy. We published a paper in the Annals of the Rheumatic Diseases describing these findings during the current reporting period. 2) Pyogenic arthritis, pyoderma gangrenosum, and acne (PAPA) syndrome PAPA syndrome is a dominantly inherited autoinflammatory disease caused by heterozygous mutations in PSTPIP1, encoding an intracellular protein that binds pyrin, the protein mutated in familial Mediterranean fever (FMF), and a key activator of interleukin 18 (IL-18). Some patients with clinical features resembling PAPA syndrome do not have demonstrable mutations in PSTPIP1. In this study, we collaborated with Dr. Scott Canna at Childrens Hospital of Philadelphia to examine the role of IL-18 in PSTPIP1 mutation-positive PAPA syndrome and mutation-negative PAPA-like conditions. Clinical and genetic data and serum samples were obtained from patients with clinical findings consistent with PAPA syndrome. Serum IL-18, IL-18 binding protein (IL-18BP), and CXCL9 levels were assessed by bead-based assay, and free IL-18 levels were assessed by enzyme-linked immunosorbent assay. The clinical manifestations of PSTPIP1-positive patients with PAPA syndrome overlapped with those of mutation-negative patients with PAPA-like conditions, but mutation-positive patients had earlier onset and a greater proportion had a history of arthritis. There was uniform elevation of total serum IL-18 in treated PSTPIP1-positive PAPA patients at levels nearly as high as those seen in NLRC4-associated autoinflammation with infantile enterocolitis patients, and well above levels found in most FMF patients. Serum IL-18 elevation in PSTPIP1-positive PAPA syndrome patients persisted despite fluctuations in disease activity. Levels of the soluble IL-18 antagonist IL-18BP were modestly elevated, and PSTPIP1-positive PAPA syndrome patients had detectable free IL-18. PSTPIP1-positive PAPA syndrome was rarely associated with elevation of CXCL9, an indicator of interferon-gamma activity, but no PSTPIP1-positive PAPA syndrome patient had a history of macrophage activation syndrome (MAS). We concluded that PSTPIP1-positive PAPA syndrome is a refractory and often disabling monogenic autoinflammatory disease associated with chronic and unopposed elevation of serum IL-18 but not with risk of MAS. The data suggest a link between pyrin inflammasome activation, IL-18, and autoinflammation, without susceptibility to MAS. We published a paper in Arthritis and Rheumatology describing these findings during the current reporting period.