New Findings Shed Light on NOD2-Associated Autoinflammatory Disease

Cleveland Clinic researchers conducted a large cohort study of the emerging entity known as NOD2-associated autoinflammatory disease (NAID). The investigation aimed to study and expand the phenotypic and genotypic features of NAID and estimate the disease’s prevalence. Below are some of the study’s key findings and their implications for understanding the newly recognized condition.

NAID Essentials

NOD2 is the acronym for nucleotide-binding oligomerization domain containing 2, a member of a gene family that encodes intracellular proteins with N-terminal caspase recruitment domains (CARDs) involved in the inflammatory response and apoptosis. NOD2 genetic variants have been associated with Crohn’s disease, Blau syndrome and, most recently, NAID. NAID is characterized by periodic fever, dermatitis, polyarthritis, and sicca-like and gastrointestinal (GI) symptoms; genotypically, it is associated with NOD2 gene mutations.

Study Methods

A Cleveland Clinic study reviewed findings among the 143 adults who presented to Cleveland Clinic with autoinflammatory phenotypes and suspected NAID from November 2009 to May 2014. All patients underwent genotyping for NOD2 mutations and were then clinically followed and prospectively studied.

Patients were divided into two groups based on the presence or absence of NOD2 mutations. NAID was diagnosed according to our previously reported criteria. The clinical phenotypes and laboratory data of all patients with NAID were analyzed and compared with those of patients negative for NOD2 variants.

Results

Among the 143 patients genotyped, 46.9 percent were found to carry one or more NOD2 mutations. The genotype frequencies ‒ 35.7 percent for IVS8+158, 11.2 percent for R702W and 14.0 percent for rare mutations ‒ were significantly higher than among healthy controls (from historical data).

Of the 67 patients positive for NOD2 mutations, 57 (85.1 percent) had autoinflammatory phenotypes diagnostic of NAID. The remaining 10 patients had Crohn’s disease (n = 5), ulcerative colitis (n= 2), Blau syndrome (n = 2) or autoimmune disease (n = 1). The incidence rate of NAID was estimated to be 3 to 7 percent of our outpatient clinic patients, based on our total outpatient volume.

The 57 NAID patients had the following profile:

• 100 percent white
• 68.4 percent female
• Mean age at onset, 33.2 (± 14.0) years
• Mean disease duration at diagnosis, 10.6 (± 8.3) years
• Sporadic disease in 93 percent of cases

Phenotypic features included periodic disease occurrence, fever (63.2 percent), dermatitis (91.2 percent) and inflammatory arthritis/arthralgia (87.7 percent). Skin disease was overrepresented by dermatitis manifested as erythematous patches or plaques on the trunk and face, and articular manifestations were characterized as oligo-/polyinflammatory arthritis mainly involving the lower extremities. Distal lower extremity swelling occurred in 29.8 percent of patients.

GI symptoms were present in 73.7 percent of patients without inflammatory bowel disease, and sicca-like symptoms were present in 56.1 percent of those without primary Sjögren syndrome. Pericarditis and pleuritis were occasionally seen, but there was no renal or CNS involvement. Acute-phase reactants were elevated (40.4 percent), and autoantibodies were largely absent, with only 8.8 percent of patients having low titers of ANA (1:80). Associated NOD2 gene mutations were primarily IVS8+158 alone (80.7 percent) and compound IVS8+158 and R702W (26.3 percent) or rare mutations.

Among the 76 patients negative for NOD2 mutations, 28 had autoimmune diseases, including inflammatory bowel disease (n =7), Sjögren syndrome (n = 6), sarcoidosis (n = 6), undifferentiated connective tissue disease (n = 4) and other rheumatic diseases (n = 5). Additionally, there were four cases of autoinflammatory disease. The other cases remained undiagnosed.

The therapeutic approach is currently empiric, depending on the clinical manifestations. Medications used to treat the disease in this cohort included NSAIDs (34.5 percent), glucocorticoids (36.4 percent), sulfasalazine (32.1 percent) and biologics (7.1 percent). Short courses of prednisone (seven to 10 days) were effective for episodes of fever, rash and arthritis, and daily oral sulfasalazine was effective for frequent flares. Three cases were treated with infliximab and tocilizumab, with some success.

Discussion: What We Know About NOD2

This study showed that NOD2 genotype frequencies are significantly higher in our population with NAID phenotypes than in healthy controls. NAID represents a genetically complex autoinflammatory disorder distinct from Crohn’s disease and Blau syndrome.

The NOD2 gene has been mapped to chromosome 16q12-21, and its mutations are schematically represented in the figure. Some of the mutations also are called variants or polymorphisms. One hundred twenty-eight NOD2 gene variants have been reported (fmf.igh.cnrs.fr/ISSAID/infevers/search.php?n=6) and are named according to the DNA sequence and protein variants.

The NOD2 protein comprises 1,040 amino acids, containing two N-terminal CARDs, a central NOD-like receptor (NACHT) or NBD, and C-terminal leucine-rich repeats (LRRs) (Figure). The NOD2 protein mainly is present in the cytosols of monocytes, macrophages, dendritic cells and intestinal endothelial cells.

Pathogenesis: A Mix of Genetics and Cofactors?

The etiopathogenesis of NAID is unclear and under investigation. Data on the potential pathogenic roles of NOD2 variants have been derived primarily from prior studies of Crohn’s disease. Normally, NOD2 expression serves as a defense mechanism of the gut, whereas disease-associated NOD2 variants may predispose to intestinal inflammation via decreased NOD2 protein function. Since both Crohn’s disease and NAID implicate GI symptoms, we speculated that a complex interaction of genetics and cofactors (GI infection) may underlie the pathogenesis of NAID (as in Crohn’s disease). The preliminary study suggested that NAID may involve alterations in the cytokine IL-17 as well as in Th17 cells and specific regulatory T cells.

NAID is more prevalent than initially thought, with an estimated incidence of about 5 percent in general rheumatology outpatients and 1 to 10 per 100,000 in the general population. This report should further increase awareness of this novel clinical entity in the medical community. Prompt recognition of the disease may reduce superfluous examinations and tests, which may cut medical care costs significantly. Rapid diagnosis and management also will bring substantial benefits to patients.

Figure. Schematic representation of the NOD2 gene and protein structures. Coding exons are represented by blocks connected with lines representing introns. (See text for abbreviation expansions.)