Heterogeneous phenotype of autoinflammatory disease in a patient with mutations in NOD2 and MEFV genes

Autoinflammatory diseases are a genetically heterogeneous group of conditions characterized by excessive activation of the innate immune system, and are distinguished from autoimmunity by the absence of autoantibodies and non-dependence on antigens (McGonagle and McDermott 2006; Martorana et al. 2017; Nigrovic et al. 2020). Aberrations in innate immune function, such as those involved in the detection of pathogens and (or) downstream signalling pathways that relay these responses, form the basis of the 5 major categories of autoinflammatory diseases. These include (i) inflammasomopathies (defects in multi-protein inflammasomes responsible for caspase-1-dependent IL-1β production), (ii) interferonopathies (defects in intracellular DNA sensors or counteracting nucleases leading to constitutive production of type I interferons), (iii) unfolded protein/cellular stress response syndromes (defects in handling of misfolded proteins resulting in activation of immune cascades, such as inflammasomes and interferon pathways), (iv) relopathies (defects in regulators of NF-κB-activity leading to hyperactivation), and (v) uncategorized (Rood and Behrens 2022). The clinical features frequently overlap and may include fever, rash, serositis, meningitis, gastrointestinal manifestations, and arthritis. A diagnosis is made based on correlation of symptoms against those of known autoinflammatory diseases (Tunca and Ozdogan 2005) and may be supported by genetic analysis (Simon et al. 2006).

With the advancement of genetic sequencing techniques, this field has grown exponentially with now recognized monogenic and polygenic origins (Pathak et al. 2017). Manifestations of digenic inheritance arising from the MEFV gene, causing the most common form of autoinflammatory disease – familial Mediterranean fever (FMF), alongside the NOD2 gene, have been previously noted (Yao et al. 2019).

The MEFV gene is located on chromosome 16 and encodes pyrin, a 781-amino acid protein that serves as a cytosolic sensor of bacterial-induced Rho GTPase inactivation. Pyrin is expressed in the cytoplasm of cells from myeloid lineages, synovial fibroblasts, and dendritic cells. Engagement and assembly of the pyrin inflammasome activates caspase-1, resulting in proinflammatory cytokine IL-1β and IL-18 production, and pyroptosis (inflammatory cell death) (Nigrovic et al. 2020). Autosomal recessive and autosomal dominant mutations in MEFV, causing excess activation of the pyrin inflammasome, can result in the clinical phenotype of FMF (OMIM # 134610, #249100) (Booty et al. 2009; Chae et al. 2011; Nigrovic et al. 2020; Tunca and Ozdogan 2005). While FMF can affect any ethnic group, the prevalence is estimated to be as high as 1:200 in certain Mediterranean populations.

Presentation of FMF usually occurs during childhood with major criteria of recurrent episodes of fever with serositis, amyloidosis and (or) favorable response to colchicine, and minor criteria encompassing recurrent fever, erysipelas-like erythema, or a first degree relative with FMF. Other features include abdominal and (or) chest pain, monoarticular arthritis, neutrophilia, elevated inflammatory markers, and amyloidosis commonly involving the kidneys.

A role for NOD2 as a gene modifier for FMF, causing more severe disease, has been suggested (Berkun et al. 2012). The NOD2 gene is located on chromosome 16 and encodes NOD2 (nucleotide-binding oligomerization domain-containing protein 2), a member of the intracellular NOD-like receptor (NLR) family of pattern recognition receptors (PRR). This innate sensor detects bacterial motifs (peptidoglycan) and promotes bacterial clearance through activation of the NF-kB pathway and induction of autophagy (Caruso et al. 2014). NOD2 is expressed primarily in monocytes but is also present in macrophages, dendritic cells, lymphocytes, epithelial and endothelial cells, as well as intestinal Paneth cells.

Defects in NOD2 are categorized as relopathies, due to dysregulated activation of the NF-kB pathway (Negroni et al. 2018; Steiner et al. 2018; Mukherjee et al. 2019). To date, pathogenic mutations in NOD2 have been associated with Blau Syndrome (OMIM 186580)(Miceli-Richard et al. 2001)/Early Onset Sarcoidosis, Crohn’s Disease (OMIM 266600)(Ogura et al. 2001; Hugot et al. 2001; King et al. 2006), and Yao Syndrome (OMIM 617321) (Yao and Shen, 2017). Conditions in this group involve autoinflammation with or without primary immunodeficiency traits (Pathak et al. 2017; Kacar et al. 2019).

Here, we report the complex medical and family history of an adult male who presented at an early age with autoinflammation and immunodeficiency. Targeted panel sequencing identified 3 missense mutations, 2 in MEFV and 1 in NOD2.

Our patient is currently a 68-year-old male of European descent who was referred to our clinic at age 64 after a remarkable and complex medical history since childhood.

Here, we describe a patient who presented with 3 heterozygous variants of uncertain significance, 2 in the MEFV gene (associated with autoinflammatory disease) and 1 in the NOD2 gene (associated with autoinflammatory disease and immunodeficiency).

The diagnosis of FMF in adults is based on the fulfillment of either 2 or more major criteria of recurrent episodes of fever with serositis, amyloidosis, favorable response to colchicine, or 1 major and 2 minor criteria of recurrent fever, erysipelas-like erythema, or a first degree relative with FMF. Our patient’s clinical phenotype did not fit the classical phenotype of FMF, given the absence of symptoms listed above. Yet, a case series by Ryan and colleagues (Ryan et al. 2010) previously reported the heterogenous and atypical FMF phenotype of a cohort of patients harbouring heterozygous MEFV mutations, including the identical 2 mutations that were present in our patient, c.1105C>T (p.Pro369Ser) and c.1223G>A (p.Arg408Gln). Both are located within exon 3 of MEFV encoding the B-box zinc finger domain (Figure 2), a region that negatively regulates activation of the pyrin inflammasome. While 17 of 22 patients did not meet the diagnostic criteria for FMF, a clustering of symptoms was reported, including 1 whose symptoms included panuveitis, inflammatory bowel disease, lethargy, and intermittent fever. Lymphadenopathy and lack of response to colchicine, the mainstay treatment for FMF, were noted in a number of patients. These symptoms overlap with our patient’s presentation (with the exception of fever) and may partially explain his complex phenotype.

The coexistence of MEFV and NOD2 genetic variants, both located in chromosome 16, is relatively common and is marked by overlapping clinical features, variable penetrance, leading to phenotypic heterogeneity and therapeutic variability (Yao et al. 2019). Case reports and cohorts of such combinations have demonstrated a high association with Crohn’s disease among patients with FMF (Berkun et al. 2012). The NOD2 mutation present in our patient, c.2104C>T (p.Arg702Trp), is considered a risk factor for Crohn’s disease, and has also been described in patients with Yao Syndrome, an autoinflammatory disease characterized by periodic fever, dermatitis, arthritis, swelling of the distal extremities, gastrointestinal and sicca-like symptoms, and serositis (Yao and Shen, 2017; Yao et al. 2019). Notably, the phenotype of our patient was not consistent with either Crohn’s disease or Yao syndrome, particularly given the lack of fever — a major criteria for Yao Syndrome. Moreover, although there is often clinical overlap between Yao Syndrome and FMF, with some case reports suggesting that patients may present features of both autoinflammatory diseases when variants in both genes are present, this has not been reported for the combination of variants identified in our patient (Yao et al. 2021).

NOD2 is also responsible for Blau Syndrome and Early Onset Sarcoidosis, the hereditary and sporadic forms (respectively) of a rare autoinflammatory disease caused by gain-of-function mutations in NOD2. Affected individuals present with non-caseating granulomatous arthritis, uveitis, and dermatitis (Tangye et al. 2022). Our patient’s symptoms are consistent with Blau syndrome, and in combination with his underlying MEFV mutations, may help to explain his complex presentation. Notably, the c.2104C>T (p.Arg702Trp) variant in NOD2 has not yet been reported in individuals with Blau Syndrome. Still, some features are not completely explained by his genetic work-up, such as malignancy, and further studies may be needed to rule out an association.

In summary, we describe a patient with a complex, longstanding, and early onset autoinflammatory disease. Genetic analysis identified 3 variants of uncertain significance in the MEFV and NOD2 genes.