Genetic analysis as a valuable key to diagnosis and treatment of periodic Fever

Inheritance of autoinflammatory diseases: shifting paradigms and nomenclature

Over 15 years have passed since the discovery of the first autoinflammatory gene, MEFV, responsible for familial Mediterranean fever. The identification of another gene, TNFRSF1A, in 1999 led to the concept of autoinflammation which characterises rheumatological conditions triggered by a defective innate immunity. Substantive progress has been made since then with the identification of 18 autoinflammatory genes accounting for up to 24 disease entities showing overlapping symptoms. The accumulation of studies reporting patients with missing or excess mutations as compared with expected numbers favours the hypothesis that these diseases are distributed along a continuum ranging from monogenic to multifactorial conditions, rather than featuring only classical modes of inheritance. Moreover, the probable interactions of environmental and epigenetic factors further obscure our understanding of the mechanisms underlying the phenotypic expression of patients. This review explores the history of autoinflammatory gene discovery, discusses the nosological disparities stemming from the clinical versus pathophysiological definition of autoinflammatory diseases and summarises various inheritance patterns. This review calls for a consistent disease nomenclature and presents a reconciling hypothesis which places different sequence variants within the autoinflammatory disease continuum. Integrating these new concepts should help to facilitate communication between health professionals and promote personalised patient care.

Horror autoinflammaticus: the molecular pathophysiology of autoinflammatory disease (*)

The autoinflammatory diseases are characterized by seemingly unprovoked episodes of inflammation, without high-titer autoantibodies or antigen-specific T cells. The concept was proposed ten years ago with the identification of the genes underlying hereditary periodic fever syndromes. This nosology has taken root because of the dramatic advances in our knowledge of the genetic basis of both mendelian and complex autoinflammatory diseases, and with the recognition that these illnesses derive from genetic variants of the innate immune system. Herein we propose an updated classification scheme based on the molecular insights garnered over the past decade, supplanting a clinical classification that has served well but is opaque to the genetic, immunologic, and therapeutic interrelationships now before us. We define six categories of autoinflammatory disease: IL-1beta activation disorders (inflammasomopathies), NF-kappaB activation syndromes, protein misfolding disorders, complement regulatory diseases, disturbances in cytokine signaling, and macrophage activation syndromes. A system based on molecular pathophysiology will bring greater clarity to our discourse while catalyzing new hypotheses both at the bench and at the bedside.

Dysregulation of innate immunity: hereditary periodic fever syndromes

The hereditary periodic fever syndromes encompass a rare group of diseases that have lifelong recurrent episodes of inflammatory symptoms and an acute phase response in common. Clinical presentation can mimic that of lymphoproliferative disorders and patients often go undiagnosed for many years. These syndromes follow an autosomal inheritance pattern, and the major syndromes are linked to specific genes, most of which are involved in regulation of the innate immune response through pathways of apoptosis, nuclear factor kappaBeta activation and cytokine production. In others, the link between the protein involved and inflammation is less clear. The recurrent inflammation can lead to complications, such as renal impairment due to amyloidosis and vasculitis, visual impairment, hearing loss, and joint destruction, depending on the specific syndrome. In recent years, treatment options for these diseases have improved significantly. Early establishment of an accurate diagnosis and start of appropriate therapy improves prognosis in these patients.

Hereditary auto-inflammatory disorders and biologics

The term auto-inflammatory disorders has been coined to describe a group of conditions characterized by spontaneously relapsing and remitting bouts of systemic inflammation without apparent involvement of antigen-specific T cells or significant production of auto-antibodies. The hereditary periodic fever syndromes are considered as the prototypic auto-inflammatory diseases, and genetic studies have yielded important new insights into innate immunity. DNA analysis has greatly enhanced the clinical characterization of these conditions, and elucidation of their molecular aetiopathogenesis has suggested that therapies may be aimed at specific targets within the immune cascade. The availability of biologic response modifiers such as inhibitors of tumour necrosis factor (TNF) and interleukin-1beta has greatly improved the outlook for some of these disorders, although effective therapies remain elusive in patients with certain conditions, including hyperimmunoglobulinaemia-D with periodic fever syndrome (HIDS) and a proportion of those with TNF-receptor associated periodic syndrome (TRAPS). Indeed, outstanding challenges and the unique potential to further elucidate molecular mechanisms in innate immunity are illustrated by the dashed early hope that TNF blockade would be a panacea for TRAPS: not only is etanercept (Enbrel) ineffective in some cases, but there are anecdotal reports of this condition being greatly exacerbated by infliximab (Remicade).

Hereditary periodic fever syndromes

The hereditary periodic fevers are a group of Mendelian disorders characterized by seemingly unprovoked fever and localized inflammation. Recent data indicate that these illnesses represent inborn errors in the regulation of innate immunity. Pyrin, the protein mutated in familial Mediterranean fever, defines an N-terminal domain found in a large family of proteins involved in inflammation and apoptosis. Through this domain pyrin may play a role in the regulation of interleukin (IL)-1beta, nuclear factor (NF)-kappaB, and leukocyte apoptosis. Cryopyrin/NALP3, another protein in this family, is mutated in three other hereditary febrile syndromes and participates in the inflammasome, a newly recognized macromolecular complex crucial to IL-1beta activation. Somewhat unexpectedly, mutations in the 55 kDa receptor for tumor necrosis factor also give rise to a dominantly inherited periodic fever syndrome, rather than immunodeficiency, a finding that has stimulated important investigations into both pathogenesis and treatment. Finally, the discovery of the genetic basis of the hyperimmunoglobulinemia D with periodic fever syndrome suggests an as yet incompletely understood connection between the mevalonate pathway and the regulation of cytokine production. These insights extend our understanding of the regulation of innate immunity in man, while providing the conceptual basis for the rational design of targeted therapies, both for the hereditary periodic fevers themselves and other inflammatory disorders as well.

Mutant forms of tumour necrosis factor receptor I that occur in TNF-receptor-associated periodic syndrome retain signalling functions but show abnormal behaviour

Tumour necrosis factor (TNF)-receptor-associated periodic syndrome (TRAPS) is a hereditary autoinflammatory disorder involving autosomal-dominant missense mutations in TNF receptor superfamily 1A (TNFRSF1A) ectodomains. To elucidate the molecular effects of TRAPS-related mutations, we transfected HEK-293 cells to produce lines stably expressing high levels of either wild-type (WT) or single mutant recombinant forms of TNFRSF1A. Mutants with single amino acid substitutions in the first cysteine-rich domain (CRD1) were produced both as full-length receptor proteins and as truncated forms lacking the cytoplasmic signalling domain (deltasig). High-level expression of either WT or mutant full-length TNFRSF1A spontaneously induced apoptosis and interleukin-8 production, indicating that the mutations in CRD1 did not abrogate signalling. Consistent with this, WT and mutant full-length TNFRSF1A formed cytoplasmic aggregates that co-localized with ubiquitin and chaperones, and with the signal transducer TRADD, but not with the inhibitor, silencer of death domain (SODD). Furthermore, as expected, WT and mutant deltasig forms of TNFRSF1A did not induce apoptosis or interleukin-8 production. However, whereas the WT full-length TNFRSF1A was expressed both in the cytoplasm and on the cell surface, the mutant receptors showed strong cytoplasmic expression but reduced cell-surface expression. The WT and mutant deltasig forms of TNFRSF1A were all expressed at the cell surface, but a proportion of the mutant receptors were also retained in the cytoplasm and co-localized with BiP. Furthermore, the mutant forms of surface-expressed deltasig TNFRSF1A were defective in binding TNF-alpha. We conclude that TRAPS-related CRD1 mutants of TNFRSF1A possess signalling properties associated with the cytoplasmic death domain, but other behavioural features of the mutant receptors are abnormal, including intracellular trafficking and TNF binding.

Complete recovery from refractory immune thrombocytopenic purpura in three patients treated with etanercept

Management of patients with immune thrombocytopenic purpura (ITP) who have persistent, severe, and symptomatic thrombocytopenia following splenectomy is difficult and empirical. No single agent or regimen provides long-term success for most patients, and for most treatments it is difficult to assess whether benefits outweigh risks. We report three consecutive patients with critical chronic refractory ITP, who responded promptly and completely following treatment with etanercept, an inhibitor of tumor necrosis factor-alpha. These patients had failed 6-11 previous treatments. In the first patient, etanercept was given for its approved indication: a flare of co-existing rheumatoid arthritis. The next two patients were treated with etanercept because of successful outcomes in the previous patients. Although etanercept appeared to be effective treatment for ITP in these 3 patients, the experimental nature of this treatment and the potential risks must be emphasized. On the basis of these case reports, a clinical trial has been initiated to systematically evaluate the efficacy and risks of etanercept in the management of children and adults with chronic ITP.

Fever of unknown origin in adults: 40 years on

A revision of the criteria of fever of unknown origin (FUO), established in 1961, is desirable because of important evolutions in medical practice and the emergence of new patient populations. The development of rapid laboratory tests and powerful diagnostic tools, such as ultrasonography, computed tomography and magnetic resonance imaging often makes hospitalization unnecessary and new categories of patients such as those with HIV infection, neutropenia, immunosuppression and nosocomial illness require an approach different from classical FUO. The more then 200 reported causes of FUO can be classified into four diagnostic categories; infections, tumours, noninfectious inflammatory diseases (NIID) and miscellaneous. A uniform classification system is highly wanted to allow comparison between different series. The reports of the 1990s show slight changes in the distribution of causes, namely less infections, less tumours, more NIID and more undiagnosed cases. A uniform diagnostic strategy cannot be determined. The initial investigation should be directed by potentially diagnostic clues revealed by extensive history, meticulous physical examination and a standard set of laboratory tests. 18Fluoro-deoxy-glucose-positron-emitted-tomography is a new valuable total body scintigraphy in the search for the site of origin of the fever. In view of the rather good long-term prognosis, a wait-and-see strategy may be more appropriate than a systematic staged approach. Elderly patients and patients with episodic fever represent two specific groups of classical FUO that require a distinct approach. HIV-associated, nosocomial and neutropenic FUO should be considered as separate clinical entities.

[TNF receptor-associated periodic syndrome (TRAPS): clinical aspects and physiopathology of a rare familial disease]

Hereditary periodic fever syndromes are defined as recurrent attacks of generalized inflammation for which no infectious or auto-immune cause can be identified. Minimal clinical variations, a unique biochemical-specific abnormality and the mode of genetic inheritance distinguish the four main diseases: familial Mediterranean fever, hyper-immunoglobulinemia D, TNF-receptor-associated periodic syndrome (TRAPS) and Muckle Wells syndrome. It presents with prolonged attacks of fever and severe localized inflammation. TRAPS is caused by dominantly inherited mutations in the gene encoding the first TNF receptor, which result in decreased serum levels of soluble TNF-receptor leading to inflammation due to unopposed TNF-alpha action. Corticosteroid treatment is not completely effective in most TRAPS patients. Preliminary experiences with recombinant TNF-receptor analogues in the treatment appear be promising.

The enlarging clinical, genetic, and population spectrum of tumor necrosis factor receptor-associated periodic syndrome

OBJECTIVE

To characterize the frequency, clinical signs, and genotypic features of tumor necrosis factor receptor-associated periodic syndrome (TRAPS) in a series of 394 patients of various ethnic origins who have recurrent inflammatory syndromes.

METHODS

Sequencing of the coding region of the TNFRSF1A gene was performed in 128 patients in whom there was a high suspicion of TRAPS, and denatured high-performance liquid chromatography was used to systematically screen for TNFRSF1A in 266 patients with recurrent inflammatory syndrome and no or only 1 Mediterranean fever gene (MEFV) mutation.

RESULTS

TNFRSF1A mutations were found in 28 (7.1%) of 394 unrelated patients. Nine (32%) of the 28 patients had a family history of recurrent inflammatory syndromes. In 13 patients, the length of the attack of inflammation was fewer than 5 days. Three of the mutations (Y20H, L67P, and C96Y) were novel. Two mutations, R92Q and (mainly) P46L, found in 12 and 10 patients, respectively, had lower penetrance compared with other mutations. TNFRSF1A mutations were found in patients of various ethnic origins, including those at risk for familial Mediterranean fever (FMF): Armenians, Sephardic Jews, and especially Arabs from Maghreb. Only 3 (10.7%) of the 28 patients had amyloidosis.

CONCLUSION

TRAPS is an underdiagnosed cause of recurrent inflammatory syndrome. Its presence in the population of persons of Mediterranean ancestry and the short duration of the attacks of inflammation can lead to a fallacious diagnosis of FMF. Because an accurate diagnosis in patients with recurrent inflammatory syndromes is crucial for proper clinical management and treatment, genetic screening for TNFRSF1A is warranted.