Periodic fever syndromes (also known as autoinflammatory diseases or autoinflammatory syndromes) are a set of disorders characterized by recurrent episodes of systemic and organ-specific inflammation. Unlike autoimmune disorders such as systemic lupus erythematosus, in which the disease is caused by abnormalities of the adaptive immune system, patients with autoinflammatory diseases do not produce autoantibodies or antigen-specific T or B cells. Instead, the autoinflammatory diseases are characterized by errors in the innate immune system.

The syndromes are diverse, but tend to cause episodes of fever, joint pains, skin rashes, abdominal pains and may lead to chronic complications such as amyloidosis.

Most autoinflammatory diseases are genetic and present during childhood. The most common genetic autoinflammatory syndrome is familial Mediterranean fever, which causes short episodes of fever, abdominal pain, serositis, lasting less than 72 hours. It is caused by mutations in the MEFV gene, which codes for the protein pyrin.

Pyrin is a protein normally present in the inflammasome. The mutated pyrin protein is thought to cause inappropriate activation of the inflammasome, leading to release of the pro-inflammatory cytokine IL-1β. Most other autoinflammatory diseases also cause disease by inappropriate release of IL-1β. Thus, IL-1β has become a common therapeutic target, and medications such as anakinra, rilonacept, and canakinumab have revolutionized the treatment of autoinflammatory diseases.

However, there are some autoinflammatory diseases that are not known to have a clear genetic cause. This includes PFAPA, which is the most common autoinflammatory disease seen in children, characterized by episodes of fever, aphthous stomatitis, pharyngitis, and cervical adenitis. Other autoinflammatory diseases that do not have clear genetic causes include adult-onset Still's disease, systemic-onset juvenile idiopathic arthritis, Schnitzler syndrome, and chronic recurrent multifocal osteomyelitis. It is likely that these diseases are multifactorial, with genes that make people susceptible to these diseases, but they require an additional environmental factor to trigger the disease.

Another example that shows that autoinflamatory conditions may not be genetic in origin is found in a report published in "Nature" which shows that diet is very important in the development of such diseases. The ingestion levels of highly saturated fats and cholesterol, (high fat diet, HFD) affects the microbiota composition of the gut. Changes in the microbiota induced by a HFD are protective against the susceptibility to develop osteomyelitis (autoimmune disease) as compared with the changes induced by a low-fat diet. The changes in the microbiome of individuals under HFD showed a reduction in "Prevotella" abundance and were accompanied by significantly reduced expression levels of pro-Interleukin-1β in distant neutrophils.

The life span in patients with Schnitzler syndrome has not been shown to differ much from the general population. Careful follow-up is advised, however. A significant proportion of patients develops a lymphoproliferative disorder as a complication, most commonly Waldenström's macroglobulinemia. This may lead to symptoms of hyperviscosity syndrome. AA amyloidosis has also been reported in people with Schnitzler syndrome.

FMF affects groups of people originating from around the Mediterranean Sea (hence its name). It is prominently present in the Armenians, Sephardi Jews (and, to a much lesser extent, Ashkenazi Jews), Cypriots and Arabs.

Familial Mediterranean fever (FMF) is a hereditary inflammatory disorder. FMF is an autoinflammatory disease caused by mutations in Mediterranean fever gene, which encodes a 781–amino acid protein called pyrin. While all ethnic groups are susceptible to FMF, it "usually occurs in people of Mediterranean origin—including Sephardic Jews, Mizrahi Jews, Armenians, Azerbaijanis, Arabs, Greeks, Turks and Italians".

The disorder has been given various names, including familial paroxysmal polyserositis, periodic peritonitis, recurrent polyserositis, benign paroxysmal peritonitis, periodic disease or periodic fever, Reimann periodic disease or Reimann's syndrome, Siegal-Cattan-Mamou disease, and Wolff periodic disease. Note that "periodic fever" can also refer to any of the periodic fever syndromes.

Cryopyrin-associated periodic syndrome (CAPS) is a group of rare, heterogeneous autoinflammatory disease characterized by interleukin 1β-mediated systemic inflammation and clinical symptoms involving skin, joints, central nervous system, and eyes. It encompasses a spectrum of three clinically overlapping autoinflammatory syndromes including familial cold autoinflammatory syndrome (FCAS, formerly termed familial cold-induced urticaria), the Muckle–Wells syndrome (MWS), and neonatal-onset multisystem inflammatory disease (NOMID, also called chronic infantile neurologic cutaneous and articular syndrome or CINCA) that were originally thought to be distinct entities, but in fact share a single genetic mutation and pathogenic pathway.

A person's sex also seems to have some role in the development of autoimmunity; that is, most autoimmune diseases are "sex-related". Nearly 75% of the more than 23.5 million Americans who suffer from autoimmune disease are women, although it is less-frequently acknowledged that millions of men also suffer from these diseases. According to the American Autoimmune Related Diseases Association (AARDA), autoimmune diseases that develop in men tend to be more severe. A few autoimmune diseases that men are just as or more likely to develop as women include: ankylosing spondylitis, type 1 diabetes mellitus, granulomatosis with polyangiitis, Crohn's disease, Primary sclerosing cholangitis and psoriasis.

The reasons for the sex role in autoimmunity vary. Women appear to generally mount larger inflammatory responses than men when their immune systems are triggered, increasing the risk of autoimmunity. Involvement of sex steroids is indicated by that many autoimmune diseases tend to fluctuate in accordance with hormonal changes, for example: during pregnancy, in the menstrual cycle, or when using oral contraception. A history of pregnancy also appears to leave a persistent increased risk for autoimmune disease. It has been suggested that the slight, direct exchange of cells between mothers and their children during pregnancy may induce autoimmunity. This would tip the gender balance in the direction of the female.

Another theory suggests the female high tendency to get autoimmunity is due to an imbalanced X chromosome inactivation. The X-inactivation skew theory, proposed by Princeton University's Jeff Stewart, has recently been confirmed experimentally in scleroderma and autoimmune thyroiditis. Other complex X-linked genetic susceptibility mechanisms are proposed and under investigation.

Unlike other autoinflammatory disorders, patients with CANDLE do not respond to IL-1 inhibition treatment in order to stop the autoinflammatory response altogether. This suggests that the condition also involves IFN dysregulation.

Infectious pathogen-associated diseases include many of the most common and costly chronic illnesses. The treatment of chronic diseases accounts for 75% of all US healthcare costs (amounting to $1.7 trillion in 2009).

Other causes or associations of disease are: a compromised immune system, environmental toxins, radiation exposure, diet and lifestyle choices, stress, and genetics. Diseases may also be multifactorial, requiring multiple factors to induce disease. For example: in a murine model, Crohn's disease can be precipitated by a norovirus, but only when both a specific gene variant is present and a certain toxin has damaged the gut.

According to the hygiene hypothesis, high levels of cleanliness expose children to fewer antigens than in the past, causing their immune systems to become overactive and more likely to misidentify own tissues as foreign, resulting in autoimmune conditions such as asthma.

The syndromes within CAPS overlap clinically, and patients may have features of more than one disorder. In a retrospective cohort of 136 CAPS patients from 16 countries, the most prevalent clinical features were fever (84% of cases, often with concurrent constitutional symptoms such as fatigue, malaise, mood disorders or failure to thrive), skin rash (either urticarial or maculopapular rash; 97% of cases) especially after cold exposure, and musculoskeletal involvement (myalgia, arthralgia, and/or arthritis, or less commonly joint contracture, patellar overgrowth, bone deformity, bone erosion and/or osteolytic lesion; 86% of cases). Less common features included ophthalmological involvement (conjunctivitis and/or uveitis, or less commonly optic nerve atrophy, cataract, glaucoma or impaired vision; 71% of cases), neurosensory hearing loss (42% of cases), neurological involvement (morning headache, papilloedema, and/or meningitis, or less commonly seizure, hydrocephalus or mental retardation; 40% of cases), and AA amyloidosis (4% of cases). Age of onset is typically in infancy or early childhood. In 57% of cases, CAPS had a chronic phenotype with symptoms present almost daily, whereas the remaining 43% of patients experienced only acute episodes. Up to 56% of patients reported a family history of CAPS. Previous studies confirm these symptoms, although the exact reported rates vary.

CRMO was once considered strictly a childhood disease, but adults have been diagnosed with it. The affected tends to range from 4 to 14 years old, with 10 as the median age. As stated above, CRMO occurs 1:1,000,000 and primarily in girls with a 5:1 ratio. That means out of six million, there will probably be 5 girls and 1 boy with the condition.

Prognosis will depend on your child's individual disease and response to treatment. It is best to discuss the prognosis with your child's pediatric rheumatologist.

Adult-onset Still's Disease is rare and has been described all over the world. The number of new cases per year is estimated to be 1.6 per 1,000,000 population. The number of people currently affected is estimated at 1.5 cases per 100,000-1,000,000 population. Onset is most common in two age ranges, between ages 15–25 and between ages of 36–46 years.

An overlap syndrome is an autoimmune disease of connective tissue in which a person presents with symptoms of two or more diseases.

Examples of overlap syndromes include mixed connective tissue disease and scleromyositis. Diagnosis depends on which diseases the patient shows symptoms and has positive antibodies for in their lab serology.

In overlap syndrome, features of the following diseases are found (most common listed):

- Systemic lupus erythematosus (SLE),

- Systemic sclerosis,

- Polymyositis,

- Dermatomyositis,

- Rheumatoid arthritis (RA)

- Sjögren's syndrome

- Eosinophilic granulomatosis with polyangiitis (EGPA)

- Autoimmune thyroiditis

- Antiphospholipid antibody syndrome

The treatment of overlap syndrome is mainly based on the use of corticosteroids and immunosuppressants. Biologic drugs, i.e. anti-TNFα or anti-CD20 monoclonal antibodies, have been recently introduced as alternative treatments in refractory cases. There are some concerns with the use of anti-TNF agents in patients with systemic autoimmune diseases due to the risk of triggering disease exacerbations.

Rare diseases are usually genetic and are therefore chronic. EURORDIS estimates that at least 80% of them have identified genetic origins. Other rare diseases are the result of infections and allergies or due to degenerative and proliferative causes.

Symptoms of some rare diseases may appear at birth or in childhood, whereas others only appear once adulthood is reached.

Research publications emphasize rare diseases that are chronic or incurable, although many short-term medical conditions are also rare diseases.

An interesting inverse relationship exists between infectious diseases and autoimmune diseases. In areas where multiple infectious diseases are endemic, autoimmune diseases are quite rarely seen. The reverse, to some extent, seems to hold true. The hygiene hypothesis attributes these correlations to the immune manipulating strategies of pathogens. While such an observation has been variously termed as spurious and ineffective, according to some studies, parasite infection is associated with reduced activity of autoimmune disease.

The putative mechanism is that the parasite attenuates the host immune response in order to protect itself. This may provide a serendipitous benefit to a host that also suffers from autoimmune disease. The details of parasite immune modulation are not yet known, but may include secretion of anti-inflammatory agents or interference with the host immune signaling.

A paradoxical observation has been the strong association of certain microbial organisms with autoimmune diseases.

For example, "Klebsiella pneumoniae" and coxsackievirus B have been strongly correlated with ankylosing spondylitis and diabetes mellitus type 1, respectively. This has been explained by the tendency of the infecting organism to produce super-antigens that are capable of polyclonal activation of B-lymphocytes, and production of large amounts of antibodies of varying specificities, some of which may be self-reactive (see below).

Certain chemical agents and drugs can also be associated with the genesis of autoimmune conditions, or conditions that simulate autoimmune diseases. The most striking of these is the drug-induced lupus erythematosus. Usually, withdrawal of the offending drug cures the symptoms in a patient.

Cigarette smoking is now established as a major risk factor for both incidence and severity of rheumatoid arthritis. This may relate to abnormal citrullination of proteins, since the effects of smoking correlate with the presence of antibodies to citrullinated peptides.

Antihistamines are not effective in treating the hives in this condition. It may respond to immunosuppressant drugs such as corticosteroids, cyclooxygenase inhibitors, interferon alpha, interleukin 1 receptor antagonists (Anakinra), perfloxacin, colchicine, cyclosporine or thalidomide. The hives may respond to treatment with PUVA, and the bone pain may respond to bisphosphonates.

Because Schnitzler's syndrome is so rare, the efficacy of different treatments cannot be compared using statistics. Nevertheless, case studies provide evidence that anakinra (otherwise known as kineret) is much more effective for Schnitzler's syndrome than any other drug, and that the improvement in symptoms associated with this treatment is dramatic. For example, Beseda and Nossent (2010) reviewed the literature concerning IL1-RA treatment (i.e. anakinra) for Schnitzler's syndrome. They concluded that, “Twenty-four patients with Schnitzler's syndrome... have been successfully treated with anakinra.” They add that “seven out of seven patients [with Schnitzler’s syndrome], that either interrupted or used anakinra every other day, had relapse of their symptoms within 24-48 h; anakinra was restarted in all patients with the same clinical efficiency.” Kluger et al. (2008) investigated the effectiveness of anakinra for a range of conditions. They searched MEDLINE for English-language trials of anakinra and abstracts from rheumatologial scientific meetings. They conclude that, “Over the last few years it has become increasingly evident that anakinra is highly effective and safe in patients with ... Schnitzler’s syndrome”. The year before, De Koning et al. (2007) reviewed the disease characteristics of Schnitzler syndrome and collected follow-up information to gain insight into long-term prognosis and treatment efficacy. They used data from 94 patients, and their conclusions about treatment for the condition are that, “There have been promising developments in therapeutic options, especially antiinterleukin-1 treatment, which induced complete remission in all 8 patients treated so far.”

Reports of individual patients treated with anakinra illustrate its effectiveness. Beseda and Nossent (ibid.) report treating a longstanding multidrug resistant Schnitzler’s syndrome patient with anakinra: “Within 24 h after the first injection, both the urticaria and the fever disappeared and have not recurred. For the past 6 months, the patient has been in clinical and biochemical remission.” Other authors report “a complete resolution of symptoms” (Dybowski et al., 2008). Crouch et al. (2007) report the effective treatment of a 52-year-old man who had been diagnosed with Schnitzler’s syndrome 8 years earlier: “On review, one week later, the patient’s systemic symptoms had resolved, and his previously elevated white cell count and inflammatory markers had normalised. The use of anakinra in our patient resulted in resolution of symptoms and has enabled cessation of oral prednisolone. Our patient remains symptom free on anakinra after 14 months of follow-up”. Similar stories are reported by Frischmeyer-Guerrerio et al. (2008), Wastiaux et al. (2007), and Eiling et al. (2007), Schneider et al. (2007). De Koning et al. (2006) treated three patients with Schnitzler’s syndrome with thalidomide and anakinra. Thalidomide was only effective for one of the three patients and was discontinued because of polyneuropathy. In contrast, for all three patients, anakinra “led to disappearance of fever and skin lesions within 24 hours. After a follow-up of 16-18 months, all patients are free of symptoms”. The authors concluded that anakinra as a treatment for Schnitzler’s syndrome “is preferable to thalidomide... as it has fewer side effects”.

As well as being more effective, anakinra is safer than the other treatments available for Schnitzler's syndrome. The Cochrane review entitled, ‘Anakinra for rheumatoid arthritis’ (Mertens and Singh, 2009 ) evaluates the (clinical effectiveness and) safety of anakinra in adult patients with rheumatoid arthritis, using data from 2876 patients, from five trials which constituted 781 randomized to placebo and 2065 to anakinra. The authors conclude, “There were no statistically significant differences noted in most safety outcomes with treatment with anakinra versus placebo - including number of withdrawals, deaths, adverse events (total and serious), and infections (total and serious). Injection site reactions were significantly increased, occurring in 1235/1729 (71%) versus 204/729 (28%) of patients treated with anakinra versus placebo, respectively”. These injection site reactions last for no more than four months, and are trivial compared to the very debilitating symptoms of Schnitzler's syndrome.

Deficiency of the interleukin-1–receptor antagonist (DIRA) is a autosomal recessive, genetic autoinflammatory syndrome resulting from mutations in "IL1RN", the gene encoding the interleukin 1 receptor antagonist. The mutations result in an abnormal protein that is not secreted, exposing the cells to unopposed interleukin 1 activity. This results in sterile multifocal osteomyelitis, periostitis (inflammation of the membrane surrounding the bones), and pustulosis due to skin inflammation from birth.

The first estimate of US prevalence for autoimmune diseases as a group was published in 1997 by Jacobson, et al. They reported US prevalence to be around 9 million, applying prevalence estimates for 24 diseases to a US population of 279 million. Jacobson's work was updated by Hayter & Cook in 2012. This study used Witebsky's postulates, as revised by Rose & Bona, to extend the list to 81 diseases and estimated overall cumulative US prevalence for the 81 autoimmune diseases at 5.0%, with 3.0% for males and 7.1% for females. The estimated community

prevalence, which takes into account the observation that many people have more than one autoimmune disease, was 4.5% overall, with 2.7% for males and 6.4% for females.

The most common known cause of the syndrome are mutations in the Proteasome Subunit, Beta Type, 8 (PSMB8) gene that codes for proteasomes that in turn break down other proteins. This occurs specifically when a mutation causes the homozygous recessive form to emerge. The mutated gene results in proteins not being degraded and oxidative proteins building up in cellular tissues, eventually leading to apoptosis, especially in muscle and fat cells.

A study conducted by Brehm et al. in November 2015 discovered additional mutations that can cause CANDLE syndrome, including PSMA3 (encodes α7), PSMB4 (encodes β7), PSMB9 (encodes β1i), and the proteasome maturation protein (POMP), with 8 mutations in total between them. An additional unknown mutation type in the original PSMB8 gene was also noted.

The cause of adult-onset Still's disease is unknown, but it presumably involves interleukin-1 (IL-1), since medications that block the action of IL-1β are effective treatments. Interleukin-18 is expressed at high levels.

These are also referred to as systemic autoimmune diseases. The autoimmune CTDs may have both genetic and environmental causes. Genetic factors may create a predisposition towards developing these autoimmune diseases. They are characterized as a group by the presence of spontaneous overactivity of the immune system that results in the production of extra antibodies into the circulation. The classic collagen vascular diseases have a "classic" presentation with typical findings that doctors can recognize during an examination. Each also has "classic" blood test abnormalities and abnormal antibody patterns. However, each of these diseases can evolve slowly or rapidly from very subtle abnormalities before demonstrating the classic features that help in the diagnosis. The classic collagen vascular diseases include:

- Systemic lupus erythematosus (SLE) – An inflammation of the connective tissues, SLE can afflict every organ system. It is up to nine times more common in women than men and strikes black women three times as often as white women. The condition is aggravated by sunlight.

- Rheumatoid arthritis – Rheumatoid arthritis is a systemic disorder in which immune cells attack and inflame the membrane around joints. It also can affect the heart, lungs, and eyes. Of the estimated 2.1 million Americans with rheumatoid arthritis, approximately 1.5 million (71 percent) are women.

- Scleroderma – an activation of immune cells that produces scar tissue in the skin, internal organs, and small blood vessels. It affects women three times more often than men overall, but increases to a rate 15 times greater for women during childbearing years, and appears to be more common among black women.

- Sjögren's syndrome – also called Sjögren's disease, is a chronic, slowly progressing inability to secrete saliva and tears. It can occur alone or with rheumatoid arthritis, scleroderma, or systemic lupus erythematosus. Nine out of 10 cases occur in women, most often at or around mid-life.

- Mixed connective tissue disease – Mixed connective-tissue disease (MCTD) is a disorder in which features of various connective-tissue diseases (CTDs) such as systemic lupus erythematosus (SLE); systemic sclerosis (SSc); dermatomyositis (DM); polymyositis (PM); anti-synthetase syndrome; and, occasionally, Sjögren syndrome can coexist and overlap. The course of the disease is chronic and usually milder than other CTDs. In most cases, MCTD is considered an intermediate stage of a disease that eventually becomes either SLE or Scleroderma.

- Undifferentiated connective tissue disease (UCTD) is a disease in which the body mistakenly attacks its own tissues. It is diagnosed when there is evidence of an existing autoimmune condition which does not meet the criteria for any specific autoimmune disease, such as systemic lupus erythematosus or scleroderma. Latent lupus and incomplete lupus are alternative terms that have been used to describe this condition.

- Psoriatic arthritis is also a collagen vascular disease.

DIRA displays a constellation of serious symptoms which include respiratory distress, as well as the following:

Rather than predisposing for infections, most of the autoinflammatory disorders lead to excessive inflammation. Many manifest themselves as periodic fever syndromes. They may involve various organs directly, as well as predisposing for long-term damage (e.g. by leading to amyloid deposition).

1. Familial Mediterranean fever

2. TNF receptor associated periodic syndrome (TRAPS)

3. Hyper-IgD syndrome (HIDS)

4. "CIAS1"-related diseases:

1. Muckle-Wells syndrome

2. Familial cold autoinflammatory syndrome

3. Neonatal onset multisystem inflammatory disease

5. PAPA syndrome (pyogenic sterile arthritis, pyoderma gangrenosum, acne)

6. Blau syndrome

7. Chronic recurrent multifocal osteomyelitis and congenital dyserythropoietic anemia (Majeed syndrome)

8. DIRA (deficiency of the IL-1 receptor antagonist)