It is currently thought that Cogan's syndrome is an autoimmune disease. The inflammation in the eye and ear are due to the patient's own immune system producing antibodies that attack the inner ear and eye tissue. Autoantibodies can be demonstrated in the blood of some patients, and these antibodies have been shown to attack inner ear tissue in laboratory studies. Infection with the bacteria "Chlamydia pneumoniae" has been demonstrated in some patients prior to the development of Cogan's syndrome, leading some researchers to hypothesize that the autoimmune disease may be initiated by the infection. "C. pneumoniae" is a common cause of mild pneumonia, and the vast majority of patients who are infected with the bacteria do not develop Cogan's syndrome.

In the United States, sarcoidosis has a prevalence of approximately 10 cases per 100,000 whites and 36 cases per 100,000 blacks. Heerfordt syndrome is present in 4.1–5.6% of those with sarcoidosis.

Cogan's syndrome is a rare, rheumatic disease characterized by inflammation of the ears and eyes. Cogan's syndrome can lead to vision difficulty, hearing loss and dizziness. The condition may also be associated with blood-vessel inflammation (called vasculitis) in other areas of the body that can cause major organ damage in 15% of those afflicted or, in a small number of cases, even death. It most commonly occurs in a person's 20s or 30s. The cause is not known. However, one theory is that it is an autoimmune disorder in which the body's immune system mistakenly attacks tissue in the eye and ear.

The exact cause of Heerfordt syndrome has not yet been definitively determined. Of those patients who have been diagnosed with Heerfordt syndrome, 15% have a close relative who also has the syndrome. One possible explanation is that the syndrome results from a combination of an environmental agent and a hereditary predisposition. "Mycobacterium" and "Propionibacteria" species have both been suggested as the environmental agent, though the evidence for this is inconclusive.

AIED is generally caused by either antibodies or immune cells that cause damage to the inner ear. There are several theories that propose a cause of AIED:

- Bystander damage – Physical damage to the inner ear may lead to cytokine release that signals for an immune response. This may be a component of the "attack/remission cycle" of Meniere's disease.

- Cross-reactions – Accidental damage of the inner ear by antibodies or T-cells that recognize an inner ear antigen that is similar to a bacterial or viral antigen

- Genetic factors – Predisposition to developing an autoimmune disorder based on genes inherited

- Intolerance – The immune system may not be aware of all the antigens present in the inner ear until physical damage releases some of these antigens. As a result, the immune system treats these unfamiliar antigens as foreign and mounts an immune response.

Currently, the cross-reactions theory appears to be the favored mechanism of AIED pathogenesis.

Autoimmune inner ear disease (AIED) was first defined by Dr. Brian McCabe in a landmark paper describing an autoimmune loss of hearing. The disease results in progressive sensorineural hearing loss (SNHL) that acts bilaterally and asymmetrically, and sometimes affects an individual's vestibular system. AIED is used to describe any disorder in which the inner ear is damaged as a result of an autoimmune response. Some examples of autoimmune disorders that have presented with AIED are Cogan's syndrome, relapsing polychondritis, systemic lupus erythematosus, granulomatosis with polyangiitis, polyarteritis nodosa, Sjogren's syndrome, and Lyme disease.

Research has come to the consensus that AIED is the result of antibodies or other immune cells that cause damage to structures of the inner ear such as the cochlea and vestibular system. Of note, AIED is the only known SNHL that responds to medical treatment, but withholding treatment for longer than three months may result in permanent hearing loss and the need for cochlear implant installation.

Although AIED has been studied extensively over the past 25 years, no clear mechanism of pathogenesis has emerged. A recent paper performed a literature review of all relevant articles dating back to 1980, and proposed a mechanism of pathogenesis which includes an inflammatory response and immune cell attack on inner ear structures. This response leads to an over-activation of other immune cells such as T helper cells, resulting in vascular changes and cochlear harm. AIED appears to be a consequence of damaged sensorineural hearing due to electrochemical disturbances, microthrombosis, and immune cell deposition. Additionally, self-reactive antibodies and T-cells contribute to the aforementioned damage. Research has suggested a valuable next step in uncovering AIED pathogenesis is inquiry into the role of interleukin-1β (IL-1β).

The life expectancy of people with A-T is highly variable. The average is approximately 25 years, but continues to improve with advances in care. The two most common causes of death are chronic lung disease (about one-third of cases) and cancer (about one-third of cases).

Overall, the estimated prevalence of Stickler syndrome is about 1 in 10,000 people. Stickler syndrome affects 1 in 7,500 to 9,000 newborns.

One possible cause of Harlequin syndrome is a lesion to the preganglionic or postganglionic cervical sympathetic fibers and parasympathetic neurons of the ciliary ganglion. It is also believed that torsion (twisting) of the thoracic spine can cause blockage of the anterior radicular artery leading to Harlequin syndrome. The sympathetic deficit on the denervated side causes the flushing of the opposite side to appear more pronounced. It is unclear whether or not the response of the undamaged side was normal or excessive, but it is believed that it could be a result of the body attempting to compensate for the damaged side and maintain homeostasis.

Since the cause and mechanism of Harlequin syndrome is still unknown, there is no way to prevent this syndrome.

Harlequin syndrome is not debilitating so treatment is not normally necessary. In cases where the individual may feel socially embarrassed, contralateral sympathectomy may be considered, although compensatory flushing and sweating of other parts of the body may occur. In contralateral sympathectomy, the nerve bundles that cause the flushing in the face are interrupted. This procedure causes both sides of the face to no longer flush or sweat. Since symptoms of Harlequin syndrome do not typically impair a person’s daily life, this treatment is only recommended if a person is very uncomfortable with the flushing and sweating associated with the syndrome.

Many professionals that are likely to be involved in the treatment of those with Stickler's syndrome, include anesthesiologists, oral and maxillofacial surgeons; craniofacial surgeons; ear, nose, and throat specialists, ophthalmologists, optometrists, audiologists, speech pathologists, physical therapists and rheumatologists.

People with A-T have a highly increased incidence (approximately 25% lifetime risk) of cancers, particularly lymphomas and leukemia, but other cancers can occur. When possible, treatment should avoid the use of radiation therapy and chemotherapy drugs that work in a way that is similar to radiation therapy (radiomimetic drugs), as these are particularly toxic for people with A-T. The special problems of managing cancer are sufficiently complicated that treatment should be done only in academic oncology centers and after consultation with physicians who have specific expertise in A-T. Unfortunately, there is no way to predict which individuals will develop cancer. Because leukemia and lymphomas differ from solid tumors in not progressing from solitary to metastatic stages, there is less need to diagnose them early in their appearance. Surveillance for leukemia and lymphoma is thus not helpful, other than considering cancer as a diagnostic possibility whenever possible symptoms of cancer (e.g. persistent swollen lymph glands, unexplained fever) arise.

Women who are A-T carriers (who have one mutated copy of the ATM gene), have approximately a two-fold increased risk for the development of breast cancer compared to the general population. This includes all mothers of A-T children and some female relatives. Current consensus is that special screening tests are not helpful, but all women should have routine cancer surveillance.

Marshall syndrome is a genetic disorder of the connective tissue which can cause hearing loss. The three most common areas to be affected are the eyes which are uncommonly large, joints and the mouth and facial structures. Marshall syndrome and Stickler syndrome closely resemble each other; in fact they are so similar, some say they are the same.

Muir–Torre was observed to occur in 14 of 50 families (28%) and in 14 of 152 individuals (9.2%) with Lynch syndrome, also known as HNPCC.

The 2 major MMR proteins involved are hMLH1 and hMSH2. Approximately 70% of tumors associated with the MTS have microsatellite instability. While germline disruption of hMLH1 and hMSH2 is evenly distributed in HNPCC, disruption of hMSH2 is seen in greater than 90% of MTS patients.

Gastrointestinal and genitourinary cancers are the most common internal malignancies. Colorectal cancer is the most common visceral neoplasm in Muir–Torre syndrome patients.

Respiratory complications are often cause of death in early infancy.

Marshall–Smith syndrome is not to be confused with:

- Marshall syndrome (aka.Periodic fever, aphthous stomatitis, pharyngitis and adenitis (PFAPA syndrome, see also: Periodic fever syndrome)

- Sotos (like) syndrome

- Weaver-Smith syndrome (WSS)

Myopia is the most common eye problem in Marshall syndrome. Cataracts also occur more frequently and detached retina less frequently than in Stickler syndrome. Myopia also is the most common problem with the eyes in Stickler syndrome. In the latter syndrome, extreme myopia may lead to severe eye problems such as detached retina more frequently than in Marshall syndrome.

Roberts syndrome is an extremely rare condition that only affects about 150 reported individuals. Although there have been only about 150 reported cases, the affected group is quite diverse and spread worldwide. Parental consanguinity (parents are closely related) is common with this genetic disorder. The frequency of Roberts syndrome carriers is unknown.

There is an association between taking aspirin for viral illnesses and the development of Reye syndrome, but no animal model of Reye syndrome has been developed in which aspirin causes the condition.

The serious symptoms of Reye syndrome appear to result from damage to cellular mitochondria, at least in the liver, and there are a number of ways that aspirin could cause or exacerbate mitochondrial damage. A potential increased risk of developing Reye syndrome is one of the main reasons that aspirin has not been recommended for use in children and teenagers, the age group for which the risk of lasting serious effects is highest.

No research has found a definitive cause of Reye syndrome, and association with aspirin has been shown through epidemiological studies. The diagnosis of "Reye Syndrome" greatly decreased in the 1980s, when genetic testing for inborn errors of metabolism was becoming available in developed countries. A retrospective study of 49 survivors of cases diagnosed as "Reye's Syndrome" showed that the majority of the surviving patients had various metabolic disorders, particularly a fatty-acid oxidation disorder medium-chain acyl-CoA dehydrogenase deficiency.

In some countries, oral mouthcare product Bonjela (not the form specifically designed for teething) has labeling cautioning against its use in children, given its salicylate content. There have been no cases of Reye syndrome following its use, and the measure is a precaution. Other medications containing salicylates are often similarly labeled as a precaution.

The Centers for Disease Control and Prevention (CDC), the U.S. Surgeon General, the American Academy of Pediatrics (AAP) and the Food and Drug Administration (FDA) recommend that aspirin and combination products containing aspirin not be given to children under 19 years of age during episodes of fever-causing illnesses. Hence, in the United States, it is advised that the opinion of a doctor or pharmacist should be obtained before anyone under 19 years of age is given any medication containing aspirin (also known on some medicine labels as acetylsalicylate, salicylate, acetylsalicylic acid, ASA, or salicylic acid).

Current advice in the United Kingdom by the Committee on Safety of Medicines is that aspirin should not be given to those under the age of 16 years, unless specifically indicated in Kawasaki disease or in the prevention of blood clot formation.

Documented cases of Reye syndrome in adults are rare. The recovery of adults with the syndrome is generally complete, with liver and brain function returning to normal within two weeks of onset. In children, however, mild to severe permanent brain damage is possible, especially in infants. Over thirty percent of the cases reported in the United States from 1981 through 1997 resulted in fatality.

Schimmelpenning syndrome appears to be sporadic rather than inherited, in almost all cases. It is thought to result from genetic mosaicism, possibly an autosomal dominant mutation arising after conception and present only in a subpopulation of cells. The earlier in embryological development such a mutation occurs, the more extensive the nevi are likely to be and the greater the likelihood of other organ system involvement.

In most cases Ballantyne syndrome causes fetal or neonatal death and in contrast, maternal involvement is limited at the most to preeclampsia.

Even in syndromes with no known etiology, the presence of the associated symptoms with a statistically improbable correlation, normally leads the researchers to hypothesize that there exists an unknown underlying cause for all the described symptoms.

There is no specific treatment or cure for individuals affected with this type of syndrome, though some of the abnormal physical features may be surgically correctable.

A syndrome is a set of medical signs and symptoms occurring together, constitutes a particular disease or disorder. The word derives from the Greek σύνδρομον, meaning "concurrence". In some instances, a syndrome is so closely linked with a pathogenesis or cause that the words "syndrome", "disease", and "disorder" end up being used interchangeably for them. This is especially true of inherited syndromes. For example, Down syndrome, Wolf–Hirschhorn syndrome, and Andersen syndrome are disorders with known pathogeneses, so each is more than just a set of signs and symptoms, despite the "syndrome" nomenclature. In other instances, a syndrome is not specific to only one disease. For example, toxic shock syndrome can be caused by various toxins; premotor syndrome can be caused by various brain lesions; and premenstrual syndrome is not a disease but simply a set of symptoms.

If an underlying genetic cause is suspected but not known, a condition may be referred to as a genetic association (often just "association" in context). By definition, an association indicates that the collection of signs and symptoms occurs in combination more frequently than would be likely by chance alone.

Syndromes are often named after the physician or group of physicians that discovered them or initially described the full clinical picture. Such eponymous syndrome names are examples of medical eponyms. Recently, there has been a shift towards naming conditions descriptively (by symptoms or underlying cause) rather than eponymously, but the eponymous syndrome names often persist in common usage.