The overall incidence is ~1/42,000 to 1/50,000 people. Types I and II are the most common types of the syndrome, whereas types III and IV are rare. Type 4 is also known as Waardenburg‐Shah syndrome (association of Waardenburg syndrome with Hirschsprung disease).

Type 4 is rare with only 48 cases reported up to 2002.

About 1 in 30 students in schools for the deaf have Waardenburg syndrome. All races and sexes are affected equally. The highly variable presentation of the syndrome makes it difficult to arrive at precise figures for its prevalence.

Waardenburg syndrome is a rare genetic disorder most often characterized by varying degrees of deafness, minor defects in structures arising from the neural crest, and pigmentation changes. It was first described in 1951. The syndrome was later found to have four types. For example, type II was identified in 1971, to describe cases where dystopia canthorum was not present. Some types are now split into subtypes, based upon the gene responsible for the condition.

Paris syndrome (, , "Pari shōkōgun") is a transient mental disorder exhibited by some individuals when visiting or going on vacation to Paris, as a result of extreme shock derived from their discovery that Paris is not what they had expected it to be. The syndrome is characterized by a number of psychiatric symptoms such as acute delusional states, hallucinations, feelings of persecution (perceptions of being a victim of prejudice, aggression, or hostility from others), derealization, depersonalization, anxiety, and also psychosomatic manifestations such as dizziness, tachycardia, sweating, and others, such as vomiting. Similar syndromes include Jerusalem syndrome and Stendhal syndrome. The condition is commonly viewed as a severe form of culture shock. It is particularly noted among Japanese travelers.

Professor Hiroaki Ota, a Japanese psychiatrist working in France, is credited as the first person to diagnose the condition in 1986. However, later work by Youcef Mahmoudia, physician with the hospital Hôtel-Dieu de Paris, indicates that Paris syndrome is "a manifestation of psychopathology related to the voyage, rather than a syndrome of the traveller." He theorized that the excitement resulting from visiting Paris causes the heart to accelerate, causing giddiness and shortness of breath, which results in hallucinations in the manner similar to the Stendhal syndrome described by Italian psychiatrist Graziella Magherini in her book "La sindrome di Stendhal".

Usher syndrome, also known as Hallgren syndrome, Usher-Hallgren syndrome, retinitis pigmentosa-dysacusis syndrome, or dystrophia retinae dysacusis syndrome, is an extremely rare genetic disorder caused by a mutation in any one of at least 11 genes resulting in a combination of hearing loss and visual impairment. It is a leading cause of deafblindness and is at present incurable.

Usher syndrome is classed into three subtypes according to onset and severity of symptoms. All three subtypes are caused by mutations in genes involved in the function of the inner ear and retina. These mutations are inherited in an autosomal recessive pattern.

Among the medical signs are dacryocystitis, seizures, intellectual disability, and paralysis, each of which is a complication resulting from the diminutive foramina. A common sign reported as a result of the disease has been a difference of the size of the eyes.

Since Usher syndrome results from the loss of a gene, gene therapy that adds the proper protein back ("gene replacement") may alleviate it, provided the added protein becomes functional. Recent studies of mouse models have shown one form of the disease—that associated with a mutation in myosin VIIa—can be alleviated by replacing the mutant gene using a lentivirus. However, some of the mutated genes associated with Usher syndrome encode very large proteins—most notably, the "USH2A" and "GPR98" proteins, which have roughly 6000 amino-acid residues. Gene replacement therapy for such large proteins may be difficult.

Craniodiaphyseal dysplasia (also known as CDD or lionitis) is an extremely rare autosomal recessive bone disorder that causes calcium to build up in the skull, disfiguring the facial features and reducing life expectancy.

These calcium deposits decrease the size of cranial foramina, and can also decrease the hole in the cervical spinal canal. In the few cases recorded, most of the sufferers died in childhood.

The underlying genetics are uncertain.

All of the causes of childhood disintegrative disorder are still unknown. Sometimes CDD surfaces abruptly within days or weeks, while in other cases it develops over a longer period of time. A Mayo Clinic report indicates: "Comprehensive medical and neurological examinations in children diagnosed with childhood disintegrative disorder seldom uncover an underlying medical or neurological cause. Although the occurrence of epilepsy is higher in children with childhood disintegrative disorder, experts don't know whether epilepsy plays a role in causing the disorder."

CDD, especially in cases of later age of onset, has also been associated with certain other conditions, particularly the following:

- Lipid storage diseases: In this condition, a toxic buildup of excess fats (lipids) takes place in the brain and nervous system.

- Subacute sclerosing panencephalitis: Chronic infection of the brain by a form of the measles virus causes subacute sclerosing panencephalitis. This condition leads to brain inflammation and the death of nerve cells.

- Tuberous sclerosis (TSC): TSC is a genetic disorder. In this disorder, tumors may grow in the brain and other vital organs like kidneys, heart, eyes, lungs, and skin. In this condition, noncancerous (benign) tumors, hamartomas, grow in the brain.

- Leukodystrophy: In this condition, the myelin sheath does not develop in a normal way causing white matter in the brain to disintegrate.

A genetic predisposition is a genetic characteristic which influences the possible phenotypic development of an individual organism within a species or population under the influence of environmental conditions. In medicine, genetic susceptibility to a disease refers to a genetic predisposition to a health problem, which may eventually be triggered by particular environmental or lifestyle factors, such as tobacco smoking or diet. Genetic testing is able to identify individuals who are genetically predisposed to certain diseases.

Chronic radiation syndrome is a constellation of health effects that occur after months or years of chronic exposure to high amounts of ionizing radiation. Chronic radiation syndrome develops with a speed and severity proportional to the radiation dose received, i.e., it is a deterministic effect of radiation exposure, unlike radiation-induced cancer. It is distinct from acute radiation syndrome in that it occurs at dose rates low enough to permit natural repair mechanisms to compete with the radiation damage during the exposure period. Dose rates high enough to cause the acute form (> ~0.1 Gy/h) are fatal long before onset of the chronic form. The lower threshold for chronic radiation syndrome is between 0.7 and 1.5 Gy, at dose rates above 0.1 Gy/yr. This condition is primarily known from the Kyshtym disaster, where 66 cases were diagnosed, and has received little mention in Western literature. A future ICRP publication, currently in draft, may recognize the condition but with higher thresholds.

In 2013, Alexander V. Akleyev described the chronology of the clinical course or CRS while presenting at ConRad in Munich, Germany. In his presentation, he defined the latent period as being 1-5 years, and the formation coinciding with the period of maximum radiation dose. The recovery period was described as being 3-12 months after exposure ceased. He concluded that "CRS represents a systemic response of the body as a whole to the chronic total body exposure in man." In 2014, Akleyev's book "Comprehensive analysis of chronic radiation syndrome, covering epidemiology, pathogenesis, pathoanatomy, diagnosis and treatment" was published by Springer.

Stendhal syndrome, Stendhal's syndrome, hyperkulturemia, or Florence syndrome is a psychosomatic disorder that causes rapid heartbeat, dizziness, fainting, confusion and even hallucinations when an individual is exposed to an experience of great personal significance, particularly viewing art. It is not listed as a recognised condition in the "Diagnostic and Statistical Manual of Mental Disorders".

Visual release hallucinations, also known as Charles Bonnet syndrome (CBS), is the experience of complex visual hallucinations in a person with partial or severe blindness. First described by Charles Bonnet in 1760, it was first introduced into English-speaking psychiatry in 1982.

Loss of language and skills related to social interaction and self-care are serious. The affected children face ongoing disabilities in certain areas and require long term care. Treatment of CDD involves both behavior therapy, environmental therapy and medications.

- Behavior therapy: The main aim of Applied Behavior Analysis (ABA) is to systematically teach the child to relearn language, self-care and social skills. The treatment programs designed in this respect "use a system of rewards to reinforce desirable behaviors and discourage problem behavior." ABA programs may be designed by a board-certified specialist in behavior analysis called a "BCBA" (Board Certified Behavior Analyst), but ABA is also widely used by a number of other health care personnel from different fields like psychologists, speech therapists, physical therapists and occupational therapists with differing levels of expertise. Parents, teachers and caregivers are instructed to use these behavior therapy methods at all times.

- Environmental Therapy: Sensory Enrichment Therapy uses enrichment of the sensory experience to improve symptoms in autism, many of which are common to CDD.

- Medications: There are no medications available to directly treat CDD. Antipsychotic medications are used to treat severe behavior problems like aggressive stance and repetitive behavior patterns. Anticonvulsant medications are used to control seizures.

Because there is uncertainty in treating suspected factitious disorder imposed on self, some advocate that health care providers first explicitly rule out the possibility that the person has another early-stage disease. Then they may take a careful history and seek medical records to look for early deprivation, childhood abuse, or mental illness. If a person is at risk to themself, psychiatric hospitalization may be initiated.

Healthcare providers may consider working with mental health specialists to help treat the underlying mood or disorder as well as to avoid countertransference. Therapeutic and medical treatment may center on the underlying psychiatric disorder: a mood disorder, an anxiety disorder, or borderline personality disorder. The patient's prognosis depends upon the category under which the underlying disorder falls; depression and anxiety, for example, generally respond well to medication and/or cognitive behavioral therapy, whereas borderline personality disorder, like all personality disorders, is presumed to be pervasive and more stable over time, and thus offers a worse prognosis.

People affected may have multiple scars on their abdomen due to repeated "emergency" operations.

In factitious disorder imposed on self, the affected person exaggerates or creates symptoms of illnesses in themselves to gain examination, treatment, attention, sympathy, and/or comfort from medical personnel. In some extreme cases, people suffering from Munchausen syndrome are highly knowledgeable about the practice of medicine and are able to produce symptoms that result in lengthy and costly medical analysis, prolonged hospital stays, and unnecessary operations. The role of "patient" is a familiar and comforting one, and it fills a psychological need in people with this syndrome. This disorder is distinct from hypochondriasis and other somatoform disorders in that those with the latter do not intentionally produce their somatic symptoms. Munchausen syndrome is distinct from other psychiatric disorders such as malingering in that Munchausen does not fabricate symptoms for material gain such as financial compensation, absence from work, or access to drugs.

Risk factors for developing factitious disorder include childhood traumas, growing up with parents/caretakers who were emotionally unavailable due to illness or emotional problems, a serious illness as a child, failed aspirations to work in the medical field, personality disorders, and low self-esteem. Factitious disorder is more common in men and is seen in young or middle-aged adults. Those with a history of working in healthcare are also at greater risk of developing it.

Arrhythmogenic Munchausen syndrome describes individuals who simulate or stimulate cardiac arrhythmias to gain medical attention.

A similar behavior called factitious disorder imposed on another has been documented in the parent or guardian of a child. The adult ensures that his or her child will experience some medical affliction, therefore compelling the child to suffer through treatments and spend a significant portion of their youth in hospitals. Furthermore, a disease may actually be initiated in the child by the parent or guardian. This condition is considered distinct from Munchausen syndrome. There is growing consensus in the pediatric community that this disorder should be renamed "medical abuse" to highlight the harm caused by the deception and to make it less likely that a perpetrator can use a psychiatric defense when harm is done.

A brainstem stroke syndrome is a condition involving a stroke of the brainstem. Because of their location, they often involve impairment both of the cranial nuclei and of the long tracts.

A person may have vertigo, dizziness and severe imbalance without the hallmark of most strokes – weakness on one side of the body. The symptoms of vertigo, dizziness or imbalance usually occur together; dizziness alone is not a sign of stroke. Brainstem stroke can also cause diplopia, slurred speech and decreased level of consciousness. A more serious outcome is locked-in syndrome.

CBS predominantly affects people with visual impairments due to old age, diabetes or other damage to the eyes or optic pathways. In particular, central vision loss due to a condition such as macular degeneration combined with peripheral vision loss from glaucoma may predispose to CBS, although most people with such deficits do not develop the syndrome.

The syndrome can also develop after bilateral optic nerve damage due to methyl alcohol poisoning.

Predisposition is the capacity we are born with to learn things such as language and concept of self. Negative environmental influences may block the predisposition (ability) we have to do some things. Behaviors displayed by animals can be influenced by genetic predispositions. Genetic predisposition towards certain human behaviors is scientifically investigated by attempts to identify patterns of human behavior that seem to be invariant over long periods of time and in very different cultures.

For example, philosopher Daniel Dennett has proposed that humans are genetically predisposed to have a theory of mind because there has been evolutionary selection for the human ability to adopt the intentional stance. The "intentional stance" is a useful behavioral strategy by which humans assume that others have minds like their own. This assumption allows you to predict the behavior of others based on personal knowledge of what you would do.

E. O. Wilson's and his book Consilience discuss the idea of genetic predisposition to behaviors

The field of evolutionary psychology explores the idea that certain behaviors have been selected for during the course of evolution.

Even though more studies are necessary for an efficient evaluation of the role played by zinc in senile osteoporosis, doctors recommend a proper supplementation of dietary zinc.

Replacement estrogen has proved to be an efficient way to combat the loss of bone mass in women when such treatment is started in the menopausal stage of their lives. John R. Lee, a Harvard graduate who wrote a book on the subject, came to the conclusion that by adding supplementation with natural progesterone to an existing natural osteoporosis treatment program, bone density was increased every year by 3-5% until it stabilized at the bone density levels expected for a 35-year-old woman, this after studies in 100 women between 38 and 83 with an average of 62 years old.

A zebibah (Arabic زبيبة "zabība", "raisin"), also known as a zabiba or zebiba, or prayer bump, is a mark on the forehead of some Muslims, due to the friction generated by repeated contact of the forehead with the prayer mat during daily prayers.

Islam requires its adherents to pray five times a day (known as salat), which involves kneeling on a prayer mat and touching the ground with one's forehead. When done firmly for extended periods of time, a prayer bump may develop. Some Muslims may consider the presence of a prayer bump to be a sign of religious dedication and piety. Some Muslims also believe that on the day of judgment, this bump will particularly fluoresce an immense white light.

In extreme cases, the callus can be thick enough to create a real bump that protrudes from the forehead. They may also develop due to frequent prayer on hard surfaces such as stone floors.

A zebibah can be a type of acanthosis nigricans, which is a sign of insulin resistance usually from type 2 diabetes. In Egypt, where zebibahs are common, the rate of diabetes was 10.2% in 2000. However, it was much larger for certain groups. For instance, the rate of diabetes was 21.9% for women aged between 45–64 years old. In addition, it was estimated that up to 56% of men and 64% of women are obese. Many of these obese people can be pre-diabetic.

MSbP is rare. A recent systematic study in Italy found that in a series of over 700 patients admitted to a pediatric ward, 4 cases met the diagnostic criteria for MSbP (0.53%). In this study, stringent diagnostic criteria were used, which required at least one test outcome or event that could not possibly have occurred without deliberate intervention by the MSbP person.

One study showed that in 93 percent of MSbP cases, the abuser is the mother or another female guardian or caregiver. This may be attributed to the prevalent socialization pattern that places females in the primary care-taking role. Of course, it could also be a gender trait rooted in genetics, as it is easy to see how females who seek attention as victims could gain an evolutionary advantage, while men seeking the same would be unfavoured for physical protection and mating. A psychodynamic model of this kind of maternal abuse exists.

MSbP may be more prevalent in the parents of those with a learning difficulty or mental incapacity, and as such the apparent patient could, in fact, be an adult.

Fathers and other male caregivers have been the perpetrators in only 7% of the cases studied. When they are not actively involved in the abuse, the fathers or male guardians of MSbP victims are often described as being distant, emotionally disengaged, and powerless. These men play a passive role in MSbP by being frequently absent from the home and rarely visiting the hospitalized child. Usually, they vehemently deny the possibility of abuse, even in the face of overwhelming evidence or their child's pleas for help.

Overall, male and female children are equally likely to be the victim of MSbP. In the few cases where the father is the perpetrator, however, the victim is three times more likely to be male.

Gay bowel syndrome was a medical term first used by Henry L Kazal and colleagues in 1976 to describe the various sexually transmitted perianal and rectal diseases and sexual traumas seen in Kazal's proctology practice, which had many gay patients.

Senile osteoporosis, formerly known as osteoporosis type II, has been recently recognized as a geriatric syndrome with a particular pathophysiology.

It has been pointed out that senile osteoporosis is the product of a skeleton in an advanced stage of life and also due to a deficiency caused by calcium, but physicians are also coming to the conclusion that multiple mechanisms in the development stages of the disease interact together and the product is an osteoporotic bone, regardless of age.

The 1951 Pont-Saint-Esprit mass poisoning, also known as Le Pain Maudit, occurred on 15 August 1951, in the small town of Pont-Saint-Esprit in southern France. More than 250 people were involved, including 50 persons interned in asylums and resulted in 7 deaths. A foodborne illness was suspected, and among these it was originally believed to be a case of "cursed bread" ("pain maudit").

Most academic sources accept ergot poisoning as the cause of the epidemic, while a few theorize other causes such as poisoning by mercury, mycotoxins, or nitrogen trichloride.