Davis and Barry 1977 tested allele frequencies in domestic cats. Among the 265 cats observed, there were 101 males and 164 females. Only one cat was recorded to have the ectrodactyly abnormality, illustrating this rare disease.

According to M.P. Ferreira, a case of ectrodactyly was found in a two-month-old male mixed Terrier dog. In another study, Carrig and co-workers also reported a series of 14 dogs with this abnormality proving that although ectrodactyly is an uncommon occurrence for dogs, it is not entirely unheard of.

In a study performed by the Department of Forestry and Natural Resources at Purdue University, approximately 2000 salamanders (687 adults and 1259 larvae) were captured from a large wetland complex and evaluated for malformations. Among the 687 adults, 54 (7.9%) were malformed. Of these 54 adults, 46 (85%) had missing (ectrodactyly), extra (polyphalangy) or dwarfed digits (brachydactyly). Among the 1259 larvae, 102 were malformed, with 94 (92%) of the malformations involving ectrodactyly, polyphalangy, and brachydactyly. Results showed few differences in the frequency of malformations among life-history changes, suggesting that malformed larvae do not suffer substantially higher mortality than their adult conspecifics.

Rothmund–Thomson syndrome (RTS), also known as poikiloderma atrophicans with cataract or poikiloderma congenitale, is a rare autosomal recessive skin condition originally described by August von Rothmund (1830–1906) in 1868. Matthew Sydney Thomson (1894–1969) published further descriptions in 1936.

There have been several reported cases associated with osteosarcoma. A hereditary genetic basis, mutations in the DNA Helicase "RECQL4" gene, causing problems during initiation of DNA replication has been implicated in the syndrome

In humans, individuals with RTS, and carrying the "RECQL4" germline mutation, can have several clinical features of accelerated aging. These features include atrophic skin and pigment changes, alopecia, osteopenia, cataracts and an increased incidence of cancer. Also in mice, "RECQL4" mutants show features of accelerated aging.

Situs inversus is generally an autosomal recessive genetic condition, although it can be X-linked or found in identical "mirror image" twins.

About 25% of individuals with situs inversus have an underlying condition known as primary ciliary dyskinesia (PCD). PCD is a dysfunction of the cilia that manifests itself during the embryologic phase of development. Normally functioning cilia determine the position of the internal organs during early embryological development, and so embryos with PCD have a 50% chance of developing situs inversus. If they do, they are said to have Kartagener syndrome, characterized by the triad of situs inversus, chronic sinusitis, and bronchiectasis. Cilia are also responsible for clearing mucus from the lung, and the dysfunction causes increased susceptibility to lung infections. Kartagener syndrome can also manifest with male infertility as functional cilia are required for proper sperm flagella function.

Triphalangeal thumb can occur in syndromes but it can also be isolated. The triphalangeal thumb can appear in combination with other malformations or syndromes.

Syndromes include:

- Holt-Oram syndrome

- Aase syndrome

- Blackfan-Diamond syndrome

- Townes-Brocks syndrome

Malformations include:

- Radial polydactyly

- Syndactyly

- Claw-like hand or foot

Malformations of the upper extremities can occur In the third to seventh embryonic week. In some cases the TPT is hereditary. In these cases, there is a mutation on chromosome 7q36. If the TPT is hereditary, it is mostly inherited as an autosomal dominant trait, non-opposable and bilateral. The sporadic cases are mostly opposable and unilateral.

The condition affects all major structures within the thorax and abdomen. Generally, the organs are simply transposed through the sagittal plane. The heart is located on the right side of the thorax, the stomach and spleen on the right side of the abdomen and the liver and gall bladder on the left side. The heart's normal right atrium occurs on the left, and the left atrium is on the right. The lung anatomy is reversed and the left lung has three lobes while the right lung has two lobes. The intestines and other internal structures are also reversed from the normal, and the blood vessels, nerves, and lymphatics are also transposed.

If the heart is swapped to the right side of the thorax, it is known as "situs inversus with dextrocardia" or "situs inversus totalis". If the heart remains on the normal left side of the thorax, a much more rare condition (1 in 2,000,000 of the general population), it is known as "situs inversus with levocardia" or "situs inversus incompletus".

Situs inversus of the optic disc may occur unilaterally or bilaterally, associated with reduced binocularity and stereoacuity resembling monofixation syndrome. It is characterized by emergence of the retinal vessels in an anomalous direction (from the nasal rather than the temporal aspect) with dysversion (tilt) of the optic disc.

A number of congenital heart defects can cause Eisenmenger syndrome, including atrial septal defects, ventricular septal defects, patent ductus arteriosus, and more complex types of acyanotic heart disease.

If the inciting defect in the heart is identified "before" it causes significant pulmonary hypertension, it can normally be repaired through surgery, preventing the disease. After pulmonary hypertension is sufficient to reverse the blood flow through the defect, however, the maladaptation is considered irreversible, and a heart–lung transplant or a lung transplant with repair of the heart is the only curative option.

Transplantation is the final therapeutic option and only for patients with poor prognosis and quality of life. Timing and appropriateness of transplantation remain difficult decisions. 5-year and 10-year survival ranges between 70% and 80%, 50% and 70%, 30% and 50%, respectively. Since the average life expectancy of patients after lung transplantation is as low as 30% at 5 years, patients with "reasonable functional status" related to Eisenmenger syndrome have "improved survival with conservative medical care" compared with transplantation.

Various medicines and therapies for pulmonary hypertension are under investigation for treatment of the symptoms.

Some recent research has suggested that a proportion of cases of migraine may be caused by PFO. While the exact mechanism remains unclear, closure of a PFO can reduce symptoms in certain cases. This remains controversial; 20% of the general population has a PFO, which for the most part, is asymptomatic. About 20% of the female population has migraines, and the placebo effect in migraine typically averages around 40%. The high frequency of these facts finding statistically significant relationships between PFO and migraine difficult (i.e., the relationship may just be chance or coincidence). In a large randomized controlled trial, the higher prevalence of PFO in migraine patients was confirmed, but migraine headache cessation was not more prevalent in the group of migraine patients who underwent closure of their PFOs.

As a group, atrial septal defects are detected in one child per 1500 live births. PFOs are quite common (appearing in 10–20% of adults), but asymptomatic, so undiagnosed. ASDs make up 30 to 40% of all congenital heart diseases that are seen in adults.

The ostium secundum atrial septal defect accounts for 7% of all congenital heart lesions. This lesion shows a male:female ratio of 1:2.

The cause of cutaneous horns is still unknown, but it is believed that exposure to radiation can trigger the condition. This is evidenced by a higher rate of cases occurring on the face and hands, areas that are often exposed to sunlight. Other cases have reported cutaneous horns arising from burn scars. As with many other wart-like skin conditions, a link to the HPV virus family, especially the HPV-2 subtype has been suggested.

The mortality rate ranges from 3–7% in a mean follow up period of 8.5 to 9.7 years. Death is often related to accidents.

Xanthochromism (also called xanthochroism or xanthism) is an unusually yellow pigmentation in an animal. It is often associated with the lack of usual red pigmentation and its replacement with yellow. The cause is usually genetic but may also be related to the animal's diet. A Cornell University survey of unusual-looking birds visiting feeders reported that 4% of such birds were described as xanthochromistic (compared with 76% albinistic). The opposite of xanthochromism, a deficiency in or complete absence of yellow pigment, is known as "axanthism".

Birds exhibiting genetic xanthochromism, especially deliberately bred mutations of several species of parrot in aviculture, are termed "lutinos". Wild birds in which xanthochromism has been recorded include yellow wagtail, wood warbler, Cape May warbler, rose-breasted grosbeak, evening grosbeak, red-bellied woodpecker, scarlet tanager, northern cardinal, great spotted woodpecker, common tailorbird, crimson-breasted shrike, kākāriki and kea.

As the horn is composed of keratin, the same material found in fingernails, the horn can usually be removed with a sterile razor.However, the underlying condition will still need to be treated. Treatments vary, but they can include surgery, radiation therapy, and chemotherapy.

Lennox–Gastaut syndrome (LGS) is a childhood-onset epilepsy that most often appears between the second and sixth year of life. LGS is characterized by a triad of signs including frequent seizures of multiple types, an abnormal EEG pattern of less than 2.5 Hz slow spike wave activity, and moderate to severe intellectual impairment.

Currently, no research has shown a higher prevalence of most leukodsytrophy types in any one place around the world. There is, however, a higher prevalence of the Canavan disease in the Jewish population for unknown reasons. 1 in 40 individuals of Ashkenazi Jewish descent are carriers of Canavan disease. This estimates to roughly 2.5%. Additionally, due to an autosomal recessive inheritance patterns, there is no significant difference found between affected males and affected females for most types of leukodystrophy including, but not limited to, metachromatic leukodystrophy, Krabbe disease, Canavan disease, and Alexander disease. The one exception to this is any type of leukodystrophy carried on a sex chromosome, such as X-linked adrenoleukodystrophy, which is carried on the X-chromosome. Because of the inheritance pattern of X-linked diseases, males are more often affected by this type of leukodystrophy, although female carriers are often symptomatic, though not as severely so as males. To date, there have been no found cases of a leukodystrophy carried on the Y chromosome.

The predominant cause of nutritional optic neuropathy is thought to be deficiency of B-complex vitamins, particularly thiamine (vitamin B), cyanocobalamin (vitamin B) and recently copper Deficiency of pyridoxine (vitamin B), niacin (vitamin B), riboflavin (vitamin B), and/or folic acid also seems to play a role. Those individuals who abuse alcohol and tobacco are at greater risk because they tend to be malnourished. Those with pernicious anemia are also at risk due to an impaired ability to absorb vitamin B from the intestinal tract.

There are several causes of toxic optic neuropathy. Among these are: ingestion of methanol (wood alcohol), ethylene glycol (automotive antifreeze), disulfiram (used to treat chronic alcoholism), halogenated hydroquinolones (amebicidal medications), ethambutol and isoniazid (tuberculosis treatment), and antibiotics such as linezolid and chloramphenicol. Tobacco is also a major cause of toxic optic neuropathy.

The primary risk factor for COPD globally is tobacco smoking. Of those who smoke, about 20% will get COPD, and of those who are lifelong smokers, about half will get COPD. In the United States and United Kingdom, of those with COPD, 80–95% are either current smokers or previously smoked. The likelihood of developing COPD increases with the total smoke exposure. Additionally, women are more susceptible to the harmful effects of smoke than men. In nonsmokers, secondhand smoke is the cause of about 20% of cases. Other types of smoke, such as, marijuana, cigar, and water-pipe smoke, also confer a risk. Water-pipe smoke appears to be as harmful as smoking cigarettes. Problems from marijuana smoke may only be with heavy use. Women who smoke during pregnancy may increase the risk of COPD in their child. For the same amount of cigarette smoking, women have a higher risk of COPD than men.

Leukodystrophy is one of a group of disorders characterized by degeneration of the white matter in the brain. The word "leukodystrophy" comes from the Greek roots "leuko", "white", "dys", "abnormal", and "troph", "growth". The leukodystrophies are caused by imperfect growth or development of the myelin sheath, the fatty covering that acts as an insulator around nerve fibers.

When damage occurs to white matter, immune responses can lead to inflammation in the CNS, along with loss of myelin. The degeneration of white matter can be seen in a MRI and used to diagnose leukodystrophy. Leukodystrophy is characterized by specific symptoms including decreased motor function, muscle rigidity, and eventually degeneration of sight and hearing. While the disease is fatal, the age of onset is a key factor as infants are given a lifespan of 2–8 years (sometimes longer), while adults typically live more than a decade after onset. There is a great lack of treatment, although cord blood and hematopoietic stem cell transplantation (bone marrow transplant) seem to help in certain types while further research is being done.

The combined incidence of the leukodystrophies is estimated at 1:7,600. The majority of types involve the inheritance of a recessive, dominant, or X-linked trait, while others, although involving a defective gene, are the result of spontaneous mutation rather than genetic inheritance.

Stenosing tenosynovitis is most commonly caused by overuse from chronic repetitive activities using the hand or the involved finger. Examples include work activities (e.g., computer use, materials handling) or recreational activities (e.g., knitting, golf, racket sports). Carpenters who use hammers suffer from this as well as those who continuously grip wood or other materials when cutting them due to having to use your hands as a clamp to hold things in place.

Primary stenosing tenosynovitis can be idiopathic, occurring in middle age women more frequently than in men, but can present also in infancy.

Secondary stenosing tenosynovitis can be caused by disease or entities that cause connective tissue disorders including the following:

- Rheumatoid arthritis and psoriatic arthritis—therefore the clinician must assess the hands for rheumatologic deformities.

- Gout

- Diabetes mellitus

- Amyloidosis

- Systemic lupus erythematosus

Others causes may include the following:

- Direct trauma to the site

- During the postpartum period

- Congenital

Intense and prolonged exposure to workplace dusts, chemicals, and fumes increases the risk of COPD in both smokers and nonsmokers. Workplace exposures are believed to be the cause in 10–20% of cases. In the United States, they are believed to be related to more than 30% of cases among those who have never smoked and probably represent a greater risk in countries without sufficient regulations.

A number of industries and sources have been implicated, including high levels of dust in coal mining, gold mining, and the cotton textile industry, occupations involving cadmium and isocyanates, and fumes from welding. Working in agriculture is also a risk. In some professions, the risks have been estimated as equivalent to that of one-half to two packs of cigarettes a day. Silica dust and fiberglass dust exposure can also lead to COPD, with the risk unrelated to that for silicosis. The negative effects of dust exposure and cigarette smoke exposure appear to be additive or possibly more than additive.

Since the histopathology of nevus anemicus is normal, nevus anemicus is a pharmacologic nevus and not an anatomic one. In most people a nevus anemicus is on a covered area and so light in appearance that no treatment is needed.