[2][3] There also exist at least two types (2E and PCWH) that can result in central nervous system (CNS) symptoms such as developmental delay and muscle tone abnormalities.

[8] Descriptions of the syndrome date back to at least the first half of the 20th century, however it is named after Dutch ophthalmologist and geneticist Petrus Johannes Waardenburg, who described it in 1951.

Other facial features associated with type 1 can include a high nasal bridge, a flat nose tip, a unibrow (synophrys), smaller edges of the nostrils (alae) or a smooth philtrum.

If two individuals with a mutation in this gene (heterozygous) have a child carrying both mutations (homozygous), for which there is a 25% chance, additional symptoms are present in the child, such as a hole in the iris (coloboma), small eyes (microphthalmia), hardened bones (osteopetrosis), macrocephaly, albinism and deafness.

These can include developmental delay, early childhood nystagmus, increased muscle tone, white matter anomalies or hypomyelination in the brain, autistic-like behaviour and the underdevelopment or complete absence of many inner-ear structures such as the vestibular system or cochlea.

Lack of a sense of smell (anosmia) due to a missing olfactory bulb in the brain may also be present.

These can include joint contractures of the fingers (camptodactyly), due to underdeveloped muscles, as well as fused digits (syndactyly) or winged scapulae.

[17][18] Waardenburg syndrome is caused by mutations in any of several genes that affect the operation of neural crest cells in embryonic development.

A small percentage of cases result from spontaneous new mutations in the gene, where no family history of the condition exists.

They are responsible for differentiating into a diverse group of cells that reach different areas of the body.

They also differentiate into the stria vascularis of the cochlea, the nerves and glia of the intestines (myenteric plexus), Schwann cells, which myelinate the peripheral nervous system to allow sufficient conductivity, odontoblasts, which produce dentin deep in the teeth, some neuroendocrine cells, connective tissue around the salivary, lacrimal, pituitary, thymus and thyroid glands, connective tissue of the eye, such as the stroma of the iris and cornea and the trabecular meshwork,[19] and melanocytes, including those in the stroma of the iris that give rise to brown eye colour through melanin.

[6] A study was done on a rare case of a double heterozygous child with each parent having only single mutations in MITF or PAX3.

[citation needed] In 1926, German physician Irmgard Mende described a family of four generations in which five children had symptoms of depigmentation of hair, skin and eyes, deafness and a "mongoloid" appearance.

[11] In 1947, Swiss ophthalmologist David Klein (1908–1993) first reported a patient with bilateral deafness, pigmentation deficiencies, characteristic facial features and malformation of the arms.

[40] The syndrome was first fully formalised and described by Dutch ophthalmologist and geneticist Petrus Johannes Waardenburg (1886–1979) in 1951.

[citation needed] Type 2 was first established in 1971 when a study noticed that some Waardenburg syndrome patients did not have dystopia canthorum.

[16] Waardenburg syndrome type 2A (with a mutation in MITF) has been found in dogs, Fleckvieh cattle, minks, mice and a golden hamster.

"[54] Although few studies have been done to link this to genes known to be involved in human Waardenburg syndrome, a genetic disruption to neural crest development would lead to this presentation in cats as well.

[55] One of the genes that leads to deafness and a white coat in cats when mutated, KIT,[56] has been found to increase MITF expression.

A mutation in a single copy of EDNRB, however, as in Waardenburg syndrome type 4A, produces the patchy white overo coat with deafness.

[58] Ferrets with Waardenburg syndrome have a small white stripe along the top or back of the head and sometimes down the back of the neck (known as a "blaze" coat pattern), or a solid-white head from nose to shoulders (known as a "panda" coat pattern).

As healthy ferrets have poor hearing, deafness may only be detected by lack of reaction to loud noises.