Congenital sensorineural deafness occurs commonly in domestic cats with a white coat. It is a congenital deafness caused by a degeneration of the inner ear. [1] Deafness is far more common in white cats than in those with other coat colours.
Congenital sensorineural deafness occurs commonly in domestic cats with a white coat. It is a congenital deafness caused by a degeneration of the inner ear. [1] Deafness is far more common in white cats than in those with other coat colours.
Domesticated cats with blue eyes and white coats are often completely deaf. [2] Charles Darwin mentions this phenomenon in his book, On the Origin of Species , to explain correlated variation. [3] Deafness can occur in white cats with yellow, green or blue irises, although it is mostly likely in white cats with blue irises. [4] In white cats with mixed-coloured eyes (odd-eyed cats), it has been found that deafness is more likely to affect the ear on the blue-eyed side. [1] Odd-eyed white cats have one blue eye and one yellow, amber, copper/orange or green coloured eye. Approximately 15–40% of the solid white cats have one or two blue eyes. [5] [ unreliable source ]
According to the ASPCA Complete Guide to Cats, "17 to 20 percent of white cats with non-blue eyes are deaf; 40 percent of "odd-eyed" white cats with one blue eye are deaf; and 65 to 85 percent of blue-eyed white cats are deaf." [6]
In one 1997 study of white cats, 72% of the animals were found to be totally deaf. The entire organ of Corti in the cochlea was found to have degenerated in the first few weeks after birth; however, even during these weeks no brain stem responses could be evoked by auditory stimuli, suggesting that these animals had never experienced any auditory sensations. It was found that some months after the organ of Corti had degenerated, the spiral ganglion of the cochlea also began to degenerate. [7]
Although few studies have been done to link this to genes known to be involved in human Waardenburg syndrome, a syndrome of hearing loss and depigmentation caused by a genetic disruption to neural crest cell development, such a disruption would lead to this presentation in cats as well. [8] Waardenburg syndrome type 2A (caused by a mutation in MITF ) has been found in many other small mammals including dogs, minks and mice, and they all display at least patchy white depigmentation and some degeneration of the cochlea and saccule, as in deaf white cats. [9] [10]
A major gene that causes a cat to have a white coat is a dominant masking gene, an allele of KIT which suppresses pigmentation and hearing. The cat would have an underlying coat colour and pattern, but when the dominant white gene is present, that pattern will not be expressed, and the cat will be deaf. A cat that is homozygous (WW) or heterozygous (Ww) for this gene will have a white coat despite the underlying pattern/colour. A cat that lacks this dominant masking gene (ww) will exhibit a coat colour/pattern. [11] KIT mutations have also led to patchy depigmentation and different coloured irises in humans, [12] and KIT has been found to increase MITF expression, the gene involved in human Waardenburg syndrome type 2A. [13]
The established link between deafness and blue eyes is found in the link between deafness, blue eyes and solid white coats. However, it is a common misconception that all white cats with blue eyes are deaf. [14] It is possible to have a cat with a naturally white coat without this gene, as an extreme form of white spotting, although this is rare – some small non-white patch usually remains.
Furthermore, there are multiple different genes responsible for blue (incl. odd) eyes, and several of these genes are not linked to masking, white coats or deafness (e.g., "Siamese" colourpoint-gene, Ojos Azules-gene, etc.). For example, solid white blue-eyed Foreign White or Ojos Azules cats are not linked to deafness. Deafness depends on the cat's genotype (genetic make-up), and not its phenotype (physical appearance). Therefore, not all solid white cats with one or two blue eyes are deaf. It is not advisable to breed from deaf white cats, as this would pass the trait along. BAER-testing (Brainstem Auditory Evoked Response) is used to test deafness in cats. [5] [15] [ unreliable source ]
Tietz syndrome, also called Tietz albinism-deafness syndrome or albinism and deafness of Tietz, is an autosomal dominant congenital disorder characterized by deafness and leucism. It is caused by a mutation in the microphthalmia-associated transcription factor (MITF) gene. Tietz syndrome was first described in 1963 by Walter Tietz (1927–2003) a German Physician working in California.
Cat coat genetics determine the coloration, pattern, length, and texture of feline fur. The variations among cat coats are physical properties and should not be confused with cat breeds. A cat may display the coat of a certain breed without actually being that breed. For example, a Neva Masquerade could wear point coloration, the stereotypical coat of a Siamese.
Heterochromia is a variation in coloration most often used to describe color differences of the iris, but can also be applied to color variation of hair or skin. Heterochromia is determined by the production, delivery, and concentration of melanin. It may be inherited, or caused by genetic mosaicism, chimerism, disease, or injury. It occurs in humans and certain breeds of domesticated animals.
Waardenburg syndrome is a group of rare genetic conditions characterised by at least some degree of congenital hearing loss and pigmentation deficiencies, which can include bright blue eyes, a white forelock or patches of light skin. These basic features constitute type 2 of the condition; in type 1, there is also a wider gap between the inner corners of the eyes called telecanthus, or dystopia canthorum. In type 3, which is rare, the arms and hands are also malformed, with permanent finger contractures or fused fingers, while in type 4, the person also has Hirschsprung's disease. There also exist at least two types that can result in central nervous system (CNS) symptoms such as developmental delay and muscle tone abnormalities.
Usher syndrome, also known as Hallgren syndrome, Usher–Hallgren syndrome, retinitis pigmentosa–dysacusis syndrome or dystrophia retinae dysacusis syndrome, is a 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 major cause of deafblindness and is at present incurable.
Point coloration is animal coat coloration with a pale body and relatively darker extremities, i.e. the face, ears, feet, tail, and scrotum. It is most recognized as the coloration of Siamese and related breeds of cat, but can be found in dogs, rabbits, rats, sheep, guinea pigs and horses as well.
Merle is a genetic pattern that can be in a dog's coat and alleles of the PMEL gene. Merle results in different colors and patterns and can affect all coat colors. The merle allele creates mottled patches of color in a solid or piebald coat, blue or odd-colored eyes, and can affect skin pigment as well. There are two general types of colored patches that will appear in a merle coat: brown/liver and black. Some breeds that can be affected by this genetic trait are Carea Leonés, Australian Shepherds, and Catahoula Leopard Dogs. This genetic trait should be taken seriously when breeding merles. Health issues are more typical and more severe when two merle-patterned dogs are bred together, so it is recommended that a merle be bred with a non-merle dog of any other color.
Microphthalmia, also referred as microphthalmos, is a developmental disorder of the eye in which one or both eyes are abnormally small and have anatomic malformations. Microphthalmia is a distinct condition from anophthalmia and nanophthalmia. Although sometimes referred to as 'simple microphthalmia', nanophthalmia is a condition in which the size of the eye is small but no anatomical alterations are present.
Leucism is a wide variety of conditions that result in the partial loss of pigmentation in an animal—causing white, pale, or patchy coloration of the skin, hair, feathers, scales, or cuticles, but not the eyes. It is occasionally spelled leukism. Some genetic conditions that result in a "leucistic" appearance include piebaldism, Waardenburg syndrome, vitiligo, Chédiak–Higashi syndrome, flavism, isabellinism, xanthochromism, axanthism, amelanism, and melanophilin mutations. Pale patches of skin, feathers, or fur can also result from injury.
Albinism-black lock-cell migration disorder is the initialism for the following terms and concepts that describe a condition affecting a person's physical appearance and physiology: (1) A – albinism, (2) B – black lock of hair, (3) C – cell migration disorder of the neurocytes of the gut, and (4) D – sensorineural deafness. The syndrome is caused by mutation in the endothelin B receptor gene (EDNRB).
A white horse is born predominantly white and stays white throughout its life. A white horse has mostly pink skin under its hair coat, and may have brown, blue, or hazel eyes. "True white" horses, especially those that carry one of the dominant white (W) genes, are rare. Most horses that are commonly referred to as "white" are actually "gray" horses whose hair coats are completely white. Gray horses may be born of any color and their hairs gradually turn white as time goes by and take on a white appearance. Nearly all gray horses have dark skin, except under any white markings present at birth. Skin color is the most common method for an observer to distinguish between mature white and gray horses.
Microphthalmia-associated transcription factor also known as class E basic helix-loop-helix protein 32 or bHLHe32 is a protein that in humans is encoded by the MITF gene.
An odd-eyed cat is a cat with one blue eye and one eye either green, yellow, amber, or brown. This is a feline form of complete heterochromia, a condition that occurs in some other animals, including humans. There is also sectoral (partial) heterochromia, where two different colours occur within the same iris. The condition most commonly affects solid white cats, but may be found in cats of any coat colour.
Gap junction beta-6 protein (GJB6), also known as connexin 30 (Cx30) — is a protein that in humans is encoded by the GJB6 gene. Connexin 30 (Cx30) is one of several gap junction proteins expressed in the inner ear. Mutations in gap junction genes have been found to lead to both syndromic and nonsyndromic deafness. Mutations in this gene are associated with Clouston syndrome.
Cat genetics describes the study of inheritance as it occurs in domestic cats. In feline husbandry it can predict established traits (phenotypes) of the offspring of particular crosses. In medical genetics, cat models are occasionally used to discover the function of homologous human disease genes.
Splashed white or splash is a horse coat color pattern in the "overo" group of spotting patterns that produces pink-skinned, white markings. Many splashed whites have very modest markings, while others have the distinctive "dipped in white paint" pattern. Blue eyes are a hallmark of the pattern, and splash may account for otherwise "solid" blue-eyed horses. Splashed white occurs in a variety of geographically divergent breeds, from Morgans in North America to Kathiawari horses in India. The splashed white pattern is also associated with congenital deafness, though most splashed whites have normal hearing. Splashed white can be caused by multiple variants across two different genes, for which genetic testing is available.
Dominant white (W) is a group of genetically related coat color alleles on the KIT gene of the horse, best known for producing an all-white coat, but also able to produce various forms of white spotting, as well as bold white markings. Prior to the discovery of the W allelic series, many of these patterns were described by the term sabino, which is still used by some breed registries.
Waardenburg Syndrome Type 2D, a subtype of the Waardenburg syndrome, is a rare congenital disorder caused by a mutation in the SLUG (SNAI2) gene. It is characterized by the lack of pigmentation in the skin, hair, and eyes as well as the abnormalities in the outer wall of the cochlea. This subtype lacks the wide distance between the eyes, known as dystopia canthorum, that is observed in most patients with Waardenburg Syndrome. Those affected, exhibit varying degrees of deafness or complete hearing loss along with heterochromia and reports of early graying. This disease is observed in the neonatal stages of early life.
Waardenburg Syndrome Type 1 is a congenital disorder that caused by a mutation in the PAX3 gene that results in abnormal development in the neural crest during early development. Type 1 results in early graying and white forelock and a notable distance between the eyes, noted as dystopia canthorum. Common symptoms of the disease also includes non-progressive hearing loss in majority of patients with Type 1. Patients can display complete or partial heterochromia and hypoplastic blue irides and congenital leukemia.
Causes of hearing loss include ageing, genetics, perinatal problems, loud sounds, and diseases. For some kinds of hearing loss the cause may be classified as of unknown cause.
