Albinism

Heling Zhao , ... Hongsheng Yang , in Developments in Aquaculture and Fisheries Science, 2015

Summary

Albinism is widespread in the creature kingdom and is acquired by the absence of melanin in the hair, eyes, or skin. Research on albinism has mainly focused on humans and mice and in that location is picayune directed enquiry on albino echinoderms. In this affiliate, the occurrence and mechanisms of albinism in the ocean cucumber Apostichopus japonicus are discussed, and nosotros conclude as follows: (ane) The lack of melanin in the body wall is the straight crusade of albinism in A. japonicus; (ii) the lack of melanocytes and melanin synthesis in melanosomes are histological characteristics of albino A. japonicus; and (3) the significantly low microphthalmia-associated transcription factor (MITF) and astacin expression levels in A. japonicus are the molecular causes of albinism.

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Albinism

Dagmar Fertl , Patricia East. Rosel , in Encyclopedia of Marine Mammals (Second Edition), 2009

Ii Albinism and Marine Mammals

Albinism is known to affect mammals, birds, fish, reptiles, and amphibians. In marine mammals, anomalously white individuals have been reported for 21 cetacean species ( Fertl et al., 1999; Fertl et al., 2004) and 7 pinniped species (e.g., Rodriguez and Bastida, 1993; Bried and Haubreux, 2000) (Fig. 2). No reports are known of anomalously white sea otters (Enhydra lutris) or sirenians. Anomalously white individuals are often presumed to be true albinos. Some of those individuals match the clarification of true albinism [e.thousand., there are well-documented reports of albino sperm whales (Physeter macrocephalus) and bottlenose dolphins (Tursiops truncatus)], simply many practice not. "Chimo," an anomalously white killer (Orcinus orca) captured for brandish in Canada, was diagnosed postmortem with Chédiak–Higashi Syndrome, (Fig. 3), a type of albinism (Taylor and Farrell, 1973). This inherited disorder is characterized by diluted pigmentation patterns that appear pale gray, eye and white claret cell abnormalities, and a shortened life span. Whales and dolphins too may appear white if extensively scarred, or covered with a mucus, such as Lobo's affliction (also known as lobomycosis) (Migaki et al., 1971).

Effigy 2. Anomalously white humpback whale (Megaptera novaeangliae) sighted off Australia. Photograph by Paul Forestell, Pacific Whale Foundation.

Figure 3. An albino killer whale, "Chimo" (Orcinus orca), postmortem diagnosed with Chédiak–Higashi syndrome. Photo by Peter Thomas.

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The Basics of Heredity

Julia E. Richards , R. Scott Hawley , in The Human Genome (Third Edition), 2011

Albinism Is Recessive

Albinism is known to be inherited in a recessive manner ( Box one.6). The fact that information technology is hereditary may not seem obvious if yous wait at someone with albinism who is born into a minor family. Merely we do find evidence that albinism is hereditary if we wait at information from a lot of families in which someone has albinism. For an individual with albinism, virtually i in four of their siblings volition likewise have albinism, and then if we expect at couples who give nascency to a large number of children, we volition sometimes find an individual with albinism who has i or more brothers and sisters who also take the trait. An individual with albinism is more probable to accept a family history of albinism than someone with the pigmented allele, so examination of albinism families that are very big and have maintained expert records on family history tin offering clues. And if one identical twin has albinism, nosotros commonly discover that the other identical twin besides has information technology, but if a fraternal twin has the albinism trait in that location is but a 25% chance that their twin will as well have it (Box one.7).

Box ane.6

How to Recognize Recessive Inheritance

Underlying concepts:

•

Both copies of the gene must be defective to crusade the phenotype.

•

The presence of a 2d "good" copy tin recoup for i lacking re-create.

•

The cell may have a lot of tolerance for reduced levels of cistron product.

Rules for what we will see in a recessive pedigree:

•

Equal numbers of males and females volition be affected.

•

Affected individuals will often have no or little family history.

•

Parents volition often both exist unaffected heterozygotes called carriers with well-nigh one-quarter of the children affected.

•

Carriers are unaffected, but may sometimes show minor aspects of the phenotype.

•

If one parent is affected and the other parent is heterozygous carrier for the aforementioned factor, then about one-half of the children will be affected.

•

If both parents are affected and lacking for the same gene, then all of the children will exist afflicted.

•

If both parents are affected with the aforementioned trait equally a result of defects in ii dissimilar genes, and so none of the children volition exist affected.

•

Risk to one child is not afflicted by how many prior births in the sibship have the trait.

•

Risk can be modified past environmental factors, mosaicism, errors in meiosis, de novo mutation, not-penetrance or age-related penetrance, which nosotros will discuss later on in the volume.

Box 1.7

Identical Twins and Fraternal Twins

Why practice researchers compare identical twins (formed when ane sperm fertilizes one egg and so the embryo splits to class two embryos) to fraternal twins (formed when two different sperm fertilize ii different eggs) instead of comparison identical twins to brothers and sisters built-in at carve up times? Because whenever the siblings are twins, they have something in common besides their genetic makeup – they have also shared the aforementioned environment in the uterus for nine months. If siblings were conceived and born at different times, the differences between them might include not only their genetic differences, just also differences in their meaning mother'southward nutrition, exposure to smoke, encounter with physical trauma, or consumption of medications. Twin studies that compare identical to fraternal twins are often used to attempt to determine how much of a characteristic tin be attributed to genetics and how much can exist attributed to environmental causes.

When we look at inheritance of the albinism trait in Figure 1.10, nosotros come across that Mendel's rules apply hither. If someone has a pigmented version of the albinism gene (the pigmented allele) forth with the albinism allele, the albinism trait is not manifested and they accept color in their skin and hair. If the individual is homozygous for albinism alleles, skin and hair color will be white. Equally with the pea plants, the heterozygous individual's coloring is determined by whether or non they have a dominant pigmented allele. Their coloring is not the intermediate skin color that would outcome from a composite average of the ii different alleles. Thus there is a human trait, absence of pigmentation, that is recessive to the ascendant trait, presence of pigmentation.

Figure i.10. Albinism family tree. In the starting time generation, we meet 2 different couples in which an private with albinism marries someone who does not take the albinism trait. Notice that all of their children have pigmented pilus and are carriers, individuals who lack the trait but carry the information. Wedlock of two carriers leads to about i-quarter of their children having the albinism trait. In many families into which a child with albinism is born, there may be no known ancestors with albinism. In rare cases, the trait might exist reported for a afar antecedent, but most ofttimes in that location will be no evident family unit history of albinism. Thus recessive information tin pass through many generations before a carrier chances to marry another carrier to a produce a child with the trait. In this case, for the data to consequence in the trait, the kid must receive an albinism allele from each parent so that they stop up with two albinism alleles.

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Inherited Disorders of the Hair

Mazen Kurban , Angela M. Christiano , in Emery and Rimoin'south Principles and Do of Medical Genetics, 2013

152.v.9.1 Albinism

Albinism is divided into iv major subtypes according to unlike genetic basis and clinical features. Type I oculocutaneous albinism (OCA1; OMIM 606952) and type Two oculocutaneous albinism (OCA2; OMIM 203200) most commonly present with light-colored hair. OCA1 occurs secondary to mutations in the tyrosinase gene which is required for the synthesis of melanin, while OCA2 occurs secondary to mutations in the P cistron which is required for regulating the PH for the normal operation of tyrosinase. Clinical features associated with albinism include decreased pigment in the eyes, decreased visual acuity, and nystagmus (68).

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Hereditary Retinal and Choroidal Dystrophies

Suma P. Shankar , in Emery and Rimoin's Principles and Practice of Medical Genetics, 2013

138.5.eight Albinism

Albinism is characterized by reduced pigmentation in the skin and pilus with ocular involvement. Patients with any class of albinism may accept ocular or visual disorders, ranging from severe to mild problems. In the by, albinism has been divided into oculocutaneous albinism and ocular albinism. In both there is a fractional or total reduction of melanin deposition on melanosomes, due to mutations in genes involved in the biosynthesis of melanin paint. There are multiple forms of oculocutaneous albinism.

Regardless of the blazon of albinism, the ocular involvement generally conforms to one of two clinical patterns: (i) congenitally subnormal visual acuity and nystagmus, and (two) normal or only minimally reduced visual vigil and no nystagmus. The first pattern is true albinism, while the latter circumstance has been termed albinoidism because of the milder visual consequences. Both patterns share mutual clinical features of photophobia, iris transillumination, and hypopigmented eyes. They differ by whether the fovea develops; hypoplasia of the fovea is a sign of true albinism. Mutations in iv genes OCA1, OCA2, OCA3 and OCA4 cause OCA, OA1 gene causes 10-linked ocular albinism, and there are several genes causing Hermansky–Pudlak syndrome and Chediak–Higashi syndrome (26).

A mutual finding to all types of albinism is aberrant retinogeniculostriate projections, with many of the temporal hemiretinal nerve fibers decussating rather than projecting ipsilaterally to the geniculate trunk. These mis-projections tin exist measured and diagnosed by visual evoked cortical potential testing. The first form of ocular albinism was described by Nettleship in a big X-linked recessive full-blooded. The afflicted males had subnormal visual acuity, translucent irides, congenital nystagmus, photophobia, hypopigmentation of the fundus, and hypoplasia of the fovea. Pigmentary mosaicism is common in female carriers, who may be symptomatic. An X-linked ocular grade was reported in black patients who had moderately pigmented fundi and no transillumination of the iris, just patients with X-linked recessive ocular albinism had giant pigment granules on microscopic examination of skin biopsy.

Autosomal recessive ocular albinism is relatively common, and females are as severely afflicted as are males. Patients have decreased visual acuities in the 20/100–20/400 range, translucent irises, built nystagmus, photophobia and strabismus. Patients are lightly pigmented at birth, and commonly develop farther pigmentation with age. In general, the more pigmentation that the patient demonstrates, such as effectually skin hair follicles and peculiarly in the retinal pigment epithelium in the posterior pole, the better is the visual prognosis. Many patients demonstrate improvement in their nystagmus and visual acuities equally pigmentation develops with historic period. Genetic counseling depends on carefully establishing the inheritance design and gene testing of the OCA genes and OA1 gene that are clinically available.

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Albinism☆

R.A. Spritz , in Reference Module in Life Sciences, 2017

Characteristics and History

Albinism is a group of genetic disorders characterized past reduced or absent-minded melanin pigmentation, with an overall estimated frequency of at to the lowest degree 1 per 20,000 in about populations. Oculocutaneous albinism (OCA) involves the eyes, hair, and skin, whereas in ocular albinism (OA) visual involvement is accompanied by merely slightly reduced pigmentation of skin and hair. The distinctive phenotype of OCA was known to the ancient Greeks and Romans, and the typical clinical features, modes of inheritance, and genetic heterogeneity of these disorders are evident even in classical descriptions. Similar phenotypes occur in a great many vertebrate species, and absent-minded catalytic activity of tyrosinase in the skin of albino mice was one of the offset enzymatic deficiencies recognized, prompting Garrod to suggest in 1908 that albinism might be an inborn error of metabolism. Indeed, there is close correspondence between the various OCA phenotypes in humans and in mice, and the study of such mice has contributed profoundly to agreement of OCA in humans.

Likewise humans and mice, OCA occurs in many different species, resulting from reduced or absent-minded biosynthesis of melanin pigment in the pare, hair, and eyes, considering of various functional defects of the specialized pigment cells, the melanocytes. Humans with OCA appear lightly complected or even nearly white (Fig. 1). Melanin plays a major protective role against ultraviolet light, and reduced pare pigmentation thus causes persons with OCA to be at high gamble for severe sunburn and eventual evolution of skin cancers induced by long-term actinic irradiation, particularly in parts of the world with high rates of lord's day exposure. The office played by melanin in the developing visual organisation is not known, only all forms of albinism are accompanied by defects of neuronal migration in the visual pathways, with consistent low vision (depression visual acuity due to reduced optic tract neuronal projections), nystagmus and strabismus, and reduced tolerance to ambient light (photophobia). These optical defects occur regardless of the specific genetic cause of albinism, and announced to event from reduced melaninization of the retinal pigment epithelium during retinal development.

Fig. 1. Patient with OCA1. Note white pilus and skin and iris transillumination.

A major consideration for persons with albinism is potential social stigmatization and consequent psychological morbidity, particularly in populations in which relatively dark skin pigmentation is the norm. It is a great tragedy that, in parts of east Africa, patients with albinism accept recently been subjected to ritual slaughter to harvest body parts, to which are attributed magical properties.

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Eye Motility Enquiry

R.V. Abadi , Due east. Pascal , in Studies in Visual Information Processing, 1995

The albino state

Albinism is a congenital, inherited disorder of melanin pigment and can be constitute throughout the animal kingdom. It is due to a metabolic error whereby the enzyme tyrosinase is either absent-minded or inactive ( Witkop 1979). This results in hypopigmentation of the hair, peel and eyes (oculocutaneous albinism - OCA) or it may be limited to the eyes (ocular albinism - OA). Considerable heterogeneity exists within albinism: at least ten different forms of OCA and 4 different types of OA have been described (Taylor 1978, Witkop 1979, O'Donnell and Greenish 1981, Van Dorp 1985, Kinnear et al 1985, Abadi and Pascal 1989). The identification of each variety of albinism is fabricated using histological, genetic, biochemical and clinical criteria.

The two most prevalent forms of OCA are tyrosinase negative OCA (TNOCA) and tyrosinase positive OCA (TPOCA). In the former no pigment is produced, indicating a total lack of the enzyme tyrosinase, whereas in the latter melanin gradually accumulates in the pilus, pare and eyes as the person becomes older. In OA the skin and hair appear similar to those of unaffected family unit members whilst the eyes show hypopigmentation. OCA and OA are characterised by like clinical ocular signs: translucent irides, pale fundi with conspicuously visible vasculature, poor foveal differentiation, a loftier incidence of large refractive errors, strabismus and congenital nystagmus. The main clinical characteristics of the albino groups described in this paper are given in Table 1.

Tabular array one. The characteristics of the four most common forms of albinism.

Characteristics of various forms of albinism
Type of albinism TNOCA TPOCA XOA AROA
Skin White — no tan Cream   →   Pink   →   can tan May be paler than sibs May be paler than sibs
Clinical appearance Pilus White White   →   yellow Normal range Normal range
Irides Pale grey   →   blue Blue   →   hazel Bluish   →   brown Blue   →   chocolate-brown
Pigment change None Increase with age Darkening of eyes with age None
Fundus Macula Periphery Hypoplasia No retinal pigment Hypoplasia Some retinal pigment Hypoplasia Every bit TNOCA Hypoplasia As TPOCA
Vision VA Photophobia 6/60 or less + + + + three/threescore   →   half dozen/18 + + to + + + iii/lx   →   6/15 + + to + + + 3/sixty   →   6/15 + + to + + +
Inheritance autosomal recessive autosomal recessive X-linked autosomal recessive
Incidence 1:37000 1:31000 1:50000 1:50000
Biochemical tests Tyrosine Tyrosine and cysteine No pigmentation
No pigmentation		 Pigmentation
Pigmentation		 Pigmentation
Pigmentation		 Pigmentation
Pigmentation
Ocular features Nystagmus, aberrant visual pathway, squint Every bit TNOCA As tTNOCA As TNOCA

TNOCA - tyrosinase negative oculocutaneous albinism

TPOCA - tyrosinase positive oculocutaneous albinism

XOA - x-linked ocular albinism

AROA - autosomal recessive ocular albinism

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Dermatology

Linda J. Vogelnest , in Equine Medicine, Surgery and Reproduction (Second Edition), 2012

Albinism and other congenital pigmentation disorders

Albinism is a congenital absenteeism of normal pigmentation due to an autosomal recessive enzymatic defect preventing normal product of melanin from melanocytes. Affected horses lack pigment in hair and skin and may have pink irides. Waardenburg-Klein syndrome occurs in American paint horses, with lack of pigment in pare and pilus, blueish irides, and possible deafness. Lethal white foal disease occurs in Overo paint horses, and along with lack of paint in hair and pare in that location are serious developmental defects of the digestive tract (e.g. colonic atresia), incompatible with life. Lethal lavander foal syndrome occurs rarely in Arabian horses; foals are born with a bluish or purplish hair coat and a range of neurological defects incompatible with life.

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Regressive Evolution

Richard Borowsky , in Biology and Development of the Mexican Cavefish, 2016

Albinism

Albinism, the complete or almost consummate absence of melanin, is a regressive change in pigmentation that has been reported in about half of all troglomorphic cavefish species surveyed (47/86  =   55%) (Romero and Green, 2005). This figure may be an overestimate, because synthesis of melanin is down-regulated in abiding darkness (Parker, 1948), presenting the possibility of misclassification of specimens fixed shortly after collection. And then, while it is common in cavefishes, albinism is past no means close to universal. Considering albinism is not more mutual in cavefishes, it would appear to be a neutral rather than advantageous trait in the cave surround. Nevertheless, in at to the lowest degree three different cave populations of Astyanax, albinism has arisen independently through mutations in the aforementioned gene, oca2. These mutations affect either the coding sequence or the command of the gene'due south expression, simply the resulting loss of oca2 part needed for melanin synthesis is the same (Protas et al., 2006). These independent convergences on the aforementioned phenotype via mutations affecting the role of the same primal poly peptide advise selection; however, oca2 is a large factor, 123   kb in length, and codes for a functional protein of 888 amino acids, and thus presents a big mutational target, suggesting that mutation and migrate may also account for its repeated involvement in albinism of A. mexicanus.

In the Pachón 10 surface hybrid cantankerous, a strong QTL for eye size nearly centers on the oca2 locus (Effigy v.1S, companion site). Humans with oculocutaneous albinism well-nigh universally have serious retinal defects (Fulton et al., 1978), and then the clan of an eye QTL with the oca2 locus may reflect a functional relationship. Thus, the selective advantage of oca2 mutations in the cave environment might simply reverberate their indirect pleiotropic effects on eye structure.

In the Pachón Ten surface hybrid cantankerous, a strong QTL for eye size almost centers on the oca2 locus (Effigy 5.1S, companion site). Humans with oculocutaneous albinism nearly universally have serious retinal defects (Fulton et al., 1978), so the association of an eye QTL with the oca2 locus may reflect a functional relationship. Thus, the selective advantage of oca2 mutations in the cavern surroundings might simply reflect their indirect pleiotropic furnishings on heart structure.

A second style in which oca2 mutants might be favored in the cave environs also hinges on pleiotropy. Both the melanin and the catecholamine synthesis pathways compete for 50-tyrosine, a shared precursor. Thus, a plausible selective advantage to loss of melanin synthesis in cavefishes is that it could increase the availability of fifty-tyrosine for synthesis of the neurotransmitters that play roles in the numerous behavioral changes in cavefishes (Bilandzija et al., 2013). Indeed, catecholamine levels, including those for norepinephrine (NE), were significantly higher in the brains of adult cavefishes than in those of surface fishes raised in the laboratory (Bilandzija et al., 2013). Furthermore, knock-downs of oca2 in surface fishes increased levels of fifty-tyrosine and dopamine (see likewise Jeffery et al. in Chapter 9).

At that place is a potential link between increased availability of NE and the increased wakefulness phenotype of the Astyanax cavefishes: the cave phenotype is abolished by treatment with propranolol, an inhibitor of β-adrenergic signaling (Duboue et al., 2012). Thus, it is tempting to hypothesize that positive pick for wakefulness drove the loss of oca2 activity to silence the melanin synthesis pathway and increment the availability of NE.

Yet, for the wakefulness trait, this link seems unlikely. Increased wakefulness of larvae was documented in three independently derived Astyanax cave populations, Tinaja, Pachón, and Molino (Duboue et al., 2011). Of the iii, Tinaja fishes are most wakeful, notwithstanding they synthesize melanin while Molino and Pachón fishes do not (encounter also Duboué and Keene in Affiliate 16). This is the opposite of the prediction of the hypothesis. Furthermore, in the F2 progeny of a Pachón X surface cantankerous, there was no significant correlation between paint land and wakefulness. Finally, I note that all five balitorid cavefishes tested exhibited pregnant increases in wakefulness compared to surface balitorids (Duboue and Borowsky, 2012), yet all take intact and functional oca2.

It is also unclear how much of an reward, if whatsoever, there would be to eliminating oca2 function in the cave environment. Assuming that silencing the melanin synthesis pathway is benign in the cavern surround, an oca2 aught phenotype is not needed to accomplish this. It has long been recognized that melanin synthesis is minimized in the dark in many species of fishes (Eigenmann, 1900; Parker, 1948), and the rule pertains to Astyanax surface fishes, as well (Romero and Green, 2005). Thus, a surface fish inbound the cave surroundings would reach the needed phenotypic land physiologically. That competition between the two biosynthetic pathways could drive the silencing of oca2 is an intriguing hypothesis, but one that needs more evidence.

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Clinical Signs Approach to Differential Diagnosis

Mark Due south. Thompson , in Pocket-sized Creature Medical Differential Diagnosis (Second Edition), 2014

Hereditary Hypopigmentation

Albinism—hereditary absence of pigment

Piebaldism—presence of white spots where melanocytes are absent

Waardenburg-Klein syndrome—affected animals accept absenteeism of melanocytes in areas of peel and hair, blue or heterochromatic optics, and are also deaf. Reported in cats, balderdash terriers, Sealyham terriers, collies, Dalmatians

Canine cyclic hematopoiesis—lethal autosomal recessive disease of collies. Greyness coat, light-colored nose, circadian episodes of neutropenia every 12–xiv days resulting in sepsis and amyloidosis

Chédiak-Higashi syndrome—rare autosomal recessive disease of blue smoke Farsi cats. Fractional oculocutaneous albinism with abnormal office of granulocytes and platelets resulting in hemorrhage, recurrent infections, and death at a young age.

Graying—age-associated, reduction of melanocyte replication.

Vitiligo—macular leukoderma and leukotrichia of nose, ears, buccal mucosa, and facial skin. Antimelanocyte antibodies establish in serum of some affected dogs. Seen about usually in Siamese cat, Belgian Tervuren, German Shepherd, collie, Rottweiler, Doberman Pinscher, Giant Schnauzer.

Nasal hypopigmentation—flavor-associated lightening of nasal planum during winter months most common in Siberian Croaking, Aureate Retriever, Labrador Retriever, and Bernese Mountain Domestic dog. Seen also in many other breeds.

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