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PubMed2003

Organization of the visual cortex in human albinism.

In albinism there is an abnormal projection of part of the temporal retina to the visual cortex contralateral to the eye. This projection, together with the normally routed fibers from nasal retina, provides a cortical hemisphere with visual input from more than the normal hemifield of visual space. In many mammalian models of albinism, a possible sensory mismatch in the visual cortex is avoided either by reorganization of the thalamocortical connections to give the abnormal input an exclusive cortical representation, or by the abnormal input being substantially suppressed. In this study we examine, with fMRI, how the human visual cortex topographically maps its input in albinism. We find that the input from temporal retina is not substantially suppressed and forms a retinotopic mapping that is superimposed on the mapping of the nasal retina in striate and extrastriate areas. The abnormal routing of temporal fibers is not total, with the line of decussation shifting to between 6 and 14 degrees into temporal retina. Our results indicate that the abnormal input to visual cortex in human albinism does not undergo topographic reorganization between the thalamus and cortex. Furthermore, the abnormal input is not significantly suppressed in either striate or extrastriate areas. The topographic mapping that we report in human does not conform, therefore, to the commonly observed patterns in other mammals but takes the form of the "true albino" pattern that has been reported rarely in cat and in the only other individual primate studied.

Adult↗
PubMed2003

Investigation of albinism genes in congenital esotropia.

PURPOSE: Esotropia is a feature of albinism. Amongst esotropic patients there may be mild unrecognised albinos. Oculocutaneous albinism shares several clinical features with congenital esotropia. It is well known that mammals with oculocutaneous albinism have misrouted retinal ganglion cell axons, most likely caused by the absence of melanin or DOPA during development. We investigated the hypothesis that mutations in the albinism genes Tyrosinase, the P Gene, and TYRP1 may also be responsible for congenital esotropia via a similar mechanism. METHODS: We screened these three genes in 21 families with congenital esotropia using single stranded conformational polymorphism analysis. RESULTS: No rare sequence variants segregating with esoptopia were detected. A novel silent mutation of the TYRP1 gene was identified in one pedigree but is not likely to be causative. Several previously reported common polymorphisms were detected but do not segregate with disease in this population. CONCLUSIONS: Rare mutations of these genes do not appear to be responsible for congenital esotropia. Although we found no evidence for segregation of common variants with disease, these require further investigation for a possible contribution to a complex threshold model. Several lines of evidence indicate a genetic componenet of congenital esotropia, however, this is the first investigation of candidate genes for this disorder.

Albinism, Oculocutaneous↗
PubMed1978

[Cytogenetics of albinism in polecats of the genus Putorius (Carnivora, Mustelidae)].

Karyotypes of two ferret species, Putorius eversmanni (2n = 38) and P. putorius (2n = 40), differ in a single Robertsonian rearrangement, resulting in decreased chromosome number in P. eversmanni. Interspecific hybrids from crosses between P. eversmanni and domesticated albino ferret P. putorius furo are fertile. Hybrid individuals have a chromosome set 2 = 39. Analysis of offspring from crosses of these hybrids showed that albinism is a recessive character. Offspring obtained from crosses between interspecific hybrid ferrets and between these hybrids and parental species was subjected to chromosome analysis. A statistically significant correlation was observed between the chromosome number and albinism. As a rule, albino hybrids have a chromosome number 2n = 40. This suggests that the locus, controlling albinism, is located at one of the two pairs of acrocentric chromsomes involved in Robertsonian rearrangement. The rare occurrence of albino hybrids with 2n = 39 may be attributed to recombination. According to our data, recombination probability is less than 0.5 which indicates that the albinism locus located near the centromere. Possible extrapolation of the data obtained for ferrets to other Mustelidae is discussed.

Albinism↗
PubMed1997

Albinism: an update.

Albinism connotes a large group of genetic disorders that are characterized by diminished ocular and oftentimes cutaneous pigmentation. These disorders are generally subclassified as oculocutaneous albinism (OCA) or ocular albinism (OA) based on the extent of their effects on the pigmentation of the skin and hair. Sometimes, different mutations in the same gene can cause OCA or OA.

Albinism↗
PubMed1987

Bunegin-Albin catheter improves air retrieval and resuscitation from lethal venous air embolism in dogs.

Three types of catheters, the single-orifice Sorenson CVP kit catheter, the right atrial (RA) port of an American Edwards 7F Swan-Ganz catheter, and the Cook Bunegin-Albin multi-orifice CVP catheter were evaluated for their ability to retrieve venous air emboli and effect on the success rate of resuscitation from venous air emboli. The catheters were inserted in anesthetized dogs in the prone position. Swan-Ganz catheters were positioned with the RA port just above the junction of the superior vena cava (SVC) and the RA, single-orifice Sorensen catheters with the orifice tip located either just above the SVC-RA junction or in the mid-RA, and Bunegin-Albin multiorifice catheters with the proximal orifice just above the SVC-RA junction and the distal orifice near the mid-RA. Dogs were then given a predetermined lethal dose of air (5 ml/kg) over 30 sec via the femoral vein. Attempts to aspirate venous air emboli were begun with first decrease in expired CO2. The amounts of air retrieved and the incidence of successful resuscitation were compared. Significantly greater percentages of injected venous air were retrieved with the Bunegin-Albin catheter (60 +/- 7%) than with the Sorenson catheter in the SVC (16 +/- 6%), with the Sorenson catheter in the mid-RA (10 +/- 3%) or with the Swan-Ganz RA port (4 +/- 1%). Resuscitation was significantly more often successful with the Bunegin-Albin catheter (six of nine dogs) than with either Sorenson catheter (zero of seven in both groups) or the Swan-Ganz RA port (one of seven).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2006

Correlation of grating acuity with letter recognition acuity in children with albinism.

PURPOSE: This study was undertaken to determine whether grating acuity in early childhood can be used as a predictor of letter recognition acuity in patients with albinism. METHODS: In this retrospective study, we compared the binocular grating acuities of children with albinism (30 at age 1, 29 at age 2, and 19 at age 3) to their letter recognition acuity at age 4-6 years. RESULTS: Mean binocular grating acuity was 2.0, 1.9, and 1.5 octaves below age matched norms at ages 1, 2, and 3 years, respectively (P<0.001 at all ages). Mean grating acuity at ages 1, 2, and 3 correlated moderately (r=0.458, 0.502, and 0.471, respectively; all with P<0.05) with mean binocular letter recognition acuity of the same children at ages 4-6. A subgroup analysis of 9 patients followed longitudinally showed strong correlation of binocular grating acuity at ages 1 and 2 with letter acuity (r=0.745, P=0.021; r=0.930, P<0.001, respectively) and moderate correlation at age 3 (r=0.685, P=0.042). In the larger group and the longitudinal subgroup, mean binocular grating acuity at ages 1 and 2 was worse than mean binocular letter recognition acuity at age 4-6 (paired-samples t-test, P<0.001). Mean binocular grating acuity at age 3 in both groups was not significantly different than mean binocular letter recognition acuity at age 4-6 (paired-samples t-test, P=0.790, 0.215, respectively). CONCLUSION: Parents should be informed that vision measured as grating acuity at age 3 provides an estimate of future letter recognition acuity in children with albinism.

Albinism, Ocular↗
PubMed1999

Albinism.

Albinism was one of the first genetic diseases to be noted in humans, but until relatively recently, little was known of the molecular mechanisms involved in its pathogenesis. Recent advances have shown us that mutations in at least seven different genes can cause a reduction in melanin pigment biosynthesis, producing the various associated clinical features associated with albinism, including hypopigmentation of the skin, hair, and eyes; optic track misrouting; foveal hypoplasia; and reduced visual acuity. Analysis of mutations in these seven genes has revealed that the phenotypic spectrum associated with albinism is broad, making molecular analysis an important part in the accurate diagnosis of this disease.

Albinism↗
PubMed2025

Multi-Omics Analysis of the Potential Mechanisms of Skin Albinism in Edangered Percocypris pingi: Abnormal Ubiquitination and Calcium Signal Inhibition.

Percocypris pingi is an endangered protected fish species in China. Its albino variants exhibit growth retardation and physiological abnormalities. Understanding its albinism mechanism holds significant scientific importance for molecular breeding programs and disease model development. This study integrated transcriptomic and proteomic analyses, combined with histopathological and molecular biological techniques, to systematically compare molecular differences in skin tissues between albino and wild-type P. pingi, with a focus on elucidating the multidimensional regulatory mechanisms underlying skin albinism. Our findings suggest that albinism in P. pingi is synergistically driven by hyperactivation of ubiquitin-mediated proteolysis (which suppressed TYR/TYRP1 enzymatic activity and disrupted the pH homeostasis of melanosomes), and inhibition of calcium signaling (which impeded melanin transport). This discovery provides novel insights into the mechanisms of pigment loss in fish species and offers a valuable reference for molecular breeding of endangered species as well as research on pigmentation-related disorders.

Animals↗
PubMed2000

Albinism: its implications for refractive development.

PURPOSE: Albinism involves the mutation of one or more of the genes associated with melanin synthesis and has many ramifications for vision. This study focuses on the refractive implications of albinism in the context of emmetropization. METHODS: Refractive, biometric, and visual acuity data were collected for a group of 25 albino individuals that included the following: 18 oculocutaneous (13 tyrosine positive, 5 tyrosine negative); 7 ocular (2 autosomal recessive, 5 sex-linked recessive). Their age range was 3 to 51 years. All exhibited horizontal pendular nystagmus. RESULTS: There were no statistically significant differences relating to albino subtype for any of the measured parameters. All the subjects had reduced visual acuity (mean: 0.90, logMAR) and overall, there was a bias toward hyperopia in their refractive errors (mean: + 1.07 D). However the refractive errors of the group covered a broad range (SD: 4.67 D) and included both high myopia and high hyperopia. An axial origin to the refractive errors is implied by the high correlation between refractive errors and axial lengths. Refractive astigmatism averaged 2.37 D and was consistently with-the-rule and highly correlated with corneal astigmatism, which was also with-the-rule. Meridional analysis of the refractive data indicated that the vertical meridian for hyperopic subjects was consistently nearer emmetropia compared to their horizontal meridian. Myopic subjects showed the opposite trend. CONCLUSIONS: The overall refractive profile of the subjects is consistent with emmetropization being impaired in albinism. However, the refractive errors of hyperopic subjects also can be explained in terms of "meridional emmetropization." The contrasting refractive profiles of myopic subjects may reflect operational constraints of the emmetropization process.

Adolescent↗
PubMed1991

Albinism--a clinician's low vision perspective.

Albinism is inherited as autosomal recessive, with one exception: Ocular albinism, which has an x-linked trait. Visual symptoms include photophobia, varying degrees of nystagmus, reduction in visual acuity from 20/30 to 20/400 and varying degrees of moderate to high amounts of corneal astigmatism. Albinism patients respond very well to low vision devices and glare filters.

Albinism, Ocular↗
PubMed1994

Periodic alternating nystagmus in humans with albinism.

PURPOSE: To quantify the spatial and temporal nature of congenital periodic alternating nystagmus (PAN) and to test the hypothesis that PAN results from a temporal shift in the null zone. METHODS: Twenty-five subjects with oculocutaneous albinism (16 tyrosinase negative and 9 tyrosinase positive) and 7 with ocular albinism (5 x-linked and 2 autosomal recessive) participated in the study. Using infrared oculography, five features of the nystagmus were examined: amplitude, frequency, waveform, beat direction, and temporal nature of the cycle. RESULTS: Twelve subjects (37.5%) exhibited a PAN. The nystagmus waveforms encountered during the PAN active phases were either jerk-with-extended-foveation or pseudocycloid, whereas a variety of oscillations (including triangular and bidirectional) were evident during the quiet phases. For most of the 12 subjects, there was an asymmetric variation in nystagmus intensity during each PAN cycle. None of the 12 demonstrated a convergence null or an abnormal head posture. CONCLUSIONS: PAN is not an uncommon oscillation among humans with albinism. Changes in gaze position markedly influenced the periodicity of the ongoing nystagmus, thus supporting the hypothesis that PAN is the result of a temporal shift in the null zone.

Adolescent↗
PubMed1976

X-linked ocular albinism. An oculocutaneous macromelanosomal disorder.

Three unrelated kindreds with the Nettleship-Falls type of X-linked ocular albinism were studied. Postmortem examination of the eyes of an affected man revealed the presence of macromelanosomes in the pigment epithelia. Skin biopsy specimens of this patient, seven other affected male, and nine carrier female kindred members revealed the presence of Fontana-positive and dopa oxidase-positive macromelanosomes within the epidermis and dermis. Although clinically this disorder has been considered to be a form of albinism confined to the eyes, these findings indicate that an unusual disturbance in melanosome production characterized by macromelanosome formation affects the skin and the eyes. Histopathologic study of the skin is a useful adjunct in the diagnosis of X-linked ocular albinism, both in the affected and the carrier states. Linkage studies confirmed the close association of the Xg blood group with this disorder.

Adult↗
PubMed2000

Identification of P gene mutations in individuals with oculocutaneous albinism in sub-Saharan Africa.

Oculocutaneous albinism (OCA) is an inherited disorder resulting in hypopigmentation of the skin, hair, and eyes. OCA type 2 (tyrosinase-positive) is the most common recessively inherited disorder among southern African Blacks. OCA2 is also seen in southern African Caucasoids, but is less frequent. The gene responsible for this type of albinism, P, is the human homolog of the mouse pink-eyed dilution gene. Mutations at this locus are also responsible for the milder hypopigmentation phenotype seen in individuals with brown oculocutaneous albinism (BOCA). A common African P mutation was identified in Black OCA2 individuals, and has since been shown to occur in Black individuals with brown OCA as well. This mutation is a 2.7 kb interstitial deletion. In this study, we undertook to screen the coding region of the P gene for mutations in the non-2.7 kb deletion alleles of OCA2 patients who did not carry the deletion allele in either one or both of their P genes. We identified four mutations (A334V, 614delA, 683insG [corrected], 727insG) in a group of 39 unrelated Black OCA2 patients with a total of 52 non-2.7 kb deletion OCA2 genes. When taking all OCA2 cases into consideration, including those homozygous for the 2.7 kb deletion mutation, these account for a further 1.7% of OCA2 mutations in southern African Blacks, increasing the overall mutation detection rate to 78.7%. Three mutations (E678K, L688F, I370T) were identified in a group of 15 Black patients with an initially unclassified type of OCA and another three mutations (IVS 14-2 (a-->g), V350M, P743L) were identified in nine Caucasoid OCA patients. Relatively few mutations, all with low frequency, were identified in the non-2.7 kb deletion OCA genes. We propose that other mutations may lie either within intronic sequence or within the promoter region of the gene.

Africa South of the Sahara↗
PubMed2005

Albinism (OCA2) in Amerindians.

Homozygosity for a mutation in the P locus mapped to the human chromosome 15q11.2-12 results in tyrosinase-positive albinism (OCA2). This type of albinism has a worldwide distribution, with a prevalence of about 1 in 36,000 among European-Americans in the United States. It has a moderate to relatively high prevalence values (1 in 28 to 1 in 6,500) in various Amerindian populations in the southwestern United States, southern Mexico, eastern Panama, and southern Brazil. The wide distribution of the gene for OCA2 in Amerindian populations, and its relatively high frequency in several of these populations, are enigmatic because of the detrimental nature of OCA2 in the presence of certain environmental conditions. The relative Darwinian fitness of individuals with this inborn error of metabolism would have been reduced in early nomadic hunting-gathering populations because of their poor visual acuity and sensitivity to the sun. Nevertheless, specific situations allowed OCA2 to increase in frequency in certain Amerindian populations at various different times in history. The present objectives are to review the literature on albinism (OCA2) in Amerindians, and propose hypotheses for the variable frequencies of the OCA2 gene in Amerindian populations, which include chance processes (founder effect, bottleneck effect, and genetic drift) in small populations, natural selection, cultural selection, and the interaction of situations that led to the increase of the frequency of the albino gene in some generations. Special emphasis is placed on those Amerindian populations with a relatively high frequency of the OCA2 gene that have been best-studied, namely, the Cuna population of eastern Panama and the Hopi population in the southwestern US. Hypothetical scripts are presented for the present relatively high frequencies of the OCA2 gene in these populations. A hypothetical script is also presented, showing how a mutant gene could have reached a relatively high frequency in a small endogamous early Mayan population and then been spread by migrating groups to other geographical regions, following the rapid increase in size of that population. Comprehensive molecular studies of OCA2 genes in Amerindian populations could yield information on the possible origin of the albino gene present in many of these populations, in addition to the gene flow that occurred among some of them in past generations. The results of these studies could lead to more informed hypotheses concerning the wide distribution of OCA2 in Amerindian populations.

Albinism, Oculocutaneous↗
PubMed2004

Mutations in the MATP gene in five German patients affected by oculocutaneous albinism type 4.

Oculocutaneous albinism (OCA) is caused by a deficiency of melanin synthesis and characterized by generalized hypopigmentation of skin, hair, and eyes. Due to the hypopigmentation of the retinal pigment epithelium, OCA is usually associated with congenital visual impairment, in addition to an increased risk of skin cancer. OCA is a genetically heterogeneous disease with distinct types resulting from mutations in different genes involved in the pathway which results in pigmentation. OCA1 is associated with mutations in the TYR gene encoding tyrosinase. OCA2 results from mutations in the P gene encoding the P protein and is the most common form of OCA. OCA3, also known as rufous/red albinism, is caused by mutations in the TYRP1 gene, which encodes the tyrosinase-related protein 1. Recently, OCA4 was described as a new form of OCA in a single patient with a splice site mutation in the MATP gene (or AIM1), the human ortholog of the murine underwhite gene. The similarity of MATP to transporter proteins suggests its involvement in transport functions, although its actual substrate is still unclear. We screened 176 German patients with albinism for mutations within the MATP gene and identified five individuals with OCA4. In this first report on West European patients, we describe 10 so far unpublished mutations, as well as two intronic variations, in addition to two known polymorphisms.

Adult↗
PubMed2005

P gene mutations associated with oculocutaneous albinism type II (OCA2).

Oculocutaneous albinism type II (OCA2) is the most common form of albinism in humans. OCA2 has been previously associated with mutations of the P gene, the human homologue to the murine pink-eyed dilution gene. The P gene encodes a 110 kDa protein containing 12 potential membrane spanning domains and is associated with melanosomal membranes. The specific function of the P protein is currently unknown but is thought to be involved in tyrosinase processing and transport. We report nine novel mutations in the P gene associated with OCA2. These include two missense mutations, c.1938A>C (p.Ile646Val) and c.1556T>C (p.Val519Ala); one nonsense mutation c.612G>A (p.Trp204X); five frameshift mutations: c.2372_2373delTC, c.1555delG, c.1938_1939insC, c.2050delT, and c.1045_1046delAT; and a splice site mutation c.1951+1G>A. We also report 12 novel polymorphisms including one amino acid substitution, c.2365_2366GC>CA (p.Ala789Glu). At present, there is no functional assay to determine if a mutation is truly pathogenic. The presence of numerous polymorphisms of the P gene in the coding region, several of which result in amino acid substitutions, makes molecular diagnosis problematic. To ensure accurate molecular diagnosis, further mutational analysis will be necessary to produce a comprehensive list of mutations associated with OCA2. This information will also help define the critical functional domains of the P protein. Mutations associated with OCA2 can be found in the Albinism Database (http://albinismdb.med.umn.edu).

Albinism, Oculocutaneous↗
PubMed2006

Is autosomal recessive deafness associated with oculocutaneous albinism a "coincidence syndrome"?

Hearing impairment is frequently found associated with pigmentary disorders in many syndromes. However, total oculocutaneous albinism (OCA) associated with deafness has been described only once, by Ziprkowski and Adam (Arch Dermatol 89:151-155, 1964) in an inbred family. A syndrome associating deafness and OCA was suggested by the authors, but two separate recessive genes segregating in this inbred group were also proposed later by Fraser (OMIM # 220900). Combined deafness and total OCA were also observed by us in a family originally reported to be nonconsanguineous but in which haplotyping showed evidence of a common ancestry: the proband was affected by both diseases, one of his sisters had only OCA and another sister had only deafness. Both the proband and his deaf sister were found to be homozygotes for the 35delG mutation (GJB2 gene), the most frequent cause of hereditary deafness. Linkage analysis with markers close to the four known OCA loci excluded linkage to OCA1, OCA2, and OCA3, and homozygosity in markers near OCA4 locus was observed. Sequencing of the corresponding gene (MATP) revealed a c.1121delT mutation, which leads to a stop codon at position 397 (L374fsX397). Clearly, the combined occurrence of deafness and albinism in this pedigree was due to mutations in two different genes, showing autosomal recessive inheritance. We speculate that the putative syndrome reported by Ziprkowski and Adam might have resulted from the co-occurrence of autosomal recessive deafness and albinism in the same pedigree, as suggested by Fraser.

Adolescent↗
PubMed1993

Amelanotic metastatic melanoma in a patient with oculocutaneous albinism.

Melanomas are rare in patients who have albinism, compared with the frequent occurrence of squamous cell carcinomas and basal cell carcinomas. This report describes amelanotic metastatic melanoma in a 58-year-old Japanese man who had tyrosinase-positive oculocutaneous albinism. A prolonged bleeding time, facioscapulohumeral muscular dystrophy, and Gilbert syndrome were also present. Superficial spreading melanoma with evidence of spontaneous regression on his right forearm was suspected as a possible primary site. Twenty-two cases of melanomas in persons who have albinism have been reported.

Albinism, Oculocutaneous↗