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PubMed2002

A 122.5-kilobase deletion of the P gene underlies the high prevalence of oculocutaneous albinism type 2 in the Navajo population.

Oculocutaneous albinism (OCA) is a genetically heterogeneous disorder. There are four known types of OCA: OCA1-OCA4. The clinical manifestations of all types of OCA include skin and hair hypopigmentation and visual impairment. Although there are a few documented observations of high frequency of albinism among Native Americans, including the Hopi, Zuni, Kuna, Jemez, Laguna, San Juan, and Navajo, no causative molecular defect has been previously reported. In the present study, we show that albinism in one Native American population, the Navajo, is caused by a LINE-mediated 122.5-kilobase deletion of the P gene, thus demonstrating that albinism in this population is OCA2. This deletion appears to be Navajo specific, because this allele was not detected in 34 other individuals with albinism who listed other Native American origins, nor has it been reported in any other ethnic group. The molecular characterization of this deletion allele allowed us to design a three-primer polymerase chain reaction system to estimate the carrier frequency in the Navajo population by screening 134 unrelated normally pigmented Navajos. The carrier frequency was found to be approximately 4.5%. The estimated prevalence of OCA2 in Navajos is between approximately 1 per 1,500 and 1 per 2,000. We further estimate that this mutation originated 400-1,000 years ago from a single founder.

Albinism, Oculocutaneous↗

PubMed2001

Health and education of children with albinism in Zimbabwe.

Albinism is a relatively common genetic condition in Zimbabwe, a tropical country in southern Africa. Those affected have little pigment in their hair, skin or eyes, in sharp contrast to the normal dark pigmentation. This article describes the responses to a self-report questionnaire covering health, social and educational aspects completed by 138 schoolchildren with albinism living in rural areas of Zimbabwe. They reported persistent skin and a myriad of eye problems. Relationships between siblings appeared good, although problems of antagonism, avoidance and fear were encountered among strangers. Knowledge about albinism was patchy; pupils were keen to be better informed. This research highlights the need for widespread dissemination of accurate information about the genetics and health management of albinism to counter the many myths and misconceptions surrounding this condition. A management programme to promote the health and education of these children in southern Africa is proposed. In conclusion, this study indicated that pupils with albinism could participate in mainstream education, with appropriate intervention to help them manage the problems associated with their low vision and sensitive skins.

Adolescent↗

PubMed1990

Hypoplastic corpus callosum in ocular albinism: indication of a global disturbance of neuronal migration.

Ocular albinism is distinguished from the more common oculocutaneous albinism by the presence of normal pigmentation of skin and hair in the former condition. Recent studies of ocular albinism have shown that the hypopigmentation of the optic fundus is associated with a number of anomalies of neuronal wiring involving the visual system. We present a patient with ocular albinism who also has a hypoplastic corpus callosum as determined by analysis of midsagittal magnetic resonance imaging scans. Previous studies of the hypoplastic corpus callosum indicate that this anomaly is a defect in neuronal migration as well. The finding of a hypoplastic corpus callosum in a patient with ocular albinism suggests a more generalized defect in neuronal migration not limited to the visual system.

Abnormalities, Multiple↗

PubMed2000

A new association of congenital hydrocephalus, albinism, megalocornea, and retinal coloboma in a syndromic child: a clinical and genetic study.

We describe a child with global developmental delay, prominent metopic suture, trigonocephaly, and cryptorchidism whose symptoms resemble the well-known 9p deletion syndrome or 9p monosomy. We also noted congenital hydrocephalus, oculocutaneous albinism, retinal coloboma, and megalocornea, which are not typical features of 9p monosomy. When a new albinism gene was localized to 9p (Chintamaneni et al., Biochem Biophys Res Commun 1991;178:227-235; Murty et al., Genomics 1992;13:227-229), we hypothesized that our patient had the 9p deletion syndrome plus albinism, with the deletion involving the albinism gene. We used FISH probes to test this hypothesis and found that the 9p region was normal, therefore excluding the 9p deletion syndrome. To our knowledge, the association of congenital hydrocephalus, albinism, megalocornea, and retinal coloboma has not been described in the literature. The purpose of this report is to describe this new association of congenital ocular and cerebral anomalies in a syndromic child.

Abnormalities, Multiple↗

PubMed2001

No effect of albinism on sedative-hypnotic sensitivity to ethanol and anesthetics.

BACKGROUND: Studies using the long-sleep (LS) X short-sleep (SS) (LSXSS) recombinant inbred mice and inbred long-sleep (ILS) by inbred short-sleep (ISS) intercrosses have found genetic linkage between Tyr albinism (c/c) and differential sensitivity to sedative-hypnotic doses of ethanol and general anesthetics. This linkage could be due to a gene or genes near Tyr or Tyr itself. With regard to the latter possibility, the absence of tyrosinase activity (encoded by Tyr) in albinos could alter tyrosine availability and thus the rate-limiting step in catecholamine synthesis. In addition, albinism is associated with altered brain development that could have pleiotropic effects on behavior. Therefore, in this study, we asked whether albinism affects sedative-hypnotic sensitivity. METHODS: Loss of righting reflex (LORR) duration was measured using doses of ethanol (4.1 g/kg), pentobarbital (70 mg/kg), isoflurane (2 g/kg), and etomidate (20 mg/kg) that were previously associated with differential sensitivity of albino versus nonalbino mice. Tyr transgenics (c/c, Tg(Tyr+)) were backcrossed to ISS (c/c) to compare pigmented (c/c, Tg(Tyr+)) and albino (c/c) mice in the context of an ISS-like background. ISS was also crossed with C57BL/6 (B6) mice heterozygous for a spontaneous albino mutation (c2j) to compare pigmented (c/+) and albino (c/c2j) mice. Pigmented B6 (c2j/+ and +/+) and albino B6 (c2j/c2j) mice were also compared (pentobarbital). RESULTS: For each sedative hypnotic, albinism had no effect on LORR duration. Each expected difference was ruled out at the 95% or 99% confidence level. For each sedative hypnotic, males were more sensitive than females even though the effect size was usually smaller than the expected albino effect size, arguing empirically that the inability to detect an albino effect was not due to systematic error or an insufficient number of mice. CONCLUSION: We conclude that the differential sensitivity associated with albinism is most likely due to a gene or genes near Tyr rather than Tyr itself.

Albinism↗

PubMed2001

Cutaneous malignancy in albinism.

Albinism is a disorder of hypopigmentation affecting the skin, appendages, and eyes. Ultraviolet light-induced cutaneous tumors are common in patients with albinism due to reduced or absent protection from melanin. Squamous cell carcinoma (SCC) is the number one skin tumor seen in patients who are albinos. Although nonmelanomatous skin cancers are more common in patients with albinism, dysplastic nevus and melanoma present a greater diagnostic challenge in this group because of their hypopigmented appearance. We report 2 cases of cutaneous malignancies in patients who had oculocutaneous albinism (OCA). The first case involves a 45-year-old man with OCA type 2 (OCA2) who developed a large SCC of the neck. The second case involves a 24-year-old man with Hermansky-Pudiak syndrome (HPS) who developed amelanotic melanoma. In both cases, hypopigmentation of the lesions contributed to a delay in diagnosis. We review the clinical, diagnostic, and therapeutic concerns for patients with albinism who have cutaneous malignancies.

Adult↗

PubMed2006

[Ocular albinism in pediatric patients with nystagmus].

PURPOSE: Presentation of diagnostic methods and results obtained in childre with nystagmus, with suspicion of ocular albinism. MATERIAL AND METHODS: Records of 9 children (range 0.2 to 5.5 years) are presented. In all cases family history, ophthalmic examination and visual evoked potentials were analyzed. RESULTS: Clinical signs of ocular albinism were found in all patients. 2 children had cutaneous albinism, VEP records of 7 children indicated abnormalities typical for albinism, clinical signs of gene carrying were found in 7 mothers. CONCLUSIONS: Clinical signs enable us to diagnose ocular albinism with relatively high probability, nevertheless characteristic VEP records confirm diagnosis in clinically difficult cases.

Albinism, Oculocutaneous↗

PubMed1988

Albinism.

Genetic abnormalities of the melanin pigment system in which the synthesis of melanin is reduced or absent are called albinism. The reduction in melanin synthesis can involve the skin, hair follicle, and eye, resulting in oculocutaneous albinism, or can be localized primarily to the eye, resulting in ocular albinism. Approximately 1 in 17,000 individuals in the United States has oculocutaneous albinism, and more than 1 per cent of the population are heterozygous for a gene producing albinism.

Albinism↗

PubMed1979

Partial oculocutaneous albinism in Mystromys albicaudatus: nonhomology with the Chediak-Higashi syndrome.

Partially albinic Mystromys albicaudatus were examined to determine if the condition in these animals was homologous with the Chediak-Higashi syndrome. Tissues and cells from partially albinic and normal Mystromys albicaudatus were studied by light and electron microscopy. No evidence of cytoplasmic granule enlargement, which is characteristic of the Chediak-Higashi syndrome, was detected in the cells of the partially albinic rats when compared to controls. It was concluded that the inherited condition of partial albinism of Mystromys albicaudatus was not homologous with the inherited partially albinic disease known as the Chediak-Higashi syndrome.

Albinism↗

PubMed1980

Albinism. Recent advances.

There have recently been several fundamental advances in our understanding of albinism, both in animals and in man. These advances have been in the division of oculocutaneous albinism into tyrosinase-negative and tyrosinase-positive forms, the demonstration of a widespread disturbance in the structure of melanosomes in X-linked ocular albinism, the description of the condition now known as autosomal recessive ocular albinism, and a peculair anatomical abnormality of the visual pathways which appears to be present in all forms of oculocutaneous and ocular albinism. Evidence has been presented which confirms that the retinogeniculate anomaly in human albinos is similar to that in animals, and it has recently been suggested that there may be two major patterns of geniculocortical projected in man, as there are in the Siamese cat.

Albinism↗

PubMed1981

A high-frequency albinism variant on the gulf coast of Papua.

An apparently recessively inherited albinism variant characterized by skin tanning, light but not white hair, uniformly pigmented irides varying in colour from hazel to dark brown, slight nystagmus, divergent strabismus, mild hyperkeratosis and only slight or absent photophobia, occurs among the Elema-speaking peoples of the Gulf Province of Papua New Guinea at frequencies indicating that the gene which produces it is polymorphic. It is readily distinguishable from both classical types of albinism, from the "redskin" variant also found in Papua New Guinea, and from the "yellow mutant" albinism of North America. The differences from the African types of "albinoidism" or "partial albinism" are less marked, and it may represent a similar mutation with simply a different distribution of the melanosomes in the two peoples, Allelism, or lack of it, with classical tyrosinase-positive albinism has not been determined.

Adult↗

PubMed2004

New method for detecting misrouted retinofugal fibers in humans with albinism by magnetoencephalography.

In humans with albinism, a large percentage of the ganglion cell axons from the temporal retina decussate abnormally in the chiasm and synapse in the contralateral LGN. The aim of this study was to determine whether the misrouting of the optic fibers can be detected by magnetoencephalography (MEG). Visually evoked magnetic fields (VEFs) were recorded from three patients with albinism. After monocular stimulation, the isofield contour maps of the VEFs showed a single current dipole pattern over the contralateral hemisphere in patients with albinism. These results clearly illustrated the reduced uncrossed retinofugal pathway of patients with albinism.

Adolescent↗

PubMed2002

Grating acuity in albinism in the first three years of life.

PURPOSE: To compare grating acuity of children 1 to 3 years old with albinism with that of age-matched normal children, and to determine whether ocular pigment and macular structure are predictive of grating visual acuity. METHODS: In this retrospective cross-sectional review of 64 children with albinism, binocular grating acuity was measured with Teller acuity cards at 1, 2, or 3 years of age. Iris transillumination and macular transparency were graded according to published scales. The presence or absence of macular melanin pigment and a rudimentary foveal reflex were assessed with direct and indirect ophthalmoscopy, respectively. RESULTS: Mean grating acuities of the children with albinism at ages 1 (2.48 cycles (cy)/degrees), 2 (3.62 cy/degrees), and 3 (5.87 cy/degrees) were 2.3, 2.1, and 1.7 octaves lower than published norms (all with P <.001). The studied variables did not correlate with visual acuity except for macular transparency at age 2 (r = 0.40; P =.030). CONCLUSIONS: Grating acuity can be used to assess the reduction in visual function in albinism in the first 3 years of life. However, grading of iris transillumination and macular transparency and recognition of an annular reflex or macular melanin do not consistently correlate with the development of vision measured by grating acuity.

Albinism, Ocular↗

PubMedDate not supplied

The value of flash visual evoked potentials in albinism.

In albinism, the majority of temporal retinal fibers serving the nasal visual field cross at the chiasm and project to the contralateral hemisphere. This misrouting is seen in hemispheric asymmetries present in the visual evoked potential (VEP). Misrouting of retinal fibers was also thought to occur in dissociated vertical deviation, Prader-Willi syndrome, and perhaps carrier states of albinism. However, recent literature is reaching the conclusion we have drawn in our laboratory: only albinism shows VEP hemispheric asymmetries that reverse when the other eye is stimulated. Use of different stimuli, recording conditions, and response criteria among investigators has created some confusion in differentiating what constitutes asymmetry. We conclude that use of a diffuse flash stimulus and a bipolar electrode derivation that compares differences between the left and right occipital hemispheres will clearly differentiate albinism from all other conditions, making it especially useful in a pediatric population.

Adolescent↗

PubMed2004

Monocular visual activation patterns in albinism as revealed by functional magnetic resonance imaging.

Human albinism is characterized by a disturbance of the chiasmatic projection system leading to predominant representation of just one eye in the contralateral hemisphere. Patients show congenital nystagmus without perceiving oscillopsia. The purpose of the present study was to demonstrate the consequences of atypical chiasmatic crossing with monocular visual stimulation using functional magnetic resonance imaging (fMRI). Sixteen patients with albinism and fifteen normally pigmented controls were stimulated with a monocular visual activation paradigm using flickering checkerboards. In patients, we observed contralaterally dominated activation of visual cortices correlating to clinical albinism parameters. This confirms albinism as a continuous range of hypopigmentation disorders. Additionally, albinos showed activation of the superior colliculus and of visual motion areas although the stimulus was stationary. Activation of visual motion areas is due probably to congenital nystagmus without a conscious correlate like oscillopsia.

Adult↗

PubMed2002

New insights into ocular albinism type 1 (OA1): Mutations and polymorphisms of the OA1 gene.

Albinism ocular type 1 (OA1) is an X-linked type of albinism that mainly effects pigment production in the eye, resulting in hypopigmentation of the retina, nystagmus, strabismus, foveal hypoplasia, abnormal crossing of the optic fibers, and reduced visual acuity. The OA1 gene is located on chromosome Xp22.32 and the coding sequence is divided into nine exons. The protein is an integral transmembrane protein that has weak similarities to G protein-coupled receptors. A total of 25 missense, two nonsense, nine frameshift, and five splicing mutations have been reported in the OA1 gene associated with OA1. There are also several deletions of some or all exons of the OA1 gene with deletions of exon 2 resulting from unequal crossing-over, due to flanking Alu repeats. Mutation and polymorphism data on this gene is available from the International Albinism Center - Albinism Database web site (http://www.cbc.umn.edu/tad).

Albinism, Ocular↗

PubMed2006

Topographical retinal function in oculocutaneous albinism.

PURPOSE: Macular hypoplasia is the major ocular finding in albinism because it underlies reduced acuity and congenital nystagmus. Anatomic studies have shown a lack of foveal differentiation. However, functional anatomy of the macula in albinism is not known. DESIGN: Observational case reports. METHODS: We measured the topology of the retinal response in two patients with oculocutaneous albinism by using simultaneous fundus monitoring and multifocal electroretinographs (ERGs). Stimuli consisted of a 103-hexagon array centered on the macula. Recording conditions eliminated nystagmus artifact. RESULTS: ERG amplitudes were reduced only in the central 5 to 10 degrees compared with adult norms. When the response was scaled by stimulation area, multifocal ERG amplitudes were constant across all retinal eccentricities. CONCLUSIONS: The results suggest a homogeneous density of cone photoreceptors across the central retina in albinism, consistent with anatomic studies showing arrest of postnatal macular development. Further normative data are needed to fully quantify macular development in young children.

Albinism, Oculocutaneous↗

PubMed2004

Efficacy of spectacles in persons with albinism.

INTRODUCTION: Patients with albinism have varying degrees of reduced vision, strabismus, iris transillumination, nystagmus, fundus hypopigmentation, and foveal hypoplasia. High refractive errors are common, but reduced vision persists due to nonrefractive factors, causing reluctance by some clinicians to prescribe spectacles. We sought to evaluate the effect of spectacle correction of refractive error on clinical findings and recorded compliance with refractive corrections, as little detailed data exist. METHODS: We prospectively examined 35 consecutive patients with albinism for whom glasses had been prescribed to determine if objective improvement in recognition visual acuity (VA), strabismus, anomalous head posture (AHP), fusion, or stereoacuity occurred with refractive correction. Parents or patients reported compliance with glasses wear (excellent: >75% of awake hours; good: 50-75% of awake hours; fair: 26-50% of awake hours; poor: <25%). RESULTS: Median age was 9.5 years (range: 3 to 30). Median refractive correction was 1.875 D spherical equivalent (range: -9.75 to +8.88 D). Glasses wear was initiated at a median age of 14 months (range: 3 months to 14 years). Mean binocular VA at distance was 20/80.9 corrected and 20/107.6 uncorrected ( P < 0.001). Mean VA at near was 20/28.4 corrected and 20/41 uncorrected ( P < 0.001). Mean strabismic deviation was 7.2 PD with glasses and 10.0 PD without glasses at distance ( P = 0.006) and 10.8 PD with glasses and 14 PD without glasses at near ( P = 0.042). Mean AHP at distance was 8.3 degrees with glasses and 7.3 degrees without glasses at distance ( P = 0.327) and 4.7 degrees both with and without glasses at near ( P = 0.308). Twenty-one patients had fusion with or without glasses, two had fusion only with glasses, and one patient had fusion only without glasses. The other patients did not have any detectable degree of fusion. Twenty-seven individuals had no stereoacuity with or without glasses, five had gross stereoacuity of 3000 seconds of arc both with and without glasses, and three had gross stereoacuity only while wearing glasses. Compliance was excellent in 29 patients, fair in four, and poor in two. CONCLUSION: This prospective study showed a significant improvement in corrected VA and alignment in persons with albinism, despite overall subnormal acuity. Some individuals also experienced improvement in binocular alignment and AHP. Compliance with spectacles was generally good. Therefore, refractive correction should be encouraged in persons with albinism as improvement in visual function is likely to occur.

Adolescent↗