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PubMed2002

Foveal hypoplasia in oculocutaneous albinism demonstrated by optical coherence tomography.

PURPOSE: To document, in vivo, the foveal morphology and thickness in a patient with oculocutaneous albinism. METHODS: Observational case report. In a 10-year-old female with oculocutaneous albinism, multiple cross-sectional scans of the fovea were performed using optical coherence tomography. RESULTS: Optical coherence tomography scans were unable to detect the foveal pit. A widespread thickening of the retina occurred throughout the entire fovea with no difference from the surrounding macula. The foveal thickness was greater than 300 microm in the eyes of this patient with oculocutaneous albinism, compared with 150 microm in the normal eye. The inner retina had a highly reflective signal on optical coherence tomography. CONCLUSION: Optical coherence tomography demonstrated in the anatomical location of the fovea a highly reflective inner retinal signal, possibly consistent with multiple layers of ganglion cells, and it confirmed foveal hypoplasia in a patient with oculocutaneous albinism.

Albinism, Oculocutaneous↗
PubMed1998

[Oculocutaneous albinism: clinical, historical and anthropological aspects].

Albinism represents a group of inherited abnormalities of the melanin pigment system in which the synthesis of melanin is absent or reduced, generalized (oculocutaneous albinism) or localised (ocular albinism). Recent molecular studies provide insight into the pathophysiological processes of pigmentation regulation and help our understanding of the genetic heterogeneity of human albinism. It rarely affects Europeans, frequently Africans, only a minority of Amerindians, who nevertheless, when an ethnic group is concerned, presents one of the highest incidence in the world. Historically, the African albinos were used as an alibi by the European theologians to support Adam's descent of humanity and by naturalists to affirm the alleged superiority of the white men. Anthropological data are mainly issued from Amerindians with contradictories attitudes towards albinos: both acceptance and rejection. Only the Kuna of Panama have given albinos a major place in their mythology, although in reality they frequently reject them.

Albinism, Oculocutaneous↗
PubMed2003

Chiasmal coefficient of flash and pattern visual evoked potentials for detection of chiasmal misrouting in albinism.

The diagnosis of albinism can be confirmed by electrophysiological examination, when chiasmal misrouting can be demonstrated. The present study describes a quantitative analysis method for this purpose. A chiasmal coefficient (CC) was calculated by correlating the differential potential over left and right hemisphere, when stimulating left versus right eye. This CC will be negative in albinism and positive in normal individuals. VEPs were recorded in 20 control subjects, four children with congenital motor nystagmus and six children with albinism. In up to 25% of the controls the CC was negative, when using flash VEP. However, with pattern VEP all had a positive CC. All children with albinism had a negative CC. Three of the four patients with congenital motor nystagmus had a positive CC, and one child had a small negative value with flash stimulation. In conclusion, determination of CC is a valuable and objective analysis method for electrophysiological determination of chiasmal misrouting. The method is relatively simple and only needs two electrode tracings. One should be aware of false-positive results when using flash stimulation. Whenever possible pattern stimulation should be used.

Adolescent↗
PubMed2000

The tyrosinase gene in gorillas and the albinism of 'Snowflake'.

The sequence of the tyrosinase (Tyr) gene coding tracts has been obtained for the gorilla (Gorilla gorilla gorilla). The five exons of the gene were sequenced in three gorillas and in a normally pigmented human. The tyrosinase gene has been found to be a very conserved locus with a very low substitution rate. Some nucleotide and amino acid differences were found between the gorilla and human tyrosinase coding sequences. One of the gorillas included in the study is the only known case of albinism in a gorilla ('Snowflake'). Mutations of the TYR gene lead to Oculocutaneous Albinism type 1 (OCA1), the most common type of albinism in humans (OMIM accession number 203100). The TYR gene encodes the tyrosinase enzyme (E.C. 1.14.18.1), whose activity was found to be completely lacking in 'Snowflake', indicating that a mutation in the Tyr gene is the likely cause of his albinism. Nonetheless, no nucleotide changes were detected that could account for the lack of Tyr product or tyrosinase activity in Snowflake, and explanations of these findings are discussed.

Albinism↗
PubMed2001

[Albinism: diagnosis by visual evoked potentials].

BACKGROUND: In albinism the majority of the nerve fibers of the optic nerve originating from an eye are innervating the contralateral hemisphere. As a result of the predominantly monocular innervation of the left and right hemispheres, the unilateral activation of the visual cortex (lateralization) can be detected with visual evoked potentials (VEP). PATIENTS AND METHODS: The VEPs were elicited with pattern onset stimulation. Five channels were recorded (2 channels over the left and right occipital lobe and 1 in the midline). 22 Patients with pendular nystagmus and 15 normal volunteers were examined. 5 of the normal volunteers were also examined with simulated pendular nystagmus (5-10 degrees, 1 Hz). The nystagmus was simulated by a simple galvanometer scanner based optical system. RESULTS: Unilateral activation of the hemispheres (lateralisation) was never detectable by normal volunteers. The lateralization of the VEP was detectable in all patients with oculocutaneous albinism with pattern onset stimulation. CONCLUSION: The pathological crossing of the nerve fibres in the optic chiasm is always detectable in oculocutaneous and ocular albinism with multichannel pattern onset VEP. The lateralization of the VEP is a more sensitive indicator of ocular albinism than other symptoms like macular hypoplasia, hypopigmentation, iris transillumination, nystagmus, reduced visual acuity et cetera.

Albinism, Ocular↗
PubMed2006

Scanning the ocular albinism 1 (OA1) gene for polymorphisms in congenital nystagmus by DHPLC.

BACKGROUND: Nystagmus is common to all types of albinism. Some subjects with nystagmus lack convincing signs of albinism, have no other visual pathway disease, and are classified as possessing congenital idiopathic nystagmus (CN). It has been postulated that CN may be a form of ocular albinism. METHODS: The presence of nystagmus, iris transillumination, and visual acuity were recorded in 39 CN and albino patients and their families. Physical characteristics were also noted. DNA from buccal swabs was obtained for use in denaturing high performance liquid chromatography (DHPLC) and chemical cleavage of mismatch (CCM) to scan several hotspots for X-linked ocular albinism (OA1) mutations. RESULTS: Two previously reported polymorphisms were confirmed: neither was found to be a causative mutation. CONCLUSION: No correlation was identified between nystagmus and OA1.

Albinism, Ocular↗
PubMed2002

A health intervention programme for children with albinism at a special school in South Africa.

The genetic condition albinism has a high frequency among the Sotho people of northern South Africa. Affected children have pale hair, eyes and skin-a dramatic contrast to the normal dark pigmentation. Their visual performance is poor and many attend special schools for the visually impaired. Children with albinism experience problems that are, on the one hand, physiological, and, on the other, social-psychological and educational in nature. In this self-report study 38 children at a rural special school described their eye and skin problems, a direct result of their lack of pigmentation, as well as strategies they adopted to manage their condition. A further section of the study deals with the social adaptation difficulties experienced by these children. The questionnaire tested for local belief systems about albinism and how these impact on the socialization of children with albinism. The intervention strategy proposed in this study is based on the assumption that any attempt to address both the health and social problems should be of a holistic, interactionist nature, and be based on the values and belief systems of the local community. In addressing the physical problems, the proposed intervention programme focuses on sensible sun protection habits from a young age and the active participation of the children. To alleviate the social problems a team (interactionist) approach including children, teachers, parents, health officials and the wider community is recommended.

Adolescent↗
PubMed1994

Molecular genetics of oculocutaneous albinism.

Albinism is a group of genetic disorders characterized by deficient synthesis of melanin pigment. In oculocutaneous albinism (OCA) the pigment deficiency involves the skin, hair, and eyes, whereas in ocular albinism (OA) the defect involves principally the visual system. Type I (tyrosinase-deficient) OCA results from deficient catalytic activity of tyrosinase, which catalyzes at least three steps in the melanin biosynthetic pathway. Type II (tyrosinase-positive) OCA results from abnormalities of the 'P' polypeptide, which may be a melanosomal tyrosine transporter. At least some forms of OA appear to represent mild presentations of types I and II OCA. The causes of several other forms of albinism have not yet been identified. Recent application of molecular genetic techniques to the study of these disorders has led to greatly improved knowledge of their molecular pathogenesis and relationships, and paves the way to improved diagnosis, carrier detection and prenatal diagnosis, and even to eventual treatment.

Albinism, Oculocutaneous↗
PubMed1996

Type I oculocutaneous albinism associated with a full-length deletion of the tyrosinase gene.

Type I oculocutaneous albinism is an autosomal recessive disorder in which the biosynthesis of melanin is reduced or absent in skin, hair, and eyes because of deficient activity of tyrosinase (EC 1.14.18.1). Type I oculocutaneous albinism is caused by mutations in the tyrosinase structural gene, TYR; however, no large TYR gene deletions have been identified previously in humans. Here we report a patient with type IB oculocutaneous albinism who is a compound heterozygote for TYR allele containing a mutation that is likely to affect pre-RNA splicing and a paternally inherited allele in which the TYR gene is completely deleted, the first such allele described to date. Aside from the albinism in the proband, his phenotype and that of his normally pigmented father is otherwise normal, suggesting that this TYR deletion does not involve other functionally important contiguous genes.

Albinism, Oculocutaneous↗
PubMed1994

Prenatal diagnosis of oculocutaneous albinism by analysis of the fetal tyrosinase gene.

Tyrosinase-negative oculocutaneous albinism, the most severe subtype of a heterogeneous group of albinism, is an autosomal recessive trait caused by mutations in the tyrosinase gene. Prenatal diagnosis had been made previously only by evaluating fetal skin obtained by biopsy, an invasive procedure that cannot be performed earlier than 19 weeks of gestation. A pregnant mother of a 9-year-old Japanese boy with tyrosinase-negative oculocutaneous albinism wanted a prenatal diagnosis. Polymerase chain reaction amplification and allele-specific oligonucleotide hybridization revealed that the child is homozygous and the parents heterozygous for the pathologic mutation of the tyrosinase gene in exon 2 (single base insertion) but not for the one in exon 1. Prenatal diagnosis was made by analyzing the tyrosinase gene in fetal cells obtained by amniocentesis at 14 weeks of gestation, which demonstrated that the fetus was heterozygous for mutant tyrosinase gene. Pregnancy was therefore continued and a normal male infant was born. This procedure, the analysis of the fetal genomic tyrosinase DNA, is a rapid and reliable approach to the prenatal diagnosis of oculocutaneous albinism at a relatively early stage of pregnancy and is safer and less invasive than previous methods using fetal skin biopsy.

Albinism↗
PubMed2005

Retinal abnormalities in human albinism translate into a reduction of grey matter in the occipital cortex.

Albinism is a genetic condition associated with abnormalities of the visual system. Defects in melanin production cause underdevelopment of the fovea, reduced retinal cell numbers and abnormal routing of ganglion cell nerve fibres at the optic chiasm. We examined 19 subjects with albinism and 26 control subjects to determine whether retinal abnormalities affect the structure of the visual cortex. Whole-brain, high-resolution anatomical magnetic resonance imaging volumes from each subject were obtained on a 1.5-T scanner and segmented into grey and white matter. A voxel-wise statistical comparison of grey and white matter volumes in the occipital lobes between the two groups was performed using voxel-based morphometry. Our analysis revealed a regionally specific decrease in grey matter volume at the occipital poles in albinism. The location of the decrease in grey matter corresponds to the cortical representation of the central visual field. This reduction is likely to be a direct result of decreased ganglion cell numbers in central retina in albinism.

Adolescent↗
PubMed2005

Misrouting of the optic nerves in albinism: estimation of the extent with visual evoked potentials.

PURPOSE: In human albinism a part of the temporal retina projects abnormally to the contralateral hemisphere. An objective VEP procedure to quantify the extent of the abnormality was devised. METHODS: Monocular VEPs were recorded in 16 subjects with albinism and in 16 controls from occipital electrodes to pattern-onset stimulation in 1 of 10 adjacent rectangular apertures along the horizontal meridian covering a total of +/-27 degrees. For each eye interhemispheric difference potentials were calculated and correlated with each other to assess the lateralization of the responses: positive and negative correlations indicate lateralization on same or opposing hemispheres, respectively. Different stimulus conditions were compared to assess the sensitivity and specificity of the procedure for the detection of the misrouting of visual projections in albinism. RESULTS: Locations that were affected by the projection abnormality were detected with a specificity of 100% and an average sensitivity of 97%. In the 16 subjects with albinism tested, the abnormal projection was confined to the central retina and varied in extent between subjects (2 degrees - 15 degrees; median, 8 degrees). The extent did not appear to be correlated with horizontal nystagmus amplitude or visual acuity. CONCLUSIONS: Because of the great interindividual variability of the projection abnormality, studies of the contribution of the abnormally projecting retina to visual perception must be preceded by the localization of the abnormality. This VEP procedure allowed the authors to identify, with high sensitivity and specificity, visual field locations that are affected by the projection abnormality.

Adult↗
PubMed2005

The ocular albinism type 1 (OA1) gene controls melanosome maturation and size.

PURPOSE: The authors took advantage of the Oa1 mutant mouse in combination with other albinism mouse models (i.e., Tyrosinase and membrane-associated transporter protein [Matp]) to study the function of Oa1, the gene mutated in ocular albinism type 1, in the RPE during development and after birth. METHODS: Enzyme activity and protein localization were analyzed by immunohistochemistry of tyrosinase (Tyr) in Oa1-null mice. Ultrastructural analysis and morphometry were performed by electron microscopy, of the RPE in Oa1-knockout mouse and double-mutant mice of Oa1 with either Tyr or Matp. RESULTS: Differently from other albinism models, Tyr activity was not impaired in Oa1-/- eyes. Hypopigmentation of the RPE in Oa1-/- mice is due to a reduced number of melanosomes. Analysis of Oa1-/-;Tyr(c-2J)/Tyr(c-2J) and Oa1-/-;Matp(uw)/Matp(uw) double-knockout mice, which display a block at stages II and III of melanosome maturation, respectively, revealed that Oa1 controls the rate of melanosome biogenesis at early stages of the organellogenesis, whereas the control on the organelle size is exerted at the final stage of melanosome development (stage IV). CONCLUSIONS: The findings indicate that Oa1 is involved in the regulation of melanosome maturation at two steps. Acting at early maturation stages, Oa1 controls the abundance of melanosomes in RPE cells. At later stages, Oa1 has a function in the maintenance of a correct melanosomal size. This study helps to define ocular albinism type 1 as a defect in melanosome organellogenesis and not in melanin production.

Albinism, Ocular↗
PubMed1997

Technical advances in prenatal diagnosis of tyrosinase-negative oculocutaneous albinism.

Technical advances in the prenatal diagnosis of tyrosinase-negative oculocutaneous albinism, the most severe subtype of this disease, are reviewed. Ultrastructural examination of hair bulb melanocytes in fetal skin during the second trimester of pregnancy was the first successful method for the prenatal diagnosis of oculocutaneous albinism. Subsequent introduction of the electron microscopic DOPA reaction test in fetal skin provided safer, more practical, and reliable information for diagnosing tyrosinase-negative oculocutaneous albinism prenatally. The recent elucidation of the specific gene mutation of tyrosinase in the affected individuals now allows the DNA-based prenatal diagnosis of tyrosinase-negative oculocutaneous albinism in the first trimester of pregnancy.

Albinism, Oculocutaneous↗
PubMed2006

[Familiar case of granular dystrophy and oculocutaneous albinism].

CLINICAL CASE: A 35-year-old female patient with blurred vision since childhood, for which no treatment had been given, presented with poor visual acuity. She had white skin and fair yellow hair. There were several well circumscribed deposits in the central and anterior corneal stroma, and iris transillumination and foveal hypoplasia were evident. The clinical diagnosis was oculo-cutaneous albinism and granular corneal dystrophy. We found oculo-cutaneous albinism in two brothers and granular dystrophy in three brothers, the mother and a son. DISCUSSION: Corneal dystrophy is an autosomal dominant disorder inherited independently of oculocutaneous albinism, which is inherited as an autosomal recessive condition. This is the first case report of granular dystrophy concurrent with oculocutaneous albinism.

Adult↗
PubMed1998

[Antenatal diagnosis of albinism fetuses by fetalscopy].

OBJECTIVE: To popularize the clinical utility of fetalscopy in antenatal diagnosis of albinism fetuses. METHODS: Fetalscopy examination was carried out in 85 high-risk pregnancy women, during 17 to 26 gestational weeks. Guided by the ultrasonography, the fetalscopy was inserted into the aminotic sac. Albinism fetuses was diagnosed by the color of the fetal hair. RESULTS: Fetalscopy were succeed in 79 of 85 high-risk women (93%). 63 fetuses were diagnosed as normal, 16 fetuses was diagnosed of albinism. There were 2 false-positive cases at 17 weeks of gestation due to mistaking wooly hair for hair. CONCLUSION: Fetalscopy is a quick, accurate, safe method in antenatal diagnosis of heredity diseases, such as albinism.

Adult↗
PubMed2001

Subnormal visual acuity syndromes (SVAS): albinism in Swedish 12-13-year-old children.

BACKGROUND: The vision of 12-13-year-olds in Sweden was examined in a field study. The study was designed as being a part of a large European-Latin American study, the DESAMI project. The objective was to evaluate the prevalence of residual amblyopia and ocular disorders, atiologies of subnormal vision and some normal visual parameters in this group of children. The children had to be born in Sweden in 1985 in order to have the opportunity to be included in the voluntary screening visual examinations. The full results of the study will be presented elsewhere. This paper presents clinical and VEP data of those children who had visual acuity of 0.8 or below in one or both eyes which could not be increased with glasses, or other visual/eye disturbances not explained as common amblyopia, i.e., subnormal visual acuity or pathological visual states of unknown cause, SVAS (subnormal visual acuity syndromes). SUBJECTS AND METHODS: In all, 1046 children were examined: 76 had visual disturbances of such severity that they were referred to a paediatric ophthalmologist (AS). Eighteen children could not be pathologically classified, and they were referred to another ophthalmological examination and VEP (visual evoked potential) recordings. VEP reveals an asymmetric response after monocular stimulation in albinism. RESULTS: Twelve children turned up for a second examination and VEP was recorded from 10 children. Nine children showed iris translucency. Seven children showed an asymmetric VEP and were classified as albinos. The albinoic VEPs could be subdivided into two types, (1) including all parts of the response and (2) partly excluding the P1/P100 potential complex. The VEP response was normal, showing symmetry and no other abnormality, in three of the children. CONCLUSIONS: The results indicate that albinism is common in Sweden. A prevalence value of approximately 1% is about 100 times higher than previous figures. This high prevalence may indicate another form of heredity, with genetical contribution to albinism from a varying number of albino genes and varying expression in the phenotypes, in the Scandinavian population. It is emphasised that in investigations of children with SVAS, electrophysiological examinations are important, not only to reveal albinism but also to exclude or verify neurometabolic conditions, for example.

Adolescent↗
PubMed2001

Subnormal visual acuity syndromes (SVAS): albinism in Swedish 12-13-year-old children.

BACKGROUND: The vision of 12-13-year-olds in Sweden was examined in a field study. The study was designed as being a part of a large European-Latin American study, the DESAMI project. The objective was to evaluate the prevalence of residual amblyopia and ocular disorders, aetiologies of subnormal vision and some normal visual parameters in this group of children. The children had to be born in Sweden in 1985 in order to have the opportunity to be included in the voluntary screening visual examinations. The full results of the study will be presented elsewhere. This paper presents clinical and VEP data of those children who had visual acuity of 0.8 or below in one or both eyes which could not be increased with glasses, or other visual/eye disturbances not explained as common amblyopia, i.e., subnormal visual acuity or pathological visual states of unknown cause, SVAS (subnormal visual acuity syndromes). SUBJECTS AND METHODS: In all, 1046 children were examined: 76 had visual disturbances of such severity that they were referred to a paediatric ophthalmologist (AS). Eighteen children could not be pathologically classified, and they were referred to another ophthalmological examination and VEP (visual evoked potential) recordings. VEP reveals an asymmetric response after monocular stimulation in albinism. RESULTS: Twelve children turned up for a second examination and VEP was recorded from 10 children. Nine children showed iris translucency. Seven children showed an asymmetric VEP and were classified as albinos. The albinoic VEPs could be subdivided into two types, (1) including all parts of the response and (2) partly excluding the P1/P100 potential complex. The VEP response was normal, showing symmetry and no other abnormality, in three of the children. CONCLUSIONS: The results indicate that albinism is common in Sweden. A prevalence value of approximately 1% is about 100 times higher than previous figures. This high prevalence may indicate another form of heredity, with genetical contribution to albinism from a varying number of albino genes and varying expression in the phenotypes, in the Scandinavian population. It is emphasised that in investigations of children with SVAS, electrophysiological examinations are important, not only to reveal albinism but also to exclude or verify neurometabolic conditions, for example.

Adolescent↗