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PubMed1997

Type 2 oculocutaneous albinism (OCA2) in Zimbabwe and Cameroon: distribution of the 2.7-kb deletion allele of the P gene.

In previous studies, we characterized a 2.7-kb interstitial deletion allele of the P gene associated with tyrosinase-positive oculocutaneous albinism (OCA2) in African Americans and Africans. In this study, we investigated the frequency of this allele among OCA2 subjects in two African countries, Zimbabwe and Cameroon. The deletion allele was most common in Zimbabwe, comprising nearly all (92%) mutant alleles, which is the highest incidence reported so far. In addition, the deletion allele was widespread but less common among OCA2 Cameroonians and accounted for 65% of the mutant alleles.

Albinism, Oculocutaneous↗
PubMedDate not supplied

Prenatal diagnosis of oculocutaneous albinism type I: review and personal experience.

Oculocutaneous albinism type I (OCA I) comprises autosomal recessive syndromes of hypopigmentation and low vision, caused by the lack of tyrosinase activity. Affected families seek genetic counseling and prenatal diagnosis as preventive measures. Until recently, prenatal diagnosis of OCA I was achieved by histologic and electron microscopic examination of fetal skin biopsies. Lately, a molecular genetic approach has become possible by the identification of the two mutated copies of the TYR gene, coding the tyrosinase, in which over 60 mutations have been identified. We report here our experience in prenatal diagnosis of OCA I using the two strategies. Thirty-four prenatal tests were performed in fetuses at risk for OCA I. In 31 cases the diagnosis was made in fetal scalp biopsies using the histological approach. The microscopic observations revealed normal melanogenesis in 26 biopsies. Five albino fetuses were diagnosed by the demonstration of arrest of melanogenesis in early stages I and II. In three pregnancies, molecular genetic tests were performed on DNA extracted from amniocytes, using direct mutation analysis (in one), and complemented by linkage analysis (in two). One albino and two normally pigmented fetuses were diagnosed. The prenatal molecular genetic test can be applied to families when at least one mutation is diagnosed in the albino patient. The histological approach is applicable in all families at risk for OCA I.

Albinism, Oculocutaneous↗
PubMed2006

Pulmonary aneurysms and intracardiac thrombi due to Behçet's disease in an African-American adolescent with oculocutaneous albinism.

Behçet's disease (BD) is a systemic vasculitis that may involve a variety of organs. We describe a girl with oculocutaneous albinism (OCA) who, on initial evaluation for popliteal artery occlusion, was noted to have multiple cardiac thrombi. She later developed hemoptysis, which was the result of bilateral pulmonary artery aneurysms. Her clinical picture was consistent with BD. She was initially treated with prednisone and cyclophosphamide, followed by maintenance therapy with infliximab. This case describes a unique patient with OCA who developed BD with large pulmonary aneurysms and has remained stable for over 1 year while receiving infliximab.

Adolescent↗
PubMed1977

Oculocutaneous albinism associated with Apert's syndrome.

Five of nine patients with Apert's syndrome (acrocephalosyndactyly) showed an associated hypopigmentation of hair, skin, and eyes. The hair color of these five patients ranged from light brown to blond, the skin was pale, and the irides hazel or blue. Iris transillumination and hypopigmentation of the fundus were present and associated with absent or diffuse foveal reflexes. Unlike most forms of classic oculocutaneous albinism, however, there was good visual acuity and no pendular nystagmus. The evidence indicated that the lack of pigmentation associated with the characteristic skeletal anomalies of Apert's syndrome resulted from a disturbance of independent, genetically related, processes occurring at a common point in gestation.

Acrocephalosyndactylia↗
PubMed1981

Oculocutaneous albinism associated with corneal mesodermal dysgenesis.

A 48-year-old woman had tyrosine-negative oculocutaneous albinism and corneal mesodermal dysgenesis of the Axenfeld type. Results of chromosome analysis were normal, and no other family members showed the association of these two conditions. The rarity with which the association has been reported suggests that this combination of findings is probably coincidental.

Albinism↗
PubMed1989

Human oculocutaneous albinism caused by single base insertion in the tyrosinase gene.

Tyrosinase-negative oculocutaneous albinism (OCA) is an inborn error of metabolism, characterized by a complete lack of melanin pigments in the eyes and skin. We have isolated and characterized the tyrosinase gene of one affected child (S.S.) with tyrosinase-negative OCA. Sequence analysis reveals a single-base insertion in the exon 2 that shifts the reading frame and introduces a premature termination signal (TGA codon) after the amino acid residue 298. Functional analysis of the mutated gene indicates that such a truncated tyrosinase lacking one potential copper-binding region is catalytically inactive. We therefore conclude that the albino phenotype of the patient S.S. is a consequence of the inactive tyrosinase caused by the nonsense mutation in the tyrosinase gene.

Albinism↗
PubMed1981

Inversion of direction-selectivity to anterior fields in neurons of nucleus of the optic tract in rabbits with ocular albinism.

Extracellular recordings were made of 46 well-isolated single units in the nucleus of the optic tract (NOT) from 27 rabbits which were paralyzed but unanesthetized. Rabbits were selected from 3 varieties with ocular albinism. These units showed short latencies (mean = 2.2 msec, S.D. = 0.4) to chiasmic stimulation suggestive of monosynaptic innervation from retinal ganglion cells. Receptive fields were large and receptive field centers were confined to the projection of the visual streak. All units showed direction selectivity in which preferred stimulus motions were always nearly horizontal in the anterior or posterior direction. The direction selectivity of the units was broad in that excitatory acceptance angles were 180 degrees. Single units recorded from NOT in albino rabbits could be classified into 4 types based on regions of direction selectivity. The most common (64%) type of unit had receptive fields with two regions of opposed direction selectivity. The preferred direction of motion was anterior in lateral and posterior visual fields and was posterior in anterior visual fields. Two smaller groups of units (13% and 11%) had receptive fields with only one preferred direction. When the receptive field was anterior, the preferred direction was posterior. When the receptive field was lateral or posterior, the preferred direction was anterior. The least commonly encountered type of unit (7%) had receptive fields with two regions of direction selectivity. Anterior visual fields gave rise to anterior direction selectivity and lateral and posterior visual fields gave rise to posterior direction selectivity. The characteristics of NOT units are similar to those described for NOT units in pigmented rabbits except for an inversion of direction selectivity to stimulation from anterior visual fields. NOT units in albino rabbits show posterior direction selectivity when stimulation arises from anterior visual fields. The difference in directional preference in the visual receptive fields of the units in the NOT of albino rabbit may be responsible for the inversion of optokinetic pursuit eye movements characteristic of albino rabbits.

Albinism↗
PubMed1983

Isolation and purification of ceruloplasmin in oculocutaneous albinism, Menkes' disease, Wilson's disease and pregnant women.

A method is reported for isolation and purification of human ceruloplasmin and apoceruloplasmin from serum. It involves a rapid and mild procedure by ion exchange chromatography on DEAE-Sephacel using a pH and ionic strength concave gradient. It was applied to serum of patients with oculocutaneous albinism, Wilson's disease, Menkes' disease and pregnant women. The ceruloplasmin obtained by this method is undegraded, and homogeneous by physico-chemical and immunochemical analysis.

Albinism↗
PubMed1994

Initiation codon mutation of the tyrosinase gene as a cause of human albinism.

Direct DNA sequence determination of PCR amplified exons of the tyrosinase gene of three British patients suffering from tyrosinase negative oculocutaneous albinism has revealed three new missense point mutations: (1) an adenine to guanine transition at codon 1 changes the initiating methionine codon into a valine codon thereby abolishing translation; (2) a thymine to cytosine transition at codon 370 changes a methionine to a threonine residue; (3) a cytosine to thymine transition at codon 367 changes a histidine to a tyrosine residue. A codon 402 change previously considered a polymorphism is assigned a pathological role.

Adult↗
PubMed1980

Pattern evoked potentials in human albinism. Evidence of two different topographical asymmetries reflecting abnormal retino-cortical projections.

In fifteen subjects with oculo-cutaneous or ocular albinism pattern-reversal visual evoked potentials (VEP) were recorded to monocular whole-field (16 degrees radius) and right and left vertical half-field (16 degrees radius) stimulation from an array of occipital electrodes. In all 15 subjects the VEP was of low amplitude and the monocular response to whole-field stimulation showed abnormal asymmetry in scalp topography. This asymmetry was similar to that produced by stimulation of the temporal half-field in the same eye. Two distinct types of VEP asymmetry were readily identified in different subjects. In 5 the major positivity of the response (P100) was distributed in the channels ipsilateral to the stimulated eye or temporal half-field, being similar in distribution to the P100 from the temporal hemifield or normal individuals. In 9 other subjects the converse occurred; the P100 was distributed contralaterally. The remaining subject was unique in that the responses from each eye had a distribution that resembled one of the two main groups. The nasal half-field responses also differentiated the two groups. On stimulation of the nasal field in the first group the P100 was usually absent or attenuated and when present it had the same topography as the temporal half-field P100. In contrast the nasal half-field P100 from the second group was always present and, although almost invariably smaller than the temporal half-field P100, it had an identical distribution. There was no correlation between these two patterns of VEP asymmetry and clinical or known genetic features. The findings confirm that in human albinos each hemisphere receives a predominantly monocular input from the contralateral eye; i.e. in addition to the temporal, half-field, approximately 20 degrees of the nasal half-field is projected to the hemisphere contralateral to each eye and not, as in normal subjects, to the ipsilateral hemisphere. Furthermore, the findings of two distinct and in some respects opposite types of VEP topographical asymmetry raises the possibility of two variants of the geniculo-cortical projection patterns existing in human albinos similar to those described in the Siamese cat.

Adolescent↗
PubMed1991

Dopa reaction test in hair bulbs of fetuses and its application to the prenatal diagnosis of albinism.

No information is available on the amount of tyrosinase normally present in fetuses. A dopa reaction test in hair bulbs from the scalp of normal fetuses obtained after abortion showed that tyrosinase is present in fetuses as early as 17 weeks. Only faint activity was detected in skin specimens other than from the scalp. This assay can serve as a quick and reliable method for the prenatal diagnosis of tyrosinase-negative albinism.

Albinism, Oculocutaneous↗
PubMed1991

Linkage analysis in X-linked ocular albinism.

We studied the linkage of X-linked Nettleship-Falls ocular albinism (OA1) to Xp22.1-Xp22.3 RFLPs at 12 loci in five families, including one in which OA1 cosegregates with a deletion of steroid sulfatase (STS). We found evidence for tight linkage of OA1 to the Xp22.3 loci DXS143, STS, and DXS452. DXS452, a newly described polymorphism detected by the probe E25B1.8, is part of the sequence family "DXS278" (pCRI-S232), but represents a single genetic locus. Every female in this study was heterozygous for the DXS452 RFLP. Thus, this marker will be extremely useful for family studies and genetic counseling. Analysis of individual recombinations suggests that OA1 maps between DXS143 and DXS85. Multipoint linkage analysis was consistent with this localization but was not statistically significant. These data suggest that OA1 lies proximal to the deletion in a previously described family with OA1 and STS deletion, but maps within the Xp22.3-Xp22.2 region.

Albinism, Ocular↗
PubMed2004

Effects of extraocular muscle surgery on 15 patients with oculo-cutaneous albinism (OCA) and infantile nystagmus syndrome (INS).

PURPOSE: The purpose of this report is to characterize the clinical and electrophysiological effects of extraocular muscle surgery in 15 patients with oculo-cutaneous albinism (OCA) and infantile nystagmus syndrome (INS). Our hypothesis is that surgery on the extraocular muscles of patients with OCA and INS changes their nystagmus and their visual function. DESIGN: Interventional, prospective, cohort, noncomparative case series. METHODS: All 15 patients had surgery on all four virgin horizontal recti; three for strabismus alone, three for nystagmus alone, five for an eccentric gaze null zone alone, and four for an eccentric gaze null zone plus strabismus. All patients have been followed for at least six months. All 15 patients had the subjective outcome measure of pre- and postoperative binocular best optically corrected acuity (BBOCA). Objective outcome measures included anomalous head posture (AHP) in nine patients, eye movement recording measures of expanded nystagmus acuity function (NAFX) in 10 patients, null zone position (NUZP) and null zone width (NUZW) in 10 patients, and foveation time (FOV) in nine patients. RESULTS: The results are summarized as follows; BBOCA increased 0.1 LogMar or greater in 14 of 15 patients. In those operated on for an AHP with or without associated strabismus the AHP improved significantly (P < .01 for all). The NAFX, NUZP, NUZW, and FOV measured from eye movement recordings showed persistent, significant increases in all patients (P < .01 for all). CONCLUSIONS: This report adds to the evidence that surgery on the extraocular muscles in patients with INS has independent neurologic and visual results.

Adolescent↗
PubMed2006

Woakes' syndrome and albinism.

Nasal polyposis is a very common and multifactorial disease. Whereas eosinophil-dominated polyps often are sensitive to anti-inflammatory treatment like corticosteroids, the therapy of polyps without eosinophils is more difficult and disappointing. We report the clinical course of a 29-year-old albino patient suffering from a extreme manifestation of Woakes' syndrome, which is characterized by severe recurrent nasal polyps, often without eosinophils on histological examination and with broadening of the nose. In this case, the recurrent fibrotic polyps without eosinophils were resistant to conventional medical and surgical treatment and required further treatment with radiotherapy with awareness of all possible future sequelae. The pathoetiology and treatment of Woakes' syndrome as well as of albinism were discussed.

Adult↗
PubMed2005

Heterologous expression of tyrosinase recapitulates the misprocessing and mistrafficking in oculocutaneous albinism type 2: effects of altering intracellular pH and pink-eyed dilution gene expression.

The processing and trafficking of tyrosinase, a melanosomal protein essential for pigmentation, was investigated in a human epithelial 293 cell line that stably expresses the protein. The effects of the pink-eyed dilution (p) gene product, in which mutations result in oculocutaneous albinism type 2 (OCA2), on the processing and trafficking of tyrosinase in this cell line were studied. The majority of tyrosinase was retained in the endoplasmic reticulum-Golgi intermediate compartment and the early Golgi compartment in the 293 cells expressing the protein. Coexpression of p could partially correct the mistrafficking of tyrosinase in 293 cells. Tyrosinase was targeted to the late endosomal and lysosomal compartments after treatment of the cells with compounds that correct the tyrosinase mistrafficking in albino melanocytes, most likely through altering intracellular pH, while the substrate tyrosine had no effect on the processing of tyrosinase. Remarkably, this heterologous expression system recapitulates the defective processing and mistrafficking of tyrosinase observed in OCA2 albino melanocytes and certain amelanotic melanoma cells. Coexpression of other melanosomal proteins in this heterologous system may further aid our understanding of the details of normal and pathologic processing of melanosomal proteins.

Albinism, Oculocutaneous↗
PubMed2004

Tyrosinase gene analysis in Japanese patients with oculocutaneous albinism.

BACKGROUND: Oculocutaneous albinism (OCA) is a heterogeneous congenital disorder. Tyrosinase is a key enzyme in melanin biosynthesis, and tyrosinase gene mutations cause the OCA1 subtype. OBJECTIVE: This study was intended evaluate the frequency and details of tyrosinase gene mutations in Japanese OCA patients. PATIENTS AND METHODS: We examined nine non-consanguineous OCA families, sequenced the tyrosinase gene of the patients and also confirmed a splicing site mutation using exon trapping system. RESULTS: Tyrosinase gene mutations were identified in five out of nine OCA families (55%). IVS2-10deltt-7t-a was present in 3 out of 18 alleles in three families (16%), P310insC was present in three alleles in three families (16%) and R278X was found in three alleles (16%), including those in one heterozygous and one compound homozygous patient. G97V (290 G-T) was found in 1 out of 18 alleles, and we could not find G97V in the mutation database. We have added this mutation as 9th mutation of Japanese OCA1 patients. In 8 of 18 alleles, four families, no tyrosinase mutations were identified. They were presumed not to be OCA1, but other subtypes of OCA. Exon trapping system demonstrated IVS2-10deltt-7t-a mutation generated the abnormal splicing site, and inserted the codon 4 bases in mRNA level resulting in premature termination codon downstream. CONCLUSION: This study provided new information about OCA1 mutations, and highlights the requirement of broader detailed search to make precise diagnosis of OCA.

Adolescent↗
PubMed1991

Variable expression of albinism within a single kindred.

We studied the albinotic characteristics in 13 members of a white family (age range, 2 to 73 years), which were graded according to severity and were correlated with visual acuity. Clinical, electrophysiologic, and biochemical characteristics of this family do not fit any known category of human albinism. The degree of heterogeneity in expression of albinotic features was unexpected. The correlation between visual acuity and nystagmus was particularly strong. The brown-haired propositus had severe skin involvement, iris transillumination, fundus hypopigmentation, and foveal hypoplasia. He had no manifest nystagmus, however, and his visual acuity was nearly normal. These observations suggest that nystagmus imposes a visual deficit beyond that related to foveal hypoplasia alone.

Adolescent↗
PubMed2000

Molecular basis of albinism in the rhesus monkey.

Sequence analysis of the tyrosinase (TYR) coding region from one albino rhesus monkey (Macaca mulatta) family revealed that the two monkeys with phenotype similar to human TYR-negative oculocutaneous albinism (OCA) were homozygous for a missense mutation (S184TER) in exon 1 at codon 184. The offspring of one of the albino monkey ("Kangkang") are all heterozygous for the S184TER mutation, but the S184TER mutation was not observed in 93 control individuals. We conclude that the point mutation is responsible and sufficient to generate the albino rhesus monkey phenotype. The rough age of the S184TER nonsense mutation may be about 0.8 million years using a rate of 0.16% per million years.

Albinism, Oculocutaneous↗