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PubMed2001

The mouse ocular albinism 1 gene product is an endolysosomal protein.

To gain insight into the role of Oa1, the mouse homolog of the human X-linked ocular albinism 1 protein, its properties and subcellular localization were investigated. Antiserum raised against an expressed segment of the Oa1 protein recognized a band of approximately 48 kDa in immunoblots of extracts of cultured mouse melan-a melanocytes, but not of cells of non-melanocyte origin. When melanocyte extracts were treated with glycopeptidase F, a approximately 44 kDa band appeared. Like the melanogenic enzyme tyrosinase, expression of Oa1 was stimulated by alpha-melanocyte stimulating hormone and inhibited by agouti signal protein. Upon density gradient centrifugation of organelles of melan-a cells, Oa1 protein colocalized with the late endosomal/lysosomal marker Lamp1, but only partial overlap was observed with melanosomal proteins in the high density region of the gradient. Immunofluorescence staining revealed that neither endogenous Oa1 nor an Oa1-green fluorescent protein fusion product colocalized with the melanosomal protein tyrosinase related protein-1 in the cell periphery. In contrast, colocalization of Oa1 and Oa1-green fluorescent protein fusion product with Lamp1 was extensive throughout the cell. These results indicate that Oa1 is a melanocyte-specific integral membrane glycoprotein localized to late endosomes/lysosomes but not mature melanosomes. Considering the microscopic findings in patients with X-linked ocular albinism 1, we speculate that Oa1 may play a role in the trafficking of vesicles to developing melanosomes.

Albinism, Ocular↗
PubMed2001

Mislocalization of melanosomal proteins in melanocytes from mice with oculocutaneous albinism type 2.

More than 10% of admissions worldwide to institutions for the visually impaired are due to some form of albinism. The most common form, oculocutaneous albinism type 2, results from mutations at the p locus. The function of the p gene is yet to be determined. It has been shown that melanocytes from p -null mice exhibit an abnormal melanosomal ultrastructure in addition to alterations in activity and localization of tyrosinase, a critical melanogenic enzyme. In light of these observations, we examined tyrosinase trafficking in p -null vs wildtype mouse melanocytes in order to explore p function. Electron microscopy of wildtype melan-a and p -null melan-p1 cells demonstrated accumulation of tyrosinase in 50 nm vesicles throughout the cell in the absence of p, an observation corroborated by an increase in tyrosinase activity in vesicle-enriched fractions from melan-p1 compared to melan-a cells. Misrouting in the absence of p was not limited to tyrosinase; a second melanosomal protein, tyrosinase-related protein 1, also trafficked incorrectly. In melan-p1, mislocalization led to secretion of tyrosinase into the medium. Adding tyrosine to the medium was found to partially correct tyrosinase trafficking and to reduce secretion; the cysteine protease inhibitor E64 also reduced secretion. We propose that p is required by melanocytes for transport of melanosomal proteins. In its absence, tyrosinase accumulates in vesicles and, in cultured melanocytes, is proteolysed and secreted.

Albinism, Oculocutaneous↗
PubMed1993

Refinement of the localization of the X-linked ocular albinism gene.

Although physical and genetic mapping studies assigned the X-linked ocular albinism gene to Xp22.3, the exact gene order in this region is still unclear. We present additional genetic mapping data concerning X-linked ocular albinism that suggests the consensus order Xpter-STS-DXS237-KAL-(OA1, DXS143)-DXS85-DXS16-Xcen.

Albinism, Ocular↗
PubMed1993

X-linked ocular albinism and sensorineural deafness: linkage to Xp22.3.

X-linked ocular albinism with late-onset sensorineural deafness (OASD) is an autonomous disorder that poses significant clinical problems, causing affected individuals to be blind and deaf by early middle age. Classical X-linked ocular albinism (without deafness; OA1) has recently been linked to markers in the Xp22.2-Xp22.3 region of the human genome. In the present report, a large South African family with OASD was investigated at the molecular level and tight linkage was found to the DXS452 locus at Xp22.3 using 25 informative meioses, with a maximum lod score of 7.1 at a recombination fraction of 0.00. These findings suggest that OA1 and OASD are allelic variants or that they may be due to contiguous gene defects.

Albinism, Ocular↗
PubMed1983

Albinism: phenotype or genotype?

As part of a combined ophthalmological, genetic, clinical, biochemical, ultrastructural and electro-physiological study of albinism we have examined over one hundred albinos, together with their heterozygote family members. Given this substantial number, we have developed a diagnostic protocol to facilitate albino classification and heterozygote detection. The major difficulty in the detection and differential diagnosis of albinism is that for a given albino, not all symptoms, either ophthalmological or cutaneous, may be manifest, whereas several may be in a non-albino. To compensate for the wide diversity in albino expression, diagnosis is typically based on the results of combinations of tests.

Adolescent↗
PubMed2006

Saccadic instabilities in albinism without nystagmus.

Albinism effects a surprising manipulation of the visual pathway in which some of the normally uncrossed axons of the temporal retina instead cross at the chiasm. An expected consequence of this misrouting is that subjects with albinism will have difficulty in specifying the targets of saccades. Usually albinos have nystagmus so the stability of their saccadic eye movements is not readily accessible, but some albinos do not have nystagmus. In these subjects it was found that they had frequent saccadic intrusions, the sizes of which were correlated with velocities of steady drifts in fixations (r = 0.802, P < 0.05). An explanation for the correlation between the amplitudes of the intrusions and the velocities of the drifts is that it is due to a common failure in the development of a saccadic system which is responsible for converting a given retinal displacement into a matching eye movement, with the extent of the failure reflecting the severity of the misrouting.

Adolescent↗
PubMed2004

Black diaphragm aniridia intraocular lens for aniridia and albinism.

BACKGROUND: Our aim was to assess the safety and efficacy of primary and secondary implantation of a black diaphragm aniridia intraocular lens (IOL) in patients that lacked a complete iris diaphragm. METHODS: This was a retrospective non-comparative study of six eyes in five patients with iris defects. The causes of such defects included congenital aniridia, traumatic aniridia, and oculocutaneous albinism. Three eyes underwent primary implantations of a black diaphragm IOL, and three eyes were given secondary implantations. The visual acuity, subjective severity of glare, postoperative anatomical outcome and any intraoperative or postoperative complications were reviewed. RESULTS: The mean follow-up period was 20.6 months (range 3-29 months). All patients showed stable or improvement in best-corrected visual acuity postoperatively. Glare and photophobia had improved subjectively in all patients after implantation of the black diaphragm IOL. Intraoperative complication included one case of hyphaema and iris damage during insertion of the IOL. Postoperative complications included intraocular inflammation with choroidal detachment, secondary glaucoma, and persistent epithelial defect after surgery. None of the patients developed decentration of IOL after surgery. CONCLUSION: The black diaphragm aniridia IOL is useful in the management of the condition in patients with iris deficiency including oculocutaneous albinism. Intraoperative and postoperative complications are not uncommon, and patients should be monitored carefully in the perioperative period.

Adult↗
PubMed2001

X-linked ocular albinism (Nettleship-Falls): a novel 29-bp deletion in exon 1. Carrier detection by ophthalmic examination and DNA analysis.

BACKGROUND: Mutations in the OA1 gene on the short arm of the X chromosome are known to cause X-linked ocular albinism (x1OA) in males. A four-generation family with this disorder, including asymptomatic carrier females, was investigated by molecular analysis of the OA1 gene. METHODS: DNA samples were available from 22 individuals of this family, including 6 affected males and 6 obligate carriers. The nine exons of the OA1 gene were amplified and further analyzed by SSCP and sequencing. RESULTS: A detailed clinical examination of the index patient and two female carriers showed the typical signs of ocular albinism. Visual evoked potential responses showed markedly asymmetrical responses from the two hemispheres in the affected person as well as in the carriers, as a result of misrouting and decussation of optic nerve fibers. Molecular genetic analysis demonstrated a previously undescribed 29-bp deletion at position 225-253 in exon 1 of the OA1 gene, which segregated in the family. CONCLUSION: Clinical examination combined with molecular genetic analysis enhances the potential for a precise diagnosis for persons at risk of x1OA and provide an accurate basis for genetic counseling.

Adult↗
PubMed2005

Molecular basis of oculocutaneous albinism type 1 in Lebanese patients.

Oculocutaneous albinism type 1 (OCA1) results from mutations in the tyrosinase gene, which lead to partial or complete loss of activity of the corresponding enzyme. A large number of mutations have been identified worldwide, providing insight into the pathogenesis of the disorder. We performed ophthalmic and dermatological exams on 30 Lebanese subjects with oculocutaneous albinism, then screened for mutations in the tyrosinase gene in an effort to establish the molecular basis of the disorder in our population and correlate it with phenotypic findings. The five exons of the gene together with the exon-intron boundaries and part of the promoter region were sequenced. Mutations were found in a total of 14 patients (47%) while no mutation was identified in the sequenced regions in 53% of patients. Fourteen different mutations were identified of which eight were novel while six had been previously reported. Mutations were mainly seen in patients with clinical findings, suggestive of OCA1A (64% of patients with OCA1A versus 25% of patients with OCA1B); therefore, the absence of mutations in some of the other patients may indicate the involvement of other genes.

Albinism, Oculocutaneous↗
PubMed1978

A syndrome associating partial albinism and immunodeficiency.

Two unrelated patients with partial albinism, frequent pyogenic infections and acute episodes of fever, neutropenia and thrombocytopenia are described. Their pigmentary dilution was characterized by large clumps of pigments in the hair shafts and an accumulation of melanosomes in melanocytes. Melanocytes had few short dendritic expansions, and keratinocytes were hypopigmented. No or few Langerhans' cells were detected in skin by electron microscopy and ATP-ase reactions. This pigmentary dilution, different from all other human albinisms, resembles the unique defect of the mutant dilute (d-d) mouse. Despite the presence of an adequate number of T and B lymphocytes, the patients were hypogammaglobulinemic, deficient in antibody production and incapable of manifesting delayed skin hypersensitivity or of rejecting skin grafts. Their leukocytes did not stimulate normal lymphocytes and could not generate cytotoxic cells during mixed leukocyte reaction. T lymphocytes of one patient were unable to exert a helper effect on the maturation of B lymphocytes into immunoglobulin-containing cells following in vitro stimulation with pokeweed mitogen. This suggests that the humoral deficiency might be secondary to a defect of helper T lymphocytes. Granulocytes did not show any morphologic abnormality, and their bactericidal activity was only moderately reduced. An increased number of polymorphonuclear leukocytes with polar distribution of Concanavaline A (Con A) receptors (capping) was found in one patient and her parents. The family histories suggest that this syndrome is transmitted as an autosomal recessive character.

Albinism↗
PubMed1982

Ophthalmic manifestations of the Hermansky-Pudlak syndrome (oculocutaneous albinism and hemorrhagic diathesis).

We report the association of oculocutaneous albinism and defective platelet function, the Hermansky-Pudlak syndrome, in two young Puerto Rican patients, a 17-year-old boy and a 9-year-old girl. Wide variation in pigmentation may obscure the diagnosis of albinism. Puerto Rican albinos are at increased risk of inheriting this autosomal recessive syndrome. Although usually mild, bleeding in affected patients can be life-threatening, especially after aspirin administration. Albino patients should be questioned about a history of bleeding and referred for hematologic consultation.

Adolescent↗
PubMed1989

Psychological aspects of albinism: an exploratory study with Nigerian (Igbo) albino subjects.

This paper reviews some studies done on the psychological aspects of albinism. Studies on the intellectual ability of albinos produce equivocal results. Results from personality studies seem more consistent and show albinos to be more emotionally unstable than non-albinos. This paper also reports a study by the author which examines the phenomenon of albinism from the albino's viewpoint. It examined the responses of three undergraduate albino subjects--one female and two males--to the author's request for each to write an essay on the merits and demerits of being an albino based on personal experiences. All consider being an albino to be more of a demerit than a merit. The demerits include conspicuous colour, delicate skin which blisters under the sun, defective sight, interpersonal, especially heterosexual, problems and society's unkind attitude. The paper ends with a discussion of possible future research in the area and a recommendation of the need for psychological rehabilitation as part of the management programme for albinos.

Adult↗
PubMed1996

The clinical spectrum of albinism in humans.

Oculocutaneous albinism is characterized by a congenital reduction or absence of melanin pigment in the skin, hair and eyes. The reduction in the hair and skin results in a change in color but no change in the development or function of these tissues, while the absence of melanin pigment in the eye leads to abnormal development and function. Of particular interest are mutations that are associated with a slow accumulation of pigment in the hair and eyes over time, while retaining the ocular defects of albinism. Analysis of these mutations might provide the insight that we need to understand the interaction between the pigment system and the development of the optic system.

Albinism, Oculocutaneous↗
PubMed2005

Amelioration of both functional and morphological abnormalities in the retina of a mouse model of ocular albinism following AAV-mediated gene transfer.

X-linked recessive ocular albinism type I (OA1) is due to mutations in the OA1 gene (approved gene symbol GPR143), which is expressed in the retinal pigment epithelium (RPE). The Oa1 (Gpr143) knockout mouse (Oa1(-/-)) model recapitulates many of the OA1 retinal morphological anomalies, including a lower number of melanosomes of increased size in the RPE. The Oa1(-/-) mouse also displays some of the retinal developmental abnormalities observed in albino patients such as misrouting of the optic tracts. Here, we show that these anomalies are associated with retinal electrophysiological abnormalities, including significant decrease in a- and b-wave amplitude and delayed recovery of b-wave amplitude from photoreceptor desensitization following bright light exposure. This suggests that lack of Oa1 in the RPE impacts on photoreceptor activity. More interestingly, adeno-associated viral vector-mediated Oa1 gene transfer to the retina of the Oa1(-/-) mouse model results in significant recovery of its retinal functional abnormalities. In addition, Oa1 retinal gene transfer increases the number of melanosomes in the Oa1(-/-) mouse RPE. Our data show that gene transfer to the adult retina unexpectedly rescues both functional and morphological abnormalities in a retinal developmental disorder, opening novel potential therapeutic perspectives for this and other forms of albinism.

Albinism, Ocular↗
PubMed2005

Choroidal amelanotic melanoma in a patient with oculocutaneous albinism.

CASE REPORT: We describe the clinical presentation of a choroidal amelanotic melanoma in a 46-year-old woman with oculocutaneous albinism. Clinical aspects, investigations, and management are presented, and findings from computed tomography and magnetic resonance imaging are described. Microscopic findings and histopathological features, demonstrating a spindle B-cell melanoma of the choroid, are also reviewed. COMMENTS: Magnetic resonance imaging may be helpful in diagnosing amelanotic melanoma in patients with oculocutaneous albinism.

Albinism, Oculocutaneous↗
PubMed1998

Repeated transmission of X-linked ocular albinism type 1 by a carrier oocyte donor.

OBJECTIVE: To report the transmission of unsuspected X-linked ocular albinism in an oocyte donor program. DESIGN: Case report. SETTING: University medical center. PATIENT(S): A 24-year-old white female oocyte donor and the outcomes of three recipient pregnancies. INTERVENTION(S): Clinical assessment and molecular diagnostic tests. MAIN OUTCOME MEASURE(S): Mutation detection. RESULT(S): Demonstration of carrier status and multiple transmissions of a mutant allele. CONCLUSION(S): We describe the transmission of a mutant allele for X-linked ocular albinism from an unsuspected carrier female oocyte donor to three independent pregnancies. We emphasize the need for diligent inquisition to clarify any unusual history of ocular or constitutional signs that might signify an X-linked disorder.

Adult↗
PubMed1994

Partial albinism with immunodeficiency (Griscelli syndrome).

Partial albinism with immunodeficiency is a rare and fatal immunologic disorder characterized by pigmentary dilution and variable cellular immunodeficiency. To define the phenotype, therapy, and outcome, we retrospectively analyzed seven consecutive patients. Primary abnormalities included a silvery-grayish sheen to the hair, large pigment agglomerations in hair shafts, and an abundance of mature melanosomes in melanocytes, with reduced pigmentation of adjacent keratinocytes. Clinical onset occurred between the ages of 4 months and 4 years and was characterized by accelerated phases (lymphohistiocytic infiltration of multiple organs, including the brain and the meninges), triggered by viral and bacterial infections. Characteristic laboratory features included pancytopenia, hypofibrinogenemia, hypertriglyceridemia, and hypoproteinemia. Consistent immunologic abnormalities were characterized by absent delayed-type cutaneous hypersensitivity and impaired natural killer cell function. Some patients had secondary hypogammaglobulinemia, impaired major histocompatibility complex-mediated cytotoxic effects, a decreased capacity of lymphocytes to trigger a mixed lymphocyte reaction, or various functional granulocytic abnormalities. The disease seems to be invariably lethal without bone marrow transplantation; the mean age at the time of death was 5 years. Bone marrow transplantation has been performed in three cases; two patients died in the immediate posttransplantation period of infectious complications, but one patient is cured after a follow-up of 5 years. We conclude that partial albinism with immunodeficiency (Griscelli syndrome) can be differentiated from Chédiak-Higashi syndrome by pathognomonic histologic features. One of the underlying immunologic defects may be a defective function of natural killer cells, predisposing the patient to virus-associated hemophagocytic syndrome or accelerated phases. The prognosis is very poor unless early bone marrow transplantation is carried out.

Adrenal Cortex Hormones↗