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PubMed1993

Pathogenesis of the platinum (cp) mutation, a model for oculocutaneous albinism.

The platinum mutation at the C (albino) locus in the mouse is a potential model for oculocutaneous albinism in humans other than type IA (tyrosinase-negative) albinism. Although tissues from mice homozygous for the mutation display substantial tyrosinase activity, cutaneous and ocular pigmentation is severely restricted in affected animals. Using specific antipeptide antisera, we demonstrate that ocular extracts from wild-type mice contain two isoforms of tyrosinase bearing either the amino-terminal PEP5 epitope or the carboxy-terminal PEP7 epitope. The latter isoform participates in a high-molecular-weight complex detectable on sucrose density gradients. In platinum mice, antiserum to the PEP7 epitope fails to recognize any protein species, and the high-molecular-weight form of tyrosinase is not detectable. Our results support a key role for this high-molecular-weight complex in melanogenesis, and suggest that mutations that interfere with the ability of tyrosinase to participate in a multimeric complex may be a cause of oculocutaneous albinism in people.

Albinism, Oculocutaneous↗

PubMed1994

Molecular basis of oculocutaneous albinism.

Oculocutaneous albinism (OCA) is a complex group of genetic disorders that have historically been defined by clinical and biochemical methods. Recent advances in the molecular biology of pigmentation have greatly increased our understanding of the complexity of this group of disorders. To date, two different types of OCA (OCA1 and OCA2) have been mapped to specific chromosomal regions. Mutations have been found in the tyrosinase locus associated with OCA1 and the human homologue to the murine pink-eyed dilution locus associated with OCA2. Analysis of these genes and their mutations will allow us to better define and categorize the different types of albinism. Further, the analysis of these genes and their mutations will provide information on the role of these gene products in melanin biosynthesis and the effect specific mutations have on the pathogenesis of albinism.

Albinism, Oculocutaneous↗

PubMed2001

Albinism and phenotype of barn swallows (Hirundo rustica) from Chernobyl.

The effects of mutation on phenotypic expression are supposed to be mainly deleterious because mutations disrupt the expression of genes that function relatively well under current environmental conditions. Thus, mutations are assumed to give rise to deviant phenotypes that are generally selected against. Radioactive contamination in the Chernobyl region of Ukraine is associated with a significant increase by a factor two to 10 in mutation rate in microsatellite markers of the barn swallow, Hirundo rustica. Barn swallows from Chernobyl had a temporally constant, elevated frequency of partial albinism compared to the situation before radioactive contamination and compared to birds from a control area. Albinism disproportionately affected the carotenoid-based plumage of the head, suggesting that carotenoid metabolism is particularly susceptible to the effects of radiation. Individuals with partially albinistic plumage had, on average, lower mean phenotypic values than other birds, and this was particularly the case for males. Furthermore, differences in phenotypic variation, as determined using Levene's test, were significantly larger in partial albinos compared to nonalbinos in males, but not in females, even though the null expectation would be the opposite due to the lower mean phenotypic values of partial albinos. Although small phenotypes were commonly associated with germline mutations, there was no general decrease in overall body size during the period 1991-2000, implying that small individuals were selected against. Because partial albinism is disfavored by natural selection, the effects of mutations are deleterious, giving rise to a balance between mutation and selection.

Albinism↗

PubMed2006

Albinism in the domestic cat (Felis catus) is associated with a tyrosinase (TYR) mutation.

Albino phenotypes are documented in a variety of species including the domestic cat. As albino phenotypes in other species are associated with tyrosinase (TYR) mutations, TYR was proposed as a candidate gene for albinism in cats. An Oriental and Colourpoint Shorthair cat pedigree segregating for albinism was analysed for association with TYR by linkage and sequence analyses. Microsatellite FCA931, which is closely linked to TYR and TYR sequence variants were tested for segregation with the albinism phenotype. Sequence analysis of genomic DNA from wild-type and albino cats identified a cytosine deletion in TYR at position 975 in exon 2, which causes a frame shift resulting in a premature stop codon nine residues downstream from the mutation. The deletion mutation in TYR and an allele of FCA931 segregated concordantly with the albino phenotype. Taken together, our results suggest that the TYR gene corresponds to the colour locus in cats and its alleles, from dominant to recessive, are as follows: C (full colour) > c(b) (burmese) > or = c(s) (siamese) > c (albino).

Albinism↗

PubMed1986

Segregation analysis of brown oculocutaneous albinism.

The segregation of brown (type IV) oculocutaneous albinism was analyzed in 18 Nigerian families. Analysis using the POINTER program showed that this type of oculocutaneous albinism was inherited in an autosomal recessive pattern, with an estimated gene frequency of 0.025 +/- 0.007 in this population. The enzyme defect responsible for brown oculocutaneous albinism is unknown.

Albinism↗

PubMed1993

Deletion analysis maps ocular albinism proximal to the steroid sulphatase locus.

We describe a pedigree in which four male members are affected by a contiguous gene abnormality involving the short arm of the X chromosome (Xp22.32). Bivariate flow cytometry of lymphoblastoid cell lines from two of these individuals and a normal male showed a 6-7 megabase deletion in affected males, and high resolution chromosomal G-banding of an obligate heterozygote showed the deletion to reside in the Xp22.32 region. Affected members had X-linked ichthyosis due to steroid sulphatase deficiency, Kallmann's syndrome, but no ocular albinism. In two out of four affected individuals studied, there was unilateral renal agenesis. Deletion analysis using the Xp22.32 markers MIC2, DXS31, DXS 89, GMGX9, DXS278, DXS143, and DXS9 showed that the deletion extended from DXS31 to DXS143 (inclusive). The absence of ocular albinism in this pedigree shows conclusively that the X-linked ocular albinism gene resides proximal to the DXS143 locus. Further, the inconstant association of unilateral renal agenesis with X-linked Kallmann's syndrome, even when the latter is caused by a complete deletion of the gene, suggests that the absence of the X-linked Kallmann gene can be compensated in renal development.

Albinism, Ocular↗

PubMed1989

The recognition and management of albinism.

Albinism is not a single entity but represents a heterogenous group of inherited disorders of pigmentation. Despite a wide variety of manifestations, all forms of albinism are characterized by several ocular features, including: nystagmus, photophobia, reduced visual acuity and a lack of stereopsis. It is the intention of this review to describe and discuss the clinical implications of albinism with particular emphasis placed on these ocular features and their effects on visual performance. Various techniques that may be employed to aid the albino will also be described.

Albinism↗

PubMed1985

Abnormal visual pathways in normally pigmented cats that are heterozygous for albinism.

The various forms of albinism affect about one in 10,000 births in the United States. An additional 1 to 2 percent of the population has normal pigmentation but is heterozygous and carries a recessive allele for albinism. The retinogeniculocortical pathways were studied in normally pigmented cats that carry a recessive allele for albinism. The cats exhibited abnormalities in their visual pathways similar to those present in homozygous albinos. These results imply that visual anomalies like those found in albinos may be present in 1 to 2 percent of the human population.

Albinism↗

PubMed1995

Oculocutaneous albinism among schoolchildren in Harare, Zimbabwe.

The term oculocutaneous albinism (OCA) covers a range of autosomal recessive genetic conditions involving hypopigmentation of the skin, hair, and eyes. In southern African black ethnic groups the tyrosinase positive form, OCA2, is predominant, with few cases of tyrosinase negative OCA1. The prevalence of OCA2 in schoolchildren in Harare, the capital city of Zimbabwe, was found to be 1 in 2833. The gene frequency for OCA2 was 0.0188, with a carrier frequency of 1 in 27. Most of the pupils with albinism belong to the majority Shona ethnic group. As consanguineous marriages are discouraged in the Shona culture this high rate is likely to be a result of genetic drift in a relatively small population showing limited mobility. OCA pupils were found in more than a third of the secondary schools in Harare, emphasising the importance of distributing information on albinism and its management widely throughout the school system.

Adolescent↗

PubMed1996

Distribution of oculocutaneous albinism in Zimbabwe.

A survey of 1.3 million schoolchildren in Zimbabwe identified a total of 278 pupils with oculocutaneous albinism (OCA), giving a prevalence of 1 in 4728. Pupils with OCA were identified in every province of the country, but the distribution was not even. In certain areas, notably the capital, Harare, and the eastern province of Manicaland, the frequency was significantly higher than in others. Although most of the pupils with albinism belonged to the majority Shona ethnic group, people with OCA were also found among the minority population groups in the country. There were almost twice as many pupils with albinism in rural compared with urban schools (248 v 129). However, the prevalence of OCA was significantly higher in urban than rural areas. These results indicate that data for a country collected solely in urban locations are likely to be biased and emphasise the need for widespread distribution of health and special educational facilities for affected people.

Adolescent↗

PubMed2007

Periodontal disease in Kuna albinism: a comparative study.

BACKGROUND: In classic albinism, all parts of the body are normal except for the absence of melanin. It is believed that lack of this pigment in periodontal tissues might influence periodontal disease progression. This study was designed to determine the relationship between periodontal diseases and albinism by comparing the clinical periodontal status of a group of native Panamanian Kuna albinos (from San Blas, Panama) to Kuna non-albinos of the same communities. METHODS: An experimental group of 30 subjects (Kuna albinos aged > or =12 years) was selected and divided into three subgroups according to age. Likewise, a control group of 30 subjects (Kuna non-albinos) was selected and divided in subgroups. RESULTS: Assessment of oral hygiene and gingival inflammation in albinos by the Silness and Löe plaque index and Löe and Silness gingival index, respectively, was unremarkable compared to control groups. No statistically significant differences were found for number of teeth present, gingival index, plaque index, clinical attachment loss (CAL), probing depth, or gingival recession. As expected, age was a factor in the severity of the periodontal disease; 58% of individuals aged > or =36 years had at least one site with CAL > or =7 mm. CONCLUSION: Based on the overwhelming similarity of results found between experimental and control groups, albinism does not represent a clinical risk factor in the pathogenesis or exacerbation of periodontal diseases for these individuals.

Adolescent↗

PubMed1986

Nettleship-Falls X-linked ocular albinism with Axenfeld's anomaly. A case report.

A Japanese male with Nettleship-Falls X-linked ocular albinism (NXOA) and associated with Axenfeld's anomaly is described here. The diagnosis of X-linked ocular albinism was difficult because of moderately pigmented fundus and lack of iris translucency, but macromelanosomes recognized by histological study of skin biopsy were helpful for diagnosis. This is the first report identifying the macromelanosomes in Japanese NXOA. A combination of ocular albinism and Axenfeld's anomaly is very rare. There might be a common defective factor for the development of these two congenital disorders.

Albinism↗

PubMed1990

Visual anomalies associated with albinism.

All mammals with hypopigmentation of the retinal pigment epithelium have abnormal visual systems. Albino mammals have been found to have: (1) reduced numbers of uncrossed optic fibers projecting to all visual centers, (2) disorganization of the pattern (lamination) of the dorsal lateral geniculate nuclei, and (3) disorganization of projections from the dorsal lateral geniculate nuclei to the visual cortex. The disorganization of central visual centers has catastrophic effects on stereovision and optokinetic nystagmus. Variable expression in oculocutaneous albinism suggests that affected individuals cannot always be identified by hypopigmentation, reduced visual acuity and nystagmus. Careful observation of foveal development in individuals even with normal vision is necessary to detect all persons with albinism. The scalp-recorded visually evoked potential designed to detect optic misrouting is the most reliable concomitant for determining albinism.

Albinism↗

PubMed1993

Eye movement changes in albinism--a case report with electronystagmographic findings.

Albinism is associated with neural anomalies including foveal hypoplasia and aberrant optic pathway projection that result in a variety of oculomotor instability. We present a 38-years-old man with oculocutaneous albinism who had horizontal jerk-type nystagmus, which showed a reverse in direction by any extraneous light stimulation which was documented by electronystagmogram. The mechanism of the nystagmus in this case is uncertain. These findings in albinism have not been reported previously, to our knowledge, and suggest a defect in the visual pathway system.

Adult↗

PubMedDate not supplied

Retinal vascular and optic nerve abnormalities in albinism.

Albinism is a condition in which the pigment melanin may not be synthesized from tyrosine. The fundus photographs of 24 eyes of 12 patients with the clinical diagnosis of either ocular or oculocutaneous albinism were reviewed. We observed two findings that to our knowledge have not been reported previously. Eighteen eyes of ten patients had prominent retinal vessels coursing through the putative macular area instead of arching around it. Large noncilioretinal vessels extended from the disc to the dysplastic "foveal zone" in eight eyes of five patients. Typical optic nerve hypoplasia (ONH) was seen in six eyes of four patients; features suggestive of ONH were present in an additional ten eyes of six patients. The cross-over (sharing) of clinical features between albinism and aniridia is striking and raises questions about pathophysiologic mechanisms.

Albinism↗

PubMed2003

Syndromic albinism: a review of genetics and phenotypes.

There are several syndromes of albinism associated with systemic pathology. These include Chediak-Higashi Syndrome (CHS), Hermansky-Pudlack Syndrome (HPS), Griscelli Syndrome (GS), Elejalde Syndrome (ES) and Cross-McKusick-Breen Syndrome (CMBS). In the last several years the genetic defects underlying some of these syndromes have been described. HPS is related to 7 genes in humans. GS is related to 3 genes: MYOVA, Rab-27A, and melanophilin (Mlph). CHS is related to one gene: LYST. The genetic defects in ES and CMBS are yet to be defined. Syndromic forms of albinism are associated with defects in the packaging of melanin and other cellular proteins. As such they are distinct from oculocutaneous albinism, which is associated with defects in the production of melanin (e.g., TRP1, P gene, and tyrosinase).

Albinism↗

PubMedDate not supplied

Duane syndrome associated with oculocutaneous albinism.

A 5-year-old female presented with signs of Duane's retraction syndrome and oculocutaneous albinism. Duane's syndrome is associated with anomalous innervation of the lateral rectus by the oculomotor nerve. Oculocutaneous albinism is associated with an increased proportion of crossed retinal ganglion fibers at the chiasm. Because Duane's syndrome and oculocutaneous albinism are both examples of ocular miswiring, a common mechanism is suggested.

Albinism, Oculocutaneous↗

PubMedDate not supplied

Albinism.

Albinism includes a group of genetic disorders with decreased pigmentation. Eye defects include foveal hypoplasia and misrouting of retinal nerve impulses. The primary concerns of those with albinism are low vision and societal misconceptions, which can also lead to social and emotional problems. Persons with albinism can live fairly normal lives when they have appropriate support and resources, including low vision rehabilitation.

Adaptation, Psychological↗