Estimation of carrier frequency of a 2.7 kb deletion allele of the P gene associated with OCA2 in African-Americans

Institute for Cancer Research, Fox Chase Cancer Center, Philadelphia, Pennsylvania 19111, USA.
Human Mutation (Impact Factor: 5.14). 01/1996; 7(4):370-3. DOI: 10.1002/(SICI)1098-1004(1996)7:4<370::AID-HUMU15>3.0.CO;2-#
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    • "OCA2 is the most common form of albinism, especially among Africans and African-Americans. There is a high incidence of OCA2 among specific African populations: 1 in 1,100 among the Ibo of Nigeria (Okoro 1975), 1 in 3,900 in South Africa (Kromberg and Jenkins 1982), 1 in 4,100 in Tanzania (Luande et al. 1985), 1 in 4,882 in Zimbabwe (Lund 1996), 1 in 5,000 in Nigeria (Barnicot, 1952), 1 in 7,900 among the Bamileke of Cameroon (Aquaron 1980, 1990) and 1 in 10,000 in African-Americans (Durham-Pierre et al. 1996). "
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    ABSTRACT: In this study, we report on a Cameroonian family from the Ewondo ethnic group, presenting with three oculocutaneous albinism type 2 (OCA2) patients homozygous for the 2.7-kb deletion of the P gene. In one of these patients OCA2 was associated with sickle cell anaemia and in two with the sickle cell trait. We took this opportunity to determine single nucleotide polymorphism (SNP) haplotypes within the P gene in this family in comparison with a group of 53 OCA2 patients homozygous for the same mutation and with a matched unrelated full-coloured control group of 49 subjects, originating from seven different ethnic groups of Southern Cameroon including Ewondo. A combination of five exonic and intronic SNPs in the OCA2 gene was genotyped by sequencing PCR products. We found 3 different haplotypes (TAGCT, TAGTT and TAGCC with frequencies of 0.66, 0.28 and 0.06, respectively) associated with the mutation in the 53 OCA2 patients, while 11 different haplotypes were observed in the control group. These observations suggest that the mutation appeared on the relatively frequent haplotype TAGCT, and that the two other haplotypes are derived from two independent recombination events. These haplotypic data, associated with a value of 1/15,000 for the prevalence of the 2.7-kb mutation, a present effective population size of 10,000,000 for Cameroon and a recombination rate of 0.0031, allowed us to estimate that this mutation originated 4,100-5,645 years ago.
    Full-text · Article · Feb 2007 · Journal of Human Genetics
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    • "The majority of individuals of sub-Saharan African heritage with OCA2 are homozygous for a common 2.7-kb deletion. The 2.7-kb deletion is less common in the US African-American population and has been found in the Puerto Rican population [Kedda et al 1994, Spritz et al 1995, Stevens et al 1995, Durham-Pierre et al 1996, Puri et al 1997, Stevens et al 1997, Kerr et al 2000, Santiago Borrero et al 2006]. "
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    ABSTRACT: Oculocutaneous albinism type 1 (OCA1) is characterized by reduced synthesis of melanin in the skin, hair, and eyes, associated with ocular findings of nystagmus, reduced iris pigment with iris translucency, reduced retinal pigment, foveal hypoplasia with significantly reduced visual acuity usually in the range of 20/100 to 20/400, and misrouting of the optic nerves resulting in alternating strabismus and reduced stereoscopic vision. Individuals with OCA1A have white hair, white skin that does not tan, and fully translucent irises that do not darken with age. At birth, individuals with OCA1B have white or very light yellow hair that darkens with age, white skin that over time develops some generalized pigment and may tan with sun exposure, and blue irises that change to green/hazel or brown/tan with age. Visual acuity may be 20/60 or better in some individuals. The diagnosis of OCA1 is established by clinical findings of hypopigmentation of the skin and hair and characteristic eye findings. Molecular genetic testing of the tyrosinase gene, TYR, is clinically available; it is rarely used in diagnosis and is most commonly used in genetic counseling for carrier detection. OCA1 is inherited in an autosomal recessive manner. At conception, the sibs of an affected individual have a 25% chance of being affected, a 50% chance of being asymptomatic carriers, and a 25% chance of being unaffected and not carriers. Prenatal diagnosis of OCA1 by fetal skin biopsy or molecular genetic testing is possible in pregnancies at 25% risk.
    Preview · Chapter · Jan 2004
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    ABSTRACT: Albinism connotes a large group of genetic disorders that are characterized by diminished ocular and oftentimes cutaneous pigmentation. These disorders are generally subclassified as oculocutaneous albinism (OCA) or ocular albinism (OA) based on the extent of their effects on the pigmentation of the skin and hair. Sometimes, different mutations in the same gene can cause OCA or OA.
    No preview · Article · Apr 1997 · Seminars in Cutaneous Medicine and Surgery
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