Diagnosing cystic fibrosis in South Africa.
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Cystic Fibrosis↗
Biomedical subjects
Michele Ramsay
Publications and source records attributed to Michele Ramsay.
DNA polymorphism and selection at the melanocortin-1 receptor gene in normally pigmented southern African individuals.
Skin pigmentation is a polygenic multifactorial trait determined by the cumulative effects of multiple genetic variants and environmental factors. Melanocortin-1 receptor (MC1R) is one of the genes involved in pigmentation, and has been implicated in the red hair and pale skin phenotype in human Caucasoid individuals. The present study was undertaken to identify variation at the MC1R locus in normally pigmented individuals in two African populations, sub-Saharan Negroids (22 unrelated individuals) and the San (17 unrelated individuals). The study showed considerable MC1R gene sequence variation with the detection of eight synonymous and three nonsynonymous mutations. This is the first report of nonsynonymous mutations in African individuals in the MC1R gene: L99I was found in a single San individual, S47I was detected in a single Negroid individual, and F196L was detected in five Negroid individuals (5/44; 0.11). The functional significance of these mutations is not known. Three of the eight synonymous mutations found, L106L (CTG --> CTA), F300F (TTC --> TTT), and T314T (ACA --> ACG) (also known as A942G), have been reported previously. T314T was the only variant that showed a significant difference between the Negroid and San populations (0.477 and 0.059, respectively; P = 1.6 x 10(-5)). Its low frequency in the San may be the result of random genetic drift in a population of small size, or selection. Several tests of neutrality of the MC1R coding region in these and other African populations were significant, suggesting that purifying selection (functional constraint) had occurred at this gene locus in Africans. This demonstrates that although some nonsynonymous MC1R mutations are tolerated in individuals with dark skin, this gene has likely played a significant role in the maintenance of dark pigmentation in Africans and normal pigment variation in non-African populations.
Africa↗
Lipoid proteinosis maps to 1q21 and is caused by mutations in the extracellular matrix protein 1 gene (ECM1).
Lipoid proteinosis (LP), also known as hyalinosis cutis et mucosae or Urbach-Wiethe disease (OMIM 247100) is a rare, autosomal recessive disorder typified by generalized thickening of skin, mucosae and certain viscera. Classical features include beaded eyelid papules and laryngeal infiltration leading to hoarseness. Histologically, there is widespread deposition of hyaline (glycoprotein) material and disruption/reduplication of basement membrane. The aetiology of LP is currently unknown. Using DNA from three affected siblings in a consanguineous Saudi Arabian family we performed genome-wide linkage and mapped the disorder to 1q21 (marker D1S498) with a two-point LOD score of 3.45 at theta = 0. A further 28 affected individuals from five other unrelated consanguineous family groups from different geographical regions also showed complete linkage and resulted in a maximum two-point LOD score of 21.85 at theta = 0. Using available markers in the interval between D1S442 and D1S305, the observed recombinants placed the gene in a 2.3 cM critical interval between D1S2344 and D1S2343 (Marshfield genetic map) corresponding to an approximately 6.5 Mb region on the UCSC physical map. Using a candidate gene approach (comparison of control versus LP gene expression in cultured fibroblasts) and subsequent direct sequencing of genomic DNA, we identified six different homozygous loss-of-function mutations in the extracellular matrix protein 1 gene (ECM1). Although the precise function of ECM1 is not known, our findings provide the first clinical indication of its relevance to skin adhesion, epidermal differentiation, wound healing, scarring, angiogenesis/angiopathy and basement membrane physiology, as well as defining the molecular basis of this inherited disorder.
Blood Vessels↗
Four novel variants in MC1R in red-haired South African individuals of European descent: S83P, Y152X, A171D, P256S.
Skin, hair and eye pigmentation is a polygenic multifactorial trait determined by the cumulative effects of multiple genetic variants and environmental factors. MC1R is one of the genes involved in pigmentation, and has been implicated in the red hair and pale skin trait in human Caucasoid individuals. This study was undertaken to investigate variants in the MC1R gene in Caucasoid individuals in South Africa, who are of European decent. Seven unrelated individuals were studied, all of whom were found to be either homozygous for a single mutation or compound heterozygous for two different mutations. We report four novel MC1R missense mutations: S83P, Y152X, A171D and P256S. This study supports the view that two mutations are necessary, but not necessarily sufficient, to give rise to the red hair and pale skin phenotype.
Codon↗
Gene expression profiling to predict lymphoma outcome.
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Gene Expression Profiling↗
Larger genetic differences within africans than between Africans and Eurasians.
The worldwide pattern of single nucleotide polymorphism (SNP) variation is of great interest to human geneticists, population geneticists, and evolutionists, but remains incompletely understood. We studied the pattern in noncoding regions, because they are less affected by natural selection than are coding regions. Thus, it can reflect better the history of human evolution and can serve as a baseline for understanding the maintenance of SNPs in human populations. We sequenced 50 noncoding DNA segments each approximately 500 bp long in 10 Africans, 10 Europeans, and 10 Asians. An analysis of the data suggests that the sampling scheme is adequate for our purpose. The average nucleotide diversity (pi) for the 50 segments is only 0.061% +/- 0.010% among Asians and 0.064% +/- 0.011% among Europeans but almost twice as high (0.115% +/- 0.016%) among Africans. The African diversity estimate is even higher than that between Africans and Eurasians (0.096% +/- 0.012%). From available data for noncoding autosomal regions (total length = 47,038 bp) and X-linked regions (47,421 bp), we estimated the pi-values for autosomal regions to be 0.105, 0.070, 0.069, and 0.097% for Africans, Asians, Europeans, and between Africans and Eurasians, and the corresponding values for X-linked regions to be 0.088, 0.042, 0.053, and 0.082%. Thus, Africans differ from one another slightly more than from Eurasians, and the genetic diversity in Eurasians is largely a subset of that in Africans, supporting the out of Africa model of human evolution. Clearly, one must specify the geographic origins of the individuals sampled when studying pi or SNP density.
Africa↗
Complete androgen insensitivity syndrome in a black South African family: a clinical and molecular investigation.
OBJECTIVE: To present the first report of a clinical and molecular investigation of a black South African family with complete androgen insensitivity syndrome (CAIS). METHODS: Biochemical and chromosomal analyses were performed. In addition, the molecular study included microsatellite analysis and DNA sequencing. RESULTS: The index case, an unmarried 21-year-old black phenotypic female patient with primary amenorrhea, was identified in the Division of Endocrinology at a tertiary hospital affiliated with the University of the Witwatersrand. A detailed family history identified further potentially affected members (on the basis of primary amenorrhea), who were also included in the study. A total of 13 family members, including 6 affected subjects, were involved in the molecular study. All affected persons had a 46,XY karyotype, female phenotype, and hormonal profiles commensurate with their clinical diagnosis. The androgen receptor gene in an affected patient was examined for mutations by DNA sequencing. Mutation screening was extended to other family members. The genetic basis for CAIS in this large family is the missense mutation, D732Y, in exon 5 of the androgen receptor ligand-binding domain. CONCLUSION: To our knowledge, this is the first case report of CAIS in South Africa in which molecular genetic techniques were used to substantiate the clinical diagnosis. The findings in this study have implications for genetic counseling in this family.
Adolescent↗