Familial clustering and linkage disequilibrium studies suggest that genetic factors predispose to vitiligo, although a clear transmission pattern and cosegregation of vitiligo with specific mutations have not been demonstrated. We collected pedigree data on vitiligo from a set of 56 multigeneration families belonging to the Paisa community from Antioquia, Colombia, with the goal of applying the unified model of complex segregation and linkage disequilibrium analyses to test the hypotheses of the existence of a major gene predisposing to vitiligo and that allelic or haplotype polymorphisms of microsatellite loci at 6p21.3-21.4 spanning HLA (D6S276, D6S265, D6S273, and D6S291) are associated with this predisposition. Minimum sibship sample size to discriminate dominant and recessive inheritance models was largely accomplished. Between the 15 models of complex segregation used, the one that best fitted the data was that of a major dominant gene and the existence of strong environmental effects acting on the recessive genotype. The penetrance and risk estimations discriminated two sets of vitiligo patients: those with early onset of vitiligo cosegregating with a dominant mode of inheritance without environmental effects, and those with late onset of vitiligo cosegregating with the recessive genotype and being influenced by environmental effects. After establishing the normal distribution of allelic frequencies and performing multiple comparisons correction, the linkage disequilibrium analysis suggested that a major genetic factor could be located at 6p21.3-21.4, because we detected significant case-control differences for allele 122 at D6S265 (Pc=0.0264) and significant linkage disequilibrium between loci D6S276 and D6S273 in the cases but not in the controls. We cannot explain these results as a consequence of evolutionary forces or as genetic stratification acting differentially on cases and controls, because there was neither deviation from the Hardy-Weinberg expectations nor genetic subdivision between cases and controls, as θ (non-biased F ST ) was not significantly different from 0.
Clear evidence has been presented correlating gene polymorphisms at 6p21.3-21.4 (containing HLA and TNF) and the predisposition to acquire multiple sclerosis (MS). In a previous study, we found that polymorphisms at HLA DQAI were associated with being or not being predisposed to MS in individuals inhabiting the tropics, where the prevalence of MS is significantly lower than in subtropical areas. Here, we tested the hypothesis that polymorphisms at D6S276, D6S265, D6S273 and D6S291 microsatellite loci are in strong linkage disequilibrium with a major genetic factor predisposing to MS. These microsatellites span the 6p21.3 region with intervals of 5 cM establishing particular landmarks for the HLA and TNF loci. Thirty-five MS patients and 35 controls, age, sex, social, ethnically and geographically matched healthy individuals, were studied. After testing the fit of gene frequencies to the normal distribution and performing the correlation for multiple comparisons, we found significant differences among the case and the control frequencies for the allele 202 belonging to the marker D6S276 (Pc=0.00455) and for the allele 114 belonging to the marker D6S265 (Pc=0.0084). For these two alleles at different loci, we found higher frequencies in the cases than in the controls. A nonsignificant p value was found in testing the existence of linkage disequilibrium among the studied loci in the cases and in the controls. In conclusion, the current study adds evidence to the established association among polymorphisms of genes located at 6p21.3-21.4 and MS. Furthermore, because of the distribution of the tested microsatellite loci, the more probable critical region could be correlated with the TNF neighborhood.
The Colombian population, for his history contains an ancestral mix of Europeans, Native Americans and Africans, these mixing ratios can be determined by Ancestry-Informative Markers (AIMs), this markers allow us to observe stratification in genetic association studies. The aim of this study was to determine the mixing ratios in a population sample of 500 individuals the Department of Cauca, Colombia with three different origins (European, Native American and African) using a set of 46 AIMs insertion-deletion (AIM-INDELs). The software STRUCTURE v 2.3.4 was used to determine the ancestral mixture. The average composition of the population of the Department of Cauca was 48% for Native American, 39% for European and 14% for African. It showed that the ancestral composition of the Department of Cauca has a greater contribution of Native Americans and Europeans compared to Africans which could be explained by the European migrations during the conquest of America.2015 Elsevier Ireland Ltd. All rights reserved.
Currently, all agencies of conformity assessment testing laboratory favor the participation in proficiency testing as a mechanism for quality assurance. In Colombia, the Genes Laboratory has been designated, since 2008, to perform, design and implement the proficiency testing for all the interested laboratories. In this report, we show the results of Colombian exercises Inter-laboratory Quality Control for the years 2013 and 2014. In both years the exercise consisted in one practical component, one theoretical mandatory component and a theoretical optional component. The participants were 23 and 20 laboratories in 2013 and 2014, respectively, representing seven different countries of Latin America and the Caribbean. For the practical component each participant laboratory receive;(1) samples of blood, saliva and/or semen stains, in this part they should report the routine own laboratory markers for each sample, (2) three optional theoretical cases of varying complexity, (3) a simple theoretical approach consistent of paternity case (father, mother and son) (2013) and a complex paternity case with a deceased father (2014). In the last two components of the exercise they had to submit only the calculations. In both years, for the practical component the consensus of 70 STR markers, distributed between autosomal and linked to the sex chromosomes, was achieved with an error rate of 1.75% and 3.07% for 2013 and 2014, respectively. On the other hand, for mandatory theoretical exercise, error rates of 21.74% (2013) and 10.63% (2014) were detected. This inter-laboratory exercise has become an important mechanism for quality assurance in the region.
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