HLA and Associated Important Diseases 260CD . During antigen presentation, CD and CD are intimately associated with the TCR and bind to the MHC molecule [ ].. Haplotype, linkage disequilibrium and HLA genes expression HL" genes are transmitted for Mendel segregation and allelic variant is expressed in a codominant mode. The set of HL" alleles present in each chromosome of the pair is denominated haplotype. The probability of a sibling having the same HL" haplotype as the other is %, different haplotypes is % and % are share only one haplotype [ ].Moreover, there is a fact that occurs in HL" genes called linkage disequilibrium which denotes that certain alleles occur together with a greater frequency than would be expected by chance non-random gametic association . Variations in the expected combinations of alleles in the population, more often or less often than would be expected from a random formation of haplotypes from alleles, could be related to linkage disequilibrium [ ]. For example, a determined population has a gene frequency of % for HLA-A* and % for HLA-B* , therefore the expected frequency for this haplotype would be . % . x . , the actual frequency is however, . % in this population, a higher frequency than expected, characterizing a positive linkage disequilibrium [ ]..
HLA and infection diseasesThe frequency and the presence of HL" alleles vary among different populations. Studies suggest that the alleles that can confer resistance to certain pathogens are prevalent in areas with endemic diseases. Furthermore, genomic analysis in families has helped to map and identify the loci related to a number of diseases. Moreover, a number of diseases have been mapped and had their related loci identified thanks to the genomic analysis of families.