Haplotypic Associations and Differentiation of MHC Class II Polymorphic Alu Insertions at Five Loci With HLA-DRB1 Alleles in 12 Minority Ethnic Populations in China

HLA Genetics for the Human Diseases

Highly polymorphic human leukocyte antigen (HLA) molecules (alleles) expressed by different classical HLA class I and class II genes have crucial roles in the regulation of innate and adaptive immune responses, transplant rejection and in the pathogenesis of numerous infectious and autoimmune diseases. To date, over 35,000 HLA alleles have been published from the IPD-IMGT/HLA database, and specific HLA alleles and HLA haplotypes have been reported to be associated with more than 100 different diseases and phenotypes. Next generation sequencing (NGS) technology developed in recent years has provided breakthroughs in various HLA genomic/gene studies and transplant medicine. In this chapter, we review the current information on the HLA genomic structure and polymorphisms, as well as the genetic context in which numerous disease associations have been identified in this region.

Regulation of expression quantitative trait loci by SVA retrotransposons within the major histocompatibility complex

Genomic and transcriptomic studies of expression quantitative trait loci (eQTL) revealed that SINE-VNTR-Alu (SVA) retrotransposon insertion polymorphisms (RIPs) within human genomes markedly affect the co-expression of many coding and noncoding genes by coordinated regulatory processes. This study examined the polymorphic SVA modulation of gene co-expression within the major histocompatibility complex (MHC) genomic region where more than 160 coding genes are involved in innate and adaptive immunity. We characterized the modulation of SVA RIPs utilizing the genomic and transcriptomic sequencing data obtained from whole blood of 1266 individuals in the Parkinson's Progression Markers Initiative (PPMI) cohort that included an analysis of human leukocyte antigen (HLA)-A regulation in a subpopulation of the cohort. The regulatory properties of eight SVAs located within the class I and class II MHC regions were associated with differential co-expression of 71 different genes within and 75 genes outside the MHC region. Some of the same genes were affected by two or more different SVA. Five SVA are annotated in the human genomic reference sequence GRCh38.p14/hg38, whereas the other three were novel insertions within individuals. We also examined and found distinct structural effects (long and short variants and the CT internal variants) for one of the SVA (R_SVA_24) insertions on the differential expression of the HLA-A gene within a subpopulation (550 individuals) of the PPMI cohort. This is the first time that many HLA and non-HLA genes (multilocus expression units) and splicing mechanisms have been shown to be regulated by eight structurally polymorphic SVA within the MHC genomic region by applying precise statistical analysis of RNA data derived from the blood samples of a human cohort population. This study shows that SVA within the MHC region are important regulators or rheostats of gene co-expression that might have potential roles in diversity, health, and disease.

Human leukocyte antigen super-locus: nexus of genomic supergenes, SNPs, indels, transcripts, and haplotypes

The human Major Histocompatibility Complex (MHC) or Human Leukocyte Antigen (HLA) super-locus is a highly polymorphic genomic region that encodes more than 140 coding genes including the transplantation and immune regulatory molecules. It receives special attention for genetic investigation because of its important role in the regulation of innate and adaptive immune responses and its strong association with numerous infectious and/or autoimmune diseases. In recent years, MHC genotyping and haplotyping using Sanger sequencing and next-generation sequencing (NGS) methods have produced many hundreds of genomic sequences of the HLA super-locus for comparative studies of the genetic architecture and diversity between the same and different haplotypes. In this special issue on 'The Current Landscape of HLA Genomics and Genetics', we provide a short review of some of the recent analytical developments used to investigate the SNP polymorphisms, structural variants (indels), transcription and haplotypes of the HLA super-locus. This review highlights the importance of using reference cell-lines, population studies, and NGS methods to improve and update our understanding of the mechanisms, architectural structures and combinations of human MHC genomic alleles (SNPs and indels) that better define and characterise haplotypes and their association with various phenotypes and diseases.

rs144012689 is a highly specific representative marker of HLA-B*15:02 in the Chinese population

Objective: To develop an accurate and rapid real-time PCR technique for HLA-B*15:02 genotyping and investigate HLA-B*15:02 allele frequency in four ethnic populations in China. Materials & methods: Based on the highly specific representative markers, a real-time PCR assay was developed for HLA-B*15:02 genotyping, and HLA-B*15:02 allele frequencies were screened in four ethnic populations of China. Sequence-based typing was used to validate the accuracy of the assay. Results: The sensitivity and specificity of the assay were 100%, and the detection limit was 0.2 ng. The frequency of HLA-B*15:02 alleles distributed in the Bouyei population was significantly higher than in the Han group (p < 0.01). Neither the Tibetan nor the Uyghur population carried the HLA-B*15:02 haplotype. Conclusion: The authors developed an accurate HLA-B*15:02 genotyping method for evaluating the risk of adverse drug reactions induced by carbamazepine in various ethnic populations in China.

Allelic and haplotypic data of MHC class II Alu insertions in Ngazidja (Comoros archipelago) and insight on its historical biology

This study aimed to analyse, for the first time, five MHC class II polymorphic Alu insertions in a population with a strong Sub-Saharan African genetic background: the Ngazidja islanders and compare its allelic and haplotypic data with Worldwide populations. The genotyping was performed in 80 individuals, using simple PCR and agarose gel electrophoresis methods. Allele and haplotype frequencies, genetic diversity, Hardy-Weinberg equilibrium deviations, normalized deviate of homozygotes and pairwise linkage disequilibrium were estimated. The phylogenetic analyses included the available population data. In Ngazidja, the MHC class II Alu insertion frequencies ranged from 0.119 for AluORF10 to 0.588 for AluDPB2. Concerning haplotypes, the most predominant were the ones with only the AluDPB2 insertion allele (AluDPB2*2-AluDQA2*1-AluDQA1*1-AluDRB1*1-AluORF10*1), followed by the theoretical ancestral haplotype with no Alu insertions (AluDPB2*1-AluDQA2*1-AluDQA1*1-AluDRB1*1-AluORF10*1) and finally the haplotype with the AluDPB2 and AluDQA1 Alu insertions (AluDPB2*2-AluDQA2*1-AluDQA1*2-AluDRB1*1-AluORF10*1) with frequencies of 19.2%, 15% and 12.9%, respectively. In the phylogenetic analyses, our results indicate that the Ngazidja people are genetically differentiated from the other populations of the analysis; we found also a new haplotype that can be probably characteristic of Sub-Saharans and finally confirm the usefulness of these markers as genetic and evolutionary tools for studying genetic variations among populations of different origins.