HLA concordance between hematopoietic stem cell transplantation patients and umbilical cord blood units: Implications for cord blood banking in admixed populations

HLA molecular study of patients in a public kidney transplant program in Guatemala

Guatemala is a country located in Central America, and while it is one of the most populated countries in the region, the genetic diversity of the population has been poorly analyzed. Currently, there are no analyses of the distribution of human leukocyte antigen (HLA) system alleles in mixed ancestry (i.e., ladino) populations in Guatemala. The HLA system exhibits the most extensive polymorphism in the human genome and has been extensively analyzed in a large number of studies related to disease association, transplantation, and population genetics (with particular importance in the understanding of diversity in the human population). Here, we present HLA typing data from 127 samples of unrelated individuals from the kidney transplant program of the San Juan de Dios General Hospital (Guatemala City) using a PCR-SSOP-based (PCR-sequence specific oligonucleotide probes) typing method. We found 16 haplotypes that accounted for 39.76 % of the total haplotype diversity, of which thirteen have been reported previously in Native American populations and three have been reported in European populations. The analyses showed no deviations from Hardy-Weinberg equilibrium, and admixture estimates calculated with k = 3 ancestral components showed that Native American was the most represented component, followed by the European component. The African component was less prominent in the Guatemala mixed ancestry sample in comparison to samples from other countries in Central America. The HLA-based admixture results for Central America showed a continuum in the distribution of Native American, European and African ancestries throughout the region, which is consistent with the complex demographic history of the region.

The immunogenetic diversity of the HLA system in Mexico correlates with underlying population genetic structure

We studied HLA class I (HLA-A, -B) and class II (HLA-DRB1, -DQB1) allele groups and alleles by PCR-SSP based typing in a total of 15,318 mixed ancestry Mexicans from all the states of the country divided into 78 sample sets, providing information regarding allelic and haplotypic frequencies and their linkage disequilibrium, as well as admixture estimates and genetic substructure. We identified the presence of 4268 unique HLA extended haplotypes across Mexico and find that the ten most frequent (HF > 1%) HLA haplotypes with significant linkage disequilibrium (Δ'≥0.1) in Mexico (accounting for 20% of the haplotypic diversity of the country) are of primarily Native American ancestry (A*02~B*39~DRB1*04~DQB1*03:02, A*02~B*35~DRB1*08~DQB1*04, A*68~B*39~DRB1*04~DQB1*03:02, A*02~B*35~DRB1*04~DQB1*03:02, A*24~B*39~DRB1*14~DQB1*03:01, A*24~B*35~DRB1*04~DQB1*03:02, A*24~B*39~DRB1*04~DQB1*03:02, A*02~B*40:02~DRB1*04~DQB1*03:02, A*68~B*35~DRB1*04~DQB1*03:02, A*02~B*15:01~DRB1*04~DQB1*03:02). Admixture estimates obtained by a maximum likelihood method using HLA-A/-B/-DRB1 as genetic estimators revealed that the main genetic components in Mexico as a whole are Native American (ranging from 37.8% in the northern part of the country to 81.5% in the southeastern region) and European (ranging from 11.5% in the southeast to 62.6% in northern Mexico). African admixture ranged from 0.0 to 12.7% not following any specific pattern. We were able to detect three major immunogenetic clusters correlating with genetic diversity and differential admixture within Mexico: North, Central and Southeast, which is in accordance with previous reports using genome-wide data. Our findings provide insights into the population immunogenetic substructure of the whole country and add to the knowledge of mixed ancestry Latin American population genetics, important for disease association studies, detection of demographic signatures on population variation and improved allocation of public health resources.