Biology subjects

Leffler, E. M.

Publications and source records attributed to Leffler, E. M..

9 recordsLinked to original sources

bioRxiv2025

Sickle cell status skews malaria parasite genotype at infection

Sickle cell hemoglobin (HbS) confers protection against symptomatic malaria caused by Plasmodium falciparum. HbS carriers with symptomatic malaria harbour parasites enriched for sickle-associated alleles (Pfsa+), which appear to partially overcome HbS-mediated protection, but their role in asymptomatic infections is unclear. Here, we conducted a cross-sectional survey of 2,246 healthy school children in a region of high malaria transmission region in Cameroon. Analysing parasite Pfsa and human HbS genotypes for 1,701 asymptomatic P. falciparum infections confirmed that heterozygous HbS (HbAS) and homozygous non-HbS (HbAA) genotypes have similar rates of asymptomatic infection. However, the HbS genotype is strongly associated with parasites carrying Pfsa+ alleles at Pfsa1 and Pfsa3 loci, indicating a selective advantage for these alleles in HbS carriers. Our findings reveal that the protective effect of HbS is complex, where HbS has a protective effect prior to symptoms against Pfsa- parasites and Pfsa+ alleles may contribute to lower rates of symptomatic disease in HbS carriers. HbS protection against malarial disease should consider both resistance and tolerance and ongoing co-evolution with parasites.

genetics↗

bioRxiv2025

Geographical variation drives adaptive equilibrium of the P. falciparum sickle-associated mutations

The recent discovery of genetic mutations in Plasmodium falciparum--the most lethal malaria parasite--that enable it to overcome the protective effects of sickle cell trait, raises fundamental questions about the underlying biological and evolutionary interactions. Here we develop a geostatistical model to compare sickle haemoglobin genotype frequencies to the Plasmodium falciparum sickle-associated alleles across global populations, and find a robust association at multiple geographical scales, implying that sickle drives positive selection for these parasite mutations. A model of parasite evolution and an analysis of local haplotype patterns suggest that key features of these mutations - that they are polymorphic in all African populations and are mutually correlated despite lying in different genome regions - are caused by geographical variation in selection pressure, and that the alleles may have been maintained by balancing selection over timescales comparable to the age of the sickle mutation itself. The predicted impact of this host-parasite interaction on disease outcomes varies widely across populations, and functional data are needed to discover the biological mechanisms involved.

genetics↗

bioRxiv2024

Phylogenetics and genomic variation of two genetically distinct Hepatocystis clades isolated from shotgun sequencing of wild primate hosts

Hepatocystis are apicomplexan parasites nested within the Plasmodium genus that infect primates and other vertebrates, yet few isolates have been genetically characterized. Using taxonomic classification and mapping characteristics, we searched for Hepatocystis infections within publicly available, blood-derived low coverage whole genome sequence (lcWGS) data from 326 wild non-human primates (NHPs) in 17 genera. We identified 30 Hepatocystis infections in Chlorocebus and Papio samples collected from locations in west, east, and south Africa. Hepatocystis cytb sequences from Papio hosts phylogenetically clustered with previously reported isolates from multiple NHP taxa whereas sequences from Chlorocebus hosts form a separate cluster, suggesting they represent a new host-specific clade of Hepatocystis. Additionally, there was no geographic clustering of Hepatocystis isolates suggesting both clades of Hepatocystis could be found in NHPs throughout sub-Saharan Africa. Across the genome, windows of high SNP density revealed candidate hypervariable loci including Hepatocystis-specific gene families possibly involved in immune evasion and genes that may be involved in adaptation to their insect vector and hepatocyte invasion. Overall, this work demonstrates how lcWGS data from wild NHPs can be leveraged to study the evolution of apicomplexan parasites and potentially test for association between host genetic variation and parasite infection. Author SummaryNon-human primates are hosts to many species of Plasmodium, the parasites that cause malaria, and a closely related group of parasites called Hepatocystis. However, due to restrictions and challenges of sampling from wild populations, we lack a complete understanding of the breadth of diversity and distribution of these parasites. Here, we provide a framework for testing already-sampled populations for parasite infections using whole genome sequences derived from whole blood samples from the host. Following taxonomic classification of these sequences using a database of reference genomes, we mapped reads to candidate parasite genomes and used an unsupervised clustering algorithm including coverage metrics to further validate infection inferences. Through this approach, we identified 30 Hepatocystis infections from two genetically distinct clades of Hepatocystis in African non-human primates and described genes that may be under immune selection in each. Most importantly, the framework here can be applied to additional sequencing datasets from non-human primates and other vertebrate hosts as well as datasets from invertebrate vectors. Therefore, this approach could greatly improve our understanding of where these parasites are found, their host-specificity, and their evolutionary history. This framework may also be adapted to study evolution in other host-pathogen groups.

evolutionary biology↗

bioRxiv2024

Characterization of Blood Group Variants in an Omani Population by Comparison of Whole Genome Sequencing and Serology

Although blood group variation was first described over a century ago, our understanding of the genetic variation affecting antigenic expression on the red blood cell surface in many populations is lacking. This deficit limits the ability to accurately type patients, especially as serological testing is not available for all described blood groups, and targeted genotyping panels may lack rare or population-specific variants. Here, we perform serological assays across 24 antigens and whole genome sequencing on 100 Omanis, a population underrepresented in genomic databases. We inferred blood group phenotypes using the most commonly typed genetic variants. The comparison of serological to inferred phenotypes resulted in an average concordance of 96.9%. Among the 22 discordances, we identify seven known variants in four blood groups that, to our knowledge, have not been previously reported in Omanis. Incorporating these variants for phenotype inference, concordance increases to 98.8%. Additionally, we describe five candidate variants in the Lewis, Lutheran, MNS, and P1 blood groups that may affect antigenic expression, although further functional confirmation is required. Notably, we identify several blood group alleles most common in African populations, likely introduced to Oman by gene flow over the last thousand years. These findings highlight the need to evaluate individual populations and their population history when considering variants to include in genotype panels for blood group typing. This research will inform future work in blood banks and transfusion services. Key PointsO_LIUtilizing whole genome sequencing to infer blood types in Omanis demonstrates high sensitivity for most blood groups C_LIO_LIPopulation history influences blood group variation, necessitating population-specific genotype panels C_LI

genomics↗

bioRxiv2024

Large-scale genotyping and meta-analysis of PIEZO1 short tandem repeat alleles suggest a modest association with malaria susceptibility

PIEZO1 forms a mechanosensitive ion channel involved in regulating calcium levels in red blood cells. E756del, a deletion allele within a short tandem repeat (STR) in PIEZO1, is common in many African populations and has been proposed to be associated with protection from malarial disease, but epidemiological evidence has been inconsistent. Here, we use Illumina sequencing of amplicons covering the PIEZO1 STR to genotype 5,558 severe malaria cases and 8,174 population controls from The Gambia, Kenya, and Malawi. We estimate a modest effect for E756del and meta-analysis with two published studies, for a total of 8,224 cases and 10,103 controls, reveals a consistent protective effect (OR=0.93, 95% CI 0.88-0.99). By comprehensively genotyping the STR, we identify additional, less common alleles, with two (Q745del and E756ins) showing consistent, but also modest, risk effects across studies. Although allele frequency differentiation between African and non-African populations could be consistent with a selective effect, we show that it is not exceptional compared with STR variants genome wide. Thus, our results support a protective effect of E756del against risk of malaria but with a much smaller effect size than initially reported.

genetics↗

bioRxiv2024

Adaptive admixture at ACKR1 (the Duffy locus) may have shaped Plasmodium vivax prevalence in Oman

Malaria in humans is largely caused by two divergent species of Plasmodium parasites, P. vivax and P. falciparum, both of which have driven the spread of protective alleles in human populations. Notably, an erythrocyte-specific Duffy null allele (FyES) confers resistance to P. vivax malaria and has been identified as a target of strong, recent positive selection in multiple African admixed populations. Here, we evaluate evidence for selection via adaptive admixture in Oman, where compared to neighboring countries, P. vivax has recently been less common. Genetic ancestry inference using whole genome sequence data from 100 Omanis suggests 9.8% (95% CI: 7.3-12.2%) of their genetic ancestry is shared with east Africa. At the Duffy locus, we find a high frequency of FyES and an increase to 76% African ancestry. Comparing with blood group serology for the same individuals, we identify an additional Duffy-null allele that is rare but present across multiple Arabian Peninsula (AP) populations. Finally, we estimate the selection coefficient at FyES as 0.031 (95% CI: 0.029-0.034) with likely introduction at least 59 generations ago, older than estimates in other African admixed populations. Although we also observe higher frequency of some P. falciparum-protective alleles in Oman than in other AP populations, African ancestry is not enriched indicating a lack of evidence for adaptive admixture driven by P. falciparum selective pressure. Together, our analyses suggest that Omans long history with east African populations resulted in early introduction and selection for Duffy null alleles and may have influenced the prevalence of P. vivax in the region.

genetics↗

bioRxiv2021

The protective effect of sickle cell haemoglobin against severe malaria depends on parasite genotype

Host genetic factors can confer resistance against malaria, raising the question of whether this has led to evolutionary adaptation of parasite populations. In this study we investigated the correlation between host and parasite genetic variation in 4,171 Gambian and Kenya children ascertained with severe malaria due to Plasmodium falciparum. We identified a strong association between sickle haemoglobin (HbS) in the host and variation in three regions of the parasite genome, including nonsynonymous variants in the acyl-CoA synthetase family member PfACS8 on chromosome 2, in a second region of chromosome 2, and in a region containing structural variation on chromosome 11. The HbS-associated parasite alleles are in strong linkage disequilibrium and have frequencies which covary with the frequency of HbS across populations, in particular being much more common in Africa than other parts of the world. The estimated protective effect of HbS against severe malaria, as determined by comparison of cases with population controls, varies greatly according to the parasite genotype at these three loci. These findings open up a new avenue of enquiry into the biological and epidemiological significance of the HbS-associated polymorphisms in the parasite genome, and the evolutionary forces that have led to their high frequency and strong linkage disequilibrium in African P. falciparum populations.

genetics↗

bioRxiv2019

New insights into malaria susceptibility from the genomes of 17,000 individuals from Africa, Asia, and Oceania

We conducted a genome-wide association study of host resistance to severe Plasmodium falciparum malaria in over 17,000 individuals from 11 malaria-endemic countries, undertaking a wide ranging analysis which identifies five replicable associations with genome-wide levels of evidence. Our findings include a newly implicated variant on chromosome 6 associated with risk of cerebral malaria, and the discovery of an erythroid-specific transcription start site underlying the association in ATP2B4. Previously reported HLA associations cannot be replicated in this dataset. We estimate substantial heritability of severe malaria (h2 ~ 23%), of which around 10% is explained by the currently identified associations. Our dataset will provide a major building block for future research on the genetic determinants of disease in these diverse human populations.

genetics↗

bioRxiv2016

A structural variant encoding hybrid glycophorins is associated with resistance to severe malaria

Plasmodium falciparum invades human red blood cells by a series of interactions between host and parasite surface proteins. Here we analyse whole genome sequence data from worldwide human populations, including 765 new genomes from across sub-Saharan Africa, and identify a diverse array of large copy number variants affecting the host invasion receptor genes GYPA and GYPB. We find that a nearby reported association with severe malaria is explained by a complex structural variant that involves the loss of GYPB and gain of two hybrid genes, each with a GYPB extracellular domain and GYPA intracellular domain. This variant reduces the risk of severe malaria by 40% and has recently risen in frequency in parts of Kenya. We show that the structural variant encodes the Dantu blood group antigen, and therefore a serologically distinct red cell phenotype. These findings demonstrate that structural variation of red blood cell invasion receptors is associated with natural resistance to P. falciparum malaria.

genomics↗