Host Genomic Variation Research Articles

Host genomic variation shapes gut microbiome diversity in threespine stickleback fish.

A major focus of host-microbe research is to understand how genetic differences, of various magnitudes, among hosts translate to differences in their microbiomes. This has been challenging for animal hosts, including humans, because it is difficult to control environmental variables tightly enough to isolate direct genetic effects on the microbiome. Our work in stickleback fish is a significant contribution because our experimental approach allowed strict control over environmental factors, including standardization of the microbiome from the earliest stage of development and unrestricted co-housing of fish in a truly common environment. Furthermore, we measured host genetic variation over 2,000 regions of the stickleback genome, comparing this information and microbiome composition data among fish from very similar and very different genetic backgrounds. Our findings highlight how differences in the host genome influence microbiome diversity and make a case for future manipulative microbiome experiments that use host systems with naturally occurring genetic variation.

Intrapopulation adaptive variance supports thermal tolerance in a reef-building coral

Coral holobionts are multi-species assemblages, which adds significant complexity to genotype-phenotype connections underlying ecologically important traits like coral bleaching. Small scale heterogeneity in bleaching is ubiquitous in the absence of strong environmental gradients, which provides adaptive variance needed for the long-term persistence of coral reefs. We used RAD-seq, qPCR and LC-MS/MS metabolomics to characterize host genomic variation, symbiont community and biochemical correlates in two bleaching phenotypes of the vertically transmitting coral Montipora capitata. Phenotype was driven by symbiosis state and host genetic variance. We documented 5 gene ontologies that were significantly associated with both the binary bleaching phenotype and symbiont composition, representing functions that confer a phenotype via host-symbiont interactions. We bred these corals and show that symbiont communities were broadly conserved in bulk-crosses, resulting in significantly higher survivorship under temperature stress in juveniles, but not larvae, from tolerant parents. Using a select and re-sequence approach, we document numerous gene ontologies selected by heat stress, some of which (cell signaling, antioxidant activity, pH regulation) have unique selection dynamics in larvae from thermally tolerant parents. These data show that vertically transmitting corals may have an adaptive advantage under climate change if host and symbiont variance interact to influence bleaching phenotype.

Genomic heterozygosity is associated with parasite abundance, but the effects are not mediated by host condition.

The online version contains supplementary material available at 10.1007/s10682-022-10175-8.

A Systematic Review of Host Genomic Variation and Neuropsychological Outcomes for Pediatric Cancer Survivors.

Pediatric survivors of brain tumors and acute lymphoblastic leukemia (ALL) are at risk for long-term deficits in their neuropsychological functioning. Researchers have begun examining associations between germline single nucleotide polymorphisms (SNPs), which interact with cancer treatment, and neuropsychological outcomes. This review synthesizes the impact of treatment-related toxicity from germline SNPs by neuropsychological domain (i.e., working memory, processing speed, psychological functioning) in pediatric survivors. By focusing on specific neuropsychological domains, this review will examine outcome measurement and critique methodology. Fourteen studies were identified and included in this review using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). All studies were published in peer-reviewed journals in English by November 24th, 2021. Reviewed studies were not of sufficient quality for a meta-analysis due to varying measurement strategies, gaps in reported descriptive variables, and low power. All neuropsychological domains evaluated in this review had associations with SNPs, except fine motor and visual integration abilities. Only five SNPs had consistent neuropsychological findings in more than one study or cohort. Future research and replication studies should use validated measures of discrete skills that are central to empirically validated models of survivors' long-term outcomes (i.e., attention, working memory, processing speed). Researchers should examine SNPs across pathophysiological pathways to investigate additive genetic risk in pediatric cancer survivors. Two SNPs were identified that confer resiliency in neuropsychological functioning, and future work should investigate resiliency genotypes and their underlying biological mechanisms.

Host genetic factors associated with the range limit of a European hantavirus.

The natural host ranges of many viruses are restricted to very specific taxa. Little is known about the molecular barriers between species that lead to the establishment of this restriction or generally prevent virus emergence in new hosts. Here, we identify genomic polymorphisms in a natural rodent host associated with a strong genetic barrier to the transmission of European Tula orthohantavirus (TULV). We analysed the very abrupt spatial transition between two major phylogenetic clades in TULV across the comparatively much wider natural hybrid zone between evolutionary lineages of their reservoir host, the common vole (Microtus arvalis). Genomic scans of 79,225 single nucleotide polymorphisms (SNPs) in 323 TULV‐infected host individuals detected 30 SNPs that were consistently associated with the TULV clades CEN.S or EST.S in two replicate sampling transects. Focusing the analysis on 199 voles with evidence of genomic admixture at the individual level (0.1–0.9) supported statistical significance for all 30 loci. Host genomic variation at these SNPs explained up to 37.6% of clade‐specific TULV infections. Genes in the vicinity of associated SNPs include SAHH, ITCH and two members of the Syngr gene family, which are involved in functions related to immune response or membrane transport. This study demonstrates the relevance of natural hybrid zones as systems not only for studying processes of evolutionary divergence and speciation, but also for the detection of evolving genetic barriers for specialized parasites.

The influence of human genetic variation on Epstein\u2013Barr virus sequence diversity

Epstein–Barr virus (EBV) is one of the most common viruses latently infecting humans. Little is known about the impact of human genetic variation on the large inter-individual differences observed in response to EBV infection. To search for a potential imprint of host genomic variation on the EBV sequence, we jointly analyzed paired viral and human genomic data from 268 HIV-coinfected individuals with CD4 + T cell count < 200/mm3 and elevated EBV viremia. We hypothesized that the reactivated virus circulating in these patients could carry sequence variants acquired during primary EBV infection, thereby providing a snapshot of early adaptation to the pressure exerted on EBV by the individual immune response. We searched for associations between host and pathogen genetic variants, taking into account human and EBV population structure. Our analyses revealed significant associations between human and EBV sequence variation. Three polymorphic regions in the human genome were found to be associated with EBV variation: one at the amino acid level (BRLF1:p.Lys316Glu); and two at the gene level (burden testing of rare variants in BALF5 and BBRF1). Our findings confirm that jointly analyzing host and pathogen genomes can identify sites of genomic interactions, which could help dissect pathogenic mechanisms and suggest new therapeutic avenues.

Genomics: the host's genotype and its relevance to bovine respiratory disease.

Genomic variation exists in cattle that affects their susceptibility to the complex of pathogens responsible for bovine respiratory disease (BRD). Heritability estimates and genome-wide association analyses (GWAA) support the role of host genomic variation in BRD susceptibility. Heritability estimates for BRD susceptibility range from 0.02 to 0.29 depending on the population, the definition of the disease, and the accuracy of diagnosis. GWAA have identified genomic regions (loci) associated with BRD in beef and dairy cattle based on a variety of BRD diagnostic criteria. National standards need to be developed for BRD diagnostics and reporting to facilitate selection. Commercial genotyping is available to predict BRD susceptibility in dairy cattle and for the selection of replacement animals. Disease pathogen profiles vary by region and can result in genetic heterogeneity where different loci are important for susceptibility to different BRD pathogens. Although the identification of the BRD pathogens may not be critical for treatment, it is of paramount importance in identifying loci that render cattle susceptible to the disease. Identification of loci associated with host susceptibility to BRD provides a foundation for genomic selection to reduce disease and opens the possibilities to a better understanding of how the host defends itself.

Recent Advances in Arsenic Research: Significance of Differential Susceptibility and Sustainable Strategies for Mitigation.

Arsenic contamination in drinking water and associated adverse outcomes are one of the major health issues in more than 50 countries worldwide. The scenario is getting even more detrimental with increasing number of affected people and newer sites reported from all over the world. Apart from drinking water, the presence of arsenic has been found in various other dietary sources. Chronic arsenic toxicity affects multiple physiological systems and may cause malignancies leading to death. Exposed individuals, residing in the same area, developed differential dermatological lesion phenotypes and varied susceptibility toward various other arsenic-induced disease risk, even after consuming equivalent amount of arsenic from the similar source, over the same duration of time. Researches so far indicate that differential susceptibility plays an important role in arsenic-induced disease manifestation. In this comprehensive review, we have identified major population-based studies of the last 20 years, indicating possible causes of differential susceptibility emphasizing arsenic methylation capacity, variation in host genome (single nucleotide polymorphism), and individual epigenetic pattern (DNA methylation, histone modification, and miRNA expression). Holistic multidisciplinary strategies need to be implemented with few sustainable yet cost-effective solutions like alternative water source, treatment of arsenic-contaminated water, new adaptations in irrigation system, simple modifications in cooking strategy, and dietary supplementations to combat this menace. Our review focuses on the present perspectives of arsenic research with special emphasis on the probable causes of differential susceptibility toward chronic arsenic toxicity and sustainable remediation strategies.

Sarcoptic mange severity is associated with reduced genomic variation and evidence of selection in Yellowstone National Park wolves (Canis lupus).

Population genetic theory posits that molecular variation buffers against disease risk. Although this “monoculture effect” is well supported in agricultural settings, its applicability to wildlife populations remains in question. In the present study, we examined the genomics underlying individual‐level disease severity and population‐level consequences of sarcoptic mange infection in a wild population of canids. Using gray wolves (Canis lupus) reintroduced to Yellowstone National Park (YNP) as our focal system, we leveraged 25 years of observational data and biobanked blood and tissue to genotype 76,859 loci in over 400 wolves. At the individual level, we reported an inverse relationship between host genomic variation and infection severity. We additionally identified 410 loci significantly associated with mange severity, with annotations related to inflammation, immunity, and skin barrier integrity and disorders. We contextualized results within environmental, demographic, and behavioral variables, and confirmed that genetic variation was predictive of infection severity. At the population level, we reported decreased genome‐wide variation since the initial gray wolf reintroduction event and identified evidence of selection acting against alleles associated with mange infection severity. We concluded that genomic variation plays an important role in disease severity in YNP wolves. This role scales from individual to population levels, and includes patterns of genome‐wide variation in support of the monoculture effect and specific loci associated with the complex mange phenotype. Results yielded system‐specific insights, while also highlighting the relevance of genomic analyses to wildlife disease ecology, evolution, and conservation.

Integration Analysis of m6A-SNPs and eQTLs Associated With Sepsis Reveals Platelet Degranulation and Staphylococcus aureus Infection are Mediated by m6A mRNA Methylation.

Sepsis is a major threat with high mortality rate for critically ill patients. Response to pathogen infection by the host immune system is a key biological process involved in the onset and development of sepsis. Heterogeneous host genome variation, especially single nucleotide polymorphisms (SNPs), has long been suggested to contribute to differences in disease progression. However, the function of SNPs located in non-coding regions remains to be elucidated. Recently, m6A mRNA modification levels were revealed to differ at SNPs. As m6A is a crucial regulator of gene expression, these SNPs might control genes by changing the m6A level on mRNA. To investigate the potential role of m6A SNPs in sepsis, we integrated m6A-SNP and expression quantitative trait loci (eQTLs) data. Analysis revealed 15,720 m6A-cis-eQTLs and 381 m6A-trans-eQTLs associated with sepsis. We identified 1321 genes as locations of m6A-cis-eQTLs. These were enriched in platelet degranulation and Staphylococcus aureus infection pathways, which are vital for the pathophysiological process of sepsis. We conclude that m6A modification of mRNA plays a very important role in sepsis, with m6A-cis-eQTLs potentially having the most effect on individual variation in sepsis progression.

Association of gut microbiota composition and copy number variation with Kasai procedure outcomes in infants with biliary atresia

Abstract Biliary atresia (BA) is the most important cause of liver cirrhosis in children. Even with an early Kasai procedure, some patients fail to establish bile drainage. The roles of the gut microbiota and host genetic variation remain unclear. We studied the sequential fecal microbiome postoperatively and performed genome-wide scanning of copy number variation in two BA infants with different outcomes. Our results showed decreased gut microbiota diversity and genetic loss at 7q36.3 in the patient with persistent jaundice. Bifidobacterium breve was increased 1 month after a successful operation in the other patient. Our findings suggest that interactions between host genome variation and the gut microbiota are novel biomarkers for disease progression or resolution in BA.

Host Genome Variation is Associated with Neurocognitive Outcome in Survivors of Pediatric Medulloblastoma

Host genome analysis is a promising source of predictive information for long-term morbidity in cancer survivors. However, studies on genetic predictors of long-term outcome, particularly neurocognitive function following chemoradiation in pediatric oncology, are limited. Here, we evaluated variation in host genome of long-term survivors of medulloblastoma and its association with neurocognitive outcome. Whole-genome sequencing was conducted on peripheral blood of long-term survivors of pediatric medulloblastoma who also completed neuropsychological testing. Cognitively impaired and less impaired survivors did not differ in exposure to chemoradiation therapy or age at treatment. Unsupervised consensus clustering yielded two distinct variant clusters that were significantly associated with neurocognitive outcome. Interestingly, 34 of the 36 significant variants were found in noncoding DNA regions with unknown regulatory function. A separate unsupervised cluster analysis of variants within DNA repair genes identified discrete variant groups that were not associated with neurocognitive outcome, suggesting that variations in genes corresponding to a single functional group may be insufficient to predict long-term outcome alone. These findings are supportive of the presence of a genetic diathesis for treatment-related neurocognitive morbidity in medulloblastoma that may be driven by variation in noncoding regulatory elements.

Genome-wide associations identify novel candidate loci associated with genetic susceptibility to tuberculosis in wild boar

Tuberculosis (TB) affects a wide range of host species worldwide. Understanding host-pathogen co-evolution remains a global challenge owing to complex interactions among host genetic factors, pathogen traits and environmental conditions. We used an endemic wild boar population that had undergone a huge increase in Mycobacterium bovis infection prevalence, from 45% in 2002/06 to 83% in 2009/12, to understand the effects of host genetics on host TB outcomes and disease dynamics. Host genomic variation was characterized using a high-density single nucleotide polymorphism (SNP) array, while host TB phenotype was assessed using both gross pathology and mycobacterial culture. Two complementary genome-wide association (GWAS) analyses were conducted: (i) infected-uninfected; and (ii) 2002/06–2009/12. The SNPs with the highest allelic frequency differences between time-periods and TB outcomes were identified and validated in a large dataset. In addition, we quantified the expression levels of some of their closest genes. These analyses highlighted various SNPs (i.e. rs81465339, rs81394585, rs81423166) and some of the closest genes (i.e. LOC102164072, BDNF/NT-3, NTRK2, CDH8, IGSF21) as candidates for host genetic susceptibility. In addition to TB-driven selection, our findings outline the putative role of demographic events in shaping genomic variation in natural populations and how population crashes and drift may impact host genetic susceptibility to TB over time.

Common Genetic Variants in Trypsin Regulating Genes Are Associated with AsparAginase-Associated Pancreatitis in Children with Acute Lymphoblastic Leukemia: A Ponte Di Legno Toxicity Working Group Study

Background: Asparaginase-associated pancreatitis (AAP) is a well-known toxicity of childhood acute lymphoblastic leukemia (ALL) therapy. Recent multi-trial group phenotyping of 465AAP caseshas documented severe complications to AAP, including 8% risk of needing assisted mechanical ventilation, 26% risk of developing pancreatic pseudocysts and 9% risk of developing persisting diabetes (Wolthers et al. Lancet Oncology, 2017) . Investigation of host genome variation associated with AAP has been limited by varying phenotype definition, inclusion criteria and small study sizes.Objectives and Methods: To investigate genetic variants associated with risk of developing AAP, this genome-wide association study reports data on 1544 children (1.0−17.9 years) from 10 ALL trial groups treated with ALL from January 2000−January 2016. The Ponte di Legno toxicity working group consensus definition (Schmiegelow et al. Lancet Oncology, 2016) was used to diagnose AAP: At least two of i) amylase, pancreatic amylase, or pancreatic lipase >3x upper normal limit (UNL), ii) abdominal pain, iii) imaging compatible with AAP. Controls included children treated for ALL with verified completion of intended asparaginase therapy, 78% of whom (1024/1320) received at least 8 injections of PEG-asparaginase without developing AAP. Germline DNA obtained after clinical remission was genotyped on Illumina Infinium Omni2.5exome-8 BeadChip arrays. Association analyses were done in PLINK and annotation in Ensembl.Results: Of 1564 patients passing genotype quality control, 244 had AAP. 205 of 244 (84%) of cases and 1185/1320 (90%) of controls were of European ancestry. Median age was 8.1 years (IQR 4.3−13.1) and 5 (IQR: 3−9) for cases and controls, respectively. After filtering, 1401908 single nucleotide polymorphisms (SNPs) with a minor allele frequency above 1% were analyzed. In logistic regression analysis, adjusting for age and ancestry, the variant rs62228256 (reference allele=C, minor allele=T (C>T)) on 20q13.2 had the strongest association to AAP (OR=3.75; 95% CI 2.33−6.04; p=5.2∙10-8). rs62228256 is located in a non-coding region without known regulatory effects. rs13228878 (A>G; OR=0.61; 95% CI 0.5−0.76; p=7.1∙10-6) and rs10273639 (C>T; OR=0.62; 95% CI 0.5−0.77; p =1.1∙10-5) were among the top 30 SNPs most significantly associated to AAP. They are in high linkage disequilibrium (R2=0.94) and located in the PRSS1-PRSS2 locus on chromosome 7. The rs13228878 A risk allele was not associated with level of amylase (p=0.1) or lipase (p=0,68) at diagnosis of AAP, age at diagnosis of AAP (p=0.63), or risk of pseudocysts (p=0.78). Using identical diagnostic criteria for pancreatitis, the major C allele in rs10273639 has been associated with pancreatitis risk in adults (Whitcomb et al. Nature Genetics, 2012; Masson et al. Gut, 2017) with identical risk allele and similar odds ratios. PRSS1 and PRSS2 encode cationic and anionic trypsinogen, respectively. rs10273639 is an expressive quantitative locus for PRSS1 and the C risk-variant is associated with elevated expression of trypsinogen in pancreatic tissue. Gain of function mutations in PRSS1, known from hereditary pancreatitis, lead to increased autoactivation, increased intra-acinar trypsin levels, and increased risk of auto-digestion leading to pancreatitis. Further investigation of previously validated SNPs known to regulate trypsin activation gave the following results for associations with AAP; rs17107315 in pancreatic secretory trypsin inhibitor (SPINK1; OR=2.87; 95% CI 1.36−5.8; p=4∙10-3), rs10436957 in chymotrypsin C (CTRC ; OR=0.69; 95% CI 0.53−0.89; p=5∙10-3) and rs4409525 in Claudin-2 (CLDN2 ; OR=1.41; 95% CI 1.08−1.83; p=1∙10-2). In total, 207 out of 244 cases were homozygous for the risk allele in rs13228878 (n=104), rs17107315 (n=1), rs10436957 (n=165) and/or rs4409525 (n=16). However, no significant additive effect of having more than one risk allele was found.Conclusion: Children who develop AAP possess the same pancreatitis risk variants as adults with non-asparaginase associated pancreatitis. This shared genetic disposition may facilitate research into pathogenesis and identification of effective interventions towards AAP. DisclosuresNo relevant conflicts of interest to declare.

The identification of copy number variation of CD209 (DCSIGN) gene among dengue patients from peninsular Malaysia

Dengue is one of the most important arthropod-borne viral infection in human. Numerous factors have been attributed to the severity of dengue infection, including host genome variation. Genomic structural variations such as copy number variation (CNVs), constitutes a substantial fraction of the human genetic variability, but its role in susceptibility to infectious diseases is not well understood. Previous studies have confirmed the role of host candidate gene CD209 variation in the susceptibility to dengue. Although the CNV of this gene has been reported in the Database of Genomic Variants (DGV), its characterization has yet to be studied. Therefore we aimed to characterize the CNV of the candidate gene CD209 among dengue fever and dengue hemorrhagic fever patients from Malaysia. We found that 19% of the dengue patients had copy number loss (copy number<2), while 36% had copy number gain (copy number>2). Analysis of genetic association between the gene copy number and vascular leakage in dengue revealed no statistical significance (P=0.9043), suggesting minimal contribution of CD209 CNV in the aetiology of dengue hemorrhagic fever. Further investigation with higher number of samples, however, is needed to confirm this finding.

The canine X chromosome is a sink for canine endogenous retrovirus transposition

The domestic dog has experienced intensive artificial selection to preserve breed phenotypes. We predicted this stress activates transposition of canine endogenous retroviruses (CERVs) to restore host genomic variation. Subsequent epigenetic silencing via DNA methylation would prevent rampant amplification. Consequently, recently inserted CERVs would show breed- and species-specific patterns of insertion and methylation. We annotated 477 CERVs and employed a Kimura two-parameter model to estimate their insertion date. We found the X chromosome to be enriched with CERV insertions, primarily in non-coding regions. With reduced representation bisulfite sequencing data from 55 dogs and 34 gray wolves, we assessed CERV methylation. Our results suggest that most CERVs inserted before species divergence and are hyper-methylated. CERV methylation is neither breed- nor species-specific and has a significant inverse correlation with age. Therefore, CERVs may impact gene expression via cis-regulation, especially on the X chromosome, but not active transposition.

Horizontal gene transfer of chromosomal Type II toxin-antitoxin systems of Escherichia coli.

Type II toxin-antitoxin systems (TAs) are small autoregulated bicistronic operons that encode a toxin protein with the potential to inhibit metabolic processes and an antitoxin protein to neutralize the toxin. Most of the bacterial genomes encode multiple TAs. However, the diversity and accumulation of TAs on bacterial genomes and its physiological implications are highly debated. Here we provide evidence that Escherichia coli chromosomal TAs (encoding RNase toxins) are 'acquired' DNA likely originated from heterologous DNA and are the smallest known autoregulated operons with the potential for horizontal propagation. Sequence analyses revealed that integration of TAs into the bacterial genome is unique and contributes to variations in the coding and/or regulatory regions of flanking host genome sequences. Plasmids and genomes encoding identical TAs of natural isolates are mutually exclusive. Chromosomal TAs might play significant roles in the evolution and ecology of bacteria by contributing to host genome variation and by moderation of plasmid maintenance.

Host genome variations and risk of infections during induction treatment for childhood acute lymphoblastic leukaemia

To investigate association of host genomic variation and risk of infections during treatment for childhood acute lymphoblastic leukaemia (ALL). We explored association of 34,000 single-nucleotide polymorphisms (SNPs) related primarily to pharmacogenomics and immune function to risk of infections among 69 ALL patients on induction therapy. Forty-eight (70%) patients experienced infectious events including 23 with positive blood cultures. Infectious events and positive blood cultures were associated significantly with 24 and 21 SNPs, respectively (P < 0.01). Classification and regression tree analysis demonstrated rs11033797 (OR51F1), rs2835265 (CBR1), rs28627172 (POLDIP3) and rs1129844 (CCL11) to be predictive of outcome. Among 61 patients for whom read-outs were available for all four SNPs, 40 of 41 patients with the worst SNP profile experienced at least one infectious event compared with five of the remaining 20 patients (Hazard ratio 9.0, 95% CI 3.4-23.5, which was unchanged after adjustments for neutrophil counts). Pathway analysis identified variations in 'G-protein-coupled receptor (GPCR) downstream signalling', 'Bile acid and bile salt metabolism' and 'Class I MHC-mediated antigen processing and presentation' to be highly predictive of infections. Our data indicate that host genomic profiling may predict the risk of infections during induction therapy. This may facilitate development of individualised supportive care.

Commentary: Lifestyle factors and colorectal cancer microsatellite instability--molecular pathological epidemiology science, based on unique tumour principle

Commentary: Lifestyle factors and colorectal cancer microsatellite instability--molecular pathological epidemiology science, based on unique tumour principle