Number Of Single Nucleotide Polymorphisms Research Articles

Double-digest RAD sequencing outperforms microsatellite loci at assigning paternity and estimating relatedness: A proof of concept in a highly promiscuous bird.

Information on genetic relationships among individuals is essential to many studies of the behaviour and ecology of wild organisms. Parentage and relatedness assays based on large numbers of single nucleotide polymorphism (SNP) loci hold substantial advantages over the microsatellite markers traditionally used for these purposes. We present a double-digest restriction site-associated DNA sequencing (ddRAD-seq) analysis pipeline that, as such, simultaneously achieves the SNP discovery and genotyping steps and which is optimized to return a statistically powerful set of SNP markers (typically 150-600 after stringent filtering) from large numbers of individuals (up to 240 per run). We explore the trade-offs inherent in this approach through a set of experiments in a species with a complex social system, the variegated fairy-wren (Malurus lamberti) and further validate it in a phylogenetically broad set of other bird species. Through direct comparisons with a parallel data set from a robust panel of highly variable microsatellite markers, we show that this ddRAD-seq approach results in substantially improved power to discriminate among potential relatives and considerably more precise estimates of relatedness coefficients. The pipeline is designed to be universally applicable to all bird species (and with minor modifications to many other taxa), to be cost- and time-efficient, and to be replicable across independent runs such that genotype data from different study periods can be combined and analysed as field samples are accumulated.

Two Groups of Cocirculating, Epidemic Clostridiodes difficile Strains Microdiversify through Different Mechanisms.

Clostridiodes difficile strains from the NAPCR1/ST54 and NAP1/ST01 types have caused outbreaks despite of their notable differences in genome diversity. By comparing whole genome sequences of 32 NAPCR1/ST54 isolates and 17 NAP1/ST01 recovered from patients infected with C. difficile we assessed whether mutation, homologous recombination (r) or nonhomologous recombination (NHR) through lateral gene transfer (LGT) have differentially shaped the microdiversification of these strains. The average number of single nucleotide polymorphisms (SNPs) in coding sequences (NAPCR1/ST54 = 24; NAP1/ST01 = 19) and SNP densities (NAPCR1/ST54 = 0.54/kb; NAP1/ST01 = 0.46/kb) in the NAPCR1/ST54 and NAP1/ST01 isolates was comparable. However, the NAP1/ST01 isolates showed 3× higher average dN/dS rates (8.35) that the NAPCR1/ST54 isolates (2.62). Regarding r, whereas 31 of the NAPCR1/ST54 isolates showed 1 recombination block (3,301–8,226 bp), the NAP1/ST01 isolates showed no bases in recombination. As to NHR, the pangenome of the NAPCR1/ST54 isolates was larger (4,802 gene clusters, 26% noncore genes) and more heterogeneous (644 ± 33 gene content changes) than that of the NAP1/ST01 isolates (3,829 gene clusters, ca. 6% noncore genes, 129 ± 37 gene content changes). Nearly 55% of the gene content changes seen among the NAPCR1/ST54 isolates (355 ± 31) were traced back to MGEs with putative genes for antimicrobial resistance and virulence factors that were only detected in single isolates or isolate clusters. Congruently, the LGT/SNP rate calculated for the NAPCR1/ST54 isolates (26.8 ± 2.8) was 4× higher than the one obtained for the NAP1/ST1 isolates (6.8 ± 2.0). We conclude that NHR-LGT has had a greater role in the microdiversification of the NAPCR1/ST54 strains, opposite to the NAP1/ST01 strains, where mutation is known to play a more prominent role.

Performance and precision of double digestion RAD (ddRAD) genotyping in large multiplexed datasets of marine fish species

The development of Genotyping-By-Sequencing (GBS) technologies enables cost-effective analysis of large numbers of Single Nucleotide Polymorphisms (SNPs), especially in “non-model” species. Nevertheless, as such technologies enter a mature phase, biases and errors inherent to GBS are becoming evident. Here, we evaluated the performance of double digest Restriction enzyme Associated DNA (ddRAD) sequencing in SNP genotyping studies including high number of samples. Datasets of sequence data were generated from three marine teleost species (>5500 samples, >2.5 × 1012 bases in total), using a standardized protocol. A common bioinformatics pipeline based on STACKS was established, with and without the use of a reference genome. We performed analyses throughout the production and analysis of ddRAD data in order to explore (i) the loss of information due to heterogeneous raw read number across samples; (ii) the discrepancy between expected and observed tag length and coverage; (iii) the performances of reference based vs. de novo approaches; (iv) the sources of potential genotyping errors of the library preparation/bioinformatics protocol, by comparing technical replicates. Our results showed use of a reference genome and a posteriori genotype correction improved genotyping precision. Individual read coverage was a key variable for reproducibility; variance in sequencing depth between loci in the same individual was also identified as an important factor and found to correlate to tag length. A comparison of downstream analysis carried out with ddRAD vs single SNP allele specific assay genotypes provided information about the levels of genotyping imprecision that can have a significant impact on allele frequency estimations and population assignment. The results and insights presented here will help to select and improve approaches to the analysis of large datasets based on RAD-like methodologies.

Association of human platelet antigen polymorphisms with platelet count and mean platelet volume

ABSTRACTObjectives: Although recent genome-wide association studies have identified a number of single nucleotide polymorphisms associated with platelet count and mean platelet volume (MPV), it is unclear whether polymorphisms in the human platelet antigens (HPA) genes are associated with platelet count and MPV. The aim of this study was to determine the association of the HPA-2, -3, -5 and -15 polymorphisms with platelet count and MPV.Methods: The HPA were genotyped by 5ˊ-nuclease assay in 139 healthy Chinese Han individuals, while platelet count and MPV from the same samples were measured using an hematology cell analyzer.Results: The platelet count was significantly lower in the individuals with the HPA-2aa genotype compared to those with HPA-2ab (P = 0.020), and significantly higher in individuals with HPA-5aa and HPA-15aa genotypes compared to those with HPA-5ab (P = 0.045) and HPA-15ab/bb (P = 0.032), respectively. On the other hand, platelet count of individuals with the HPA-3aa and HPA-3ab/bb genotypes did not differ significantly (P = 0.084). The MPV was significantly lower in individuals with HPA-5aa genotype compared to those with HPA-5ab (P = 0.001) but did not differ among the HPA-2, -3 and -15 genotypes. Furthermore, HPA-2, -5 and -15 polymorphisms were identified as independent factors for the platelet count and HPA-5 polymorphism was shown as an independent factor for MPV.Conclusions: This study demonstrates that HPA-2, -5 and -15 polymorphisms are associated with the platelet count while HPA-5 polymorphism is associated with MPV. This finding will further our understanding of the association of HPA polymorphisms with platelet-related diseases.

Identification of candidate genes associated with fibromyalgia susceptibility in southern Spanish women: the al-\xc1ndalus project

BackgroundCandidate-gene studies on fibromyalgia susceptibility often include a small number of single nucleotide polymorphisms (SNPs), which is a limitation. Moreover, there is a paucity of evidence in Europe. Therefore, we compared genotype frequencies of candidate SNPs in a well-characterised sample of Spanish women with fibromyalgia and healthy non-fibromyalgia women.MethodsA total of 314 women with a diagnosis of fibromyalgia (cases) and 112 non-fibromyalgia healthy (controls) women participated in this candidate-gene study. Buccal swabs were collected for DNA extraction. Using TaqMan™ OpenArray™, we analysed 61 SNPs of 33 genes related to fibromyalgia susceptibility, symptoms, or potential mechanisms.ResultsWe observed that the rs841 and rs1799971 GG genotype was more frequently observed in fibromyalgia than in controls (p = 0.04 and p = 0.02, respectively). The rs2097903 AT/TT genotypes were also more often present in the fibromyalgia participants than in their control peers (p = 0.04). There were no differences for the remaining SNPs.ConclusionsWe identified, for the first time, associations of the rs841 (guanosine triphosphate cyclohydrolase 1 gene) and rs2097903 (catechol-O-methyltransferase gene) SNPs with higher risk of fibromyalgia susceptibility. We also confirmed that the rs1799971 SNP (opioid receptor μ1 gene) might confer genetic risk of fibromyalgia. We did not adjust for multiple comparisons, which would be too stringent and yield to non-significant differences in the genotype frequencies between cases and controls. Our findings may be biologically meaningful and informative, and should be further investigated in other populations. Of particular interest is to replicate the present study in a larger independent sample to confirm or refute our findings. On the other hand, by including 61 SNPs of 33 candidate-genes with a strong rationale (they were previously investigated in relation to fibromyalgia susceptibility, symptoms or potential mechanisms), the present research is the most comprehensive candidate-gene study on fibromyalgia susceptibility to date.

Bleeding predictors in patients following venous thromboembolism treated with vitamin K antagonists: Association with increased number of single nucleotide polymorphisms

IntroductionSingle nucleotide polymorphisms (SNP) in genes encoding proteins involved in metabolism and action of vitamin K antagonists (VKA) affect anticoagulation stability. We investigated how those polymorphisms influence bleeding rates in patients following venous thromboembolism (VTE). Materials and methodsIn 324 patients following unprovoked VTE, 143 (44%) on warfarin and 181 (56%) on acenocoumarol, we recorded bleeds within the preceding 24 months. We assessed eight SNP, including those in cytochrome P450 isoform 2C9 (CYP2C9) and isoform 4F2 (CYP4F2), vitamin K epoxide reductase complex subunit 1 (VKORC1), gamma-glutamyl carboxylase (GGCX), apolipoprotein E (APOE) and multidrug resistance gene 1 (MDR1). ResultsWithin 48 months before enrolment, bleeding events occurred in 80 (25%) patients, including 14 (4%) major bleeds. Patients with bleeds had 16.2% lower median time in therapeutic range (TTR) and were more often carriers of CYP2C9*3 variant (26 [33%] vs. 19 [8%], p < 0.001) compared with the remainder. Bleeding occurred more frequently in patients with ≥4 SNP compared with the remainder (27 [34%] vs. 47 [19%], p = 0.009) with no intergroup differences of TTR. Number of SNP was one of the predictors of any bleeding. The regression model for major bleeding including factors such as CYP2C9*3 c. 1075 C, VKORC1 c. -1639 A and APOE c. 388 C showed good predictive ability (area under the curve - 0.79). ConclusionsIn VTE patients on the maintenance treatment with VKA, bleeding episodes are associated with CYP2C9 gene variations and increased number of SNP of genes involved in the action and metabolism of VKA.

Impact of Multiple Single-Nucleotide Polymorphisms Within mprF on Daptomycin Resistance in Staphylococcus aureus.

A number of single nucleotide polymorphisms (SNPs) within the mprF open reading frame (ORF) have been associated with daptomycin-resistance (DAP-R) in Staphylococcus aureus. Such SNPs have been found throughout the mprF ORF, although there are clearly preferred "hot spots" within this gene frequently linked to DAP-R phenotype. These mprF SNPs are often correlated with a gain-in-function phenotype, either in terms of increased production (synthase activity) and/or enhanced translocation (translocase activity) of lysyl-phosphatidylglycerol (L-PG) within its cell membrane. However, it is unclear if multiple hot spot mprF SNPs can accumulate within mprF ORFs and cause additive elevations of DAP minimum inhibitory concentrations (MICs). In this study, we used a previously well-characterized plasmid complementation system in S. aureus Newman ΔmprF mutant to express: (1) single point-mutated forms of mprF ORFs cloned from two DAP-R S. aureus strains (mprFS295L or mprFT345A) and (2) dual point-mutated forms of mprF ORFs simultaneously harboring SNPs in the central bifunctional domain and synthase domain in MprF, respectively (mprFS295L+L826F or mprFT345A+L826F). The current study revealed that, although individual hot spot point mutations within mprF ORF can recapitulate signature DAP-R-associated phenotypes (i.e., increased DAP MICs, enhanced surface positive charge, and increased L-PG synthesis), accumulation of such hot spot point mutations paradoxically caused reduction in these latter three metrics.

Epidemiological aspects of healthcare-associated infections and microbial genomics.

Hospital-acquired infections (HAIs) are a cause of continuously increasing morbidity and mortality. Most of these infections are caused by a limited set of bacterial species, which share the capability to efficiently spread from patient to patient and to easily acquire antibiotic resistance determinants. This renders correct and rapid species identification and antibiotic susceptibility testing (AST) important and underscores the relevance of bacterial epidemiological typing. The latter is needed for the sensitive detection and exact tracing of nosocomial spread of these potentially multidrug-resistant microorganisms (MDRO). Many microbial typing technologies have been developed and put to some level of executive practice, but it seems that the continued evolution in methodology has currently reached an apex: there is likely to be scientific and practical consensus on the ultimate typing potential of bacterial whole-genome sequencing (WGS). The possibility to perform pan-genomic nucleotide-to-nucleotide comparisons between strains belonging to a single species and to detect even minute changes in nucleotide order will identify closely related organisms, while upon accumulation of such mutations, independent descend can be assumed. Calibration of difference levels [i.e. number of single nucleotide polymorphisms (SNPs)] into categories of inter-strain relatedness needs to be performed in order to generate robust, portable typing schemes. Here, we will briefly discuss the state of affairs regarding bacterial epidemiology based upon WGS, its relatedness with the nomenclature of former typing approaches and the continuing need for a global typing language.

Induced Pluripotent Stem Cells Reveal Common Neurodevelopmental Genome Deprograming in Schizophrenia.

Schizophrenia is a neurodevelopmental disorder characterized by complex aberrations in the structure, wiring, and chemistry of multiple neuronal systems. The abnormal developmental trajectory of the brain is established during gestation, long before clinical manifestation of the disease. Over 200 genes and even greater numbers of single nucleotide polymorphisms and copy number variations have been linked with schizophrenia. How does altered function of such a variety of genes lead to schizophrenia? We propose that the protein products of these altered genes converge on a common neurodevelopmental pathway responsible for the development of brain neural circuit and neurotransmitter systems. The results of a multichanneled investigation using induced pluripotent stem cell (iPSCs)- and embryonic stem cell (ESCs)-derived neuronal committed cells (NCCs) indicate an early (preneuronal) developmental-genomic etiology of schizophrenia and that the dysregulated developmental gene networks are common to genetically unrelated cases of schizophrenia. The results support a "watershed" mechanism in which mutations within diverse signaling pathways affect the common pan-ontogenic mechanism, integrative nuclear (n)FGFR1 signaling (INFS). Dysregulation of INFS in schizophrenia NCCs deconstructs coordinated gene networks and leads to formation of new networks by the dysregulated genes. This genome deprograming affects critical gene programs and pathways for neural development and functions. Studies show that the genomic deprograming reflect an altered nFGFR1-genome interactions and deregulation of miRNA genes by nFGFR1. In addition, changes in chromatin topology imposed by nFGFR1 may play a role in coordinate gene dysregulation in schizophrenia.

Penalized classification for optimal statistical selection of markers from high-throughput genotyping: application in sheep breeds

The identification of individuals’ breed of origin has several practical applications in livestock and is useful in different biological contexts such as conservation genetics, breeding and authentication of animal products. In this paper, penalized multinomial regression was applied to identify the minimum number of single nucleotide polymorphisms (SNPs) from high-throughput genotyping data for individual assignment to dairy sheep breeds reared in Sicily. The combined use of penalized multinomial regression and stability selection reduced the number of SNPs required to 48. A final validation step on an independent population was carried out obtaining 100% correctly classified individuals. The results using independent analysis, such as admixture, Fst, principal component analysis and random forest, confirmed the ability of these methods in selecting distinctive markers. The identified SNPs may constitute a starting point for the development of a SNP based identification test as a tool for breed assignment and traceability of animal products.

Effect of minor allele frequency on the number of single nucleotide polymorphisms needed for accurate parentage assignment: A methodology illustrated using Atlantic salmon

Effect of minor allele frequency on the number of single nucleotide polymorphisms needed for accurate parentage assignment: A methodology illustrated using Atlantic salmon

Diversity in Grain Amaranths and Relatives Distinguished by Genotyping by Sequencing (GBS).

The genotyping by sequencing (GBS) method has become a molecular marker technology of choice for many crop plants because of its simultaneous discovery and evaluation of a large number of single nucleotide polymorphisms (SNPs) and utility for germplasm characterization. Genome representation and complexity reduction are the basis for GBS fingerprinting and can vary by species based on genome size and other sequence characteristics. Grain amaranths are a set of three species that were domesticated in the New World to be high protein, pseudo-cereal grain crops. The goal of this research was to employ the GBS technique for diversity evaluation in grain amaranth accessions and close relatives from six Amaranthus species and determine genetic differences and similarities between groupings. A total of 10,668 SNPs were discovered in 94 amaranth accessions with ApeKI complexity reduction and 10X genome coverage Illumina sequencing. The majority of the SNPs were species specific with 4,568 and 3,082 for the two grain amaranths originating in Central America Amaranthus cruentus and A. hypochondriacus and 3,284 found amongst both A. caudatus, originally domesticated in South America, and its close relative, A. quitensis. The distance matrix based on shared alleles provided information on the close relationships of the two cultivated Central American species with each other and of the wild and cultivated South American species with each other, as distinguished from the outgroup with two wild species, A. powellii and A. retroflexus. The GBS data also distinguished admixture between each pair of species and the geographical origins and seed colors of the accessions. The SNPs we discovered here can be used for marker development for future amaranth study.

Abstract IA8: The genetics and genomics of African esophageal cancer

Abstract Esophageal squamous cell carcinoma (ESCC) is common in many Black populations of sub-Saharan Africa, with high incidence regions in Eastern and Southern Africa. Clinical presentation in Africa is late, and treatment is mainly palliative with a very poor prognosis. Various environmental risk factors have been identified, but the possible contribution of inherited genetic variants to disease risk is an important question which is unresolved. Also, limited data are available on the somatic mutations which are driving tumor development. This presentation will review current knowledge on the role of germline genetic variants and somatic mutations in the development of African ESCC. Genetic association studies of African ESCC have been limited to the analysis of small numbers of single nucleotide polymorphisms (SNPs) in candidate genes, and carried out only in the Black and Mixed Ancestry populations of the Western Cape of South Africa. Several positive associations have been reported, particularly in the Mixed Ancestry population, but none have achieved genome-wide levels of significance or been replicated in independent studies. We are currently testing SNPs which have been associated with ESCC in genome-wide association studies (GWAS) from Asian and European populations for association with ESCC in the South African population. Black cases with a histologically confirmed diagnosis of ESCC and matching population controls were recruited, after informed consent and institutional ethical approval, from the Western Cape and Gauteng provinces of South Africa. SNPs were genotyped either by individual TaqMan assays (Applied Biosystems) or in a multiplex MassARRAY (Agena Bioscience) and genotypes were tested for association. Our initial studies found no significant evidence of association at previously reported GWAS loci ATP1B2, CASP8, c20orf54, HEATR3, PDE4D, PLCE1, PTPN2, RUNX1, SMG6, ST6GAL1, TMEM173 and UNC5L loci. However, evidence for association was observed for the SNP rs2239815 at XBP1 on chromosome 22q12 (OR =1.41, P = 0.00087), and the SNPs rs4822983 (OR = 1.31, P = 0.0013) and rs1033667 (OR = 1.29, P = 0.0025) in CHEK2. Genotyping of a larger SNP panel in an expanded collection of cases and controls is in progress to extend these findings. Detection of somatic mutations in ESCC tumour tissue has in the past been limited to sequencing of candidate genes and copy number studies, with TP53 mutations being detected in a minority of South African and Kenyan patients. We have carried out pilot whole exome sequencing in 10 matched blood/tumour pairs from South African ESCC patients and detected mutations in TP53, ATR, GNAS, MAGI2, FBXW7, FLT3, NFE2L2, TET2 and ZNF750. Follow up sequencing of the TP53 gene detected missense or truncating mutations in 18/26 (69%) of tumours. A recent sequencing study of 59 Malawian ESCC patients (Liu et al) observed recurrent mutations in TP53, CDKN2A, NFE2L2, CHEK2, NOTCH1, FAT1 and FBXW7, and transcriptomic profiles were used to divide ESCCs into 3 subtypes. Priorities for the future should include well powered GWAS in high risk populations from several African countries, with collaborative studies to compare genetic risk factors across populations and meta-analysis to provide power to detect risk loci with moderate effects. Whole-exome or whole genome sequencing of substantial panels of blood/tumour pairs are needed to establish the major drivers of tumorigenesis in African ESCC and to derive mutational signatures which may provide insight into causal environmental factors. Citation Format: Christopher G. Mathew. The genetics and genomics of African esophageal cancer [abstract]. In: Proceedings of the AACR International Conference: New Frontiers in Cancer Research; 2017 Jan 18-22; Cape Town, South Africa. Philadelphia (PA): AACR; Cancer Res 2017;77(22 Suppl):Abstract nr IA8.

Genome-wide scan for runs of homozygosity identifies potential candidate genes associated with local adaptation in Valle del Belice sheep

BackgroundBecause very large numbers of single nucleotide polymorphisms (SNPs) are now available throughout the genome, they are particularly suitable for the detection of genomic regions where a reduction in heterozygosity has occurred and they offer new opportunities to improve the accuracy of inbreeding (F) estimates. Runs of homozygosity (ROH) are contiguous lengths of homozygous segments of the genome where the two haplotypes inherited from the parents are identical. Here, we investigated the occurrence and distribution of ROH using a medium-dense SNP panel to characterize autozygosity in 516 Valle del Belice sheep and to identify the genomic regions with high ROH frequencies.ResultsWe identified 11,629 ROH and all individuals displayed at least one ROH longer than 1 Mb. The mean value of F estimated from ROH longer than1 Mb was 0.084 ± 0.061. ROH that were shorter than 10 Mb predominated. The highest and lowest coverages of Ovis aries chromosomes (OAR) by ROH were on OAR24 and OAR1, respectively. The number of ROH per chromosome length displayed a specific pattern, with higher values for the first three chromosomes. Both number of ROH and length of the genome covered by ROH varied considerably between animals. Two hundred and thirty-nine SNPs were considered as candidate markers that may be under directional selection and we identified 107 potential candidate genes. Six genomic regions located on six chromosomes, corresponding to ROH islands, are presented as hotspots of autozygosity, which frequently coincided with regions of medium recombination rate. According to the KEGG database, most of these genes were involved in multiple signaling and signal transduction pathways in a wide variety of cellular and biochemical processes. A genome scan revealed the presence of ROH islands in genomic regions that harbor candidate genes for selection in response to environmental stress and which underlie local adaptation.ConclusionsThese results suggest that natural selection has, at least partially, a role in shaping the genome of Valle del Belice sheep and that ROH in the ovine genome may help to detect genomic regions involved in the determinism of traits under selection.

A 1204-single nucleotide polymorphism and insertion–deletion polymorphism panel for massively parallel sequencing analysis of DNA mixtures

Massively parallel sequencing (MPS) technology enables the simultaneous analysis of a huge number of single nucleotide polymorphisms (SNPs) and insertion–deletion polymorphisms (indels). MPS also enables the detection of the alleles of minor contributors in a highly unbalanced DNA mixture. In this study, we established a 1204-marker panel optimized for MPS consisting of 987 autosomal markers (964 SNPs and 23 indels), 27 X-chromosome SNPs, 61 Y-chromosome markers (56 SNPs and 5 indels), and 129 mitochondrial SNPs. The DNA samples of six unrelated individuals (two men and four women), 26 nondegraded DNA mixtures (with minor to major ratios of 1:29, 1:39, 1:79, and 1:99), and eight highly artificially degraded DNA mixtures (with minor to major ratios of 1:29, 1:39, 1:79, and 1:99) were analyzed through MPS by using the panel. A scoring system was developed to determine the minor contributors in DNA mixtures based on the genotypes identified using MPS. The genotypes of the 1204 markers were successfully profiled through MPS by using the custom-designed panel. The efficiency of MPS for analyzing these highly degraded samples was lower than that for analyzing nondegraded samples. All minor contributors in the 26 nondegraded and 8 degraded DNA mixtures were accurately assigned using this scoring system based on 964 autosomal SNPs. An association between the observed reads ratio and theoretical ratio of the minor component was noted for nondegraded mixtures. In conclusion, we established a 1204-marker individual identification panel for MPS that successfully analyzed autosomal, X-chromosome, Y-chromosome, and mitochondrial SNPs and indels simultaneously. In combination with the newly developed scoring system, the panel can accurately identify minor contributors in nondegraded and highly degraded DNA mixtures.

Development of F1 hybrid population and the high-density linkage map for European aspen (Populus tremula L.) using RADseq technology

BackgroundRestriction-site associated DNA sequencing (RADseq) technology was recently employed to identify a large number of single nucleotide polymorphisms (SNP) for linkage mapping of a North American and Eastern Asian Populus species. However, there is also the need for high-density genetic linkage maps for the European aspen (P. tremula) as a tool for further mapping of quantitative trait loci (QTLs) and marker-assisted selection of the Populus species native to Europe.ResultsWe established a hybrid F1 population from the cross of two aspen parental genotypes diverged in their phenological and morphological traits. We performed RADseq of 122 F1 progenies and two parents yielding 15,732 high-quality SNPs that were successfully identified using the reference genome of P. trichocarpa. 2055 SNPs were employed for the construction of maternal and paternal linkage maps. The maternal linkage map was assembled with 1000 SNPs, containing 19 linkage groups and spanning 3054.9 cM of the genome, with an average distance of 3.05 cM between adjacent markers. The paternal map consisted of 1055 SNPs and the same number of linkage groups with a total length of 3090.56 cM and average interval distance of 2.93 cM. The linkage maps were employed for QTL mapping of one-year-old seedlings height variation. The most significant QTL (LOD = 5.73) was localized to LG5 (96.94 cM) of the male linkage map, explaining 18% of the phenotypic variation.ConclusionsThe set of 15,732 SNPs polymorphic in aspen and high-density genetic linkage maps constructed for the P. tremula intra-specific cross will provide a valuable source for QTL mapping and identification of candidate genes facilitating marker-assisted selection in European aspen.

A common variant in ARHGEF10 alters delta-6 desaturase activity and influence susceptibility to hypertriglyceridemia

Numbers of single nucleotide polymorphisms (SNPs) associated with fatty acid desaturase activities have been previously identified within the FADS1-FADS2 gene cluster, which encodes delta-5 (D5D) and delta-6 (D6D) desaturases, respectively. We aimed at further characterizing the genetic variability associated with D5D and D6D activities on a genome-wide scale. We conducted a genome-wide association study of D5D and D6D activities in a cohort of 141 individuals from the greater Quebec City metropolitan area using the Illumina HumanOmni5-Quad BeadChip. Estimates of D5D and D6D activities were computed using product-to-precursor fatty acid ratios, arachidonic acid (AA)/dihomo-gamma-linolenic acid (DGLA) for D5D, and DGLA/linoleic acid (LA) for D6D. Levels of fatty acids were measured by gas chromatography in plasma phospholipids. We identified 24 previously reported SNPs associated with fatty acid levels and desaturase activities as significantly associated with D5D activity within the FADS1-FADS2 gene cluster (lead SNP rs174566/A>G). Furthermore, we identified 5 novel loci potentially associated with D5D activity at chromosomes 1, 6, 4, 8 and 19. A novel SNP associated with D6D activity and mapped to the ARHGEF10 locus (rs2280885/A>G) was identified, with carriers of the rare allele showing a significant increase in D6D activity and plasma triglyceride levels. After multiple testing correction by permutation, only rs174566 and rs2280885 remained significantly associated to D5D and D6D activity estimates, respectively. These results confirm previous genetic associations within the FADS1-FADS2 gene cluster with D5D activity. A novel genetic variation associated with higher D6D activity within the ARHGEF10 gene is potentially altering plasma triglyceride levels.

Association of human platelet antigens polymorphisms with susceptibility to hepatitis C virus infection in Chinese population.

Hepatitis C virus (HCV) is a major cause of chronic hepatitis. Previous studies have identified a number of single nucleotide polymorphisms that are associated with HCV infection. Human platelet antigens (HPAs) polymorphisms play an important role in several diseases. Here, we demonstrated the association of the HPA-2, HPA-3, HPA-5 and HPA-15 polymorphisms with susceptibility to HCV infection in Chinese population. Overall, 118 patients with HCV and 167 controls were genotyped for HPAs. There were no significant differences in the allele and genotype frequency distribution for the HPA-3, HPA-5 and HPA-15 systems between the patients with chronic HCV infection and the healthy controls (p>.05). However, the genotype frequency of HPA-2aa was significantly lower, while HPA-2ab/bb was significantly higher in patients than that in the controls (p=.006). The allele frequency of HPA-2a in patients was significantly lower than that in the control group (p=.005). In contrast, HPA-2b in patients was significantly higher than that in the control group (p=.005). We conclude that HPA-2 polymorphism is associated with susceptibility to HCV infection, and individuals carrying the HPA-2b allele may have a higher risk of HCV infection compared with individuals carrying HPA-2a.

Late-Onset Alzheimer’s Disease Polygenic Risk Profile Score Predicts Hippocampal Function

BackgroundWe explored the cumulative effect of several late-onset Alzheimer’s disease (LOAD) risk loci using a polygenic risk profile score (RPS) approach on measures of hippocampal function, cognition, and brain morphometry. MethodsIn a sample of 231 healthy control subjects (19–55 years of age), we used an RPS to study the effect of several LOAD risk loci reported in a recent meta-analysis on hippocampal function (determined by its engagement with blood oxygen level–dependent functional magnetic resonance imaging during episodic memory) and several cognitive metrics. We also studied effects on brain morphometry in an overlapping sample of 280 subjects. ResultsThere was almost no significant association of LOAD-RPS with cognitive or morphometric measures. However, there was a significant negative relationship between LOAD-RPS and hippocampal function (familywise error [small volume correction-hippocampal region of interest] p < .05). There were also similar associations for risk score based on APOE haplotype, and for a combined LOAD-RPS + APOE haplotype risk profile score (p < .05 familywise error [small volume correction-hippocampal region of interest]). Of the 29 individual single nucleotide polymorphisms used in calculating LOAD-RPS, variants in CLU, PICALM, BCL3, PVRL2, and RELB showed strong effects (p < .05 familywise error [small volume correction-hippocampal region of interest]) on hippocampal function, though none survived further correction for the number of single nucleotide polymorphisms tested. ConclusionsThere is a cumulative deleterious effect of LOAD risk genes on hippocampal function even in healthy volunteers. The effect of LOAD-RPS on hippocampal function in the relative absence of any effect on cognitive and morphometric measures is consistent with the reported temporal characteristics of LOAD biomarkers with the earlier manifestation of synaptic dysfunction before morphometric and cognitive changes.

Discovery and genomic analyses of hybridization between divergent lineages of Trypanosoma congolense, causative agent of Animal African Trypanosomiasis.

Hybrid populations and introgressive hybridization remain poorly documented in pathogenic micro-organisms, as such that genetic exchange has been argued to play a minor role in their evolution. Recent work demonstrated the existence of hybrid microsatellite profiles in Trypanosoma congolense, a parasitic protozoan with detrimental effects on livestock productivity in sub-Saharan Africa. Here, we present the first population genomic study of T.congolense, revealing a remarkable number of single nucleotide polymorphisms (SNPs), small insertions/deletions (indels) and gene deletions among 56 parasite genomes from ten African countries. One group of parasites from Zambia was particularly diverse, displaying a substantial number of heterozygous SNP and indel sites compared to T.congolense parasites from the nine other sub-Saharan countries. Genomewide 5-kb phylogenetic analyses based on phased SNP data revealed that these parasites were the product of hybridization between phylogenetically distinct T.congolense lineages. Other parasites within the same region in Zambia presented a mosaic of haplotypic ancestry and genetic variability, indicating that hybrid parasites persisted and recombined beyond the initial hybridization event. Our observations challenge traditional views of trypanosome population biology and encourage future research on the role of hybridization in spreading genes for drug resistance, pathogenicity and virulence.