Genome‐wide association study identifies quantitative trait loci affecting hematological traits in an F2 intercross between Landrace and Korean native pigs

Changes affecting the status of health and robustness can bring about physiological alterations including hematological parameters in swine. To identify quantitative trait loci (QTL) associated with eight hematological traits (one leukocyte trait, six erythrocyte traits and one platelet trait), we conducted a genome‐wide association study using the PorcineSNP60K BeadChip in a resource population derived from an intercross between Landrace and Korean native pigs. A total of 36 740 SNPs from 816 F₂ progeny were analyzed for each blood‐related trait after filtering for quality control. Data were analyzed by the genome‐wide rapid association using mixed model and regression (GRAMMAR) approach. A total of 257 significant SNPs (P < 1.36 × 10^?6) on SSC3, 6, 8, 13 and 17 were identified for blood‐related traits in this study. Interestingly, the genomic region between 17.9 and 130 Mb on SSC8 was found to be significantly associated with red blood cell, mean corpuscular volume and mean corpuscular hemoglobin. Our results include the identification of five significant SNPs within five candidate genes (KIT, IL15, TXK, ARAP2 and ERG) for hematopoiesis. Further validation of these identified SNPs could give valuable information for understanding the variation of hematological traits in pigs.     

A genome‐wide association study for the incidence of persistent bovine viral diarrhea virus infection in cattle

Bovine viral diarrhea viruses (BVDV) comprise a diverse group of viruses that cause disease in cattle. BVDV may establish both transient and persistent infections depending on the developmental stage of the animal at exposure. The objective was to determine whether genomic regions harboring single nucleotide polymorphisms (SNPs) could be associated with the presence or absence of persistent BVDV infection. A genome‐wide association approach based on 777 000 SNP markers was used. Samples of animals identified as positive (n = 1200) or negative (n = 1200) for the presence of BVDV in skin samples (n = 1200) were used. DNA samples were combined in 24 pools (100 animals per pool). One SNP, significant at the 5 percent genome‐wide level (P = 9.41 × 10^?8), was detected on chromosome 14, located at position 80 675 176 bp. Fifteen SNPs, residing on chromosomes 1, 2, 6, 8, 10, 15 and 18, were moderately associated (P < 1 × 10^?5) with persistent BVDV infection. Results show that genes harboring or neighboring significant SNPs are involved in leucopenia, signal transduction, RNA splicing and DNA methylation processes.     

Genome‐wide association analysis identifies quantitative trait loci for growth in a Landrace purebred population

Growth‐related traits are complex and economically important in the livestock industry. The aim of this study was to identify quantitative trait loci (QTL) and the associated positional candidate genes affecting growth in pigs. A genome‐wide association study (GWAS) was performed using the porcine single‐nucleotide polymorphism (SNP) 60K bead chip. A mixed‐effects model and linear regression approach were used for the GWAS. The data used in the study included 490 purebred Landrace pigs. All experimental animals were genotyped with 39 438 SNPs located throughout the pig autosomes. We identified a strong association between a SNP marker on chromosome 16 and body weight at 71 days of age (ALGA0092396, P = 5.35 × 10^?9, Bonferroni adjusted P < 0.05). The SNP marker was located near the genomic region containing IRX4, which encodes iroquois homeobox 4. This SNP marker could be useful in the selective breeding program after validating its effect on other populations.     

Expression of candidate genes for residual feed intake in Angus cattle

Residual feed intake (RFI) has been adopted in Australia for the purpose of genetic improvement in feed efficiency in beef cattle. RFI is the difference between the observed feed intake of an animal and the predicted feed intake based on its size and growth rate over a test period. Gene expression of eight candidate genes (AHSG, GHR, GSTM1, INHBA, PCDH19, S100A10, SERPINI2 and SOD3), previously identified as differentially expressed between divergent lines of high‐ and low‐RFI animals, was measured in an unselected population of 60 steers from the Angus Society Elite Progeny Test Program using quantitative real‐time PCR. Results showed that the levels of gene expression were significantly correlated with RFI. The genes explain around 33.2% of the phenotypic variance in RFI, and prediction equations using the expression data are reasonably accurate estimators of RFI. The association of these genes with economically important traits, such as other feed efficiency‐related traits and fat, growth and carcass traits, was investigated as well. The expression of these candidate genes was significantly correlated with feed conversion ratio and daily feed intake, which are highly associated with RFI, suggesting a functional role for these genes in modulating feed utilisation. The expression of these genes did not show any association with average daily gain, eye muscle area and carcass composition.     

Genetic markers on BTA14 predictive for residual feed intake in beef steers and their effects on carcass and meat quality traits

With the high cost of feed for animal production, genetic selection for animals that metabolize feed more efficiently could result in substantial cost savings for cattle producers. The purpose of this study was to identify DNA markers predictive for differences among cattle for traits associated with feed efficiency. Crossbred steers were fed a high‐corn diet for 140 days and average daily feed intake (ADFI), average daily gain (ADG), and residual feed intake (RFI) phenotypes were obtained. A region on chromosome 14 was previously associated with RFI in this population of animals. To develop markers with the highest utility for predicting an animal's genetic potential for RFI, we genotyped additional markers within this chromosomal region. These polymorphisms were genotyped on the same animals (n = 1066) and tested for association with ADFI, ADG and RFI. Six markers within this region were associated with RFI (P ≤ 0.05). After conservative correction for multiple testing, one marker at 25.09 Mb remained significant (P = 0.02) and is responsible for 3.6% of the RFI phenotypic variation in this population of animals. Several of these markers were also significant for ADG, although none were significant after correction. Marker alleles with positive effects on ADG corresponded to lower RFI, suggesting an effect increasing growth without increasing feed intake. All markers were also assessed for their effects on meat quality and carcass traits. All of the markers associated with RFI were associated with adjusted fat thickness (AFT, P ≤ 0.009) and three were also associated with hot carcass weight (HCW, P ≤ 0.003). Marker alleles associated with lower RFI were also associated with reduced AFT, and if they were associated for HCW, the effect was an increase in weight. These markers may be useful as prediction tools for animals that utilize feed more efficiently; however, validation with additional populations of cattle is required.     

Genetic contributions to precocity traits in racing Thoroughbreds

Adaptation to early training and racing (i.e. precocity), which is highly variable in racing Thoroughbreds, has implications for the selection and training of horses. We hypothesised that precocity in Thoroughbred racehorses is heritable. Age at first sprint training session (work day), age at first race and age at best race were used as phenotypes to quantify precocity. Using high‐density SNP array data, additive SNP heritability () was estimated to be 0.17, 0.14 and 0.17 for the three traits respectively. In genome‐wide association studies (GWAS) for age at first race and age at best race, a 1.98‐Mb region on equine chromosome 18 (ECA18) was identified. The most significant association was with the myostatin (MSTN) g.66493737C>T SNP (P = 5.46 × 10^?12 and P = 1.89 × 10^?14 respectively). In addition, two SNPs on ECA1 (g.37770220G>A and g.37770305T>C) within the first intron of the serotonin receptor gene HTR7 were significantly associated with age at first race and age at best race. Although no significant associations were identified for age at first work day, the MSTN:g.66493737C>T SNP was among the top 20 SNPs in the GWAS (P = 3.98 × 10^?5). Here we have identified variants with potential roles in early adaptation to training. Although there was an overlap in genes associated with precocity and distance aptitude (i.e. MSTN), the HTR7 variants were more strongly associated with precocity than with distance. Because HTR7 is closely related to the HTR1A gene, previously implicated in tractability in young Thoroughbreds, this suggests that behavioural traits may influence precocity.     

Whole Genome Association Studies of Residual Feed Intake and Related Traits in the Pig

Background

Residual feed intake (RFI), a measure of feed efficiency, is the difference between observed feed intake and the expected feed requirement predicted from growth and maintenance. Pigs with low RFI have reduced feed costs without compromising their growth. Identification of genes or genetic markers associated with RFI will be useful for marker-assisted selection at an early age of animals with improved feed efficiency.

Methodology/Principal findings

Whole genome association studies (WGAS) for RFI, average daily feed intake (ADFI), average daily gain (ADG), back fat (BF) and loin muscle area (LMA) were performed on 1,400 pigs from the divergently selected ISU-RFI lines, using the Illumina PorcineSNP60 BeadChip. Various statistical methods were applied to find SNPs and genomic regions associated with the traits, including a Bayesian approach using GenSel software, and frequentist approaches such as allele frequency differences between lines, single SNP and haplotype analyses using PLINK software. Single SNP and haplotype analyses showed no significant associations (except for LMA) after genomic control and FDR. Bayesian analyses found at least 2 associations for each trait at a false positive probability of 0.5. At generation 8, the RFI selection lines mainly differed in allele frequencies for SNPs near (<0.05 Mb) genes that regulate insulin release and leptin functions. The Bayesian approach identified associations of genomic regions containing insulin release genes (e.g., GLP1R, CDKAL, SGMS1) with RFI and ADFI, of regions with energy homeostasis (e.g., MC4R, PGM1, GPR81) and muscle growth related genes (e.g., TGFB1) with ADG, and of fat metabolism genes (e.g., ACOXL, AEBP1) with BF. Specifically, a very highly significantly associated QTL for LMA on SSC7 with skeletal myogenesis genes (e.g., KLHL31) was identified for subsequent fine mapping.

Conclusions/significance

Important genomic regions associated with RFI related traits were identified for future validation studies prior to their incorporation in marker-assisted selection programs.     

A genome‐wide association study in Caucasian women suggests the involvement of HLA genes in the severity of facial solar lentigines

Solar lentigines are a common feature of sun‐induced skin ageing. Little is known, however, about the genetic factors contributing to their development. In this genome‐wide association study, we aimed to identify genetic loci associated with solar lentigines on the face in 502 middle‐aged French women. Nine SNPs, gathered in two independent blocks on chromosome 6, exhibited a false discovery rate below 25% when looking for associations with the facial lentigine score. The first block, in the 6p22 region, corresponded to intergenic SNPs and also exhibited a significant association with forehead lentigines (P = 1.37 × 10^?8). The second block, within the 6p21 HLA region, was associated with decreased HLA‐C expression according to several eQTL databases. Interestingly, these SNPs were also in high linkage disequilibrium with the HLA‐C*0701 allele (r² = 0.95). We replicated an association recently found by GWAS in the IRF4 gene. Finally, a complementary study on 44 selected candidate SNPs revealed novel associations in the MITF gene. Overall, our results point to several mechanisms involved in the severity of facial lentigines, including HLA/immunity and the melanogenesis pathway.     

Genome‐wide association study reveals novel genes for the ear size in sheep (Ovis aries)

Variations in ear size can be observed in livestock such as sheep; however, the genetic basis of variable ear size in sheep is still poorly understood. To investigate causative genes associated with ear size in sheep, a genome‐wide association study was performed in 115 adult Duolang sheep with different‐sized floppy ears using the Ovine Infinium HD BeadChip. We found 38 significant SNPs at the genome‐wide or chromosome‐wise 5% significance level after Bonferroni correction. The most significant association (P = 1.61 × 10^?6) was found at SNP rs402740419, located in the DCC gene, which plays a critical role in ear development. Also, we observed two additional significant SNPs, rs407891215 in PTPRD and rs407769095 in SOX5, both of which are functionally associated with ear developmental processes. Our results are useful for future sheep breeding and provide insights into the genetic basis of ear size development in sheep and other livestock.     

Analysis of the genetic architecture of maize kernel size traits by combined linkage and association mapping

Kernel size‐related traits are the most direct traits correlating with grain yield. The genetic basis of three kernel traits of maize, kernel length (KL), kernel width (KW) and kernel thickness (KT), was investigated in an association panel and a biparental population. A total of 21 single nucleotide polymorphisms (SNPs) were detected to be most significantly (P < 2.25 × 10^?6) associated with these three traits in the association panel under four environments. Furthermore, 50 quantitative trait loci (QTL) controlling these traits were detected in seven environments in the intermated B73 × Mo17 (IBM) Syn10 doubled haploid (DH) population, of which eight were repetitively identified in at least three environments. Combining the two mapping populations revealed that 56 SNPs (P < 1 × 10^?3) fell within 18 of the QTL confidence intervals. According to the top significant SNPs, stable‐effect SNPs and the co‐localized SNPs by association analysis and linkage mapping, a total of 73 candidate genes were identified, regulating seed development. Additionally, seven miRNAs were found to situate within the linkage disequilibrium (LD) regions of the co‐localized SNPs, of which zma‐miR164e was demonstrated to cleave the mRNAs of Arabidopsis CUC1, CUC2 and NAC6 in vitro. Overexpression of zma‐miR164e resulted in the down‐regulation of these genes above and the failure of seed formation in Arabidopsis pods, with the increased branch number. These findings provide insights into the mechanism of seed development and the improvement of molecular marker‐assisted selection (MAS) for high‐yield breeding in maize.     

Evaluation of the causality of the low‐density lipoprotein receptor gene (LDLR) for serum lipids in pigs

A significant quantitative trait locus (QTL) for low‐density lipoprotein cholesterol (LDL‐C) and total cholesterol (TC) was identified around the LDLR gene on chromosome 2 (SSC2) in a White Duroc × Erhualian F₂ resource population and Sutai pigs in our previous study. However, in previous reports, the causality of LDLR with serum lipids is controversial in pigs. To systematically assess the causality of LDLR with serum lipids, association analyses were successively performed in three populations: Sutai pigs, a White Duroc × Erhualian F₂ resource population and a Duroc × (Landrace × Large White) population. We first performed a haplotype‐based association study with 60K SNP genotyping data and evidenced the significant association with LDL‐C and TC around the LDLR gene region. We also found that there is more than one QTL for LDL‐C and TC on SSC2. Then, we evaluated the causalities of two missense mutations, c.1812C>T and c.1520A>G, with LDL‐C and TC. We revealed that the c.1812C>T SNP showed the strongest association with LDL‐C (P = 5.40 × 10^?11) and TC (P = 3.64 × 10^?8) and explained all the QTL effect in Sutai pigs. Haplotype analysis found that two missense SNPs locate within a 1.93‐Mb haplotype block. One major haplotype showed the strongest significant association with LDL‐C (P = 4.62 × 10^?18) and TC (P = 1.06 × 10^?9). However, the c.1812C>T SNP was not identified in the White Duroc × Erhualian intercross, and the association of c.1520A>G with both LDL‐C and TC did not achieve significance in this F₂ population, suggesting population heterogeneity. Both missense mutations were identified in the Duroc × (Landrace × Large White) population and showed significant associations with LDL‐C and TC. Our data give evidence that the LDLR gene should be a candidate causative gene for LDL‐C and TC in pigs, but heterogeneity exists in different populations.     

A novel susceptibility locus in MST1 and gene‐gene interaction network for Crohn's disease in the Chinese population

The incidence of Crohn's disease is increasing in many Asian countries, but considerable differences in genetic susceptibility have been reported between Western and Asian populations. This study aimed to fine‐map 23 previously reported Crohn's disease genes and identify their interactions in the Chinese population by Illumina‐based targeted capture sequencing. Our results showed that the genetic polymorphism A>G at rs144982232 in MST1 showed the most significant association (P = 1.78 × 10^?5; odds ratio = 4.87). JAK2 rs1159782 (T>C) was also strongly associated with Crohn's disease (P = 2.34 × 10^?4; odds ratio = 3.72). Gene‐gene interaction analysis revealed significant interactions between MST1 and other susceptibility genes, including NOD2, MUC19 and ATG16L1 in contributing to Crohn's disease risk. Main genetic associations and gene‐gene interactions were verified using ImmunoChip data set. In conclusion, a novel susceptibility locus in MST1 was identified. Our analysis suggests that MST1 might interact with key susceptibility genes involved in autophagy and bacterial recognition. These findings provide insight into the genetic architecture of Crohn's disease in Chinese and may partially explain the disparity of genetic signals in Crohn's disease susceptibility across different ethnic populations by highlighting the contribution of gene‐gene interactions.     

A genome‐wide association study for reading and language abilities in two population cohorts

Candidate genes have been identified for both reading and language, but most of the heritable variance in these traits remains unexplained. Here, we report a genome‐wide association meta‐analysis of two large cohorts: population samples of Australian twins and siblings aged 12–25 years (n = 1177 from 538 families), and a younger cohort of children of the UK Avon Longitudinal Study of Parents and their Children (aged 8 and 9 years; maximum n = 5472). Suggestive association was indicated for reading measures and non‐word repetition (NWR), with the greatest support found for single nucleotide polymorphisms (SNPs) in the pseudogene, ABCC13 (P = 7.34 × 10^?8), and the gene, DAZAP1 (P = 1.32 × 10^?6). Gene‐based analyses showed significant association (P < 2.8 × 10^?6) for reading and spelling with genes CD2L1, CDC2L2 and RCAN3 in two loci on chromosome 1. Some support was found for the same SNPs having effects on both reading skill and NWR, which is compatible with behavior genetic evidence for influences of reading acquisition on phonological‐task performance. The results implicate novel candidates for study in additional cohorts for reading and language abilities.     

Genome‐wide Linkage and Association Analyses to Identify Genes Influencing Adiponectin Levels: The GEMS Stud

Adiponectin has a variety of metabolic effects on obesity, insulin sensitivity, and atherosclerosis. To identify genes influencing variation in plasma adiponectin levels, we performed genome‐wide linkage and association scans of adiponectin in two cohorts of subjects recruited in the Genetic Epidemiology of Metabolic Syndrome Study. The genome‐wide linkage scan was conducted in families of Turkish and southern European (TSE, n = 789) and Northern and Western European (NWE, N = 2,280) origin. A whole genome association (WGA) analysis (500K Affymetrix platform) was carried out in a set of unrelated NWE subjects consisting of approximately 1,000 subjects with dyslipidemia and 1,000 overweight subjects with normal lipids. Peak evidence for linkage occurred at chromosome 8p23 in NWE subjects (lod = 3.10) and at chromosome 3q28 near ADIPOQ, the adiponectin structural gene, in TSE subjects (lod = 1.70). In the WGA analysis, the single‐nucleotide polymorphisms (SNPs) most strongly associated with adiponectin were rs3774261 and rs6773957 (P < 10^?7). These two SNPs were in high linkage disequilibrium (r² = 0.98) and located within ADIPOQ. Interestingly, our fourth strongest region of association (P < 2 × 10^?5) was to an SNP within CDH13, whose protein product is a newly identified receptor for high‐molecular‐weight species of adiponectin. Through WGA analysis, we confirmed previous studies showing SNPs within ADIPOQ to be strongly associated with variation in adiponectin levels and further observed these to have the strongest effects on adiponectin levels throughout the genome. We additionally identified a second gene (CDH13) possibly influencing variation in adiponectin levels. The impact of these SNPs on health and disease has yet to be determined.     

Genome‐wide linkage analysis for human longevity: Genetics of Healthy Aging Study

Clear evidence exists for heritability of human longevity, and much interest is focused on identifying genes associated with longer lives. To identify such longevity alleles, we performed the largest genome‐wide linkage scan thus far reported. Linkage analyses included 2118 nonagenarian Caucasian sibling pairs that have been enrolled in 15 study centers of 11 European countries as part of the Genetics of Healthy Aging (GEHA) project. In the joint linkage analyses, we observed four regions that show linkage with longevity; chromosome 14q11.2 (LOD = 3.47), chromosome 17q12‐q22 (LOD = 2.95), chromosome 19p13.3‐p13.11 (LOD = 3.76), and chromosome 19q13.11‐q13.32 (LOD = 3.57). To fine map these regions linked to longevity, we performed association analysis using GWAS data in a subgroup of 1228 unrelated nonagenarian and 1907 geographically matched controls. Using a fixed‐effect meta‐analysis approach, rs4420638 at the TOMM40/APOE/APOC1 gene locus showed significant association with longevity (P‐value = 9.6 × 10^?8). By combined modeling of linkage and association, we showed that association of longevity with APOEε4 and APOEε2 alleles explain the linkage at 19q13.11‐q13.32 with P‐value = 0.02 and P‐value = 1.0 × 10^?5, respectively. In the largest linkage scan thus far performed for human familial longevity, we confirm that the APOE locus is a longevity gene and that additional longevity loci may be identified at 14q11.2, 17q12‐q22, and 19p13.3‐p13.11. As the latter linkage results are not explained by common variants, we suggest that rare variants play an important role in human familial longevity.     

Genome‐wide association study of genetic factors related to confectionery intake: Potential roles of the ADIPOQ gene

Objective: The excessive consumption of confectionery might have adverse effects on human health. To screen genetic factors associated with confectionery‐intake frequency, a genome‐wide association study (GWAS) in Japan was conducted. Design and Methods: For the discovery phase (stage 1), we conducted a GWAS of 939 noncancer patients in a cancer hospital. Additive models were used to test associations between genotypes of approximately 500,000 single‐nucleotide polymorphisms (SNPs) and the confectionery‐intake score (based on intake frequency). We followed‐up association signals with P < 1 × 10^?5 and minor allele frequency >0.01 in stage 1 by genotyping the SNPs of 4,491 participants in a cross‐sectional study within a cohort (replication phase [stage 2]). Results: We identified 12 SNPs in stage 1 that were potentially related to confectionery intake. In stage 2, this association was replicated for one SNP (rs822396; P = 0.049 for stage 2 and 4.2 × 10^?5 for stage 1+2) in intron 1 of the ADIPOQ gene, which encodes the adipokine adiponectin. Conclusions: Given the biological plausibility and previous relevant findings, the association of an SNP in the ADIPOQ gene with a preference for confectionery is worthy of follow‐up and provides a good working hypothesis for experimental testing.     

Genome‐wide association analysis and gene set enrichment analysis with SNP data identify genes associated with 305‐day milk yield in Holstein dairy cows

Milk production traits, such as 305‐day milk yield (305MY), have been under direct selection to improve production in dairy cows. Over the past 50 years, the average milk yield has nearly doubled, and over 56% of the increase is attributable to genetic improvement. As such, additional improvements in milk yield are still possible as new loci are identified. The objectives of this study were to detect SNPs and gene sets associated with 305MY in order to identify new candidate genes contributing to variation in milk production. A population of 781 primiparous Holstein cows from six central Washington dairies with records of 305MY and energy corrected milk were used to perform a genome‐wide association analysis (GWAA) using the Illumina BovineHD BeadChip (777 962 SNPs) to identify QTL associated with 305MY (P < 1.0 × 10^?5). A gene set enrichment analysis with SNP data (GSEA‐SNP) was performed to identify gene sets (normalized enrichment score > 3.0) and leading edge genes (LEGs) influencing 305MY. The GWAA identified three QTL comprising 34 SNPs and 30 positional candidate genes. In the GSEA‐SNP, five gene sets with 58 unique and 24 shared LEGs contributed to 305MY. Identification of QTL and LEGs associated with 305MY can provide additional targets for genomic selection to continue to improve 305MY in dairy cattle.