A panel of ancestry informative markers to estimate and correct potential effects of population stratification in Han Chinese

Whole mitochondrial genome analysis in highland Tibetans: further matrilineal genetic structure exploration

Introduction: The Qinghai-Tibet Plateau is one of the last terrestrial environments conquered by modern humans. Tibetans are among the few high-altitude settlers in the world, and understanding the genetic profile of Tibetans plays a pivotal role in studies of anthropology, genetics, and archaeology. Methods: In this study, we investigated the maternal genetic landscape of Tibetans based on the whole mitochondrial genome collected from 145 unrelated native Lhasa Tibetans. Molecular diversity indices, haplotype diversity (HD), Tajima's D and Fu's Fs were calculated and the Bayesian Skyline Plot was obtained to determining the genetic profile and population fluctuation of Lhasa Tibetans. To further explore the genetic structure of Lhasa Tibetans, we collected 107 East Asian reference populations to perform principal component analysis (PCA), multidimensional scaling (MDS), calculated Fst values and constructed phylogenetic tree. Results: The maternal genetic landscape of Tibetans showed obvious East Asian characteristics, M9a (28.28%), R (11.03%), F1 (12.41%), D4 (9.66%), N (6.21%), and M62 (4.14%) were the dominant haplogroups. The results of PCA, MDS, Fst and phylogenetic tree were consistent: Lhasa Tibetans clustered with other highland Tibeto-Burman speakers, there was obvious genetic homogeneity of Tibetans in Xizang, and genetic similarity between Tibetans and northern Han people and geographically adjacent populations was found. In addition, specific maternal lineages of Tibetans also be determined in this study. Discussion: In general, this study further shed light on long-time matrilineal continuity on the Tibetan Plateau and the genetic connection between Tibetans and millet famers in the Yellow River Basin, and further revealed that multiple waves of population interaction and admixture during different historical periods between lowland and highland populations shaped the maternal genetic profile of Tibetans.

Forensic Features and Genetic Structure Analyses of the Beijing Han Nationality Disclosed by a Self-Developed Panel Containing a Series of Ancestry Informative Deletion/Insertion Polymorphism Loci

The utilization of the ancestry informative markers to disclose the ancestral composition of a certain population and explore the genetic affinities between diverse populations is beneficial to inferring the biogeographic ancestry of unknown individuals and assisting in case detection, as well as avoiding the impacts of population stratification during genome-wide association analysis studies. In the present study, we applied an in-house ancestry informative deletion/insertion polymorphic multiplex amplification system to investigate the ancestral compositions of the Beijing Han population and analyze the genetic relationships between the Beijing Han population and 31 global reference populations. The results demonstrated that 32 loci of this self-developed panel containing 39 loci significantly contributed to the inference of genetic information for the Beijing Han population. The results of multiple population genetics statistical analyses indicated that the ancestral component and genetic architecture of the Beijing Han population were analogous to the reference East Asian populations, and that the Beijing Han population was genetically close to the reference East Asian populations.

MicroRNA Variants and HLA-miRNA Interactions are Novel Rheumatoid Arthritis Susceptibility Factors

Genome-wide association studies have identified >100 genetic risk factors for rheumatoid arthritis. However, the reported genetic variants could only explain less than 40% heritability of rheumatoid arthritis. The majority of the heritability is still missing and needs to be identified with more studies with different approaches and populations. In order to identify novel function SNPs to explain missing heritability and reveal novel mechanism pathogenesis of rheumatoid arthritis, 4 HLA SNPs (HLA-DRB1, HLA-DRB9, HLA-DQB1, and TNFAIP3) and 225 common SNPs located in miRNA, which might influence the miRNA target binding or pre-miRNA stability, were genotyped in 1,607 rheumatoid arthritis and 1,580 matched normal individuals. We identified 2 novel SNPs as significantly associated with rheumatoid arthritis including rs1414273 (miR-548ac, OR = 0.84, p = 8.26 × 10^-4) and rs2620381 (miR-627, OR = 0.77, p = 2.55 × 10^-3). We also identified that rs5997893 (miR-3928) showed significant epistasis effect with rs4947332 (HLA-DRB1, OR = 4.23, p = 0.04) and rs2967897 (miR-5695) with rs7752903 (TNFAIP3, OR = 4.43, p = 0.03). In addition, we found that individuals who carried 8 risk alleles showed 15.38 (95%CI: 4.69-50.49, p < 1.0 × 10^-6) times more risk of being affected by RA. Finally, we demonstrated that the targets of the significant miRNAs showed enrichment in immune related genes (p = 2.0 × 10^-5) and FDA approved drug target genes (p = 0.014). Overall, 6 novel miRNA SNPs including rs1414273 (miR-548ac, p = 8.26 × 10^-4), rs2620381 (miR-627, p = 2.55 × 10^-3), rs4285314 (miR-3135b, p = 1.10 × 10^-13), rs28477407 (miR-4308, p = 3.44 × 10^-5), rs5997893 (miR-3928, p = 5.9 × 10^-3) and rs45596840 (miR-4482, p = 6.6 × 10^-3) were confirmed to be significantly associated with RA in a Chinese population. Our study suggests that miRNAs might be interesting targets to accelerate understanding of the pathogenesis and drug development for rheumatoid arthritis.

Genomic insight into the population history of Central Han Chinese

BACKGROUND

In recent decades, considerable attention has been paid to exploring the population genetic characteristics of Han Chinese, mainly documenting a north-south genetic substructure. However, the central Han Chinese have been largely underrepresented in previous studies.

AIM

To infer a comprehensive understanding of the homogenisation process and population history of Han Chinese.

SUBJECTS AND METHODS

We collected samples from 122 Han Chinese from seven counties of Hubei province in central China and genotyped 534,000 genome-wide SNPs. We compared Hubei Han with both ancient and present-day Eurasian populations using Principal Component Analysis, ADMIXTURE, f statistics, qpWave and qpAdm.

RESULTS

We observed Hubei Han Chinese are at a genetically intermediate position on the north-south Han Chinese cline. We have not detected any significant genetic substructure in the studied groups from seven different counties. Hubei Han show significant evidence of genetic admixture deriving about 63% of ancestry from Tai-Kadai or Austronesian-speaking southern indigenous groups and 37% from Tungusic or Mongolic related northern populations.

CONCLUSIONS

The formation of Han Chinese has involved extensive admixture with Tai-Kadai or Austronesian-speaking populations in the south and Tungusic or Mongolic speaking populations in the north. The convenient transportation and central location of Hubei make it the key region for the homogenisation of Han Chinese.

Combined Low-/High-Density Modern and Ancient Genome-Wide Data Document Genomic Admixture History of High-Altitude East Asians

The Tibetan Plateau (TP) is considered to be one of the last terrestrial environments conquered by the anatomically modern human. Understanding of the genetic background of highland Tibetans plays a pivotal role in archeology, anthropology, genetics, and forensic investigations. Here, we genotyped 22 forensic genetic markers in 1,089 Tibetans residing in Nagqu Prefecture and collected 1,233,013 single nucleotide polymorphisms (SNPs) in the highland East Asians (Sherpa and Tibetan) from the Simons Genome Diversity Project and ancient Tibetans from Nepal and Neolithic farmers from northeastern Qinghai-Tibetan Plateau from public databases. We subsequently merged our two datasets with other worldwide reference populations or eastern ancient Eurasians to gain new insights into the genetic diversity, population movements, and admixtures of high-altitude East Asians via comprehensive population genetic statistical tools [principal component analysis (PCA), multidimensional scaling plot (MDS), STRUCTURE/ADMIXTURE, f3 , f4 , qpWave/qpAdm, and qpGraph]. Besides, we also explored their forensic characteristics and extended the Chinese National Database based on STR data. We identified 231 alleles with the corresponding allele frequencies spanning from 0.0005 to 0.5624 in the forensic low-density dataset, in which the combined powers of discrimination and the probability of exclusion were 1-1.22E-24 and 0.999999998, respectively. Additionally, comprehensive population comparisons in our low-density data among 57 worldwide populations via the Nei's genetic distance, PCA, MDS, NJ tree, and STRUCTURE analysis indicated that the highland Tibeto-Burman speakers kept the close genetic relationship with ethnically close populations. Findings from the 1240K high-density dataset not only confirmed the close genetic connection between modern Highlanders, Nepal ancients (Samdzong, Mebrak, and Chokhopani), and the upper Yellow River Qijia people, suggesting the northeastern edge of the TP served as a geographical corridor for ancient population migrations and interactions between highland and lowland regions, but also evidenced that late Neolithic farmers permanently colonized into the TP by adopting cold-tolerant barley agriculture that was mediated via the acculturation of idea via the millet farmer and not via the movement of barley agriculturalist as no obvious western Eurasian admixture signals were identified in our analyzed modern and ancient populations. Besides, results from the qpAdm-based admixture proportion estimation and qpGraph-based phylogenetic relationship reconstruction consistently demonstrated that all ancient and modern highland East Asians harbored and shared the deeply diverged Onge/Hoabinhian-related eastern Eurasian lineage, suggesting a common Paleolithic genetic legacy existed in high-altitude East Asians as the first layer of their gene pool.

Next generation sequencing of a set of ancestry-informative SNPs: ancestry assignment of three continental populations and estimating ancestry composition for Mongolians

When traditional short tandem repeat profiling fails to provide valuable information to arrest the criminal, forensic ancestry inference of the biological samples left at the crime scene will probably offer investigative leads and facilitate the investigation process of the case. That is why there are consistent efforts in developing panels for ancestry inference in forensic science. Presently, a 30-plex next generation sequencing-based assay was exploited in this study by assembling well-differentiated single nucleotide polymorphisms for ancestry assignment of unknown individuals from three continental populations (African, European and East Asian). And meanwhile, relatively balanced population-specific differentiation values were maintained to avoid the over-estimation or under-estimation of co-ancestry proportions in individuals with admixed ancestry. The principal component analysis and STRUCTURE analysis of reference populations, test populations and the studied Mongolian group indicated that the novel assay was efficient enough to determine the ancestry origin of an unknown individual from the three continental populations. Besides, ancestry membership proportion estimations for the Mongolian group revealed that a large fraction of the ancestry was contributed by East Asian genetic component (approximately 83.9%), followed by European (approximately 12.6%) and African genetic components (approximately 3.5%), respectively. And next generation sequencing technology applied in this study offers possibility to incorporate more single nucleotide polymorphisms for individual identification and phenotype prediction into the same assay to provide as many as possible investigative clues in the future.

PGG.Han: the Han Chinese genome database and analysis platform

As the largest ethnic group in the world, the Han Chinese population is nonetheless underrepresented in global efforts to catalogue the genomic variability of natural populations. Here, we developed the PGG.Han, a population genome database to serve as the central repository for the genomic data of the Han Chinese Genome Initiative (Phase I). In its current version, the PGG.Han archives whole-genome sequences or high-density genome-wide single-nucleotide variants (SNVs) of 114 783 Han Chinese individuals (a.k.a. the Han100K), representing geographical sub-populations covering 33 of the 34 administrative divisions of China, as well as Singapore. The PGG.Han provides: (i) an interactive interface for visualization of the fine-scale genetic structure of the Han Chinese population; (ii) genome-wide allele frequencies of hierarchical sub-populations; (iii) ancestry inference for individual samples and controlling population stratification based on nested ancestry informative markers (AIMs) panels; (iv) population-structure-aware shared control data for genotype-phenotype association studies (e.g. GWASs) and (v) a Han-Chinese-specific reference panel for genotype imputation. Computational tools are implemented into the PGG.Han, and an online user-friendly interface is provided for data analysis and results visualization. The PGG.Han database is freely accessible via http://www.pgghan.org or https://www.hanchinesegenomes.org.

Targeted resequencing of 358 candidate genes for autism spectrum disorder in a Chinese cohort reveals diagnostic potential and genotype-phenotype correlations

Autism spectrum disorder (ASD) is a childhood neuropsychiatric disorder with a complex genetic architecture. The diagnostic potential of a targeted panel of ASD genes has only been evaluated in small cohorts to date and is especially understudied in the Chinese population. Here, we designed a capture panel with 358 genes (111 syndromic and 247 nonsyndromic) for ASD and sequenced a Chinese cohort of 539 cases evaluated with the Autism Diagnostic Interview‐Revised (ADI‐R) and the Autism Diagnostic Observation Schedule (ADOS) as well as 512 controls. ASD cases were found to carry significantly more ultra‐rare functional variants than controls. A subset of 78 syndromic and 54 nonsyndromic genes was the most significantly associated and should be given high priority in the future screening of ASD patients. Pathogenic and likely pathogenic variants were detected in 9.5% of cases. Variants in SHANK3 and SHANK2 were the most frequent, especially in females, and occurred in 1.2% of cases. Duplications of 15q11–13 were detected in 0.8% of cases. Variants in CNTNAP2 and MEF2C were correlated with epilepsy/tics in cases. Our findings reveal the diagnostic potential of ASD genetic panel testing and new insights regarding the variant spectrum. Genotype–phenotype correlations may facilitate the diagnosis and management of ASD.

A set of novel SNP loci for differentiating continental populations and three Chinese populations

In recent years, forensic geneticists have begun to develop some ancestry informative marker (AIM) panels for ancestry analysis of regional populations. In this study, we chose 48 single nucleotide polymorphisms (SNPs) from SPSmart database to infer ancestry origins of continental populations and Chinese subpopulations. Based on the genetic data of four continental populations (African, American, East Asian and European) from the CEPH-HGDP database, the power of these SNPs for differentiating continental populations was assessed. Population genetic structure revealed that distinct ancestry components among these continental populations could be discerned by these SNPs. Another novel population set from 1000 Genomes Phase 3 was treated as testing populations to further validate the efficiency of the selected SNPs. Twenty-two populations from CEPH-HGDP database were classified into three known populations (African, East Asian, and European) based on their biogeographical regions. Principal component analysis and Bayes analysis of testing populations and three known populations indicated these testing populations could be correctly assigned to their corresponding biogeographical origins. For three Chinese populations (Han, Mongolian, and Uygur), multinomial logistic regression analyses indicated that these 48 SNPs could be used to estimate ancestry origins of these populations. Therefore, these SNPs possessed the promising potency in ancestry analysis among continental populations and some Chinese populations, and they could be used in population genetics and forensic research.

Selection of Optimal Ancestry Informative Markers for Classification and Ancestry Proportion Estimation in Pigs

Using small sets of ancestry informative markers (AIMs) constitutes a cost-effective method to accurately estimate the ancestry proportions of individuals. This study aimed to generate a small and effective number of AIMs from ∼60 K single nucleotide polymorphism (SNP) data of porcine and estimate three ancestry proportions [East China pig (ECHP), South China pig (SCHP), and European commercial pig (EUCP)] from Asian breeds and European domestic breeds. A total of 186 samples of 10 pure breeds were divided into three groups: ECHP, SCHP, and EUCP. Using these samples and a one-vs.-rest SVM classifier, we found that using only seven AIMs could completely separate the three groups. Subsequently, we utilized supervised ADMIXTURE to calculate ancestry proportions and found that the 129 AIMs performed well on ancestry estimates when pseudo admixed individuals were used. Furthermore, another 969 samples of 61 populations were applied to evaluate the performance of the 129 AIMs. We also observed that the 129 AIMs were highly correlated with estimates using ∼60 K SNP data for three ancestry components: ECHP (Pearson correlation coefficient (r) = 0.94), SCHP (r = 0.94), and EUCP (r = 0.99). Our results provided an example of using a small number of pig AIMs for classifications and estimating ancestry proportions with high accuracy and in a cost-effective manner.

Genetic structure, divergence and admixture of Han Chinese, Japanese and Korean populations

Background

Han Chinese, Japanese and Korean, the three major ethnic groups of East Asia, share many similarities in appearance, language and culture etc., but their genetic relationships, divergence times and subsequent genetic exchanges have not been well studied.

Results

We conducted a genome-wide study and evaluated the population structure of 182 Han Chinese, 90 Japanese and 100 Korean individuals, together with the data of 630 individuals representing 8 populations wordwide. Our analyses revealed that Han Chinese, Japanese and Korean populations have distinct genetic makeup and can be well distinguished based on either the genome wide data or a panel of ancestry informative markers (AIMs). Their genetic structure corresponds well to their geographical distributions, indicating geographical isolation played a critical role in driving population differentiation in East Asia. The most recent common ancestor of the three populations was dated back to 3000 ~ 3600 years ago. Our analyses also revealed substantial admixture within the three populations which occurred subsequent to initial splits, and distinct gene introgression from surrounding populations, of which northern ancestral component is dominant.

Conclusions

These estimations and findings facilitate to understanding population history and mechanism of human genetic diversity in East Asia, and have implications for both evolutionary and medical studies.

Relationship between Modulator Recognition Factor 2/AT-rich Interaction Domain 5B Gene Variations and Type 2 Diabetes Mellitus or Lipid Metabolism in a Northern Chinese Population

Background:

Four single nucleotide polymorphisms (SNPs) in the modulator recognition factor 2/AT-rich interaction domain 5B (MRF2/ARID5B) gene located at chromosome 10q21.2 have been shown to be associated with both type 2 diabetes mellitus (T2DM) and coronary artery disease in a Japanese cohort. This study aimed to investigate the relationship between these SNPs (rs2893880, rs10740055, rs7087507, rs10761600) and new-onset T2DM and lipid metabolism in a Northern Chinese population.

Methods:

This was a case-control study. The rs2893880, rs10740055, rs7087507, and rs10761600 genetic variants were genotyped by SNPscan and analyzed in relation to T2DM susceptibility in 2000 individuals (999 with newly diagnosed T2DM and 1001 controls without diabetes mellitus). Associations between the MRF2/ARID5B genetic models and T2DM were determined by multivariate logistic regression.

Results:

Regarding the rs10740055 SNP, AA was associated with a higher risk of T2DM compared with codominant-type CC (adjusted by sex, age, and body mass index [BMI], P = 0.041, odds ratio [OR] = 1.421, 95% confidence interval [CI] 1.014–1.991). Meanwhile, AA individuals were at increased risk of presenting with T2DM compared with individuals with CC or a single C (adjusted by sex, age, and BMI, P = 0.034, OR = 1.366, 95% CI 1.023–1.824). With respect to rs10761600, AT contributed to a higher risk of T2DM compared with AA (adjusted by sex, age, and BMI, P = 0.013, OR = 1.585, 95% CI 1.101–2.282), while TT also increased the risk of presenting with T2DM compared with AA or A (adjusted by sex, age, and BMI, P = 0.004, OR = 1.632, 95% CI 1.166–2.284). High-density lipoprotein cholesterol (HDL-C) levels were significantly different among the three genotypes of rs7087507 in the controls (P = 0.048) (GG>GA).

Conclusions:

The present results identified MRF2/ARID5B as a potential susceptibility gene for new-onset T2DM in a Northern Chinese population, while the rs7087507 SNP was associated with HDL-C levels. Further larger studies are required to validate these findings.

Homozygous p.Ser267Phe in SLC10A1 is associated with a new type of hypercholanemia and implications for personalized medicine

SLC10A1 codes for the sodium-taurocholate cotransporting polypeptide (NTCP), which is a hepatocellular transporter for bile acids (BAs) and the receptor for hepatitis B and D viruses. NTCP is also a target of multiple drugs. We aimed to evaluate the medical consequences of the loss of function mutation p.Ser267Phe in SLC10A1. We identified eight individuals with homozygous p.Ser267Phe mutation in SLC10A1 and followed up for 8–90 months. We compared their total serum BAs and 6 species of BAs with 170 wild-type and 107 heterozygous healthy individuals. We performed in-depth medical examinations and exome sequencing in the homozygous individuals. All homozygous individuals had persistent hypercholanemia (P = 5.8 × 10^–29). Exome sequencing excluded the involvement of other BA metabolism-associated genes in the hypercholanemia. Although asymptomatic, all individuals had low vitamin D levels. Of six adults that were subjected to bone mineral density analysis, three presented with osteoporosis/osteopenia. Sex hormones and blood lipids were deviated in all subjects. Homozygosity of p.Ser267Phe in SLC10A1 is associated with asymptomatic hypercholanemia. Individuals with homozygous p.Ser267Phe in SLC10A1 are prone to vitamin D deficiency, deviated sex hormones and blood lipids. Surveillance of these parameters may also be needed in patients treated with drugs targeting NTCP.

Multi-InDel Analysis for Ancestry Inference of Sub-Populations in China

Ancestry inference is of great interest in diverse areas of scientific researches, including the forensic biology, medical genetics and anthropology. Various methods have been published for distinguishing populations. However, few reports refer to sub-populations (like ethnic groups) within Asian populations for the limitation of markers. Several InDel loci located very tightly in physical positions were treated as one marker by us, which is multi-InDel. The multi-InDel shows potential as Ancestry Inference Marker (AIM). In this study, we performed a genome-wide scan for multi-InDels as AIM. After examining the F_ST distributions in the 1000 Genomes Database, 12 candidates were selected and validated for eastern Asian populations. A multiplexed assay was developed as a panel to genotype 12 multi-InDel markers simultaneously. Ancestry component analysis with STRUCTURE and principal component analysis (PCA) were employed to estimate its capability for ancestry inference. Furthermore, ancestry assignments of trial individuals were conducted. It proved to be very effective when 210 samples from Han and Tibetan individuals in China were tested. The panel consisting of multi-InDel markers exhibited considerable potency in ancestry inference, and was suggested to be applied in forensic practices and genetic population studies.

Genetic Variation of 25 Y-Chromosomal and 15 Autosomal STR Loci in the Han Chinese Population of Liaoning Province, Northeast China

In the present study, we investigated the genetic characteristics of 25 Y-chromosomal and 15 autosomal short tandem repeat (STR) loci in 305 unrelated Han Chinese male individuals from Liaoning Province using AmpFISTR^® Yfiler^® Plus and Identifiler^TM PCR amplification kits. Population comparison was performed between Liaoning Han population and different ethnic groups to better understand the genetic background of the Liaoning Han population. For Y-STR loci, the overall haplotype diversity was 0.9997 and the discrimination capacity was 0.9607. Gene diversity values ranged from 0.4525 (DYS391) to 0.9617 (DYS385). Rst and two multi-dimensional scaling plots showed that minor differences were observed when the Liaoning Han population was compared to the Jilin Han Chinese, Beijing Han Chinese, Liaoning Manchu, Liaoning Mongolian, Liaoning Xibe, Shandong Han Chinese, Jiangsu Han Chinese, Anhui Han Chinese, Guizhou Han Chinese and Liaoning Hui populations; by contrast, major differences were observed when the Shanxi Han Chinese, Yunnan Bai, Jiangxi Han Chinese, Guangdong Han Chinese, Liaoning Korean, Hunan Tujia, Guangxi Zhuang, Gansu Tibetan, Xishuangbanna Dai, South Korean, Japanese and Hunan Miao populations. For autosomal STR loci, DP ranged from 0.9621 (D2S1338) to 0.8177 (TPOX), with PE distributing from 0.7521 (D18S51) to 0.2988 (TH01). A population comparison was performed and no statistically significant differences were detected at any STR loci between Liaoning Han, China Dong, and Shaanxi Han populations. The results showed that the 25 Y-STR and 15 autosomal STR loci in the Liaoning Han population were valuable for forensic applications and human genetics, and Liaoning Han was an independent endogenous ethnicity with a unique subpopulation structure.

Genotyping of the c.1423C>T (p.P475S) polymorphism in the ADAMTS13 gene by APLP and HRM assays: Northeastern Asian origin of the mutant

ADAMTS13 is a von Willebrand factor-cleaving protease. The mutant types of p.P475S (c.1423C>T) polymorphism in ADAMTS13 have a reduced activity in comparison with the wild type. In the present study, we investigated the frequency of the C-to-T substitution in 2584 genomic DNA samples from 25 Asian, European, and African populations using APLP (amplified product length polymorphism) and/or HRM (high-resolution melting) assays. Allele T (ADAMTS13(∗)T) was detected only in Asian populations and its frequency was observed to decrease gradually from north to south in 24 East Asian populations. Almost all ADAMTS13(∗)T were associated with ABO(∗)O. These results suggested that ADAMTS13(∗)T had occurred on a chromosome with ABO(∗)O in a northern part of East Asia. This SNP is useful as an ancestry-informative marker, and the present genotyping techniques are applicable to the investigation of an association between this SNP and aortic dissection (Kobayashi et al., 2012).

Tracking crop varieties using genotyping-by-sequencing markers: a case study using cassava (Manihot esculenta Crantz)

Background

Accurate identification of crop cultivars is crucial in assessing the impact of crop improvement research outputs. Two commonly used identification approaches, elicitation of variety names from farmer interviews and morphological plant descriptors, have inherent uncertainty levels. Genotyping-by-sequencing (GBS) was used in a case study as an alternative method to track released varieties in farmers’ fields, using cassava, a clonally propagated root crop widely grown in the tropics, and often disseminated through extension services and informal seed systems. A total of 917 accessions collected from 495 farming households across Ghana were genotyped at 56,489 SNP loci along with a “reference library” of 64 accessions of released varieties and popular landraces.

Results

Accurate cultivar identification and ancestry estimation was accomplished through two complementary clustering methods: (i) distance-based hierarchical clustering; and (ii) model-based maximum likelihood admixture analysis. Subsequently, 30 % of the identified accessions from farmers’ fields were matched to specific released varieties represented in the reference library. ADMIXTURE analysis revealed that the optimum number of major varieties was 11 and matched the hierarchical clustering results. The majority of the accessions (69 %) belonged purely to one of the 11 groups, while the remaining accessions showed two or more ancestries. Further analysis using subsets of SNP markers reproduced results obtained from the full-set of markers, suggesting that GBS can be done at higher DNA multiplexing, thereby reducing the costs of variety fingerprinting. A large proportion of discrepancy between genetically unique cultivars as identified by markers and variety names as elicited from farmers were observed. Clustering results from ADMIXTURE analysis was validated using the assumption-free Discriminant Analysis of Principal Components (DAPC) method.

Conclusion

We show that genome-wide SNP markers from increasingly affordable GBS methods coupled with complementary cluster analysis is a powerful tool for fine-scale population structure analysis and variety identification. Moreover, the ancestry estimation provides a framework for quantifying the contribution of exotic germplasm or older improved varieties to the genetic background of contemporary improved cultivars.

Electronic supplementary material

The online version of this article (doi:10.1186/s12863-015-0273-1) contains supplementary material, which is available to authorized users.

Reveel: large-scale population genotyping using low-coverage sequencing data

MOTIVATION

Population low-coverage whole-genome sequencing is rapidly emerging as a prominent approach for discovering genomic variation and genotyping a cohort. This approach combines substantially lower cost than full-coverage sequencing with whole-genome discovery of low-allele frequency variants, to an extent that is not possible with array genotyping or exome sequencing. However, a challenging computational problem arises of jointly discovering variants and genotyping the entire cohort. Variant discovery and genotyping are relatively straightforward tasks on a single individual that has been sequenced at high coverage, because the inference decomposes into the independent genotyping of each genomic position for which a sufficient number of confidently mapped reads are available. However, in low-coverage population sequencing, the joint inference requires leveraging the complex linkage disequilibrium (LD) patterns in the cohort to compensate for sparse and missing data in each individual. The potentially massive computation time for such inference, as well as the missing data that confound low-frequency allele discovery, need to be overcome for this approach to become practical.

RESULTS

Here, we present Reveel, a novel method for single nucleotide variant calling and genotyping of large cohorts that have been sequenced at low coverage. Reveel introduces a novel technique for leveraging LD that deviates from previous Markov-based models, and which is aimed at computational efficiency as well as accuracy in capturing LD patterns present in rare haplotypes. We evaluate Reveel's performance through extensive simulations as well as real data from the 1000 Genomes Project, and show that it achieves higher accuracy in low-frequency allele discovery and substantially lower computation cost than previous state-of-the-art methods.

AVAILABILITY AND IMPLEMENTATION

http://reveel.stanford.edu/

CONTACT

: serafim@cs.stanford.edu

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

Fine-scale population structure of Malays in Peninsular Malaysia and Singapore and implications for association studies

Fine scale population structure of Malays - the major population in Malaysia, has not been well studied. This may have important implications for both evolutionary and medical studies. Here, we investigated the population sub-structure of Malay involving 431 samples collected from all states from peninsular Malaysia and Singapore. We identified two major clusters of individuals corresponding to the north and south peninsular Malaysia. On an even finer scale, the genetic coordinates of the geographical Malay populations are in correlation with the latitudes (R² = 0.3925; P = 0.029). This finding is further supported by the pairwise F_ST of Malay sub-populations, of which the north and south regions showed the highest differentiation (F_{ST [North–south]} = 0.0011). The collective findings therefore suggest that population sub-structure of Malays are more heterogenous than previously expected even within a small geographical region, possibly due to factors like different genetic origins, geographical isolation, could result in spurious association as demonstrated in our analysis. We suggest that cautions should be taken during the stage of study design or interpreting the association signals in disease mapping studies which are expected to be conducted in Malay population in the near future.

Evaluating information content of SNPs for sample-tagging in re-sequencing projects

Sample-tagging is designed for identification of accidental sample mix-up, which is a major issue in re-sequencing studies. In this work, we develop a model to measure the information content of SNPs, so that we can optimize a panel of SNPs that approach the maximal information for discrimination. The analysis shows that as low as 60 optimized SNPs can differentiate the individuals in a population as large as the present world, and only 30 optimized SNPs are in practice sufficient in labeling up to 100 thousand individuals. In the simulated populations of 100 thousand individuals, the average Hamming distances, generated by the optimized set of 30 SNPs are larger than 18, and the duality frequency, is lower than 1 in 10 thousand. This strategy of sample discrimination is proved robust in large sample size and different datasets. The optimized sets of SNPs are designed for Whole Exome Sequencing, and a program is provided for SNP selection, allowing for customized SNP numbers and interested genes. The sample-tagging plan based on this framework will improve re-sequencing projects in terms of reliability and cost-effectiveness.

The p.Ser267Phe variant in SLC10A1 is associated with resistance to chronic hepatitis B

In the past 50 years there have been considerable efforts to identify the cellular receptor of hepatitis B virus (HBV). Recently, in vitro evidence from several groups has shown that the sodium-taurocholate cotransporting polypeptide (NTCP, which is encoded by SLC10A1 and transports bile acids into hepatic cells in enterohepatic recirculation) is a strong candidate. In particular, in vitro the p.Ser267Phe variation of SLC10A1 results in loss of HBV receptor function. We tested the role of NTCP as a receptor for HBV in chronic hepatitis B patients using a genetic association study. We selected SLC10A1 variants from 189 exomes. We used Sanger sequencing to follow up the association of the various SLC10A1 variants in a Han Chinese cohort of 1899 chronic hepatitis B patients and 1828 healthy controls. We further investigated the potential impact of the p.Ser267Phe variant on NTCP function using structural analysis. The p.Ser267Phe variant was associated with healthy status (P = 5.7 × 10(-23) , odds ratio = 0.36) irrespective of hepatitis B virus surface antibody status (P = 6.2 × 10(-21) and 1.5 × 10(-10) , respectively, when the cases were compared with hepatitis B virus surface antibody-positive and -negative controls). The variation was also associated with a lower incidence of acute-on-chronic liver failure (P = 0.007). The estimated heritability explained by this single variation was ∼3.2%. The population prevented fraction was around 13.0% among the southern Chinese. Our structural modeling showed that the p.Ser267Phe variant might interfere with ligand binding, thereby preventing HBV from cellular entry.

CONCLUSION

The p.Ser267Phe NTCP variant is significantly associated with resistance to chronic hepatitis B and a lower incidence of acute-on-chronic liver failure. Our results support that NTCP is a cellular receptor for HBV in human infection.

Genetic variability and phylogenetic analysis of Han population from Guanzhong region of China based on 21 non-CODIS STR loci

In the present study, we presented the population genetic data and their forensic parameters of 21 non-CODIS autosomal STR loci in Chinese Guanzhong Han population. A total of 166 alleles were observed with corresponding allelic frequencies ranging from 0.0018 to 0.5564. No STR locus was observed to deviate from the Hardy-Weinberg equilibrium and linkage disequilibriums after applying Bonferroni correction. The cumulative power of discrimination and probability of exclusion of all the 21 STR loci were 0.99999999999999999993814 and 0.999998184, respectively. The results of genetic distances, phylogenetic trees and principal component analysis revealed that the Guanzhong Han population had a closer relationship with Ningxia Han, Tujia and Bai groups than other populations tested. In summary, these 21 STR loci showed a high level of genetic polymorphisms for the Guanzhong Han population and could be used for forensic applications and the studies of population genetics.

Population-specific common SNPs reflect demographic histories and highlight regions of genomic plasticity with functional relevance

BACKGROUND

Population differentiation is the result of demographic and evolutionary forces. Whole genome datasets from the 1000 Genomes Project (October 2012) provide an unbiased view of genetic variation across populations from Europe, Asia, Africa and the Americas. Common population-specific SNPs (MAF > 0.05) reflect a deep history and may have important consequences for health and wellbeing. Their interpretation is contextualised by currently available genome data.

RESULTS

The identification of common population-specific (CPS) variants (SNPs and SSV) is influenced by admixture and the sample size under investigation. Nine of the populations in the 1000 Genomes Project (2 African, 2 Asian (including a merged Chinese group) and 5 European) revealed that the African populations (LWK and YRI), followed by the Japanese (JPT) have the highest number of CPS SNPs, in concordance with their histories and given the populations studied. Using two methods, sliding 50-SNP and 5-kb windows, the CPS SNPs showed distinct clustering across large genome segments and little overlap of clusters between populations. iHS enrichment score and the population branch statistic (PBS) analyses suggest that selective sweeps are unlikely to account for the clustering and population specificity. Of interest is the association of clusters close to recombination hotspots. Functional analysis of genes associated with the CPS SNPs revealed over-representation of genes in pathways associated with neuronal development, including axonal guidance signalling and CREB signalling in neurones.

CONCLUSIONS

Common population-specific SNPs are non-randomly distributed throughout the genome and are significantly associated with recombination hotspots. Since the variant alleles of most CPS SNPs are the derived allele, they likely arose in the specific population after a split from a common ancestor. Their proximity to genes involved in specific pathways, including neuronal development, suggests evolutionary plasticity of selected genomic regions. Contrary to expectation, selective sweeps did not play a large role in the persistence of population-specific variation. This suggests a stochastic process towards population-specific variation which reflects demographic histories and may have some interesting implications for health and susceptibility to disease.