Population genetics--making sense out of sequence

Massively parallel sequencing of a forensic combined panel of 107-plex STR loci and 292-plex SNP loci in the Han Chinese population

Massively parallel sequencing (MPS), a well-established strategy for forensic DNA profiling, enables the simultaneous sequencing of multiple targeted loci of multiple samples at a single-base resolution with high coverage. In this study, we developed a novel typing system by combining solution-based hybrid capture methods with MPS to target as many as 107 short tandem repeats (STRs) and 292 single nucleotide polymorphisms (SNPs) in the Han Chinese population. Completely accurate and concordant STR genotypes were obtained when compared to typing results generated from conventional capillary electrophoresis analysis, with six loci exhibiting inferior performance due to allele dropout or even locus dropout. The locus detection success reached 85.2 % for STRs at a DNA input of 10 ng and 95.61 % for SNPs at a DNA input of 5 ng. Mixture studies substantiated the considerable potential of our system in identifying minor contributor alleles at both STR and SNP loci. Additionally, the system demonstrated full inferential abilities in distinguishing first-degree kinship from unrelated individual pairs and achieved significant effectiveness of 99.78 % and 80.2 % for the identification of second- and third-degree kinship, respectively. These findings indicated that our novel typing system is highly discriminative and informative when used in the Han Chinese population and would be highly efficient for use in paternity testing and complex kinship analysis.

Genetic Diversity and Forensic Utility of X-STR Loci in Punjabi and Kashmiri Populations: Insights into Population Structure and Ancestry

Background: X-chromosomal short tandem repeats (X-STRs) are crucial in forensic applications, particularly in complex kinship cases, and play an important role in population genetics. However, there is limited data on X-STR variation in Pakistani populations, especially among ethnic groups like Kashmiri and Punjabi. Methodology: This study investigates the forensic and genetic properties of 12 X-STRs from the Investigator Argus X-12 Kit (QIAGEN, Hilden, Germany) in 125 families (75 Kashmiri, 50 Punjabi) from Azad Jammu and Kashmir and Punjab, Pakistan. Results: In both populations, a total of 222 alleles were identified across the 12 X-STR loci (Punjabi 171 alleles, Kashmiri 161 alleles), with allele frequencies ranging from 0.0056 to 0.3033. DXS10148 was the most polymorphic locus with 28 alleles, while DXS7132 was the least polymorphic with 9 alleles. Most loci were in linkage equilibrium, except for the DXS10135/DXS10148 pair in males, with no loci exhibiting significant linkage disequilibrium in females. The combined power of discrimination was 0.999 999 9977 for Kashmiri males, 0.999 999 999 999 9746 for Kashmiri females, and 0.999 999 999 999 9781 for Punjabi females. In Kashmiri males, 34, 31, 28, and 32 haplotypes were observed across the four linkage groups (LG1, LG2, LG3, and LG4), though these groups did not form stable haplotypes, as indicated by Linkage Equilibrium within and significant Linkage Disequilibrium between groups. Conclusions: Genetic structure analysis using Principal Component Analysis and STRUCTURE revealed distinct clustering patterns for the Kashmiri and Punjabi populations, indicating unique genetic backgrounds and ancestry influences, particularly distinguishing them from East Asian populations. This study provides a comprehensive analysis of X-STR variation in Punjabi and Kashmiri populations, offering valuable insights for forensic and population genetic studies.

Patterns of Change in Nucleotide Diversity Over Gene Length

Nucleotide diversity at a site is influenced by the relative strengths of neutral and selective population genetic processes. Therefore, attempts to estimate Effective population size based on the diversity of synonymous sites demand a better understanding of their selective constraints. The nucleotide diversity of a gene was previously found to correlate with its length. In this work, I measure nucleotide diversity at synonymous sites and uncover a pattern of low diversity towards the translation initiation site of a gene. The degree of reduction in diversity at the translation initiation site and the length of this region of reduced diversity can be quantified as "Effect Size" and "Effect Length" respectively, using parameters of an asymptotic regression model. Estimates of Effect Length across bacteria covaried with recombination rates as well as with a multitude of translation-associated traits such as the avoidance of mRNA secondary structure around translation initiation site, the number of rRNAs, and relative codon usage of ribosomal genes. Evolutionary simulations under purifying selection reproduce the observed patterns and diversity-length correlation and highlight that selective constraints on the 5'-region of a gene may be more extensive than previously believed. These results have implications for the estimation of effective population size, and relative mutation rates, and for genome scans of genes under positive selection based on "silent-site" diversity.

Genomic and demographic processes differentially influence genetic variation across the human X chromosome

Many forces influence genetic variation across the genome including mutation, recombination, selection, and demography. Increased mutation and recombination both lead to increases in genetic diversity in a region-specific manner, while complex demographic patterns shape patterns of diversity on a more global scale. While these processes act across the entire genome, the X chromosome is particularly interesting because it contains several distinct regions that are subject to different combinations and strengths of these forces: the pseudoautosomal regions (PARs) and the X-transposed region (XTR). The X chromosome thus can serve as a unique model for studying how genetic and demographic forces act in different contexts to shape patterns of observed variation. We therefore sought to explore diversity, divergence, and linkage disequilibrium in each region of the X chromosome using genomic data from 26 human populations. Across populations, we find that both diversity and substitution rate are consistently elevated in PAR1 and the XTR compared to the rest of the X chromosome. In contrast, linkage disequilibrium is lowest in PAR1, consistent with the high recombination rate in this region, and highest in the region of the X chromosome that does not recombine in males. However, linkage disequilibrium in the XTR is intermediate between PAR1 and the autosomes, and much lower than the non-recombining X. Finally, in addition to these global patterns, we also observed variation in ratios of X versus autosomal diversity consistent with population-specific evolutionary history as well. While our results were generally consistent with previous work, two unexpected observations emerged. First, our results suggest that the XTR does not behave like the rest of the recombining X and may need to be evaluated separately in future studies. Second, the different regions of the X chromosome appear to exhibit unique patterns of linked selection across different human populations. Together, our results highlight profound regional differences across the X chromosome, simultaneously making it an ideal system for exploring the action of evolutionary forces as well as necessitating its careful consideration and treatment in genomic analyses.

Patterns of change in nucleotide diversity over gene length

Nucleotide diversity at a site is influenced by the relative strengths of neutral and selective population genetic processes. Therefore, attempts to identify sites under positive selection require an understanding of the expected diversity in its absence. The nucleotide diversity of a gene was previously found to correlate with its length. In this work, I measure nucleotide diversity at synonymous sites and uncover a pattern of low diversity towards the translation initiation site (TIS) of a gene. The degree of reduction in diversity at the TIS and the length of this region of reduced diversity can be quantified as "Effect Size" and "Effect Length" respectively, using parameters of an asymptotic regression model. Estimates of Effect Length across bacteria covaried with recombination rates as well as with a multitude of fast-growth adaptations such as the avoidance of mRNA secondary structure around TIS, the number of rRNAs, and relative codon usage of ribosomal genes. Thus, the dependence of nucleotide diversity on gene length is governed by a combination of selective and non-selective processes. These results have implications for the estimation of effective population size and relative mutation rates based on "silent-site" diversity, and for pN/pS-based prediction of genes under selection.

Main Polymorphisms in Aspirin-Exacerbated Respiratory Disease

Aspirin exacerbated respiratory disease (AERD) is a condition caused by increased bronchoconstriction in people with asthma after taking aspirin or another NSAID. Molecular analysis of the human genome has opened up new perspectives on human polymorphisms and disease. This study was conducted to identify the genetic factors that influence this disease due to its unknown genetic factors. We evaluated research studies, letters, comments, editorials, eBooks, and reviews. PubMed/MEDLINE, Web of Sciences, Cochrane Library, and Scopus were searched for information. We used the keywords polymorphisms, aspirin-exacerbated respiratory disease, asthma, allergy as search terms. This study included 38 studies. AERD complications were associated with polymorphisms in ALOX15, EP2, ADRB2, SLC6A12, CCR3, CRTH2, CysLTs, DPCR1, DPP10, FPR2, HSP70, IL8, IL1B, IL5RA, IL-13, IL17RA, ILVBL, TBXA2R, TLR3, HLA-DRB and HLA-DQ, HLA-DR7, HLA-DP. AERD was associated with heterogeneity in gene polymorphisms, making it difficult to pinpoint specific gene changes. Therefore, diagnosing and treating AERD may be facilitated by examining common variants involving the disease.

Botryosphaeriaceae gene machinery: Correlation between diversity and virulence

The Botryosphaeriaceae family comprises numerous fungal pathogens capable of causing economically meaningful diseases in a wide range of crops. Many of its members can live as endophytes and turn into aggressive pathogens following the onset of environmental stress events. Their ability to cause disease may rely on the production of a broad set of effectors, such as cell wall-degrading enzymes, secondary metabolites, and peptidases. Here, we conducted comparative analyses of 41 genomes representing six Botryosphaeriaceae genera to provide insights into the genetic features linked to pathogenicity and virulence. We show that these Botryosphaeriaceae genomes possess a large diversity of carbohydrate-active enzymes (CAZymes; 128 families) and peptidases (45 families). Botryosphaeria, Neofusicoccum, and Lasiodiplodia presented the highest number of genes encoding CAZymes involved in the degradation of the plant cell wall components. The genus Botryosphaeria also exhibited the highest abundance of secreted CAZymes and peptidases. Generally, the secondary metabolites gene cluster profile was consistent in the Botryosphaeriaceae family, except for Diplodia and Neoscytalidium. At the strain level, Neofusicoccum parvum NpBt67 stood out among all the Botryosphaeriaceae genomes, presenting a higher number of secretome constituents. In contrast, the Diplodia strains showed the lowest richness of the pathogenicity- and virulence-related genes, which may correlate with their low virulence reported in previous studies. Overall, these results contribute to a better understanding of the mechanisms underlying pathogenicity and virulence in remarkable Botryosphaeriaceae species. Our results also support that Botryosphaeriaceae species could be used as an interesting biotechnological tool for lignocellulose fractionation and bioeconomy.

The emergence of genotypic divergence and future precision medicine applications

Genotypic divergence is a term adapted from population genetics and intimately linked to evolution. We use divergence here to emphasize the differences that set individuals apart in any cohort. The history of genetics is filled with descriptions of genotypic differences, but causal inference of interindividual biological variation has been scarce. We suggest that the practice of precision medicine requires a divergent approach, an approach dependent on the causal interpretation of previous convergent (and preliminary) knowledge in the field. This knowledge has relied on convergent descriptive syndromology (lumping), which has overemphasized a reductionistic gene determinism on the quest of seeking associations without causal understanding. Regulatory variants with small effect and somatic mutations are some of the modifying factors that lead to incomplete penetrance and intrafamilial variable expressivity often observed in apparently monogenic clinical disorders. A truly divergent approach to precision medicine requires splitting, that is, the consideration of different layers of genetic phenomena that interact causally in a nonlinear fashion. This chapter reviews convergences and divergences in genetics and genomics, aiming to discuss what can be causally understood to approximate the as-yet utopian lands of Precision Medicine for patients with neurodegenerative disorders.

Genetic polymorphisms of 17 X-STR loci in two Tunisian populations from Sousse and Makthar

BACKGROUND

Tunisia has a complex demographic history of migrations from within Africa, Europe, and the Middle East. However, only one population study based on X-STR markers has been reported so far.

AIM

To investigate the genetic polymorphisms of 17 X-STRs in two Tunisian populations from the cities of Sousse and Makthar, and to reveal the genetic relationships with other reference populations.

SUBJECTS AND METHODS

A total of 194 unrelated healthy individuals were analysed for 17 X-STR markers.

RESULTS

Our results indicate that DXS6809 is the most polymorphic locus, whereas DXS6807 is the least informative marker in the populations of Sousse and Makthar. In addition, forensic statistical parameters, such as the power of discrimination in males and females, as well as the mean of exclusion in duos and trios, reveal that the panel of 17 X-STRs is highly informative and useful in different forensic applications. Overall, pairwise genetic distances (Fst) and non-metric MDS plots demonstrate clustering of different populations according to their geographic locations and their historical relationships.

CONCLUSION

Overall, the study of X-STR markers of the Tunisian populations can help to promote the establishment of a forensic DNA reference database in Tunisia and provide reference for future anthropological research.

Molecular Alterations of the Endocannabinoid System in Psychiatric Disorders

The therapeutic benefits of the current medications for patients with psychiatric disorders contrast with a great variety of adverse effects. The endocannabinoid system (ECS) components have gained high interest as potential new targets for treating psychiatry diseases because of their neuromodulator role, which is essential to understanding the regulation of many brain functions. This article reviewed the molecular alterations in ECS occurring in different psychiatric conditions. The methods used to identify alterations in the ECS were also described. We used a translational approach. The animal models reproducing some behavioral and/or neurochemical aspects of psychiatric disorders and the molecular alterations in clinical studies in post-mortem brain tissue or peripheral tissues were analyzed. This article reviewed the most relevant ECS changes in prevalent psychiatric diseases such as mood disorders, schizophrenia, autism, attentional deficit, eating disorders (ED), and addiction. The review concludes that clinical research studies are urgently needed for two different purposes: (1) To identify alterations of the ECS components potentially useful as new biomarkers relating to a specific disease or condition, and (2) to design new therapeutic targets based on the specific alterations found to improve the pharmacological treatment in psychiatry.

Rare diseases: human genome research is coming home

After a long and largely disappointing detour, Genome Research has reidentified Rare Diseases as a major opportunity for improving health care and a clue to understanding gene and genome function. In this Special Issue of CSH Molecular Case Studies on Rare Diseases, several invited Perspectives, numerous Case Reports, and this Editorial itself address recent breakthroughs as well as unsolved problems in this wide field. These range from exciting prospects for gap-free diagnostic whole-genome sequencing to persisting problems related to identifying and distinguishing pathogenic and benign variants; and from the good news that soon, the United Kingdom will no longer be the only country to have introduced whole-genome sequencing into health care to the sobering conclusion that in many countries the clinical infrastructure for bringing Genome Medicine to the patient is still lacking. With less than 5000 genes firmly implicated in disease, the identification of at least twice as many disease genes is a major challenge, and the elucidation of their function is an even larger task. But given the renewed interest in rare diseases, their importance for health care, and the vast and growing spectrum of concepts and methods for studying them, the future of Human Genome Research is bright.

Genetic characterization of the highlander Tibetan population from Qinghai-Tibet Plateau revealed by X chromosomal STRs

Tibetans are considered an East Asian ethnic group and primarily live in the high Tibetan plateau, the western Sichuan and Yunnan mountains of central and southern China, and areas throughout the Himalayas and around the Tibetan plateau. These people exhibit rare molecular machinery that allows them to adapt to hypoxic environments in the Qinghai-Tibet Plateau and make them a potential candidate for providing insights related to medical genetic, molecular medicine and human population studies. In the current study, we have genotyped 549 individuals with Investigator Argus X-12 Kit. For 12 X-STRs, a total of 174 unique alleles were found, among them DXS10134 and DXS10135 were the most polymorphic loci. All of the loci were in Hardy-Weinberg Equilibrium (HWE). The numbers of observed haplotypes in Highlander Tibetans males were 161,112, 96 and 108, respectively, whereas haplotype diversities (HD) were 0.9959, 0.9880, 0.9809 and 0.9873, respectively. The combined discrimination power for males (PDm) was 0.999 999 99701 and for females (PDf) was 0.999 999 999 999 9958. This study represents an extensive report on X chromosomal STR markers variation in the Highlander Tibetans population for forensic applications and population genetic studies.

The Heart of Silk Road "Xinjiang," Its Genetic Portray, and Forensic Parameters Inferred From Autosomal STRs

The Xinjiang Uyghur Autonomous Region of China (XUARC) harbors almost 50 ethnic groups including the Uyghur (UGR: 45.84%), Han (HAN: 40.48%), Kazakh (KZK: 6.50%), Hui (HUI: 4.51%), Kyrgyz (KGZ: 0.86%), Mongol (MGL: 0.81%), Manchu (MCH: 0.11%), and Uzbek (UZK: 0.066%), which make it one of the most colorful regions with abundant cultural and genetic diversities. In our previous study, we established allelic frequency databases for 14 autosomal short tandem repeats (STRs) for four minority populations from XUARC (MCH, KGZ, MGL, and UZK) using the AmpFlSTR® Identifiler PCR Amplification Kit. In this study, we genotyped 2,121 samples using the GoldenEye™ 20A Kit (Beijing PeopleSpot Inc., Beijing, China) amplifying 19 autosomal STR loci for four major ethnic groups (UGR, HAN, KZK, and HUI). These groups make up 97.33% of the total XUARC population. The total number of alleles for all the 19 STRs in these populations ranged from 232 (HAN) to 224 (KZK). We did not observe any departures from the Hardy-Weinberg equilibrium (HWE) in these populations after sequential Bonferroni correction. We did find minimal departure from linkage equilibrium (LE) for a small number of pairwise combinations of loci. The match probabilities for the different populations ranged from 1 in 1.66 × 1023 (HAN) to 6.05 × 1024 (HUI), the combined power of exclusion ranged from 0.999 999 988 (HUI) to 0.999 999 993 (UGR), and the combined power of discrimination ranged from 0.999 999 999 999 999 999 999 983 (HAN) to 0.999 999 999 999 999 999 999 997 (UGR). Genetic distances, principal component analysis (PCA), STRUCTURE analysis, and the phylogenetic tree showed that genetic affinity among studied populations is consistent with linguistic, ethnic, and geographical classifications.

Emerging Insights Into Chronic Renal Disease Pathogenesis in Hypertension From Human and Animal Genomic Studies

The pathogenic links between elevated blood pressure and chronic kidney disease remain obscure. This article examines progress in population genetics and in animal models of hypertension and chronic kidney disease. It also provides a critique of the application of genome-wide association studies to understanding the heritability of renal function. Emerging themes identified indicate that heritable risk of chronic kidney disease in hypertension can arise from genetic variation in (1) glomerular and tubular protein handling mechanisms; (2) autoregulatory capacity of the renal vasculature; and (3) innate and adaptive immune mechanisms. Increased prevalence of hypertension-associated chronic kidney disease that occurs with aging may reflect amplification of heritable risks by normal aging processes affecting immunity and autoregulation.

Polygenic risk scores: the future of cancer risk prediction, screening, and precision prevention

Genome-wide association studies (GWASs) have shown that the genetic architecture of cancers are highly polygenic and enabled researchers to identify genetic risk loci for cancers. The genetic variants associated with a cancer can be combined into a polygenic risk score (PRS), which captures part of an individual's genetic susceptibility to cancer. Recently, PRSs have been widely used in cancer risk prediction and are shown to be capable of identifying groups of individuals who could benefit from the knowledge of their probabilistic susceptibility to cancer, which leads to an increased interest in understanding the potential utility of PRSs that might further refine the assessment and management of cancer risk. In this context, we provide an overview of the major discoveries from cancer GWASs. We then review the methodologies used for PRS construction, and describe steps for the development and evaluation of risk prediction models that include PRS and/or conventional risk factors. Potential utility of PRSs in cancer risk prediction, screening, and precision prevention are illustrated. Challenges and practical considerations relevant to the implementation of PRSs in health care settings are discussed.

Population genetic data for 12 X-STR loci in the Central Saudi region using investigator Argus X-12 amplification kit

BACKGROUND

X-chromosome short tandem repeat (X-STR) markers are important in forensic identity investigations and kinship analysis.

SUBJECT AND METHODS

In the current study, the distribution of 12 X-STR loci located in four linkage groups was evaluated using Investigator^® Argus X-12 Amplification Kit in 200 unrelated healthy individuals (105 males and 95 females) from the central region of Saudi Arabia in order to develop an allelic frequency database for the markers included in the kit.

RESULTS

DXS10146 locus was the most informative with 21 alleles, while DXS8378 locus was the least with five alleles. Forensic parameters showed that all X-STRs loci, either as individual markers or as linkage groups, provide genetic information with high discrimination that is appropriate for forensic purposes with polymorphism information content (PIC), power of exclusion (PE), and paternity index (PI) varying from 0.61211 to 0.917979, 0.38722 to 0.842949, and 0.038416 to 0.16367, respectively. The pairwise genetic distance fixation index (Fst) results showed that the Saudi population is genetically closer to the Egyptian and Emirati populations and distant to the Turkish population.

CONCLUSION

The current study revealed that Investigator^® Argus 12 X-STR kit would support the forensic application, kinship testing involving female offspring, and human identification in the Saudi population.

X-chromosomal STR based genetic polymorphisms and demographic history of Sri Lankan ethnicities and their relationship with global populations

A new 16 X-short tandem repeat (STR) multiplex PCR system has recently been developed for Sr Lankans, though its applicability in evolutionary genetics and forensic investigations has not been thoroughly assessed. In this study, 838 unrelated individuals covering all four major ethnic groups (Sinhalese, Sri Lankan Tamils, Indian Tamils and Moors) in Sri Lanka were successfully genotyped using this new multiplex system. The results indicated a high forensic efficiency for the tested loci in all four ethnicities confirming its suitability for forensic applications of Sri Lankans. Allele frequency distribution of Indian Tamils showed subtle but statistically significant differences from those of Sinhalese and Moors, in contrast to frequency distributions previously reported for autosomal STR alleles. This suggest a sex biased demographic history among Sri Lankans requiring a separate X-STR allele frequency database for Indian Tamils. Substantial differences observed in the patterns of LD among the four groups demand the use of a separate haplotype frequency databases for each individual ethnicity. When analysed together with other 14 world populations, all Sri Lankan ethnicities except Indian Tamils clustered closely with populations from Indian Bhil tribe, Bangladesh and Europe reflecting their shared Indo-Aryan ancestry.

RET compound inheritance in Chinese patients with Hirschsprung disease: lack of penetrance from insufficient gene dysfunction

Hirschsprung disease (HSCR) is a neurocristopathy characterized by the absence of enteric ganglia along variable lengths of the intestine. Genetic defects play a major role in HSCR pathogenesis with nearly 50% of patients having a structural or regulatory deficiency in the major susceptibility gene RET. However, complete molecular defects remain poorly characterized in most patients. Here, we performed detailed genetic, molecular, and populational investigations of rare null mutations and modifiers at the RET locus. We first verified the pathogenicity of three RET splice site mutants (c.1879 + 1G > A, c.2607 + 5G > A and c.2608-3C > G) at the RNA level. We also identified significantly higher risk allele (genotype) frequencies, and their over-transmission, from unaffected parents to affected offspring of three functionally independent enhancer variants (rs2506030, rs7069590 and rs2435357, with odd ratios (OR) of 2.09, 2.71 and 7.59, respectively, P < 0.001). These three common variants are in significant (P < 4.64 × 10^-186) linkage disequilibrium in the Han Chinese population with ~ 60% of them carrying at least one copy and > 10% with two copies. We show that RET compound inheritance of rare and common variants prevails in 64% (seven out of 11) of Chinese HSCR families. This study supports the idea that common RET variants can modify the penetrance of rare null RET mutations in HSCR, and the combined high susceptibility allele dosage may constitute the unique raised "risk baseline" among the Chinese population.

Forensic applications and genetic characterization of Liaoning Han population revealed by extended set of autosomal STRs

BACKGROUND

Microsatellites or short tandem repeats (STRs) are considered the gold standard for forensic investigations and autosomal STRs are used for routine forensic personal identification.

AIM

To provide a precise population database on an extended set of STRs which has never been done before and explore the forensic characteristics of 20 autosomal STRs.

SUBJECTS AND METHODS

In the current study, we explored the genetic characteristics of 20 STRs loci in 1138 unrelated Han individuals using Goldeneye® 20A multiplex amplification system kit in the Liaoning Han population. Additionally, phylogenetic analysis based on the Nei's standard genetic distance was performed between the Han population and other relevant populations.

RESULTS

A total of 253 alleles were observed while allelic frequencies ranged from 0.00043 to 0.5369. The combined discrimination power was 99.99999999999999999999789% and the combined exclusion power was 99.999998231%. Most of the loci were in HWE while only five pairs were out of LE. Population genetic analysis showed that the Han population has similarities with other East Asian populations.

CONCLUSION

GoldenEyeTM 20A kit detects high diversity in the Liaoning Han population. These STRs which are part of this kit can be used for forensic investigations. Population genetic analysis showed that the Han population is different from the minority populations of Xinjiang.

Genetic diversity, forensic feature, and phylogenetic analysis of Guizhou Tujia population via 19 X-STRs

BACKGROUND

X-chromosome short tandem repeats (X-STRs) with unique sex-linkage inheritance models play a complementary role in forensic science. Guizhou is a multiethnic province located in southwest China and some genetic evidence focusing on X-STRs for various minorities was reported. However, population data of Guizhou Tujia are scarce.

METHODS

A total of 507 Guizhou Tujia individuals were profiled using the AGCU X-19 STR kit. Allele frequencies and forensic parameters were calculated. Additionally, population genetic relationships between Guizhou Tujia and other 19 populations were explored.

RESULTS

A total of 257 alleles with the allele frequencies ranged from 0.0013 to 0.6098 were found. The combined power of discrimination in males and females and mean exclusion chances in all case scenarios were all greater than 0.99999. Population comparisons showed Guizhou Tujia had a homogeneity with all Han populations from different administrative regions, and other ethnic populations residing in Guizhou, while had obviously genetic heterogeneity with the Altaic family populations except Xibe.

CONCLUSION

Nineteen X-STRs can afford a reliable and informative database of Guizhou Tujia population for human identification and paternity testing, especially in complex biological relations. The genetic relationships of Chinese are significantly influenced by the geographic position and ethnolinguistic origin.

A Genome-Wide Study of Single-Nucleotide Polymorphisms in MicroRNAs and Further In Silico Analysis Reveals Their Putative Role in Susceptibility to Late-Onset Alzheimer's Disease

Late-onset Alzheimer's disease (LOAD) is a neurodegenerative disorder of growing relevance in an aging society for which predictive biomarkers are needed. Many genes involved in LOAD are tightly controlled by microRNAs (miRNAs), which can be modulated by single-nucleotide polymorphisms (SNPs). Our aim was to determine the association between SNPs in miRNAs and LOAD. We selected all SNPs in pre-miRNAs with a minor allele frequency (MAF) > 1% and genotyped them in a cohort of 229 individuals diagnosed with LOAD and 237 unrelated healthy controls. In silico analyses were performed to predict the effect of SNPs on miRNA stability and detect downstream pathways. Four SNPs were associated with LOAD risk with a p value < 0.01 (rs74704964 in hsa-miR-518d, rs71363366 in hsa-miR-1283-2, rs11983381 in hsa-miR-4653, and rs10934682 in hsa-miR-544b). In silico analyses support a possible functional effect of those SNPs in miRNA levels and in the regulation of pathways of relevance for the development of LOAD. Although the results are promising, additional studies are needed to validate the association between SNPs in miRNAs and the risk of developing LOAD. Graphical abstract.

Polygenic Scores to Assess Atherosclerotic Cardiovascular Disease Risk: Clinical Perspectives and Basic Implications

An individual's susceptibility to atherosclerotic cardiovascular disease is influenced by numerous clinical and lifestyle factors, motivating the multifaceted approaches currently endorsed for primary and secondary cardiovascular disease prevention. With growing knowledge of the genetic basis of atherosclerotic cardiovascular disease-in particular, coronary artery disease-and its contribution to disease pathogenesis, there is increased interest in understanding the potential clinical utility of a genetic predictor that might further refine the assessment and management of atherosclerotic cardiovascular disease risk. Rapid scientific and technological advances have enabled widespread genotyping efforts and dynamic research in the field of coronary artery disease genetic risk prediction. In this review, we describe how genomic analyses of coronary artery disease have been leveraged to create polygenic risk scores. We then discuss evaluations of the clinical utility of these scores, pertinent mechanistic insights gleaned, and practical considerations relevant to the implementation of polygenic risk scores in the health care setting.

Pharmacogenomic landscape of VIP genetic variants in Jordanian Arabs and comparison with worldwide populations

The pharmacogenomics has lately become a focal field of research that investigates the influence of genetic variations of drug-metabolizing enzymes and their receptors and downstream proteins on the interindividual variability in response to medications and adverse drug reactions. Therefore, it is significantly important to study and analyze the variations in drug response between different ethnic groups and populations. The current study aimed to detect the distribution of the genotype and allele frequencies in several very important pharmacogenetic (VIP) gene polymorphisms in the Jordanian population of Arab descent. This study involved 500 unrelated Jordanian individuals of Arab descent. A total of 65 VIP variants located within 33 candidate genes were randomly selected from the PharmGKB database and genotyped using the MassARRAY (iPLEX GOLD) system. The chi-square test was used to evaluate the significant differences of minor allele and genotype frequencies between the Jordanian and other populations including CHE, ASW, CEU, CHB, CDX, GIH, GBR, JPT, LWK, MXL, TSI, YRI, CAR, and ACB. This study revealed six variants were not in Hardy Weinberg equilibrium (HWE) (P-value > 0.05) and ten SNPs showed monomorphic features. Most of the remaining forty-nine variant frequencies were significantly different from the compared ethnic groups (P-value < 0.05). The results of this study may be helpful to develop safer treatment by applying the concept of personalized medicine based on the profile of VIP pharmacogene variants of the Jordanian population of Arab descent.

Genetic characterization of 19 X-STRs in Sierra Leone population from Freetown

A total of 550 individuals (265 males and 285 females) from Sierra Leone, a west-African coastal country, were genotyped using the Microreader™ 19X ID System kit. No significant deviations from the Hardy-Weinberg equilibrium were observed. A total of 250 alleles were identified with corresponding allele frequencies spanning from 0.0012 to 0.6762. PIC of the loci ranged from 0.4615 to 0.9481. The CPE, CPD_F, and CPD_M were 0.9999997856, 0.999999999999999999995774, and 0.999999999998997, respectively. The highly combined MEC_Kruger, MEC_Kishida, MEC_Desmarais, and MEC_{Desmarais Duo} were achieved as 0.99999992508, 0.999999999990802, 0.999999999990836, and 0.99999998412, respectively. Genetic comparisons revealed that genetic homogeneity existed in similar ethno origin or geographic origin populations. This is a pioneering genetic investigation using the Microreader™ 19X ID System kit in the population of Sierra Leone.

Genetic characterization of 15 autosomal STRs in the interior Sindhi population of Pakistan and their phylogenetic relationship with other populations

Genetic structure of a population can be influenced by evolutionary processes and cultural histories which can alter the frequencies of different variants at particular genetic markers. These characteristics make DNA evidence suitable for forensic applications. Little relevant data are available from the interior Sindhi population; thus, in the current study, we have investigated 15 autosomal STRs in 181 unrelated individuals belonging to the interior parts of Sindh Pakistan, to establish its lineage and parameters of forensic interest. These STRs revealed a high power of discrimination (CPD), power of exclusion (CPE) and matching probability (CMP) are 0.9999999999999999968997, 0.99998612 and 3.1003 × 10^-18 respectively. The genetic distances, neighbour-joining (NJ) tree, interactivity test and principal component analysis (PCA) based on 15 autosomal STR loci showed that the interior Sindhi population had a closer genetic relationship with Pakistani populations and distant relationships with regional (India and Afghanistan) populations. The present findings exhibited that STRs included in AmpFLSTR Identifiler kit (Applied Biosystems) are genetically polymorphic in the interior Sindhi population of Pakistan. This study provides valuable population genetic data for the genetic information study, forensic human individual identification and paternity testing.

Thinking About the Evolution of Complex Traits in the Era of Genome-Wide Association Studies

Many traits of interest are highly heritable and genetically complex, meaning that much of the variation they exhibit arises from differences at numerous loci in the genome. Complex traits and their evolution have been studied for more than a century, but only in the last decade have genome-wide association studies (GWASs) in humans begun to reveal their genetic basis. Here, we bring these threads of research together to ask how findings from GWASs can further our understanding of the processes that give rise to heritable variation in complex traits and of the genetic basis of complex trait evolution in response to changing selection pressures (i.e., of polygenic adaptation). Conversely, we ask how evolutionary thinking helps us to interpret findings from GWASs and informs related efforts of practical importance.

Social communication deficits and restricted repetitive behavior symptoms in Tourette syndrome

Background: Autism spectrum disorders (ASD) have been found to occur more frequently in individuals with Tourette syndrome (TS) than in the general population. Similarities exist between ASD and TS clinically, which suggests a potential relationship between the two conditions. Purpose: The purpose of this study was to explore the occurrence of autism-related features in ASD and TS, focusing on areas of overlap and difference. Patients and methods: This study examined the nature and extent of autistic traits as measured by the Social Communication Questionnaire (SCQ) in a sample with a diagnosis of TS, a sample diagnosed to have ASD, and a normative general population sample. Results: The TS sample had significantly higher mean SCQ scores than the general population, but generally lower scores than the ASD sample. The group differences in mean SCQ scores between the TS and ASD sample were significant except in the domain of restricted repetitive behaviours (RRB). Conclusion: This suggests that ASD traits occur commonly in the TS population, with a significant overlap in certain clinical features. This was especially the case for complex movements or repetitive behaviours, which may represent either: i) a shared phenotype which is subclinical, ii) a phenocopy where some clinical symptoms mimic each other, or iii) a co-morbidity. Awareness of this association can be useful in identifying these symptoms as part of the comprehensive assessment of TS and addressing these to improve the overall clinical outcomes in these patients.

Decomposition feature selection with applications in detecting correlated biomarkers of bipolar disorders

Feature selection is an important initial step of exploratory analysis in biomedical studies. Its main objective is to eliminate the covariates that are uncorrelated with the outcome. For highly correlated covariates, traditional feature selection methods, such as the Lasso, tend to select one of them and eliminate the others, although some of the eliminated ones are still scientifically valuable. To alleviate this drawback, we propose a feature selection method based on covariate space decomposition, referred herein as the "Decomposition Feature Selection" (DFS), and show that this method can lead to scientifically meaningful results in studies with correlated high dimensional data. The DFS consists of two steps: (i) decomposing the covariate space into disjoint subsets such that each of the subsets contains only uncorrelated covariates and (ii) identifying significant predictors by traditional feature selection within each covariate subset. We demonstrate through simulation studies that the DFS has superior practical performance over the Lasso type methods when multiple highly correlated covariates need to be retained. Application of the DFS is demonstrated through a study of bipolar disorders with correlated biomarkers.

Inferring the distribution of selective effects from a time inhomogeneous model

We have developed a Poisson random field model for estimating the distribution of selective effects of newly arisen nonsynonymous mutations that could be observed as polymorphism or divergence in samples of two related species under the assumption that the two species populations are not at mutation-selection-drift equilibrium. The model is applied to 91Drosophila genes by comparing levels of polymorphism in an African population of D. melanogaster with divergence to a reference strain of D. simulans. Based on the difference of gene expression level between testes and ovaries, the 91 genes were classified as 33 male-biased, 28 female-biased, and 30 sex-unbiased genes. Under a Bayesian framework, Markov chain Monte Carlo simulations are implemented to the model in which the distribution of selective effects is assumed to be Gaussian with a mean that may differ from one gene to the other to sample key parameters. Based on our estimates, the majority of newly-arisen nonsynonymous mutations that could contribute to polymorphism or divergence in Drosophila species are mildly deleterious with a mean scaled selection coefficient of -2.81, while almost 86% of the fixed differences between species are driven by positive selection. There are only 16.6% of the nonsynonymous mutations observed in sex-unbiased genes that are under positive selection in comparison to 30% of male-biased and 46% of female-biased genes that are beneficial. We also estimated that D. melanogaster and D. simulans may have diverged 1.72 million years ago.

Identification of Disease Susceptibility Alleles in the Next Generation Sequencing Era

The development of next generation sequencing (NGS) technologies has transformed the study of human genetic variation. In less than a decade, NGS has facilitated the discovery of causal mutations in both rare, monogenic diseases and common, heterogeneous disorders, leading to unprecedented improvements in disease diagnosis and treatment strategies. Given the rapid evolution of NGS platforms, it is now possible to analyze whole genomes and exomes quickly and affordably. Further, emerging NGS applications, such as single-cell sequencing, have the power to address specific issues like somatic variation, which is yielding new insights into the role of somatic mutations in cancer and late-onset diseases. Despite limitations associated with current iterations of NGS technologies, the impact of this approach on identifying disease-causing variants has been significant. This chapter provides an overview of several NGS platforms and applications and discusses how these technologies can be used in concert with experimental and computational strategies to identify variants with a causative effect on disease development and progression.

Genomic and Phenomic Research in the 21st Century

The field of human genomics has changed dramatically over time. Initial genomic studies were predominantly restricted to rare disorders in small families. Over the past decade, researchers changed course from family-based studies and instead focused on common diseases and traits in populations of unrelated individuals. With further advancements in biobanking, computer science, electronic health record (EHR) data, and more affordable high-throughput genomics, we are experiencing a new paradigm in human genomic research. Rapidly changing technologies and resources now make it possible to study thousands of diseases simultaneously at the genomic level. This review will focus on these advancements as scientists begin to incorporate phenome-wide strategies in human genomic research to understand the etiology of human diseases and develop new drugs to treat them.

Genetic analysis of 12 X-STRs for forensic purposes in Liaoning Manchu population from China

X-chromosomal short tandem repeats (X-STRs) have been widely used in forensic practice involving complicated cases of kinship and also play an increasingly important role in population genetics. X-STRs have been studied in regional populations of China but there is a lack of data for the Manchu population. In this study, we have investigated the forensic genetic properties of 12 X-STRs in the Investigator Argus X-12 Kit (QIAGEN, Hilden, Germany) in 772 Manchu (male = 514, female = 258) individuals from the Xiuyan and Huanren Manchu autonomous counties of Liaoning province. We observed a total of 166 alleles at 12 X-STR loci with allele frequencies ranging from 0.001295to 0.615285. The most polymorphic locus was DXS10135 with 24 alleles while DXS7423 was the least polymorphic locus with 5 alleles. We found significant linkage disequilibrium (LD) between the following pairs of markers for males: DXS10103/DXS10101, DXS10135/DXS10146, DXS10101/DXS10148, DXS10135/DXS10148, DXS7423/DXS10148 and DXS10079/DXS10148. For females, LD was only observed for DXS10103/DXS10101. The combined power of discrimination was 0.9999999979699 for males and 0.999999999999998 for females. The numbers of observed haplotypes in Manchu males were 310, 172, 182 and 172 in four linkage groups; LG1, LG2, LG3 and LG4, respectively, however, these linkage groups did not form stable haplotypes as indicated by linkage equilibrium (LE) of STRs within the groups and significant LD between the groups. This study represents an extensive report on X-STR marker variation in the Manchu population for forensic applications and population genetic studies.

Genetic variation of 17 X-chromosome STR loci in Tunisian population of Nabeul

In the present study, the genetic variations of 17 X-STR markers (DXS8378, DXS9898, DXS7133, GATA31E08, GATA172D05, DXS6801, DXS7423, DXS6809, DXS6799, DXS7132, DXS9902, DXS6800, DXS6789, DXS10075, DXS10079, DXS6807, and DXS6803) were analyzed in 139 unrelated individuals in Nabeul, aiming to perform an X-STR database for anthropological and forensic purposes. Our results indicate that DXS6809 was the most polymorphic locus, whereas DXS6807 was the least informative marker. In addition, the obtained values for the statistical parameters of forensic interest, i.e., the power of discrimination in males (PD_M) and females (PD_F), as well as the mean exclusion chance in duos (MEC_D) and trios (MEC_T) have demonstrated that this panel of 17 X-STRs is highly informative and useful for forensic application and anthropological research. Additionally, pairwise genetic distances based on F_ST were calculated between Nabeul population and other populations extracted from the literature. Genetic distances were represented in a non-metric MDS plot and clustering of populations according to their geographic locations and their historical relationship was detected.

Forensic characterization of 15 autosomal STRs in four populations from Xinjiang, China, and genetic relationships with neighboring populations

The Xinjiang Uyghur Autonomous Region of China (XUARC) harbors 47 ethnic groups including the Manchu (MCH: 0.11%), Mongols (MGL: 0.81%), Kyrgyz (KGZ: 0.86%) and Uzbek (UZK: 0.066%). To establish DNA databases for these populations, allele frequency distributions for 15 autosomal short tandem repeat (STR) loci were determined using the AmpFlSTR Identifiler PCR amplification kit. There was no evidence of departures from Hardy-Weinberg equilibrium (HWE) in any of the four populations and minimal departure from linkage equilibrium (LE) for a very small number of pairwise combinations of loci. The probabilities of identity for the different populations ranged from 1 in 1.51 × 1017 (MCH) to 1 in 9.94 × 1018 (MGL), the combined powers of discrimination ranged from 0.99999999999999999824 (UZK) to 0.9999999999999999848 (MCH) and the combined probabilities of paternal exclusion ranged from 0.9999979323 (UZK) to 0.9999994839 (MCH). Genetic distances, a phylogenetic tree and principal component analysis (PCA) revealed that the MCH, KGZ and UZK are genetically closer to the Han population of Liaoning and the Mongol population of Mongolia while the MGL are closer to Han, Japanese, Korean, Malaysian, Hong Kong Han and Russians living in China.

Copy Number Variation in Fungi and Its Implications for Wine Yeast Genetic Diversity and Adaptation

In recent years, copy number (CN) variation has emerged as a new and significant source of genetic polymorphisms contributing to the phenotypic diversity of populations. CN variants are defined as genetic loci that, due to duplication and deletion, vary in their number of copies across individuals in a population. CN variants range in size from 50 base pairs to whole chromosomes, can influence gene activity, and are associated with a wide range of phenotypes in diverse organisms, including the budding yeast Saccharomyces cerevisiae. In this review, we introduce CN variation, discuss the genetic and molecular mechanisms implicated in its generation, how they can contribute to genetic and phenotypic diversity in fungal populations, and consider how CN variants may influence wine yeast adaptation in fermentation-related processes. In particular, we focus on reviewing recent work investigating the contribution of changes in CN of fermentation-related genes in yeast wine strains and offer notable illustrations of such changes, including the high levels of CN variation among the CUP genes, which confer resistance to copper, a metal with fungicidal properties, and the preferential deletion and duplication of the MAL1 and MAL3 loci, respectively, which are responsible for metabolizing maltose and sucrose. Based on the available data, we propose that CN variation is a substantial dimension of yeast genetic diversity that occurs largely independent of single nucleotide polymorphisms. As such, CN variation harbors considerable potential for understanding and manipulating yeast strains in the wine fermentation environment and beyond.

Regional evaluation of childhood acute lymphoblastic leukemia genetic susceptibility loci among Japanese

Genome-wide association studies (GWAS) performed mostly in populations of European and Hispanic ancestry have confirmed an inherited genetic basis for childhood acute lymphoblastic leukemia (ALL), but these associations are less clear in other races/ethnicities. DNA samples from ALL patients (aged 0–19 years) previously enrolled onto a Tokyo Children’s Cancer Study Group trial were collected during 2013–2015, and underwent single nucleotide polymorphism (SNP) microarray genotyping resulting in 527 B-cell ALL for analysis. Cases and control data for 3,882 samples from the Nagahama Study Group and Aichi Cancer Center Study were combined, and association analyses across 10 previous GWAS-identified regions were performed after targeted SNP imputation. Linkage disequilibrium (LD) patterns in Japanese and other populations were evaluated using the varLD score based on 1000 Genomes data. Risk associations for ARID5B (rs10821936, OR = 1.84, P = 6 × 10⁻¹⁷) and PIP4K2A (rs7088318, OR = 0.76, P = 2 × 10⁻⁴) directly transferred to Japanese, and the IKZF1 association was detected by an alternate SNP (rs1451367, OR = 1.52, P = 2 × 10⁻⁶). Marked regional LD differences between Japanese and Europeans was observed for most of the remaining loci for which associations did not transfer, including CEBPE, CDKN2A, CDKN2B, and ELK3. This study represents a first step towards characterizing the role of genetic susceptibility in childhood ALL risk in Japanese.

Common Variants Confer Susceptibility to Barrett's Esophagus: Insights from the First Genome-Wide Association Studies

Eight loci have been identified by the two genome-wide association studies of Barrett's esophagus that have been conducted to date. Esophageal adenocarcinoma cases were included in the second study following evidence that predisposing genetic variants for this cancer overlap with those for Barrett's esophagus. Genes with roles in embryonic development of the foregut are adjacent to 6 of the loci identified (FOXF1, BARX1, FOXP1, GDF7, TBX5, and ALDH1A2). An additional locus maps to a gene with known oncogenic potential (CREB-regulated transcription coactivator 1), but expression quantitative trait data implicates yet another gene involved in esophageal development (PBX4). These results strongly support a model whereby dysregulation of genes involved in esophageal and thoracic development increases susceptibility to Barrett's esophagus and esophageal adenocarcinoma, probably by reducing anatomical antireflux mechanisms. An additional signal at 6p21 in the major histocompatibility complex also reinforces evidence that immune and inflammatory response to reflux is involved in the development of both diseases. All of the variants identified are intronic or intergenic rather than coding and are presumed to be or to mark regulatory variants. As with genome-wide association studies of other diseases, the functional variants at each locus are yet to be identified and the genes affected need confirming. In this chapter as well as discussing the biology behind each genome-wide association signal, we review the requirements for successfully conducting genome-wide association studies and discuss how progress in understanding the genetic variants that contribute to Barrett's esophagus/esophageal adenocarcinoma susceptibility compares to other cancers.

Genetic studies of alcohol dependence in the context of the addiction cycle

Family, twin and adoption studies demonstrate clearly that alcohol dependence and alcohol use disorders are phenotypically complex and heritable. The heritability of alcohol use disorders is estimated at approximately 50-60% of the total phenotypic variability. Vulnerability to alcohol use disorders can be due to multiple genetic or environmental factors or their interaction which gives rise to extensive and daunting heterogeneity. This heterogeneity makes it a significant challenge in mapping and identifying the specific genes that influence alcohol use disorders. Genetic linkage and (candidate gene) association studies have been used now for decades to map and characterize genomic loci and genes that underlie the genetic vulnerability to alcohol use disorders. These approaches have been moderately successful in identifying several genes that contribute to the complexity of alcohol use disorders. Recently, genome-wide association studies have become one of the major tools for identifying genes for alcohol use disorders by examining correlations between millions of common single-nucleotide polymorphisms with diagnosis status. Genome-wide association studies are just beginning to uncover novel biology; however, the functional significance of results remains a matter of extensive debate and uncertainty. In this review, we present a select group of genome-wide association studies of alcohol dependence, as one example of a way to generate functional hypotheses, within the addiction cycle framework. This analysis may provide novel directions for validating the functional significance of alcohol dependence candidate genes. This article is part of the Special Issue entitled "Alcoholism".

The OncoArray Consortium: A Network for Understanding the Genetic Architecture of Common Cancers

BACKGROUND

Common cancers develop through a multistep process often including inherited susceptibility. Collaboration among multiple institutions, and funding from multiple sources, has allowed the development of an inexpensive genotyping microarray, the OncoArray. The array includes a genome-wide backbone, comprising 230,000 SNPs tagging most common genetic variants, together with dense mapping of known susceptibility regions, rare variants from sequencing experiments, pharmacogenetic markers, and cancer-related traits.

METHODS

The OncoArray can be genotyped using a novel technology developed by Illumina to facilitate efficient genotyping. The consortium developed standard approaches for selecting SNPs for study, for quality control of markers, and for ancestry analysis. The array was genotyped at selected sites and with prespecified replicate samples to permit evaluation of genotyping accuracy among centers and by ethnic background.

RESULTS

The OncoArray consortium genotyped 447,705 samples. A total of 494,763 SNPs passed quality control steps with a sample success rate of 97% of the samples. Participating sites performed ancestry analysis using a common set of markers and a scoring algorithm based on principal components analysis.

CONCLUSIONS

Results from these analyses will enable researchers to identify new susceptibility loci, perform fine-mapping of new or known loci associated with either single or multiple cancers, assess the degree of overlap in cancer causation and pleiotropic effects of loci that have been identified for disease-specific risk, and jointly model genetic, environmental, and lifestyle-related exposures.

IMPACT

Ongoing analyses will shed light on etiology and risk assessment for many types of cancer. Cancer Epidemiol Biomarkers Prev; 26(1); 126-35. ©2016 AACR.

Genetic markers: Potential candidates for cardiovascular disease

The effective prevention of cardiovascular disease depends upon the ability to recognize the high-risk individuals at an early stage of the disease or long before the development of adverse events. Evolving technologies in the fields of proteomics, metabolomics, and genomics have played a significant role in the discovery of cardiovascular biomarkers, but so far these methods have achieved the modest success. Hence, there is a crucial need for more reliable, suitable, and lasting diagnostic and therapeutic markers to screen the disease well in time to start the clinical aid to the patients. Gene polymorphisms associated with the cardiovascular disease play a decisive role in the disease onset. Therefore, the genetic marker evaluation to classify high-risk patients from low-risk patients trends an effective approach to patient management and care. Currently, there are no genetic markers available for extensive adoption as risk factors for coronary vascular disease, yet, there are numerous promising, biologically acceptable candidates. Many of these gene biomarkers, alone or in combination, can play an essential role in the prediction of cardiovascular risk. The present review highlights some putative emerging genetic biomarkers that could facilitate more authentic and fast diagnosis of CVD. This review also briefly describes few technological approaches employed in the biomarker search.

[A monogenic model of schizophrenia: a shift in paradigms]

Advanced genome technologies, including genome-wide association studies, next generation sequencing analysis, whole exome sequencing, encourage the development of theoretical insights on the role of genetic factors in schizophrenia. In this context, the author considers a monogenic model of schizophrenia and its evolution.

A Statistical Approach for Testing Cross-Phenotype Effects of Rare Variants

Increasing empirical evidence suggests that many genetic variants influence multiple distinct phenotypes. When cross-phenotype effects exist, multivariate association methods that consider pleiotropy are often more powerful than univariate methods that model each phenotype separately. Although several statistical approaches exist for testing cross-phenotype effects for common variants, there is a lack of similar tests for gene-based analysis of rare variants. In order to fill this important gap, we introduce a statistical method for cross-phenotype analysis of rare variants using a nonparametric distance-covariance approach that compares similarity in multivariate phenotypes to similarity in rare-variant genotypes across a gene. The approach can accommodate both binary and continuous phenotypes and further can adjust for covariates. Our approach yields a closed-form test whose significance can be evaluated analytically, thereby improving computational efficiency and permitting application on a genome-wide scale. We use simulated data to demonstrate that our method, which we refer to as the Gene Association with Multiple Traits (GAMuT) test, provides increased power over competing approaches. We also illustrate our approach using exome-chip data from the Genetic Epidemiology Network of Arteriopathy.

Practical Calling Approach for Exome Array-Based Genome-Wide Association Studies in Korean Population

Exome-based genotyping arrays are cost-effective and have recently been used as alternative platforms to whole-exome sequencing. However, the automated clustering algorithm in an exome array has a genotype calling problem in accuracy for identifying rare and low-frequency variants. To address these shortcomings, we present a practical approach for accurate genotype calling using the Illumina Infinium HumanExome BeadChip. We present comparison results and a statistical summary of our genotype data sets. Our data set comprises 14,647 Korean samples. To solve the limitation of automated clustering, we performed manual genotype clustering for the targeted identification of 46,076 variants that were identified using GenomeStudio software. To evaluate the effects of applying custom cluster files, we tested cluster files using 804 independent Korean samples and the same platform. Our study firstly suggests practical guidelines for exome chip quality control in Asian populations and provides valuable insight into an association study using exome chip.

Mapping asthma-associated variants in admixed populations

Admixed populations arise when two or more previously isolated populations interbreed. Mapping asthma susceptibility loci in an admixed population using admixture mapping (AM) involves screening the genome of individuals of mixed ancestry for chromosomal regions that have a higher frequency of alleles from a parental population with higher asthma risk as compared with parental population with lower asthma risk. AM takes advantage of the admixture created in populations of mixed ancestry to identify genomic regions where an association exists between genetic ancestry and asthma (in contrast to between the genotype of the marker and asthma). The theory behind AM is that chromosomal segments of affected individuals contain a significantly higher-than-average proportion of alleles from the high-risk parental population and thus are more likely to harbor disease-associated loci. Criteria to evaluate the applicability of AM as a gene mapping approach include: (1) the prevalence of the disease differences in ancestral populations from which the admixed population was formed; (2) a measurable difference in disease-causing alleles between the parental populations; (3) reduced linkage disequilibrium (LD) between unlinked loci across chromosomes and strong LD between neighboring loci; (4) a set of markers with noticeable allele-frequency differences between parental populations that contributes to the admixed population (single nucleotide polymorphisms (SNPs) are the markers of choice because they are abundant, stable, relatively cheap to genotype, and informative with regard to the LD structure of chromosomal segments); and (5) there is an understanding of the extent of segmental chromosomal admixtures and their interactions with environmental factors. Although genome-wide association studies have contributed greatly to our understanding of the genetic components of asthma, the large and increasing degree of admixture in populations across the world create many challenges for further efforts to map disease-causing genes. This review, summarizes the historical context of admixed populations and AM, and considers current opportunities to use AM to map asthma genes. In addition, we provide an overview of the potential limitations and future directions of AM in biomedical research, including joint admixture and association mapping for asthma and asthma-related disorders.

Alcohol Dependence Genetics: Lessons Learned From Genome-Wide Association Studies (GWAS) and Post-GWAS Analyses

BACKGROUND

Alcohol dependence (AD) is a complex psychiatric disorder and a significant public health problem. Twin and family-based studies have consistently estimated its heritability to be approximately 50%, and many studies have sought to identify specific genetic variants associated with susceptibility to AD. These studies have been primarily linkage or candidate gene based and have been mostly unsuccessful in identifying replicable risk loci. Genome-wide association studies (GWAS) have improved the detection of specific loci associated with complex traits, including AD. However, findings from GWAS explain only a small proportion of phenotypic variance, and alternative methods have been proposed to investigate the associations that do not meet strict genome-wide significance criteria.

METHODS

This review summarizes all published AD GWAS and post-GWAS analyses that have sought to exploit GWAS data to identify AD-associated loci.

RESULTS

Findings from AD GWAS have been largely inconsistent, with the exception of variants encoding the alcohol-metabolizing enzymes. Analyses of GWAS data that go beyond standard association testing have demonstrated the polygenic nature of AD and the large contribution of common variants to risk, nominating novel genes and pathways for AD susceptibility.

CONCLUSIONS

Findings from AD GWAS and post-GWAS analyses have greatly increased our understanding of the genetic etiology of AD. However, it is clear that larger samples will be necessary to detect loci in addition to those that encode alcohol-metabolizing enzymes, which may only be possible through consortium-based efforts. Post-GWAS approaches to studying the genetic influences on AD are increasingly common and could greatly increase our knowledge of both the genetic architecture of AD and the specific genes and pathways that influence risk.

Gene hunting in autism spectrum disorder: on the path to precision medicine

Autism spectrum disorder is typical of the majority of neuropsychiatric syndromes in that it is defined by signs and symptoms, rather than by aetiology. Not surprisingly, the causes of this complex human condition are manifold and include a substantial genetic component. Recent developments in gene-hunting technologies and methods, and the resulting plethora of genetic findings, promise to open new avenues to understanding of disease pathophysiology and to contribute to improved clinical management. Despite remarkable genetic heterogeneity, evidence is emerging for converging pathophysiology in autism spectrum disorder, but how this notion of convergent pathways will translate into therapeutics remains to be established. Leveraging genetic findings through advances in model systems and integrative genomic approaches could lead to the development of new classes of therapies and a personalised approach to treatment.