A genomewide admixture mapping panel for Hispanic/Latino populations

A Genome-Wide Association Study of Vertical Cup-Disc Ratio in a Latino Population

Purpose

Vertical cup-disc ratio (VCDR) is used as a clinical assessment measure to identify and monitor glaucomatous damage to the optic nerve. Previous genetic studies conducted in European and Asian populations have identified many loci associated with VCDR. The genetic factors in other ethnic populations, such as Latino, influencing VCDR remain to be determined. Here, we describe the first genome-wide association study (GWAS) on VCDR in Latino individuals.

Methods

We conducted this GWAS on VCDR using 4537 Latino individuals who were genotyped by using either the Illumina OmniExpress BeadChip (∼730K markers) or the Illumina Hispanic/SOL BeadChip (∼2.5 million markers). Study subjects were 40 years of age and older. Linear regression, adjusting for age, sex, and principal components of genetic ancestry, was conducted to assess the associations between single nucleotide polymorphisms (SNPs) and VCDR. We imputed SNPs from the 1000 Genomes Project to integrate additional SNPs not directly genotyped.

Results

We replicated two previously reported SNPs that reached GWAS significance, rs1900005 and rs7916697, in the ATOH7-PBLD region, as well as identified two suggestive associations in the CDC7-TGFBR3 region on chromosome 1p22.1 and in the ZNF770-DPH6 region on chromosome 15q14. We discovered a novel SNP, rs56238729 (P = 1.22 × 10⁻¹³), in the ATOH7-PBLD region that is significantly associated with VCDR in Latino individuals. We replicated eight previously reported regions, including COL8A1, CDKN2B-CDKN2BAS, BMP2, and CHEK2 (P < 2.17 × 10⁻³).

Conclusions

Our results discovered a novel SNP that is significantly associated with VCDR in Latino individuals and confirmed previously reported loci, providing further insight into the genetic architecture of VCDR.

Genetics of ancestry-specific risk for relapse in acute lymphoblastic leukemia

The causes of individual relapses in children with acute lymphoblastic leukemia (ALL) remain incompletely understood. We evaluated the contribution of germline genetic factors to relapse in 2225 children treated on Children's Oncology Group trial AALL0232. We identified 302 germline single-nucleotide polymorphisms (SNPs) associated with relapse after adjusting for treatment and ancestry and 715 additional SNPs associated with relapse in an ancestry-specific manner. We tested for replication of these relapse-associated SNPs in external data sets of antileukemic drug pharmacokinetics and pharmacodynamics and an independent clinical cohort. 224 SNPs were associated with rapid drug clearance or drug resistance, and 32 were replicated in the independent cohort. The adverse risk associated with black and Hispanic ancestries was attenuated by addition of the 4 SNPs most strongly associated with relapse in these populations (for blacks: model without SNPs hazard ratio (HR)=2.32, P=2.27 × 10-4, model with SNPs HR=1.07, P=0.79; for Hispanics: model without SNPs HR=1.7, P=8.23 × 10-5, model with SNPs HR=1.31, P=0.065). Relapse SNPs associated with asparaginase resistance or allergy were overrepresented among SNPs associated with relapse in the more asparaginase intensive treatment arm (20/54 in Capizzi-methorexate arm vs 8/54 in high-dose methotrexate arm, P=0.015). Inherited genetic variation contributes to race-specific and treatment-specific relapse risk.

Human Demographic History Impacts Genetic Risk Prediction across Diverse Populations

The vast majority of genome-wide association studies (GWASs) are performed in Europeans, and their transferability to other populations is dependent on many factors (e.g., linkage disequilibrium, allele frequencies, genetic architecture). As medical genomics studies become increasingly large and diverse, gaining insights into population history and consequently the transferability of disease risk measurement is critical. Here, we disentangle recent population history in the widely used 1000 Genomes Project reference panel, with an emphasis on populations underrepresented in medical studies. To examine the transferability of single-ancestry GWASs, we used published summary statistics to calculate polygenic risk scores for eight well-studied phenotypes. We identify directional inconsistencies in all scores; for example, height is predicted to decrease with genetic distance from Europeans, despite robust anthropological evidence that West Africans are as tall as Europeans on average. To gain deeper quantitative insights into GWAS transferability, we developed a complex trait coalescent-based simulation framework considering effects of polygenicity, causal allele frequency divergence, and heritability. As expected, correlations between true and inferred risk are typically highest in the population from which summary statistics were derived. We demonstrate that scores inferred from European GWASs are biased by genetic drift in other populations even when choosing the same causal variants and that biases in any direction are possible and unpredictable. This work cautions that summarizing findings from large-scale GWASs may have limited portability to other populations using standard approaches and highlights the need for generalized risk prediction methods and the inclusion of more diverse individuals in medical genomics.

Human Demographic History Impacts Genetic Risk Prediction across Diverse Populations

The vast majority of genome-wide association studies (GWASs) are performed in Europeans, and their transferability to other populations is dependent on many factors (e.g., linkage disequilibrium, allele frequencies, genetic architecture). As medical genomics studies become increasingly large and diverse, gaining insights into population history and consequently the transferability of disease risk measurement is critical. Here, we disentangle recent population history in the widely used 1000 Genomes Project reference panel, with an emphasis on populations underrepresented in medical studies. To examine the transferability of single-ancestry GWASs, we used published summary statistics to calculate polygenic risk scores for eight well-studied phenotypes. We identify directional inconsistencies in all scores; for example, height is predicted to decrease with genetic distance from Europeans, despite robust anthropological evidence that West Africans are as tall as Europeans on average. To gain deeper quantitative insights into GWAS transferability, we developed a complex trait coalescent-based simulation framework considering effects of polygenicity, causal allele frequency divergence, and heritability. As expected, correlations between true and inferred risk are typically highest in the population from which summary statistics were derived. We demonstrate that scores inferred from European GWASs are biased by genetic drift in other populations even when choosing the same causal variants and that biases in any direction are possible and unpredictable. This work cautions that summarizing findings from large-scale GWASs may have limited portability to other populations using standard approaches and highlights the need for generalized risk prediction methods and the inclusion of more diverse individuals in medical genomics.

A continuum of admixture in the Western Hemisphere revealed by the African Diaspora genome

The African Diaspora in the Western Hemisphere represents one of the largest forced migrations in history and had a profound impact on genetic diversity in modern populations. To date, the fine-scale population structure of descendants of the African Diaspora remains largely uncharacterized. Here we present genetic variation from deeply sequenced genomes of 642 individuals from North and South American, Caribbean and West African populations, substantially increasing the lexicon of human genomic variation and suggesting much variation remains to be discovered in African-admixed populations in the Americas. We summarize genetic variation in these populations, quantifying the postcolonial sex-biased European gene flow across multiple regions. Moreover, we refine estimates on the burden of deleterious variants carried across populations and how this varies with African ancestry. Our data are an important resource for empowering disease mapping studies in African-admixed individuals and will facilitate gene discovery for diseases disproportionately affecting individuals of African ancestry.

Admixture in Latin America

Latin Americans arguably represent the largest recently admixed populations in the world. This reflects a history of massive settlement by immigrants (mostly Europeans and Africans) and their variable admixture with Natives, starting in 1492. This process resulted in the population of Latin America showing an extensive genetic and phenotypic diversity. Here we review how genetic analyses are being applied to examine the demographic history of this population, including patterns of mating, population structure and ancestry. The admixture history of Latin America, and the resulting extensive diversity of the region, represents a natural experiment offering an advantageous setting for genetic association studies. We review how recent analyses in Latin Americans are contributing to elucidating the genetic architecture of human complex traits.

Family-based exome-wide assessment of maternal genetic effects on susceptibility to childhood B-cell acute lymphoblastic leukemia in hispanics

BACKGROUND

Children of Hispanic ancestry have a higher incidence of acute lymphoblastic leukemia (ALL) compared with other ethnic groups, but to the authors' knowledge, the genetic basis for these racial disparities remain incompletely understood. Genome-wide association studies of childhood ALL to date have focused on inherited genetic effects; however, maternal genetic effects (the role of the maternal genotype on phenotype development in the offspring) also may play a role in ALL susceptibility.

METHODS

The authors conducted a family-based exome-wide association study of maternal genetic effects among Hispanics with childhood B-cell ALL using the Illumina Infinium HumanExome BeadChip. A discovery cohort of 312 Guatemalan and Hispanic American families and an independent replication cohort of 152 Hispanic American families were used.

RESULTS

Three maternal single-nucleotide polymorphisms (SNPs) approached the study threshold for significance after correction for multiple testing (P<1.0 × 10^-6 ): MTL5 rs12365708 (testis expressed metallothionein-like protein [tesmin]) (relative risk [RR], 2.62; 95% confidence interval [95% CI], 1.61-4.27 [P = 1.8 × 10^-5 ]); ALKBH1 rs6494 (AlkB homolog 1, histone H2A dioxygenase) (RR, 3.77; 95% CI, 1.84-7.74 [P = 3.7 × 10^-5 ]); and NEUROG3 rs4536103 (neurogenin 3) (RR, 1.75; 95% CI, 1.30-2.37 [P = 1.2 × 10^-4 ]). Although effect sizes were similar, these SNPs were not nominally significant in the replication cohort in the current study. In a meta-analysis comprised of the discovery cohort and the replication cohort, these SNPs were still not found to be statistically significant after correction for multiple comparisons (rs12365708: pooled RR, 2.27 [95% CI, 1.48-3.50], P = 1.99 × 10^-4 ; rs6494: pooled RR, 2.31 [95% CI, 1.38-3.85], P = .001; and rs4536103: pooled RR, 1.67 [95% CI, 1.29-2.16] P = 9.23 × 10^-5 ).

CONCLUSIONS

In what to the authors' knowledge is the first family-based based exome-wide association study to investigate maternal genotype effects associated with childhood ALL, the results did not implicate a strong role of maternal genotype on disease risk among Hispanics; however, 3 maternal SNPs were identified that may play a modest role in susceptibility. Cancer 2016;122:3697-704. © 2016 American Cancer Society.

Genotypically determined ancestry across an infertile population: ovarian reserve and response parameters are not influenced by continental origin

OBJECTIVE

To evaluate the relationship between genetic ethnicity using ancestry informative markers (AIMs) and ovarian reserve and response parameters as evidenced by FSH, antimüllerian hormone (AMH), basal antral follicle count (BAFC), and total oocyte yield in IVF.

DESIGN

Retrospective.

SETTING

Academic medical center.

PATIENTS(S)

A total of 2,508 infertile patients undergoing IVF at a single center.

INTERVENTION(S)

Patients were genotyped for 32 AIMs and analyzed for differences in allele frequencies. A validated Bayesian clustering algorithm was then used to assign individuals into one of four ethnic populations: European, African, Central/South Asian, or East Asian.

MAIN OUTCOME MEASURE(S)

FSH, AMH, BAFC, and oocyte yield variation.

RESULT(S)

After controlling for age and body mass index, genetic ethnicity had no impact on AMH, BAFC, and oocyte yield. FSH was found to be lower in patients of Central/South Asian ancestry (6.46 ng/mL vs. 6.97 ng/mL); however, the absolute difference is of little clinical significance. Subgroup analyses of 1,327 patients restricted to those with limited genetic admixture as determined by AIMs indicated that FSH, AMH, BAFC, and oocyte yield were equivalent.

CONCLUSION(S)

When determining ethnicity using AIMs, ethnic background does not have an impact on markers of ovarian reserve or ovarian response. Specifically, no differences were found in AMH, BAFC, or oocyte yield relative to genotypic ethnicity. Using AIMs rather than self-reported ethnicity allows for elimination of reporting biases and nonreporting of ethnicity, which can confound data. Based upon these data, specific recommendations for ovarian reserve testing should thus be made based on other factors besides ethnic background.

A variant at 9p21.3 functionally implicates CDKN2B in paediatric B-cell precursor acute lymphoblastic leukaemia aetiology

Paediatric B-cell precursor acute lymphoblastic leukaemia (BCP-ALL) is the most common cancer of childhood, yet little is known about BCP-ALL predisposition. In this study, in 2,187 cases of European ancestry and 5,543 controls, we discover and replicate a locus indexed by rs77728904 at 9p21.3 associated with BCP-ALL susceptibility (Pcombined=3.32 × 10(-15), OR=1.72) and independent from rs3731217, the previously reported ALL-associated variant in this region. Of correlated SNPs tagged by this locus, only rs662463 is significant in African Americans, suggesting it is a plausible causative variant. Functional analysis shows that rs662463 is a cis-eQTL for CDKN2B, with the risk allele associated with lower expression, and suggests that rs662463 influences BCP-ALL risk by regulating CDKN2B expression through CEBPB signalling. Functional analysis of rs3731217 suggests it is associated with BCP-ALL by acting within a splicing regulatory element determining CDKN2A exon 3 usage (P=0.01). These findings provide new insights into the critical role of the CDKN2 locus in BCP-ALL aetiology.

Strong Selection at MHC in Mexicans since Admixture

Mexicans are a recent admixture of Amerindians, Europeans, and Africans. We performed local ancestry analysis of Mexican samples from two genome-wide association studies obtained from dbGaP, and discovered that at the MHC region Mexicans have excessive African ancestral alleles compared to the rest of the genome, which is the hallmark of recent selection for admixed samples. The estimated selection coefficients are 0.05 and 0.07 for two datasets, which put our finding among the strongest known selections observed in humans, namely, lactase selection in northern Europeans and sickle-cell trait in Africans. Using inaccurate Amerindian training samples was a major concern for the credibility of previously reported selection signals in Latinos. Taking advantage of the flexibility of our statistical model, we devised a model fitting technique that can learn Amerindian ancestral haplotype from the admixed samples, which allows us to infer local ancestries for Mexicans using only European and African training samples. The strong selection signal at the MHC remains without Amerindian training samples. Finally, we note that medical history studies suggest such a strong selection at MHC is plausible in Mexicans.

African Ancestry Is Associated with Higher Intraocular Pressure in Latinos

PURPOSE

Intraocular pressure (IOP) is a major risk factor, as well as the only modifiable risk factor, for glaucoma. Racial differences have been observed in IOP measurements with individuals of African descent experiencing the highest IOP when compared with other ethnic groups. The purpose of this study was to examine the relationship between genetic ancestry and IOP in Latinos.

DESIGN

Population-based genetic association study.

PARTICIPANTS

A total of 3541 participants recruited from the Los Angeles Latino Eye Study.

METHODS

Study participants were genotyped using the Illumina OmniExpress BeadChip (∼730K markers). We used STRUCTURE to estimate individual genetic ancestry. Simple and multiple linear regression, as well as quantile regression, analyses were performed to investigate the relationship between genetic ancestry and IOP.

MAIN OUTCOME MEASURES

The relationship between genetic ancestry and IOP in Latinos.

RESULTS

African ancestry was significantly associated with higher IOP in Latinos in our simple linear regression analysis (P = 0.002). After adjusting for age, gender, body mass index, systolic blood pressure, central corneal thickness, and type 2 diabetes, this association remained significant (P = 0.0005). The main association was modified by a significant interaction between African ancestry and hypertension (P = 0.037), with hypertensive individuals experiencing a greater increase in IOP with increasing African ancestry.

CONCLUSIONS

To our knowledge, we demonstrate for the first time that African ancestry and its interaction with hypertension are associated with higher IOP in Latinos.

Genomic Insights into the Ancestry and Demographic History of South America

South America has a complex demographic history shaped by multiple migration and admixture events in pre- and post-colonial times. Settled over 14,000 years ago by Native Americans, South America has experienced migrations of European and African individuals, similar to other regions in the Americas. However, the timing and magnitude of these events resulted in markedly different patterns of admixture throughout Latin America. We use genome-wide SNP data for 437 admixed individuals from 5 countries (Colombia, Ecuador, Peru, Chile, and Argentina) to explore the population structure and demographic history of South American Latinos. We combined these data with population reference panels from Africa, Asia, Europe and the Americas to perform global ancestry analysis and infer the subcontinental origin of the European and Native American ancestry components of the admixed individuals. By applying ancestry-specific PCA analyses we find that most of the European ancestry in South American Latinos is from the Iberian Peninsula; however, many individuals trace their ancestry back to Italy, especially within Argentina. We find a strong gradient in the Native American ancestry component of South American Latinos associated with country of origin and the geography of local indigenous populations. For example, Native American genomic segments in Peruvians show greater affinities with Andean indigenous peoples like Quechua and Aymara, whereas Native American haplotypes from Colombians tend to cluster with Amazonian and coastal tribes from northern South America. Using ancestry tract length analysis we modeled post-colonial South American migration history as the youngest in Latin America during European colonization (9–14 generations ago), with an additional strong pulse of European migration occurring between 3 and 9 generations ago. These genetic footprints can impact our understanding of population-level differences in biomedical traits and, thus, inform future medical genetic studies in the region.

South America is home to over 400 million people who share a rich demographic history, including settlement by Native Americans, European colonization, and the African slave trade. We use genomic data to infer which populations from Europe and the Americas contributed to these admixture events. We provide evidence for multiple origins of the Native American ancestry of admixed South American Latinos. The Native American ancestral component correlates strongly with geography, indicating that admixture occurred between European colonists and local Native American populations throughout South America. We also show that the European ancestry of South American Latinos comes mainly from the Iberian peninsula, however, a significant number of Argentinians have European ancestry from other Southern European regions. The genetic signal of European admixture in South American populations is younger than the signal observed in Mexico and the Caribbean. We find evidence for a second pulse of European migration to many regions of South America subsequent to the original colonization. These results demonstrate the heterogeneous nature of the Latino population in South America and help elucidate the complex genetic and admixture events that shaped the population structure of the region.

High interpopulation homogeneity in Central Argentina as assessed by Ancestry Informative Markers (AIMs)

The population of Argentina has already been studied with regard to several genetic markers, but much more data are needed for the appropriate definition of its genetic profile. This study aimed at investigating the admixture patterns and genetic structure in Central Argentina, using biparental markers and comparing the results with those previously obtained by us with mitochondrial DNA (mtDNA) in the same samples. A total of 521 healthy unrelated individuals living in 13 villages of the Córdoba and San Luis provinces were tested. The individuals were genotyped for ten autosomal ancestry informative markers (AIMs). Allele frequencies were compared with those of African, European and Native American populations, chosen to represent parental contributions. The AIM estimates indicated a greater influence of the Native American ancestry as compared to previous studies in the same or other Argentinean regions, but smaller than that observed with the mtDNA tests. These differences can be explained, respectively, by different genetic contributions between rural and urban areas, and asymmetric gene flow occurred in the past. But a most unexpected finding was the marked interpopulation genetic homogeneity found in villages located in diverse geographic environments across a wide territory, suggesting considerable gene flow.

Association of serum lipids with outcomes in Hispanic hemodialysis patients of the West versus East Coasts of the United States

BACKGROUND

Paradoxical associations exist between serum lipid levels and mortality in patients on maintenance hemodialysis (MHD) including those of Hispanic origin. However, there are significant racial and ethnic variations in patients of 'Hispanic' background. We hypothesized that clinically meaningful differences existed in the association between lipids and survival in Hispanic MHD patients on the West versus East Coast.

METHODS

We examined the survival impact of serum lipids in a 2-year cohort of 15,109 MHD patients of Hispanic origin being treated in California, Texas, representing the West versus New York, New Jersey and Florida representing the East Coast, using Cox models with various degrees of adjustments.

RESULTS

The association of serum total and HDL cholesterol with mortality follows a U-shaped pattern in Hispanic patients residing in the West. This is in contrast to Hispanic patients in the East Coast whose survival seems to improve with increasing total and HDL cholesterol levels. Elevated serum LDL levels in Hispanic patients on the West Coast are associated with a significant increase in mortality, while this association is not observed in patients residing on the East Coast.

CONCLUSIONS

Substantial differences exist in the association of serum lipids with mortality in MHD patients of Hispanic background depending on whether they reside on the West or East Coast of the United States. These geographical variances most likely reflect ethnic, racial and genetic distinctions, which are usually ignored. Future studies should take into account these critical variations in a population of patients who make up a significant portion of our society.

Genetic and phenotypic differentiation of an Andean intermediate altitude population

Highland populations living permanently under hypobaric hypoxia have been subject of extensive research because of the relevance of their physiological adaptations for the understanding of human health and disease. In this context, what is considered high altitude is a matter of interpretation and while the adaptive processes at high altitude (above 3000 m) are well documented, the effects of moderate altitude (below 3000 m) on the phenotype are less well established. In this study, we compare physiological and anthropometric characteristics as well as genetic variations in two Andean populations: the Calchaquíes (2300 m) and neighboring Collas (3500 m). We compare their phenotype and genotype to the sea-level Wichí population. We measured physiological (heart rate, oxygen saturation, respiration rate, and lung function) as well as anthropometric traits (height, sitting height, weight, forearm, and tibia length). We conducted genome-wide genotyping on a subset of the sample (n = 74) and performed various scans for positive selection. At the phenotypic level (n = 179), increased lung capacity stood out in both Andean groups, whereas a growth reduction in distal limbs was only observed at high altitude. At the genome level, Calchaquíes revealed strong signals around PRKG1, suggesting that the nitric oxide pathway may be a target of selection. PRKG1 was highlighted by one of four selection tests among the top five genes using the population branch statistic. Selection tests results of Collas were reported previously. Overall, our study shows that some phenotypic and genetic differentiation occurs at intermediate altitude in response to moderate lifelong selection pressures.

Inherited NUDT15 variant is a genetic determinant of mercaptopurine intolerance in children with acute lymphoblastic leukemia

PURPOSE

Mercaptopurine (MP) is the mainstay of curative therapy for acute lymphoblastic leukemia (ALL). We performed a genome-wide association study (GWAS) to identify comprehensively the genetic basis of MP intolerance in children with ALL.

PATIENTS AND METHODS

The discovery GWAS and replication cohorts included 657 and 371 children from two prospective clinical trials. MP dose intensity was a marker for drug tolerance and toxicities and was defined as prescribed dose divided by the planned protocol dose during maintenance therapy; its association with genotype was evaluated using a linear mixed-effects model.

RESULTS

MP dose intensity varied by race and ethnicity and was negatively correlated with East Asian genetic ancestry (P < .001). The GWAS revealed two genome-wide significant loci associated with dose intensity: rs1142345 in TPMT (Tyr240Cys, present in *3A and *3C variants; P = 8.6 × 10(-9)) and rs116855232 in NUDT15 (P = 8.8 × 10(-9)), with independent replication. Patients with TT genotype at rs116855232 were exquisitely sensitive to MP, with an average dose intensity of 8.3%, compared with those with TC and CC genotypes, who tolerated 63% and 83.5% of the planned dose, respectively. The NUDT15 variant was most common in East Asians and Hispanics, rare in Europeans, and not observed in Africans, contributing to ancestry-related differences in MP tolerance. Of children homozygous for either TPMT or NUDT15 variants or heterozygous for both, 100% required ≥ 50% MP dose reduction, compared with only 7.7% of others.

CONCLUSION

We describe a germline variant in NUDT15 strongly associated with MP intolerance in childhood ALL, which may have implications for treatment individualization in this disease.

A genome-wide association study of susceptibility to acute lymphoblastic leukemia in adolescents and young adults

Acute lymphoblastic leukemia (ALL) in adolescents and young adults (AYA) is characterized by distinct presenting features and inferior prognosis compared with pediatric ALL. We performed a genome-wide association study (GWAS) to comprehensively identify inherited genetic variants associated with susceptibility to AYA ALL. In the discovery GWAS, we compared genotype frequency at 635 297 single nucleotide polymorphisms (SNPs) in 308 AYA ALL cases and 6,661 non-ALL controls by using a logistic regression model with genetic ancestry as a covariate. SNPs that reached P ≤ 5 × 10(-8) in GWAS were tested in an independent cohort of 162 AYA ALL cases and 5,755 non-ALL controls. We identified a single genome-wide significant susceptibility locus in GATA3: rs3824662, odds ratio (OR), 1.77 (P = 2.8 × 10(-10)) and rs3781093, OR, 1.73 (P = 3.2 × 10(-9)). These findings were validated in the replication cohort. The risk allele at rs3824662 was most frequent in Philadelphia chromosome (Ph)-like ALL but also conferred susceptibility to non-Ph-like ALL in AYAs. In 1,827 non-selected ALL cases, the risk allele frequency at this SNP was positively correlated with age at diagnosis (P = 6.29 × 10(-11)). Our results from this first GWAS of AYA ALL susceptibility point to unique biology underlying leukemogenesis and potentially distinct disease etiology by age group.

Pathogenic EFHC1 mutations are tolerated in healthy individuals dependent on reported ancestry

OBJECTIVE

Screening for specific coding mutations in the EFHC1 gene has been proposed as a means of assessing susceptibility to juvenile myoclonic epilepsy (JME). To clarify the role of these mutations, especially those reported to be highly penetrant, we sought to measure the frequency of exonic EFHC1 mutations across multiple population samples.

METHODS

To find and test variants of large effect, we sequenced all EFHC1 exons in 23 JME and 23 non-JME idiopathic generalized epilepsy (IGE) Hispanic patients, and 60 matched controls. We also genotyped specific EFHC1 variants in IGE cases and controls from multiple ethnic backgrounds, including 17 African American IGE patients, with 24 matched controls, and 92 Caucasian JME patients with 103 matched controls. These variants are reported to be pathogenic, but are also found among unphenotyped individuals in public databases. All subjects were from the New York City metro area and all controls were required to have no family history of seizures.

RESULTS

We found the reportedly pathogenic EFHC1 P77T-R221H (rs149055334-rs79761183) JME haplotype in one Hispanic control and in two African American controls. Public databases also show that the EFHC1 P77T-R221H JME haplotype is present in unphenotyped West African ancestry populations, and we show that it can be found at appreciable frequency in healthy individuals with no family history of epilepsy. We also found a novel splice-site mutation in a single Hispanic JME patient, the effect of which is unknown.

SIGNIFICANCE

Our findings raise questions about the effect of reportedly pathogenic EFHC1 mutations on JME. One intriguing possibility is that some EFHC1 mutations may be pathogenic only when introduced into specific genetic backgrounds. By focusing on data from multiple populations, including the understudied Hispanic and Black/African American populations, our study highlights that for complex traits like JME, the body of evidence necessary to infer causality is high.

A parameter to quantify the degree of genetic mixing among individuals in hybrid populations

Hybridization between genetically distinct taxa is a complex evolutionary process. One challenge to studying hybrid populations is quantifying the degree to which non-native genes have become evenly mixed among individuals in the population. In this paper, we present a variance-based parameter, md, that measures the degree to which non-native genes are evenly distributed among individuals in a population. The parameter has a minimum value of 0 for populations in which individuals from multiple taxa are present but have not interbred, and a maximum value of 1 for populations in which all individuals have the same amount of non-native ancestry. A recurrence equation showed that relatively few generations of random mating are required for md to approach 1 (indicating a well-mixed population), and that md is independent of initial amounts of non-native ancestry. The parameter is mathematically equivalent to FST and we show how existing formulae for FST can be used to estimate md when diagnostic loci are available. Computer simulations showed this estimator to have very little bias for realistic amounts of data.

Native American ancestry is associated with severe diabetic retinopathy in Latinos

PURPOSE

Diabetic retinopathy (DR) is a leading cause of blindness in working age adults. Studies have observed that Latinos have a higher prevalence of DR than whites. The purpose of this study is to test the association between genetic admixture and severe DR in Latinos with type 2 diabetes mellitus (T2DM).

METHODS

We conducted a case-control study using 944 T2DM subjects from the Los Angeles Latino Eye Study. Cases (n = 135) were defined as proliferative or severe nonproliferative DR subjects. Controls (n = 809) were other diabetic subjects in the cohort. Genotyping was performed on the Illumina OmniExpress BeadChip. We estimated genetic ancestry in Latinos using STRUCTURE with the HapMap reference panels. Univariate and multivariate logistic regression analyses were used to test the relationship between the proportions of genetic ancestry and severe DR.

RESULTS

Native American ancestry (NAA) in Latino T2DM subjects is associated significantly with severe DR (P = 0.002). The association remained significant (P = 0.005) after adjusting for age, sex, duration of diabetes, hemoglobin A1c, body mass index, systolic blood pressure, education, and income. We also validated the NAA estimates in Latinos using ADMIXTURE with the 1000 Genomes Project reference panels and obtained consistent results.

CONCLUSIONS

Our results demonstrate for the first time to our knowledge that NAA is a significant risk factor for severe DR in Latinos.

Human genetics. The genetics of Mexico recapitulates Native American substructure and affects biomedical traits

Mexico harbors great cultural and ethnic diversity, yet fine-scale patterns of human genome-wide variation from this region remain largely uncharacterized. We studied genomic variation within Mexico from over 1000 individuals representing 20 indigenous and 11 mestizo populations. We found striking genetic stratification among indigenous populations within Mexico at varying degrees of geographic isolation. Some groups were as differentiated as Europeans are from East Asians. Pre-Columbian genetic substructure is recapitulated in the indigenous ancestry of admixed mestizo individuals across the country. Furthermore, two independently phenotyped cohorts of Mexicans and Mexican Americans showed a significant association between subcontinental ancestry and lung function. Thus, accounting for fine-scale ancestry patterns is critical for medical and population genetic studies within Mexico, in Mexican-descent populations, and likely in many other populations worldwide.

Enhanced methods for local ancestry assignment in sequenced admixed individuals

Inferring the ancestry at each locus in the genome of recently admixed individuals (e.g., Latino Americans) plays a major role in medical and population genetic inferences, ranging from finding disease-risk loci, to inferring recombination rates, to mapping missing contigs in the human genome. Although many methods for local ancestry inference have been proposed, most are designed for use with genotyping arrays and fail to make use of the full spectrum of data available from sequencing. In addition, current haplotype-based approaches are very computationally demanding, requiring large computational time for moderately large sample sizes. Here we present new methods for local ancestry inference that leverage continent-specific variants (CSVs) to attain increased performance over existing approaches in sequenced admixed genomes. A key feature of our approach is that it incorporates the admixed genomes themselves jointly with public datasets, such as 1000 Genomes, to improve the accuracy of CSV calling. We use simulations to show that our approach attains accuracy similar to widely used computationally intensive haplotype-based approaches with large decreases in runtime. Most importantly, we show that our method recovers comparable local ancestries, as the 1000 Genomes consensus local ancestry calls in the real admixed individuals from the 1000 Genomes Project. We extend our approach to account for low-coverage sequencing and show that accurate local ancestry inference can be attained at low sequencing coverage. Finally, we generalize CSVs to sub-continental population-specific variants (sCSVs) and show that in some cases it is possible to determine the sub-continental ancestry for short chromosomal segments on the basis of sCSVs.

Advances in sequencing technologies are dramatically changing the volume and type of data collected in genetic studies. Although most genetic studies so far have focused on individuals of European ancestry, recent studies are increasingly being performed in individuals of admixed ancestry (i.e., with recent ancestors from multiple continents, e.g., Latino Americans). A key component in such studies is the accurate inference of continental ancestry at each segment in the genome of these individuals. In this work we present accurate and robust methods that use continent-specific variants (i.e., genetic variants observed only in individuals of a given continent), now readily accessible through sequencing technology, to perform extremely fast and accurate inference of the ancestral origin of each genomic segment in recently admixed individuals.

The Andean adaptive toolkit to counteract high altitude maladaptation: genome-wide and phenotypic analysis of the Collas

During their migrations out of Africa, humans successfully colonised and adapted to a wide range of habitats, including extreme high altitude environments, where reduced atmospheric oxygen (hypoxia) imposes a number of physiological challenges. This study evaluates genetic and phenotypic variation in the Colla population living in the Argentinean Andes above 3500 m and compares it to the nearby lowland Wichí group in an attempt to pinpoint evolutionary mechanisms underlying adaptation to high altitude hypoxia. We genotyped 730,525 SNPs in 25 individuals from each population. In genome-wide scans of extended haplotype homozygosity Collas showed the strongest signal around VEGFB, which plays an essential role in the ischemic heart, and ELTD1, another gene crucial for heart development and prevention of cardiac hypertrophy. Moreover, pathway enrichment analysis showed an overrepresentation of pathways associated with cardiac morphology. Taken together, these findings suggest that Colla highlanders may have evolved a toolkit of adaptative mechanisms resulting in cardiac reinforcement, most likely to counteract the adverse effects of the permanently increased haematocrit and associated shear forces that characterise the Andean response to hypoxia. Regulation of cerebral vascular flow also appears to be part of the adaptive response in Collas. These findings are not only relevant to understand the evolution of hypoxia protection in high altitude populations but may also suggest new avenues for medical research into conditions where hypoxia constitutes a detrimental factor.

Interethnic admixture and the evolution of Latin American populations

A general introduction to the origins and history of Latin American populations is followed by a systematic review of the data from molecular autosomal assessments of the ethnic/continental (European, African, Amerindian) ancestries for 24 Latin American countries or territories. The data surveyed are of varying quality but provide a general picture of the present constitution of these populations. A brief discussion about the applications of these results (admixture mapping) is also provided. Latin American populations can be viewed as natural experiments for the investigation of unique anthropological and epidemiological issues.

Genomics of racial and ethnic disparities in childhood acute lymphoblastic leukemia

Although the cure rates of childhood acute lymphoblastic leukemia (ALL) have improved dramatically in the past 40 years, not all children have benefited equally from this impressive progress. Racial and ethnic disparities in the incidence and treatment outcome of childhood ALL persist, with Hispanic children having an elevated risk of developing ALL and one of the lowest survival rates after ALL therapy. A critical barrier to progress is the lack of an understanding of the causes of ALL disparities, particularly racial and ethnic differences in ALL biology. In this review, the authors summarize the current knowledge on population variation in childhood ALL incidence and treatment outcome, discuss the contributing genetic and nongenetic variables, and highlight possible therapeutic interventions to mitigate disparities in ALL.

Reconstructing the population genetic history of the Caribbean

The Caribbean basin is home to some of the most complex interactions in recent history among previously diverged human populations. Here, we investigate the population genetic history of this region by characterizing patterns of genome-wide variation among 330 individuals from three of the Greater Antilles (Cuba, Puerto Rico, Hispaniola), two mainland (Honduras, Colombia), and three Native South American (Yukpa, Bari, and Warao) populations. We combine these data with a unique database of genomic variation in over 3,000 individuals from diverse European, African, and Native American populations. We use local ancestry inference and tract length distributions to test different demographic scenarios for the pre- and post-colonial history of the region. We develop a novel ancestry-specific PCA (ASPCA) method to reconstruct the sub-continental origin of Native American, European, and African haplotypes from admixed genomes. We find that the most likely source of the indigenous ancestry in Caribbean islanders is a Native South American component shared among inland Amazonian tribes, Central America, and the Yucatan peninsula, suggesting extensive gene flow across the Caribbean in pre-Columbian times. We find evidence of two pulses of African migration. The first pulse—which today is reflected by shorter, older ancestry tracts—consists of a genetic component more similar to coastal West African regions involved in early stages of the trans-Atlantic slave trade. The second pulse—reflected by longer, younger tracts—is more similar to present-day West-Central African populations, supporting historical records of later transatlantic deportation. Surprisingly, we also identify a Latino-specific European component that has significantly diverged from its parental Iberian source populations, presumably as a result of small European founder population size. We demonstrate that the ancestral components in admixed genomes can be traced back to distinct sub-continental source populations with far greater resolution than previously thought, even when limited pre-Columbian Caribbean haplotypes have survived.

Latinos are often regarded as a single heterogeneous group, whose complex variation is not fully appreciated in several social, demographic, and biomedical contexts. By making use of genomic data, we characterize ancestral components of Caribbean populations on a sub-continental level and unveil fine-scale patterns of population structure distinguishing insular from mainland Caribbean populations as well as from other Hispanic/Latino groups. We provide genetic evidence for an inland South American origin of the Native American component in island populations and for extensive pre-Columbian gene flow across the Caribbean basin. The Caribbean-derived European component shows significant differentiation from parental Iberian populations, presumably as a result of founder effects during the colonization of the New World. Based on demographic models, we reconstruct the complex population history of the Caribbean since the onset of continental admixture. We find that insular populations are best modeled as mixtures absorbing two pulses of African migrants, coinciding with the early and maximum activity stages of the transatlantic slave trade. These two pulses appear to have originated in different regions within West Africa, imprinting two distinguishable signatures on present-day Afro-Caribbean genomes and shedding light on the genetic impact of the slave trade in the Caribbean.

Inherited GATA3 variants are associated with Ph-like childhood acute lymphoblastic leukemia and risk of relapse

Recent genomic profiling of childhood acute lymphoblastic leukemia (ALL) identified a high-risk subtype with an expression signature resembling that of Philadelphia chromosome-positive ALL and poor prognosis (Ph-like ALL). However, the role of inherited genetic variation in Ph-like ALL pathogenesis remains unknown. In a genome-wide association study (GWAS) of 511 ALL cases and 6,661 non-ALL controls, we identified a susceptibility locus for Ph-like ALL (GATA3, rs3824662; P = 2.17 × 10(-14), odds ratio (OR) = 3.85 for Ph-like ALL versus non-ALL; P = 1.05 × 10(-8), OR = 3.25 for Ph-like ALL versus non-Ph-like ALL), with independent validation. The rs3824662 risk allele was associated with somatic lesions underlying Ph-like ALL (CRLF2 rearrangement, JAK gene mutation and IKZF1 deletion) and with variation in GATA3 expression. Finally, genotype at the GATA3 SNP was also associated with early treatment response and risk of ALL relapse. Our results provide insights into interactions between inherited and somatic variants and their role in ALL pathogenesis and prognosis.

Association, interaction, and replication analysis of genes encoding serotonin transporter and 5-HT3 receptor subunits A and B in alcohol dependence

On the basis of the converging evidence showing regulation of drinking behavior by 5-HT3AB receptors and the serotonin transporter, we hypothesized that the interactive effects of genetic variations in the genes HTR3A, HTR3B, and SLC6A4 confer greater susceptibility to alcohol dependence (AD) than do their effects individually. We examined the associations of AD with 22 SNPs across HTR3A, HTR3B, and two functional variants in SLC6A4 in 500 AD and 280 healthy control individuals of European descent. We found that the alleles of the low-frequency SNPs rs33940208:T in HTR3A and rs2276305:A in HTR3B were inversely and nominally significantly associated with AD with odds ratio (OR) and 95 % confidence interval of 0.212 and 0.073, 0.616 (P = 0.004) and 0.261 and 0.088, 0.777 (P = 0.016), respectively. Further, our gene-by-gene interaction analysis revealed that two four-variant models that differed by only one SNP carried a risk for AD (empirical P < 1 × 10(-6) for prediction accuracy of the two models based on 10(6) permutations). Subsequent analysis of these two interaction models revealed an OR of 2.71 and 2.80, respectively, for AD (P < 0.001) in carriers of genotype combinations 5'-HTTLPR:LL/LS(SLC6A4)-rs1042173:TT/TG(SLC6A4)-rs1176744:AC(HTR3B)-rs3782025:AG(HTR3B) and 5'-HTTLPR:LL/LS(SLC6A4)-rs10160548:GT/TT(HTR3A)-rs1176744:AC(HTR3B)-rs3782025:AG(HTR3B). Combining all five genotypes resulted in an OR of 3.095 (P = 2.0 × 10(-4)) for AD. Inspired by these findings, we conducted the analysis in an independent sample, OZ-ALC-GWAS (N = 6699), obtained from the NIH dbGAP database, which confirmed the findings, not only for all three risk genotype combinations (Z = 4.384, P = 1.0 × 10(-5); Z = 3.155, P = 1.6 × 10(-3); and Z = 3.389, P = 7.0 × 10(-4), respectively), but also protective effects for rs33940208:T (χ (2) = 3.316, P = 0.0686) and rs2276305:A (χ (2) = 7.224, P = 0.007). These findings reveal significant interactive effects among variants in SLC6A4-HTR3A-HTR3B affecting AD. Further studies are needed to confirm these findings and characterize the molecular mechanisms underlying these effects.

Genetic admixture and obesity: recent perspectives and future applications

The process of the colonization of the New World that occurred centuries ago served as a natural experiment, creating unique combinations of genetic material in newly formed admixed populations. Through a genetic admixture approach, the identification and genotyping of ancestry informative markers have allowed for the estimation of proportions of ancestral parental populations among individuals in a sample. These admixture estimates have been used in different ways to understand the genetic contributions to individual variation in obesity and body composition parameters, particularly among diverse admixed groups known to differ in obesity prevalence within the United States. Although progress has been made through the use of genetic admixture approaches, further investigations are needed in order to explore the interaction of environmental factors with the degree of genetic ancestry in individuals. A challenge to confront at this time would be to further stratify and define environments in progressively more granular terms, including nutrients, muscle biology, stress responses at the cellular level, and the social and built environments.

Multi-ethnic distribution of clinically relevant CYP2C genotypes and haplotypes

To determine CYP2C19 and CYP2C8 allele frequencies, 28 coding and/or functional variants were genotyped in 1250 African-American, Asian, Caucasian, Hispanic and Ashkenazi Jewish (AJ) individuals. The combined CYP2C19 variant allele frequencies ranged from ∼0.30 to 0.41; however, the CYP2C8 frequencies were much lower (∼0.04-0.13). After incorporating previously reported CYP2C9 genotyping results from these populations (36 total CYP2C variants), 16 multi-ethnic CYP2C haplotypes were inferred with frequencies >0.5%. Notably, the 2C19*17-2C9*1-2C8*2 haplotype was identified among African-Americans (8%) and Hispanics (2%), indicating that CYP2C19*17 does not always tag a CYP2C haplotype that encodes efficient CYP2C-substrate metabolism. The 2C19*1-2C9*2-2C8*3 haplotype was identified in all populations except African-Americans and additional novel haplotypes were identified in selected populations (for example, 2C19*2-2C9*1-2C8*4 and 2C19*4B-2C9*1-2C8*1), together indicating that both CYP2C19*17 and *2 can be linked with other CYP2C loss-of-function alleles. These results have important implications for pharmacogenomic association studies involving the CYP2C locus and are clinically relevant when administering CYP2C-substrate medications.

Inference of human continental origin and admixture proportions using a highly discriminative ancestry informative 41-SNP panel

Background

Accurate determination of genetic ancestry is of high interest for many areas such as biomedical research, personal genomics and forensics. It remains an important topic in genetic association studies, as it has been shown that population stratification, if not appropriately considered, can lead to false-positive and -negative results. While large association studies typically extract ancestry information from available genome-wide SNP genotypes, many important clinical data sets on rare phenotypes and historical collections assembled before the GWAS area are in need of a feasible method (i.e., ease of genotyping, small number of markers) to infer the geographic origin and potential admixture of the study subjects. Here we report on the development, application and limitations of a small, multiplexable ancestry informative marker (AIM) panel of SNPs (or AISNP) developed specifically for this purpose.

Results

Based on worldwide populations from the HGDP, a 41-AIM AISNP panel for multiplex application with the ABI SNPlex and a subset with 31 AIMs for the Sequenome iPLEX system were selected and found to be highly informative for inferring ancestry among the seven continental regions Africa, the Middle East, Europe, Central/South Asia, East Asia, the Americas and Oceania. The panel was found to be least informative for Eurasian populations, and additional AIMs for a higher resolution are suggested. A large reference set including over 4,000 subjects collected from 120 global populations was assembled to facilitate accurate ancestry determination. We show practical applications of this AIM panel, discuss its limitations for admixed individuals and suggest ways to incorporate ancestry information into genetic association studies.

Conclusion

We demonstrated the utility of a small AISNP panel specifically developed to discern global ancestry. We believe that it will find wide application because of its feasibility and potential for a wide range of applications.

A genome-wide association study of central corneal thickness in Latinos

PURPOSE

Central corneal thickness (CCT) is a clinically important risk factor for primary open-angle glaucoma and keratoconus. Genetic factors controlling CCT in Latinos, the most populous minority population in the United States, are unclear. Here we describe the first genome-wide association study (GWAS) report of CCT in Latinos.

METHODS

We performed a GWAS for CCT on 1768 Latinos recruited in the Los Angeles Latino Eye Study (LALES) using Illumina's HumanOmniExpress BeadChip (∼730K markers). To discover additional associated single-nucleotide polymorphisms (SNPs), we imputed SNPs based on the 1000 Genomes Project reference panels. All subjects were 40 years of age and older. We used linear regression with adjustment for age, sex, and principal components of genetic ancestry.

RESULTS

we replicated the involvement of several previously reported loci, SUCH AS RXRA-COL5A1, FOXO1, and ZNF469, for CCT in Latinos (P 0.002). moreover, we discovered novel SNPS, RS3118515, RS943423, RS3118594, AND RS3132307, THAT REACHED GWAS SIGNIFICANCE (P 5 10(8)) in the uncharacterized LOC100506532 (GENE TYPE: miscRNA) for CCT in Latinos. By conditional analysis, we demonstrate that rs3118515 in this gene is responsible for the GWAS signal in the chromosome 9 RXRA-COL5A1 region in Latinos. Moreover, multiple sources of ENCODE evidence suggest that rs3118515 is in a regulatory region. Reverse-transcription PCR products indicated that transcripts of LOC100506532 surrounding rs3118515 were expressed in human corneas.

CONCLUSIONS

We discovered novel SNPs for CCT in Latinos and provided the first reported evidence of the corneal expression of LOC100506532. These results help to further increase our understanding of the genetic architecture of CCT.

Novel susceptibility variants at 10p12.31-12.2 for childhood acute lymphoblastic leukemia in ethnically diverse populations

BACKGROUND

Acute lymphoblastic leukemia (ALL) is the most common cancer in children and the incidence of ALL varies by ethnicity. Although accumulating evidence indicates inherited predisposition to ALL, the genetic basis of ALL susceptibility in diverse ancestry has not been comprehensively examined.

METHODS

We performed a multiethnic genome-wide association study in 1605 children with ALL and 6661 control subjects after adjusting for population structure, with validation in three replication series of 845 case subjects and 4316 control subjects. Association was tested by two-sided logistic regression.

RESULTS

A novel ALL susceptibility locus at 10p12.31-12.2 (BMI1-PIP4K2A, rs7088318, P = 1.1 × 10(-11)) was identified in the genome-wide association study, with independent replication in European Americans, African Americans, and Hispanic Americans (P = .001, .009, and .04, respectively). Association was also validated at four known ALL susceptibility loci: ARID5B, IKZF1, CEBPE, and CDKN2A/2B. Associations at ARID5B, IKZF1, and BMI1-PIP4K2A variants were consistent across ethnicity, with multiple independent signals at IKZF1 and BMI1-PIP4K2A loci. The frequency of ARID5B and BMI1-PIP4K2A variants differed by ethnicity, in parallel with ethnic differences in ALL incidence. Suggestive evidence for modifying effects of age on genetic predisposition to ALL was also observed. ARID5B, IKZF1, CEBPE, and BMI1-PIP4K2A variants cumulatively conferred strong predisposition to ALL, with children carrying six to eight copies of risk alleles at a ninefold (95% confidence interval = 6.9 to 11.8) higher ALL risk relative to those carrying zero to one risk allele at these four single nucleotide polymorphisms.

CONCLUSIONS

These findings indicate strong associations between inherited genetic variation and ALL susceptibility in children and shed new light on ALL molecular etiology in diverse ancestry.

Softwares and methods for estimating genetic ancestry in human populations

The estimation of genetic ancestry in human populations has important applications in medical genetic studies. Genetic ancestry is used to control for population stratification in genetic association studies, and is used to understand the genetic basis for ethnic differences in disease susceptibility. In this review, we present an overview of genetic ancestry estimation in human disease studies, followed by a review of popular softwares and methods used for this estimation.

Trade-offs in relative limb length among Peruvian children: extending the thrifty phenotype hypothesis to limb proportions

Background and Methods

Both the concept of ‘brain-sparing’ growth and associations between relative lower limb length, childhood environment and adult disease risk are well established. Furthermore, tibia length is suggested to be particularly plastic under conditions of environmental stress. The mechanisms responsible are uncertain, but three hypotheses may be relevant. The ‘thrifty phenotype’ assumes that some components of growth are selectively sacrificed to preserve more critical outcomes, like the brain. The ‘distal blood flow’ hypothesis assumes that blood nutrients decline with distance from the heart, and hence may affect limbs in relation to basic body geometry. Temperature adaptation predicts a gradient of decreased size along the limbs reflecting decreasing tissue temperature/blood flow. We examined these questions by comparing the size of body segments among Peruvian children born and raised in differentially stressful environments. In a cross-sectional sample of children aged 6 months to 14 years (n = 447) we measured head circumference, head-trunk height, total upper and lower limb lengths, and zeugopod (ulna and tibia) and autopod (hand and foot) lengths.

Results

Highland children (exposed to greater stress) had significantly shorter limbs and zeugopod and autopod elements than lowland children, while differences in head-trunk height were smaller. Zeugopod elements appeared most sensitive to environmental conditions, as they were relatively shorter among highland children than their respective autopod elements.

Discussion

The results suggest that functional traits (hand, foot, and head) may be partially protected at the expense of the tibia and ulna. The results do not fit the predictions of the distal blood flow and temperature adaptation models as explanations for relative limb segment growth under stress conditions. Rather, our data support the extension of the thrifty phenotype hypothesis to limb growth, and suggest that certain elements of limb growth may be sacrificed under tough conditions to buffer more functional traits.

Ancient admixture in human history

Population mixture is an important process in biology. We present a suite of methods for learning about population mixtures, implemented in a software package called ADMIXTOOLS, that support formal tests for whether mixture occurred and make it possible to infer proportions and dates of mixture. We also describe the development of a new single nucleotide polymorphism (SNP) array consisting of 629,433 sites with clearly documented ascertainment that was specifically designed for population genetic analyses and that we genotyped in 934 individuals from 53 diverse populations. To illustrate the methods, we give a number of examples that provide new insights about the history of human admixture. The most striking finding is a clear signal of admixture into northern Europe, with one ancestral population related to present-day Basques and Sardinians and the other related to present-day populations of northeast Asia and the Americas. This likely reflects a history of admixture between Neolithic migrants and the indigenous Mesolithic population of Europe, consistent with recent analyses of ancient bones from Sweden and the sequencing of the genome of the Tyrolean "Iceman."

Ancient admixture in human history

Population mixture is an important process in biology. We present a suite of methods for learning about population mixtures, implemented in a software package called ADMIXTOOLS, that support formal tests for whether mixture occurred and make it possible to infer proportions and dates of mixture. We also describe the development of a new single nucleotide polymorphism (SNP) array consisting of 629,433 sites with clearly documented ascertainment that was specifically designed for population genetic analyses and that we genotyped in 934 individuals from 53 diverse populations. To illustrate the methods, we give a number of examples that provide new insights about the history of human admixture. The most striking finding is a clear signal of admixture into northern Europe, with one ancestral population related to present-day Basques and Sardinians and the other related to present-day populations of northeast Asia and the Americas. This likely reflects a history of admixture between Neolithic migrants and the indigenous Mesolithic population of Europe, consistent with recent analyses of ancient bones from Sweden and the sequencing of the genome of the Tyrolean "Iceman."

Cardiovascular disease in rheumatoid arthritis: a systematic literature review in latin america

Background. Cardiovascular disease (CVD) is the major predictor of poor prognosis in rheumatoid arthritis (RA) patients. There is an increasing interest to identify "nontraditional" risk factors for this condition. Latin Americans (LA) are considered as a minority subpopulation and ethnically different due to admixture characteristics. To date, there are no systematic reviews of the literature published in LA and the Caribbean about CVD in RA patients. Methods. The systematic literature review was done by two blinded reviewers who independently assessed studies for eligibility. The search was completed through PubMed, LILACS, SciELO, and Virtual Health Library scientific databases. Results. The search retrieved 10,083 potential studies. A total of 16 articles concerning cardiovascular risk factors and measurement of any cardiovascular outcome in LA were included. The prevalence of CVD in LA patients with RA was 35.3%. Non-traditional risk factors associated to CVD in this population were HLA-DRB1 shared epitope alleles, rheumatoid factor, markers of chronic inflammation, long duration of RA, steroids, familial autoimmunity, and thrombogenic factors. Conclusions. There is limited data about CVD and RA in LA. We propose to evaluate cardiovascular risk factors comprehensively in the Latin RA patient and to generate specific public health policies in order to diminish morbi-mortality rates.

Human population admixture in Asia

Genetic admixture in human, the result of inter-marriage among people from different well-differentiated populations, has been extensively studied in the New World, where European colonization brought contact between peoples of Europe, Africa, and Asia and the Amerindian populations. In Asia, genetic admixing has been also prevalent among previously separated human populations. However, studies on admixed populations in Asia have been largely underrepresented in similar efforts in the New World. Here, I will provide an overview of population genomic studies that have been published to date on human admixture in Asia, focusing on population structure and population history.

Genome-wide association study identifies germline polymorphisms associated with relapse of childhood acute lymphoblastic leukemia

With the use of risk-directed therapy for childhood acute lymphoblastic leukemia (ALL), outcome has improved dramatically in the past 40 years. However, a substantial portion of patients, many of whom have no known risk factors, experience relapse. Taking a genome-wide approach, in the present study, we evaluated the relationships between genotypes at 444 044 single nucleotide polymorphisms (SNPs) with the risk of relapse in 2535 children with newly diagnosed ALL after adjusting for genetic ancestry and treatment regimen. We identified 134 SNPs that were reproducibly associated with ALL relapse. Of 134 relapse SNPs, 133 remained prognostic after adjusting for all known relapse risk factors, including minimal residual disease, and 111 were significant even among patients who were negative for minimal residual disease after remission induction therapy. The C allele at rs7142143 in the PYGL gene was associated with 3.6-fold higher risk of relapse than the T allele (P = 6.7 × 10(-9)). Fourteen of the 134 relapse SNPs, including variants in PDE4B and ABCB1, were also associated with antileukemic drug pharmacokinetics and/or pharmacodynamics. In the present study, we systematically identified host genetic variations related to treatment outcome of childhood ALL, most of which were prognostic independent of known risk factors for relapse, and some of which also influenced outcome by affecting host dis-position of antileukemic drugs. All trials are registered at www.clinicaltrials.gov or www.cancer.gov (COG P9904: NCT00005585; COG P9905: NCT00005596; COG P9906: NCT00005603; St Jude Total XIIIB: NCI-T93-0101D; and St Jude Total XV: NCT00137111).

Genetic predictors for cardiovascular disease in hispanics

A less favorable cardiovascular risk factor profile but paradoxically lower cardiovascular morbidity and mortality have been observed in Hispanics--a pattern often referred to as the Hispanic paradox. It has been proposed that the specific genetic susceptibility of this admixed population and gene-environment interactions may partly explain the paradox. During the past few years, there have been major advances in the identification of genetic risk factors using genome-wide association studies (GWAS) for cardiovascular disease, especially in Caucasians. However, no GWAS of cardiovascular disease have been reported in Hispanics. In the Costa Rican Heart Study, we reported both the consistency and disparity of genetic effects on risk of coronary heart disease (CHD) between Hispanics and other ethnic groups. We demonstrated that the improvement in the identified genetic markers on discrimination of CHD in Hispanics was modest. Future genetic research on Hispanics should consider the diversity in genetic structure, lifestyle, and socioeconomics among various subpopulations and comprehensively evaluate potential gene-environment interactions in relation to cardiovascular risk.

Genotype Imputation for Latinos Using the HapMap and 1000 Genomes Project Reference Panels

Genotype imputation is a vital tool in genome-wide association studies (GWAS) and meta-analyses of multiple GWAS results. Imputation enables researchers to increase genomic coverage and to pool data generated using different genotyping platforms. HapMap samples are often employed as the reference panel. More recently, the 1000 Genomes Project resource is becoming the primary source for reference panels. Multiple GWAS and meta-analyses are targeting Latinos, the most populous, and fastest growing minority group in the US. However, genotype imputation resources for Latinos are rather limited compared to individuals of European ancestry at present, largely because of the lack of good reference data. One choice of reference panel for Latinos is one derived from the population of Mexican individuals in Los Angeles contained in the HapMap Phase 3 project and the 1000 Genomes Project. However, a detailed evaluation of the quality of the imputed genotypes derived from the public reference panels has not yet been reported. Using simulation studies, the Illumina OmniExpress GWAS data from the Los Angles Latino Eye Study and the MACH software package, we evaluated the accuracy of genotype imputation in Latinos. Our results show that the 1000 Genomes Project AMR + CEU + YRI reference panel provides the highest imputation accuracy for Latinos, and that also including Asian samples in the panel can reduce imputation accuracy. We also provide the imputation accuracy for each autosomal chromosome using the 1000 Genomes Project panel for Latinos. Our results serve as a guide to future imputation based analysis in Latinos.