A homogenizing process of selection has maintained an \u27ultra-slow\u27 acetylation NAT2 variant in humans

N-acetyltransferase 2 (NAT2) is an important enzyme involved in the metabolism of a wide spectrum of naturally occurring xenobiotics, including therapeutic drugs and common environmental carcinogens. Extensive polymorphism in NAT2 gives rise to a wide interindividual variation in acetylation capacity which influences individual susceptibility to various drug-induced adverse reactions and cancers. Striking patterns of geographic differentiation have been described for the main slow acetylation variants of the NAT2 gene, suggesting the action of natural selection at this locus. In the present study, we took advantage of the whole-genome sequence data available from the 1000 Genomes project to investigate the global patterns of population genetic differentiation at NAT2 and determine whether they are atypical compared to the remaining variation of the genome. The non-synonymous substitution c.590G\u3eA (rs1799930) defining the slow NAT2*6 haplotype cluster exhibited an unusually low FST value when compared to the genome average (FST = 0.006, P-value = 0.016). It was pointed out as the most likely target of a homogenizing process of selection promoting the same allelic variant in globally distributed populations. The rs1799930 A allele has been associated with the slowest acetylation capacity in vivo and its substantial correlation with the subsistence strategy adopted by past human populations suggests that it may have conferred a selective advantage in populations shifting from foraging to agricultural and pastoral activities in the Neolithic period. Results of neutrality tests further supported an adaptive evolution of the NAT2 gene through either balancing selection or directional selection acting on multiple standing slow-causing variants

Différenciation génétique des populations humaines pour les gènes de la réponse aux médicaments

Response to drug treatment can be highly variable between individuals, both in terms of therapeutic effect (efficacy) and of adverse reactions (toxicity).Genetic factors affecting drug pharmacodynamics and pharmacokinetics play a major role in this inter-individual variability. Some of these factors are heterogeneously distributed among human populations. Local adaptation of populations to their environment partly explained those differences. Indeed,during human evolution, populations had to cope with changes in their chemical environment that triggered selective pressures on genes involved in xenobiotic response. Those genes are the same ones that influence drug response today.The tremendous recent advances in genotyping and sequencing technologies now provide access to the genome-wide patterns of genetic variation in a growing number of human populations, facilitating our understanding of the genetic mechanisms underlying complex traits such as drug response. Population genetic tools allow the identification of variants showing an unusual pattern of genetic differentiation among human populations and the determination of the role played by natural selection in shaping the atypical patterns observed.In this thesis, we have applied these tools on both SNP-chip genotyping data and Next Generation Sequencing data to analyze the genetic differentiation patterns of human populations for genes involved in drug response. We show that a nearly complete selective sweep in East Asia in the genomic region of the VKORC1 gene is responsible for an heterogeneous distribution of theVKORC1 functional variant and can explain the inter-population genetic differences in response to oral anti-vitamin K anticoagulants. Extending the analysis to all major pharmacogenes, we have identified new variants of potential relevance to pharmacogenetics which could explain inter-population and inter-individual differences in drug response. Finally, by a comprehensive analysis of the NAT2 gene, we evidence a homogenizing selection process targeting a functional variant associated with a very slow acetylation phenotype. These results emphasize the crucial role of natural selection in the inter-population and inter-individual drug response variability.They also illustrate the relevance of population genetics studies for a better understanding of the genetic component underlying drug response and complex traits.Tous les individus ne répondent pas de la même façon à un même traitement médicamenteux, tant sur le plan pharmacologique (efficacité) que sur le plan toxicologique (effets indésirables). Des facteurs génétiques affectant la pharmacocinétique et la pharmacodynamie des médicaments jouent un rôle déterminant dans cette variabilité interindividuelle de réponse. Certains de ces facteurs sont distribués de manière hétérogène entre les populations humaines. Ces différences s’expliquent en partie par des phénomènes d’adaptation locale des populations à leur environnement. Au cours de son histoire, l’homme a dû en effet faire face à des changements de son environnement chimique, qui ont entraîné des pressions de sélection naturelle sur les gènes intervenant dans la réponse de l’organisme aux xénobiotiques. Ce sont ces mêmes gènes qui, aujourd’hui, influencent la réponse aux médicaments.La formidable accélération des progrès de la génétique donne accès aujourd’hui à la variabilité génétique des populations humaines sur l’ensemble du génome, facilitant la découverte et la compréhension des mécanismes génétiques à l’origine des traits complexes comme la réponse aux médicaments. Les outils de la génétique des populations permettent notamment d’identifier des variants affichant un niveau de différenciation génétique inhabituel entre les populations humaines et de déterminer dans quelle mesure la sélection naturelle a joué un rôle dans les profils atypiques observés.Dans cette thèse, nous avons appliqué ces outils à des données de génotypage et de séquençage pour analyser les profils de différenciation génétique des populations humaines pour les gènes de la réponse aux médicaments. Nous avons ainsi démontré qu’une sélection positive récente en Asie de l’Est dans la région génomique du gène VKORC1 était responsable d’une hétérogénéité de distribution du variant fonctionnel de VKORC1, à l’origine des différences de sensibilité génétique aux anticoagulant oraux de type antivitamine K entre les populations humaines. Puis, en étendant notre analyse à l’ensemble des pharmacogènes majeurs, nous avons identifié de nouveaux variants potentiellement intéressants en pharmacogénétique pour expliquer les différences de réponse aux médicaments entre les populations humaines et les individus. Enfin, l’étude approfondie du gène NAT2 nous a permis de révéler un processus de sélection homogénéisante ciblant un variant fonctionnel associé à un phénotype d’acétylation très lent. Ces résultats soulignent l’influence déterminante de la sélection naturelle dans la variabilité de réponse aux médicaments entre les populations et les individus. Ils montrent l’apport de la génétique des populations pour une meilleure compréhension de la composante génétique de la réponse aux médicaments et des traits complexes

Genetic Differentiation of Human Populations for Genes Involved in Drug Response

Tous les individus ne répondent pas de la même façon à un même traitement médicamenteux, tant sur le plan pharmacologique (efficacité) que sur le plan toxicologique (effets indésirables). Des facteurs génétiques affectant la pharmacocinétique et la pharmacodynamie des médicaments jouent un rôle déterminant dans cette variabilité interindividuelle de réponse. Certains de ces facteurs sont distribués de manière hétérogène entre les populations humaines. Ces différences s’expliquent en partie par des phénomènes d’adaptation locale des populations à leur environnement. Au cours de son histoire, l’homme a dû en effet faire face à des changements de son environnement chimique, qui ont entraîné des pressions de sélection naturelle sur les gènes intervenant dans la réponse de l’organisme aux xénobiotiques. Ce sont ces mêmes gènes qui, aujourd’hui, influencent la réponse aux médicaments.La formidable accélération des progrès de la génétique donne accès aujourd’hui à la variabilité génétique des populations humaines sur l’ensemble du génome, facilitant la découverte et la compréhension des mécanismes génétiques à l’origine des traits complexes comme la réponse aux médicaments. Les outils de la génétique des populations permettent notamment d’identifier des variants affichant un niveau de différenciation génétique inhabituel entre les populations humaines et de déterminer dans quelle mesure la sélection naturelle a joué un rôle dans les profils atypiques observés.Dans cette thèse, nous avons appliqué ces outils à des données de génotypage et de séquençage pour analyser les profils de différenciation génétique des populations humaines pour les gènes de la réponse aux médicaments. Nous avons ainsi démontré qu’une sélection positive récente en Asie de l’Est dans la région génomique du gène VKORC1 était responsable d’une hétérogénéité de distribution du variant fonctionnel de VKORC1, à l’origine des différences de sensibilité génétique aux anticoagulant oraux de type antivitamine K entre les populations humaines. Puis, en étendant notre analyse à l’ensemble des pharmacogènes majeurs, nous avons identifié de nouveaux variants potentiellement intéressants en pharmacogénétique pour expliquer les différences de réponse aux médicaments entre les populations humaines et les individus. Enfin, l’étude approfondie du gène NAT2 nous a permis de révéler un processus de sélection homogénéisante ciblant un variant fonctionnel associé à un phénotype d’acétylation très lent. Ces résultats soulignent l’influence déterminante de la sélection naturelle dans la variabilité de réponse aux médicaments entre les populations et les individus. Ils montrent l’apport de la génétique des populations pour une meilleure compréhension de la composante génétique de la réponse aux médicaments et des traits complexes.Response to drug treatment can be highly variable between individuals, both in terms of therapeutic effect (efficacy) and of adverse reactions (toxicity).Genetic factors affecting drug pharmacodynamics and pharmacokinetics play a major role in this inter-individual variability. Some of these factors are heterogeneously distributed among human populations. Local adaptation of populations to their environment partly explained those differences. Indeed,during human evolution, populations had to cope with changes in their chemical environment that triggered selective pressures on genes involved in xenobiotic response. Those genes are the same ones that influence drug response today.The tremendous recent advances in genotyping and sequencing technologies now provide access to the genome-wide patterns of genetic variation in a growing number of human populations, facilitating our understanding of the genetic mechanisms underlying complex traits such as drug response. Population genetic tools allow the identification of variants showing an unusual pattern of genetic differentiation among human populations and the determination of the role played by natural selection in shaping the atypical patterns observed.In this thesis, we have applied these tools on both SNP-chip genotyping data and Next Generation Sequencing data to analyze the genetic differentiation patterns of human populations for genes involved in drug response. We show that a nearly complete selective sweep in East Asia in the genomic region of the VKORC1 gene is responsible for an heterogeneous distribution of theVKORC1 functional variant and can explain the inter-population genetic differences in response to oral anti-vitamin K anticoagulants. Extending the analysis to all major pharmacogenes, we have identified new variants of potential relevance to pharmacogenetics which could explain inter-population and inter-individual differences in drug response. Finally, by a comprehensive analysis of the NAT2 gene, we evidence a homogenizing selection process targeting a functional variant associated with a very slow acetylation phenotype. These results emphasize the crucial role of natural selection in the inter-population and inter-individual drug response variability.They also illustrate the relevance of population genetics studies for a better understanding of the genetic component underlying drug response and complex traits

Positive selection in the chromosome 16 VKORC1 genomic region has contributed to the variability of anticoagulant response in humans

VKORC1 (vitamin K epoxide reductase complex subunit 1, 16p11.2) is the main genetic determinant of human response to oral anticoagulants of antivitamin K type (AVK). This gene was recently suggested to be a putative target of positive selection in East Asian populations. In this study, we genotyped the HGDP-CEPH Panel for six VKORC1 SNPs and downloaded chromosome 16 genotypes from the HGDP-CEPH database in order to characterize the geographic distribution of footprints of positive selection within and around this locus. A unique VKORC1 haplotype carrying the promoter mutation associated with AVK sensitivity showed especially high frequencies in all the 17 HGDP-CEPH East Asian population samples. VKORC1 and 24 neighboring genes were found to lie in a 505 kb region of strong linkage disequilibrium in these populations. Patterns of allele frequency differentiation and haplotype structure suggest that this genomic region has been submitted to a near complete selective sweep in all East Asian populations and only in this geographic area. The most extreme scores of the different selection tests are found within a smaller 45 kb region that contains VKORC1 and three other genes (BCKDK, MYST1 (KAT8), and PRSS8) with different functions. Because of the strong linkage disequilibrium, it is not possible to determine if VKORC1 or one of the three other genes is the target of this strong positive selection that could explain present-day differences among human populations in AVK dose requirement. Our results show that the extended region surrounding a presumable single target of positive selection should be analyzed for genetic variation in a wide range of genetically diverse populations in order to account for other neighboring and confounding selective events and the hitchhiking effect.This work was supported by the Spanish National Institute for Bioinformatics (www.inab.org). PL is supported by a PhD fellowship from ‘‘Acción Estratégica de Salud, en el Marco del Plan Nacional de Investigación Científica, Desarrollo e Innovación Tecnológica 2008–2011’

Atypical patterns of genetic differentiation observed for <i>VKORC1</i> SNPs.

<p>Genome-wide empirical distributions of <i>F_ST</i> values were constructed from 644,143 SNPs having a MAF ≥0.001 at the global level. Individual values of <i>F_ST</i> calculated for each of the seven <i>VKORC1</i> SNPs are plotted against their global MAF. The functional rs9923231 SNP is shown in red. The 50^th, 95^th and 99^th percentiles are indicated as dotted, dashed and full red lines, respectively.</p

Detailed analysis of a 1.1 Mb genomic region surrounding the <i>VKORC1</i> gene locus in East Asia.

<p>The boundaries of the region displayed (chr16:30,271,572-31,391,123; UCSC human genome build hg18) were chosen so as to include the three clusters of significant scores detected in East Asia by the selection tests in the 2 Mb region centered on <i>VKORC1</i> (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0053049#pone-0053049-g003" target="_blank">Figure 3</a>). (<b>A</b>) <b>Name and location of genes.</b> Exons are displayed as blue boxes and the transcribed strand is indicated with an arrow. Genes located in the block of strong LD encompassing <i>VKORC1</i> and including the SNPs in the red box shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0053049#pone-0053049-g004" target="_blank">Figure 4C</a>, are highlighted in the grey area. (<b>B</b>) <b>XP-EHH results in East Asia.</b> The significance of the XP-EHH scores (−log₁₀ empirical <i>p</i>-value) are shown for individual SNPs with a MAF ≥0.01 in East Asia. Horizontal dashed lines indicate 0.05 and 0.01 chromosome-wide significance levels. Recombination hotspots detected in HapMap Phase II data are indicated by red vertical dotted lines. The data and methods used to derive these hotspots are available from the HapMap website (<a href="http://www.hapmap.org/" target="_blank">http://www.hapmap.org/</a>) <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0053049#pone.0053049-McVean1" target="_blank">[83]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0053049#pone.0053049-Winckler1" target="_blank">[84]</a>. (<b>C</b>) <b>LD plot.</b> Pairwise LD values, depicted as <i>D</i>’, are shown for SNPs with a MAF ≥0.01 in East Asia. <i>D</i>’ values are displayed in different colors from yellow to red for <i>D</i>’ = 0 to <i>D</i>’ = 1, respectively. The red box highlights SNPs included in the LD block encompassing <i>VKORC1.</i> The plot was produced using the snp.plotter R package <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0053049#pone.0053049-Luna1" target="_blank">[74]</a>.</p

Results of the inter-regional <i>F_ST</i>, intra-regional <i>F_ST</i>, XP-EHH and iHS tests in the seven geographic regions.

a<p>Derived allele frequency estimated at the global level.</p>b<p><i>F_ST</i> estimated at the inter-regional level, <i>i.e.</i> between a given geographic region and the remaining ones.</p>c<p><i>P</i>-values are derived from the genome-wide empirical distribution of <i>F_ST</i> values.</p>d<p><i>F_ST</i> estimated at the intra-regional level, <i>i.e.</i> among populations within a region.</p>e<p><i>P</i>-values are derived from the empirical distribution of the iHS and XP-EHH scores along the chromosome 16.</p>*<p><i>p</i><0.05; ** <i>p</i><0.01; *** <i>p</i><0.005.</p><p>NA: Not Applicable (for iHS: when a gap>200 kb between successive SNPs is found in the region in the region delimited by the SNPs where the EHH value drops below 0.05 around the core SNP).</p

Distribution of –log₁₀ (<i>p-</i>values) for four selection tests across a 2 Mb region centered on <i>VKORC1</i>.

<p>A black vertical line indicates the physical position of <i>VKORC1</i> on chromosome 16. Horizontal red dotted and dashed lines show 0.05 and 0.01 chromosome-wide significance levels, respectively. The selection tests (inter-regional <i>F_ST</i>, XP-CLR, XP-EHH and iHS, respectively) were separately applied in each of the seven geographic regions.</p

Positive selection in the chromosome 16 VKORC1 genomic region has contributed to the variability of anticoagulant response in humans

VKORC1 (vitamin K epoxide reductase complex subunit 1, 16p11.2) is the main genetic determinant of human response to oral anticoagulants of antivitamin K type (AVK). This gene was recently suggested to be a putative target of positive selection in East Asian populations. In this study, we genotyped the HGDP-CEPH Panel for six VKORC1 SNPs and downloaded chromosome 16 genotypes from the HGDP-CEPH database in order to characterize the geographic distribution of footprints of positive selection within and around this locus. A unique VKORC1 haplotype carrying the promoter mutation associated with AVK sensitivity showed especially high frequencies in all the 17 HGDP-CEPH East Asian population samples. VKORC1 and 24 neighboring genes were found to lie in a 505 kb region of strong linkage disequilibrium in these populations. Patterns of allele frequency differentiation and haplotype structure suggest that this genomic region has been submitted to a near complete selective sweep in all East Asian populations and only in this geographic area. The most extreme scores of the different selection tests are found within a smaller 45 kb region that contains VKORC1 and three other genes (BCKDK, MYST1 (KAT8), and PRSS8) with different functions. Because of the strong linkage disequilibrium, it is not possible to determine if VKORC1 or one of the three other genes is the target of this strong positive selection that could explain present-day differences among human populations in AVK dose requirement. Our results show that the extended region surrounding a presumable single target of positive selection should be analyzed for genetic variation in a wide range of genetically diverse populations in order to account for other neighboring and confounding selective events and the hitchhiking effect.This work was supported by the Spanish National Institute for Bioinformatics (www.inab.org). PL is supported by a PhD fellowship from ‘‘Acción Estratégica de Salud, en el Marco del Plan Nacional de Investigación Científica, Desarrollo e Innovación Tecnológica 2008–2011’