L’anémie falciforme est une maladie monogénique causée par une mutation dans le locus de la β-globine. Malgré le fait que l’anémie falciforme soit une maladie monogénique, cette maladie présente une grande hétérogénéité clinique. On présume que des facteurs environnementaux et génétiques contribuent à cette hétérogénéité. Il a été observé qu’un haut taux d’hémoglobine fœtale (HbF) diminuait la sévérité et la mortalité des patients atteints de l’anémie falciforme. Le but de mon projet était d’identifier des variations génétiques modifiant la sévérité clinique de l’anémie falciforme. Dans un premier temps, nous avons effectué la cartographie-fine de trois régions précédemment associées avec le taux d’hémoglobine fœtale. Nous avons ensuite effectué des études d’association pan-génomiques avec deux complications cliniques de l’anémie falciforme ainsi qu’avec le taux d’hémoglobine fœtale. Hormis les régions déjà identifiées comme étant associées au taux d’hémoglobine fœtale, aucun locus n’a atteint le niveau significatif de la puce de génotypage. Pour identifier des groupes de gènes modérément associés au taux d’hémoglobine fœtale qui seraient impliqués dans de mêmes voies biologiques, nous avons effectué une étude des processus biologiques. Finalement, nous avons effectué l’analyse de 19 exomes de patients Jamaïcains ayant des complications cliniques mineures de l’anémie falciforme. Compte tenu de la taille des cohortes de réplication disponibles, nous n’avons pas les moyens de valider statistiquement les variations identifiées par notre étude. Cependant, nos résultats fournissent de bons gènes candidats pour des études fonctionnelles et pour les réplications futures. Nos résultats suggèrent aussi que le β-hydroxybutyrate en concentration endogène pourraient influencer le taux d’hémoglobine fœtale. De plus, nous montrons que la cartographie-fine des régions associées par des études pan-génomiques peut identifier des signaux d’association additionnels et augmenter la variation héritable expliquée par cette région. / Sickle cell disease is a monogenic disease caused by a mutation in the β-globin locus. Although it is a monogenic disease, it shows a high clinical heterogeneity. Environmental and genetic factors are thought to play a role in this heterogeneity. It has been observed that a high fetal hemoglobin (HbF) levels correlates with a diminution of the severity and mortality of patients with sickle cell disease. The goal of my project was to identify genetic modifiers of the clinical severity of sickle cell disease. First, I performed the fine-mapping of three regions previously associated with HbF levels. Second, I performed genome-wide association studies with two clinical complications of sickle cell disease as well as with HbF levels. Since no new loci reached array-wide significance for HbF levels, I performed a pathway analysis to identify additional HbF loci of smaller effect size that might implicate shared biological processes. Finally, I performed the analysis of 19 whole exomes from Jamaican sickle cell disease patients with very mild complications. In conclusion, given the sample size of the replication cohorts available, we do not currently have the means to statistically validate the association signals. However, these results provide good candidate genes for functional studies and for future replication. Our results also suggest that β-hydroxybutyrate in endogenous levels could influence HbF levels. Furthermore, we show that fine-mapping the loci associated in genome-wide association studies can identify additional signals and increase the explained heritable variation.

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Mieux comprendre les mécanismes de la résistance aux antibiotique est un enjeu important dans la lutte contre les maladies infectieuses, qui fait face à la propagation de bactéries multi-résistantes. Les études d'association à l'échelle des génomes sont des outils puissants pour explorer les polymorphismes liés aux variations phénotypiques dans une population. Leur cadre méthodologique est très documenté pour les eucaryotes, mais leur application aux bactéries est très récente. Durant cette thèse, j'ai cherché à rendre ces outils mieux adaptés aux génomes plastiques des bactéries, principalement en travaillant sur la représentation des variations génétiques. En effet, parce que les bactéries ont la capacité à échanger du matériel génétique avec leur environnement, leurs génomes peuvent être trop différents au sein d'une espèce pour être alignés contre une référence. La description des variations par des fragments de séquence de longueur k, les k-mers, offre la flexibilité nécessaire mais ne permet pas une interprétation directe des résultats obtenus. La méthode mise au point teste l'association de ces k-mers avec le phénotype, et s'appuie sur un graphe de De Bruijn pour permettre la visualisation du contexte génomique des k-mers identifiés par le test, sous forme de graphes. Cette vue synthétique renseigne sur la nature de la séquence identifiée: il peut par exemple s'agir de polymorphisme local dans un gène ou de l'acquisition d'un gène dans un plasmide. Le type de variant représenté dans un graphe peut être prédit avec une bonne performance à partir de descripteurs du graphe, rendant plus opérationnelles les approches par k-mers pour l'étude des génomes bactériens / The emergence and spread of multi-drug resistance has become a major worldwide public health concern, calling for better understanding of the underlying resistance mechanisms. Genome-wide association studies are powerful tools to finely map the genetic polymorphism linked to the phenotypic variability observed in a population. However well documented for eukaryotic genome analysis, these studies were only recently applied to prokaryota.Through this PhD project, I searched how to better adapt these tools to the highly plastic bacterial genomes, mainly by working on the representation of the genetic variations in these genomes. Indeed, because the bacteria have the faculty to acquire genetic material by a means other than direct inheritance from a parent cell, their genomes can differ too much within a species to be aligned against a reference. A representation using sequence fragments of length k - the so-called k-mers - offers the required flexibility but generates redundancy and does not allow for a direct interpretation of the identified associations. The method we set up tests the association of these k-mers with the phenotype, and takes advantage of a De Bruijn graph (DBG) built over all genomes to remove the local redundancy of k-mers, and offer a visualisation of the genomic context of the k-mers identified by the test. This synthetic view as DBG subgraphs informs on the nature of the identified sequence: e.g. local polymorphism in a gene or gene acquired through a plasmid. The type of variant can be predicted correctly in 96% of the cases from descriptors of the subgraphs, providing a tractable framework for k-mer-based association studies

La Maladie Thrombo-Embolique Veineuse (MTEV) est une maladie dont les facteurs de risque sont à la fois environnementaux et génétiques. Les facteurs de risque génétiques bien établis sont les déficits en anti-thrombine, en protéine S, en protéine C, la mutation du Facteur V de Leiden (FVL), la mutation du Facteur (F) II G20210A, ainsi que le gène ABO dont les allèles A1 et B augmentent le risque de MTEV par rapport aux allèles A2 et O. Alors qu’une part importante de l’héritabilité de la MTEV reste inexpliquée, les études contemporaines se heurtent à un manque de puissance pour découvrir de nouveaux facteurs génétiques dont les effets sont de plus en plus faibles. En vue d’augmenter la puissance de détection de nouveaux gènes de susceptibilité à la MTEV, j’ai recherché les déterminismes génétiques de deux de ses phénotypes intermédiaires : les taux d’activité plasmatique du FVIII et les taux d’antigénémie de sa protéine de transport, le Facteur de von Willebrand (vWF). Dans un premier temps, j’ai réalisé une analyse de liaison des taux de FVIII et de vWF à partir d’un échantillon de cinq grandes familles franco-canadiennes (totalisant 255 personnes) recrutées via un cas de MTEV avec mutation FVL. Quatre régions liées aux taux de FVIII et/ou vWF ont été identifiées. L’une de ces régions correspondait au locus du gène ABO déjà connu pour influencer les taux de FVIII et vWF. La recherche de gènes candidats au sein des autres signaux de liaison s’est effectuée par l’étude in silico d’une analyse d’association pangénomique de la MTEV incluant 419 cas et 1228 témoins. Deux gènes candidats ont été identifiés : STAB2 et BAI3. J’ai ensuite réalisé des études d’associations de cinq polymorphismes de BAI3. L’un d’entre eux était d’une part associé à une élévation des taux de vWF (résultat obtenu dans un échantillon de 108 familles nucléaires en bonne santé et reproduit dans un échantillon de 916 patients non apparentés atteints de MTEV), et d’autre part associé au risque de survenue de MTEV parmi les sujets non porteurs de mutations FVL et FII de deux échantillons cas-témoins (respectivement 916 cas et 801 témoins, et 250 cas et 607 témoins). Quant à STAB2, durant le courant de ma thèse, deux de ces polymorphismes ont été décrits comme associés aux taux de FVIII et vWF au cours d’une vaste étude d’association pangénomique (GWAS) menée par le consortium CHARGE rassemblant 23 600 personnes. Dans un second temps, j’ai réalisé une méta-analyse de trois GWAS des taux de FVIII et vWF. Ces analyses avaient été conduites avec l’échantillon des cinq grandes familles franco-canadiennes et deux échantillons de 972 et 570 patients atteints de MTEV. Elles étaient ajustées sur les polymorphismes du gène ABO permettant de distinguer les allèles A1, A2, B et O, dans l’optique d’augmenter la puissance des analyses en diminuant la variance résiduelle des phénotypes. Aucun polymorphisme n’était associé ni aux taux de vWF ni à ceux de FVIII après prise en compte de la correction de Bonferroni pour tests multiples (p<10-7). Cependant, parmi les onze gènes qui présentaient des polymorphismes associés aux taux de vWF ou de FVIII avec une significativité p<10-5, de manière intéressante se trouvait STAB2. Cette étude a de plus permis de confirmer les associations nouvellement découvertes de polymorphismes situés dans les gènes VWF, STXBP5 et STX2. / The Venous Thromboembolism (VTE) risk factors are environmental and genetic. The well established risk factors are anti-thrombin, protein C, protein S deficiency, Factor V Leiden and factor II mutation and ABO gene, with A1 and B allele increasing the risk of VTE. While an important part of VTE heritability remains unexplained, contemporary studies fail to discover new susceptibility genes with weaker effects. In order to increase the discovery power, I searched for genetic geterminism of two intermediary phenotypes of VTE : Factor VIII plasmatic activity (FVIII) and von Willebrand factor antigenemia (vWF)First, I performed a linkage study of FVIII and vWF from a sample of 5 large pedigrees (N=255). Four loci have been identified. One included ABO gene. I searched for candidate genes located in the others loci by studying in silico results from o Genome Wide Association Study (GWAS) of the VTE including 419 cases and and 1228 controls. témoins. Two candidate genes were identified : STAB2 et BAI3. Then I performed association studies of five SNPs in BAI3 with FVIII and vWF. One of them was associated to vWF (in a sample of 108 nuclear families and 916 VTE patients), and associated to VTE in two case-controls samples (respectively 916 cases and 801 controls, and 250 cases et 607 controls).Second, I performed a meta-analysis of three GWAS of FVIII and vWF from the same 5 pedigrees and two samples of VTE (N=972 and 570) adjusted on ABO blood group. No polymorphisms were significant after Bonferoni correction (p<10-7). Nevertheless, among 11 genes carrying polymorphisms with a p<10-5, interestingly was STAB2. Futhermore, this study allowed to confirm newly discoverd association with VWF, STXBP5 et STX2.

Introdução: Com a sofisticação das técnicas de análise do DNA, a medicina moderna tem à sua disposição boas possibilidades para elucidar quadros clínicos indefinidos em pacientes que possuem microrrearranjos cromossômicos complexos. O desenvolvimento da técnica de MLPA (Multiplex ligation-dependent probe amplification) aliado à tecnologia dos arrays (WGAS - whole genome array screening) possibilitou analisar de uma só vez, diferentes regiões de interesse clínico no genoma humano. Objetivo: O presente trabalho teve como objetivo estudar pacientes com atraso de desenvolvimento neuropsicomotor (ADNPM) associado à malformação congênita (MC) com cariótipo prévio normal ou inconclusivo. Material e métodos: Participaram do estudo 71 pacientes com ADNPM associado à MC que foram analisados utilizando o teste de MLPA com os kits P036 e P064, seguido de WGAS com as diferentes plataformas (Agilent, Affymetrix e Illumina). Resultados: Entre os 33 pacientes com alterações patogênicas e de significado clínico incerto (VOUS) encontramos: 12 pacientes com deleção, 5 com duplicação e 16 com duplicações e deleções (dup/del) concomitantes. Foram 29 pacientes com alterações patogênicas conclusivas, 4 pacientes com CNVs classificadas como VOUS e 15 pacientes tiveram resultado de array normal além dos outros 23 que apresentaram alterações benignas, ou por não apresentarem genes na região alterada, ou por serem genes sem fenótipos descritos, ou ainda, as alterações foram herdadas de genitores normais. Na casuística total foram encontrados 4 pacientes com regiões de perda de heterozigosidade. Conclusões: A utilização de uma estratégia combinada utilizando diferentes kits de MLPA, com capacidade para detectar as principais microalterações genômicas patogênicas conhecidas, associada à aplicação do WGAS possibilitou a detecção de alterações submicroscópicas, bem como a correlação clínica adequada para pacientes não diagnosticados pela citogenética clássica. Dessa forma, nosso estudo sugere um novo modelo para a aplicação combinada desses testes que representa uma alternativa de bom custo-benefício para a triagem genômica e definição diagnóstica dos pacientes com quadros sindrômicos complexos e suas famílias / Introduction: The recent technological advances on DNA-based techniques have established in modern medicine good opportunities to elucidate undefined clinical cases in patients with complex chromosomal microrearrangements. The performance of MLPA (Multiplex ligation-dependent probe amplification) technique together with array technologies (WGAS - whole genome array screening) created the possibility of one single experiment to analyze different regions of interest in the human genome. Objective: Patients with psychomotor delay (PSMD) associated with multiple congenital anomalies who had normal or inconclusive G-band-karyotype (MCA) were studied in order to understand the genotype-phenotype correlations. Material and methods: This study involved 71 patients with psychomotor delay (PSMD) associated with multiple congenital anomalies (MCA) analyzed by MLPA (P036 and P064 kits), followed by WGAS different platforms (Agilent, Affymetrix e Illumina®). Results: Among 33 patients with pathogenic and uncertain (VOUS) copy number variations (CNV) were found: 12 deletions, 5 duplications and 16 concomitant duplication and deletion (dup/del). There were 29 patients with conclusive pathogenic findings, 4 patients with VOUS and 16 patients with normal array, but others 23 patients with benign results, which means there is no gene content in the region involved, or because these genes were not linked to phenotype, or even due to CNVs inherited of healthy parents. From the whole casuistic, 4 individuals presented loss of heterozygosity (LOH) regions. Conclusions: The use of a combined strategy of analysis (MLPA - WGAS) with a high capacity to detect pathogenic CNVs allows unraveling microscopic imbalances, and consequently, offers an adequate clinical correlation for patients not previously diagnosed by classical cytogenetics. In conclusion, this study suggests a new model for the combined application of these techniques, which represents an optimal alternative for a genomic screening and diagnostic establishment in patients with rare complex disorders and their families

Introdução: Com a sofisticação das técnicas de análise do DNA, a medicina moderna tem à sua disposição boas possibilidades para elucidar quadros clínicos indefinidos em pacientes que possuem microrrearranjos cromossômicos complexos. O desenvolvimento da técnica de MLPA (Multiplex ligation-dependent probe amplification) aliado à tecnologia dos arrays (WGAS - whole genome array screening) possibilitou analisar de uma só vez, diferentes regiões de interesse clínico no genoma humano. Objetivo: O presente trabalho teve como objetivo estudar pacientes com atraso de desenvolvimento neuropsicomotor (ADNPM) associado à malformação congênita (MC) com cariótipo prévio normal ou inconclusivo. Material e métodos: Participaram do estudo 71 pacientes com ADNPM associado à MC que foram analisados utilizando o teste de MLPA com os kits P036 e P064, seguido de WGAS com as diferentes plataformas (Agilent, Affymetrix e Illumina). Resultados: Entre os 33 pacientes com alterações patogênicas e de significado clínico incerto (VOUS) encontramos: 12 pacientes com deleção, 5 com duplicação e 16 com duplicações e deleções (dup/del) concomitantes. Foram 29 pacientes com alterações patogênicas conclusivas, 4 pacientes com CNVs classificadas como VOUS e 15 pacientes tiveram resultado de array normal além dos outros 23 que apresentaram alterações benignas, ou por não apresentarem genes na região alterada, ou por serem genes sem fenótipos descritos, ou ainda, as alterações foram herdadas de genitores normais. Na casuística total foram encontrados 4 pacientes com regiões de perda de heterozigosidade. Conclusões: A utilização de uma estratégia combinada utilizando diferentes kits de MLPA, com capacidade para detectar as principais microalterações genômicas patogênicas conhecidas, associada à aplicação do WGAS possibilitou a detecção de alterações submicroscópicas, bem como a correlação clínica adequada para pacientes não diagnosticados pela citogenética clássica. Dessa forma, nosso estudo sugere um novo modelo para a aplicação combinada desses testes que representa uma alternativa de bom custo-benefício para a triagem genômica e definição diagnóstica dos pacientes com quadros sindrômicos complexos e suas famílias / Introduction: The recent technological advances on DNA-based techniques have established in modern medicine good opportunities to elucidate undefined clinical cases in patients with complex chromosomal microrearrangements. The performance of MLPA (Multiplex ligation-dependent probe amplification) technique together with array technologies (WGAS - whole genome array screening) created the possibility of one single experiment to analyze different regions of interest in the human genome. Objective: Patients with psychomotor delay (PSMD) associated with multiple congenital anomalies who had normal or inconclusive G-band-karyotype (MCA) were studied in order to understand the genotype-phenotype correlations. Material and methods: This study involved 71 patients with psychomotor delay (PSMD) associated with multiple congenital anomalies (MCA) analyzed by MLPA (P036 and P064 kits), followed by WGAS different platforms (Agilent, Affymetrix e Illumina®). Results: Among 33 patients with pathogenic and uncertain (VOUS) copy number variations (CNV) were found: 12 deletions, 5 duplications and 16 concomitant duplication and deletion (dup/del). There were 29 patients with conclusive pathogenic findings, 4 patients with VOUS and 16 patients with normal array, but others 23 patients with benign results, which means there is no gene content in the region involved, or because these genes were not linked to phenotype, or even due to CNVs inherited of healthy parents. From the whole casuistic, 4 individuals presented loss of heterozygosity (LOH) regions. Conclusions: The use of a combined strategy of analysis (MLPA - WGAS) with a high capacity to detect pathogenic CNVs allows unraveling microscopic imbalances, and consequently, offers an adequate clinical correlation for patients not previously diagnosed by classical cytogenetics. In conclusion, this study suggests a new model for the combined application of these techniques, which represents an optimal alternative for a genomic screening and diagnostic establishment in patients with rare complex disorders and their families

Des anomalies biochimiques de la voie sérotonine-N-acétylsérotonine-mélatonine ont été observées dans les Troubles du Spectre Autistique (TSA) et la prématurité. Cependant, les mécanismes moléculaires de régulation de cette voie et les causes des anomalies biochimiques observées dans ces maladies sont encore mal connus. Afin de mieux comprendre les bases génétiques de la voie sérotonine-N-acétylsérotonine-mélatonine, nous avons utilisé une approche de génétique quantitative au travers de deux populations d’étude indépendantes, dans lesquelles des paramètres de cette voie ont été mesurés. Ces deux cohortes, composées d’une part de plus de 250 familles avec autisme et plus de 300 témoins et d’autre part, de 183 nouveau-nés dont 93 nés très prématurés, incluent ainsi des individus présentant deux situations pathologiques différentes associées à des anomalies de cette voie. Une première étude de la voie sérotonine-N-acétylsérotonine-mélatonine dans les familles avec TSA a permis d’obtenir des estimations de l’héritabilité au sens strict, allant de 0,22 pour la mélatonine à 0,72 pour la N-acétylsérotonine (NAS). Des études d’association portant dans un premier temps sur une liste de 812 gènes candidats pour la régulation de la voie sérotonine-NAS-mélatonine et dans un second temps sur tout le génome, n’ont pas permis d’identifier des variants significativement associés aux traits biochimiques. Cependant, des études d’association par gènes ont permis d’identifier trois nouveaux gènes candidats (IL21R, JMJD7 et MAPKBP1) pour la régulation de cette voie dans les familles avec TSA ainsi qu’un nouveau gène (RAET1G) dans la cohorte de nouveau-nés prématurés et témoins. Enfin une étude biochimique des phénol-sulfotransférases (PST) dans les familles avec TSA a mis en évidence une faible activité enzymatique chez 29% des patients en comparaison avec les témoins (5ème percentile). Le séquençage et le génotypage du nombre de copies des gènes de la famille SULT1A1 n’ont pas permis d’identifier des variations génétiques associées aux TSA, à l’activité PST, ou aux taux de sérotonine et de mélatonine. En conclusion, ces résultats confirment la complexité de l’architecture génétique de la voie sérotonine-NAS-mélatonine. D’autre part, ils ont permis de mettre en évidence une héritabilité élevée de cette voie et d’identifier de nouveaux gènes candidats pour comprendre la diversité inter-individuelle de cette voie chez les personnes avec TSA, les enfants prématurés et la population générale. / Biochemical abnormalities of the serotonin-N-acetylserotonin-melatonin pathway have been reported in many clinical conditions such as Autism Spectrum Disorders and preterm birth. However, molecular mechanisms underlying this pathway regulation, as well as the causes of these biochemical abnormalities remain largely unknown. The aim of this study was thus to characterize the genetic basis of the serotonin-N-acetylserotonin-melatonin pathway. To do so, we used a quantitative genetic approach in two independent populations that were previously biochemically explored for this pathway. One cohort consisted of more than 250 families with ASD and more than 300 controls and the other was composed of 183 infants including 93 very preterm newborns. Both cohorts included individuals with clinical conditions associated with disruptions of the serotonin-N-acetylserotonin-melatonin pathway. Narrow sense heritability analysis of this pathway showed relatively high estimates, ranging from 0.22 for melatonin to 0.72 for N-acetyserotonin (NAS). First, candidate-gene association studies including 812 genes related to the serotonin-NAS-melatonin pathway, then genome-wide association studies were conducted. These analyses did not identify any variant associated at the genome-wide significance level. However, a gene-based approach identified three new candidate genes (IL21R, JMJD7 and MAPKBP1) for the regulation of the pathway in families with ASD as well as one gene (RAET1G) in the cohort of preterm and term newborns. Finally, a biochemical exploration of the phenol-sulfotransferases (PST) in families with ASD revealed a decreased enzyme activity in 29% of patients compared with controls (5th percentile). SULT1A1-4 genes were then sequenced and copy number variants (CNV) were genotyped. No genetic variant could be significantly associated with PST activity, melatonin and serotonin levels, or ASD status. In conclusion, these results confirm the complexity of serotonin-NAS-melatonin pathway genetic architecture. Furthermore, this study revealed high heritability of this pathway and identified new candidate genes to understand the inter-individual variability of this pathway in ASD, preterm birth and the general population.

Widely effective treatment for alcohol use disorder is not yet available, because the exact biological mechanisms that underlie this disorder are not completely understood. One way to gain a better understanding of these mechanisms is to examine the genetic frameworks that contribute to the risk for developing this disorder. This dissertation examines genetic association data in combination with gene expression networks in the brain to identify functional groups of genes associated with alcohol consumption and dependence. The first study took advantage of the behavioral complexity of human samples, and experimental capabilities provided by mouse models, by co-analyzing gene expression networks in the mesolimbocortical system of acute alcohol-treated mice and human genetic alcohol dependence association data. This study successfully identified ethanol-responsive gene expression networks with overrepresentation of genes suggestively associated with alcohol dependence in an independent human sample, indicating that gene expression networks in mouse models are informative for identifying mechanistic networks relevant to the risk for developing dependence. The second study aimed to identify quantitative trait loci for voluntary alcohol drinking behaviors under an intermittent ethanol access paradigm, in the genetically complex Diversity Outbred mice. After determining high heritability for alcohol consumption and dependence amongst the progenitor strains, we identified several specific genetic loci associated with these traits. One locus replicated results from a human association study of alcohol consumption, and provided insight to the potentially contributing genes. Finally, we identified alcohol consumption-correlated gene expression networks in the prefrontal cortex of these mice. We also mapped quantitative trait loci for network expression levels, some of which overlapped with the behavioral loci, indicating that the functions represented by these modules mediate the relationship between the genotypes in that region and drinking behaviors. Overall, our studies revealed neuroplastic and ubiquitin-related genes pathways involved in alcohol consumption in mice and humans, and that likely contribute to the risk for developing dependence.

Pubertal timing displays wide, normally distributed variation in a healthy population of sexually maturing adolescents. However, like many complex traits, factors contributing to the variation are not well understood. Epigenetic regulation may contribute to some of the population variation. The role that epigenetics, specifically DNA methylation and histone acetylation, may play in regulating pubertal timing was investigated in C57BL/6 female mice: investigating whether population variation in pubertal timing among inbred mice could be explained by environmental factors; whether perturbing the epigenome using a histone deacetylase inhibitor or methyl-donor would alter pubertal timing; and examining genome-wide methylation patterns in hypothalami of early versus late maturing mice. Results demonstrate that measurable micro-environmental factors have only negligible effects on pubertal timing; pubertal timing was significantly altered by administration of epigenetic modifying agents; differences in methylation patterns are subtle. This initial evidence supports the involvement of epigenetic mechanisms in regulating pubertal timing.

Pubertal timing displays wide, normally distributed variation in a healthy population of sexually maturing adolescents. However, like many complex traits, factors contributing to the variation are not well understood. Epigenetic regulation may contribute to some of the population variation. The role that epigenetics, specifically DNA methylation and histone acetylation, may play in regulating pubertal timing was investigated in C57BL/6 female mice: investigating whether population variation in pubertal timing among inbred mice could be explained by environmental factors; whether perturbing the epigenome using a histone deacetylase inhibitor or methyl-donor would alter pubertal timing; and examining genome-wide methylation patterns in hypothalami of early versus late maturing mice. Results demonstrate that measurable micro-environmental factors have only negligible effects on pubertal timing; pubertal timing was significantly altered by administration of epigenetic modifying agents; differences in methylation patterns are subtle. This initial evidence supports the involvement of epigenetic mechanisms in regulating pubertal timing.