Chez les espèces fruitières, la floraison est un évènement majeur qui influencera fortement la fructification. Ce processus, finement régulé par de nombreux facteurs génétiques et environnementaux, est encore peu connu. Chez le cerisier doux (Prunus avium), les fleurs ne s’épanouissent qu’après avoir satisfait des besoins en froid et en chaud. Les effets du changement climatique sur la floraison sont déjà notables et pourraient induire d’importantes pertes économiques. La compréhension des déterminants génétiques et moléculaires impliqués dans la floraison permettra l’amélioration des programmes de sélection variétale visant l’obtention d’arbres adaptés aux futures conditions climatiques. L’objectif de cette thèse est d’accroître les connaissances sur ces déterminants et d’identifier les gènes contrôlant la floraison chez le cerisier. En étudiant les deux familles intra spécifiques ‘Regina’ × ‘Lapins’ et ‘Regina’ × ‘Garnet’, la détection de nombreux quantitative trait loci (QTL) sur l’ensemble des groupes de liaisons (GL) a permis de confirmer la forte implication des besoins en froid dans la floraison ainsi que la complexité de ces caractères. Un QTL à effet majeur a été localisé sur le GL4. Dans les régions couvertes par les QTL contrôlant la date de floraison, une centaine de gènes candidats (GC) pour ce caractère a été identifiée. Un sous ensemble de ces GC a ensuite été étudié pour leur expression au cours du développement des bourgeons par PCR quantitative (qPCR). A terme, ces travaux serviront de bases pour l’identification et la sélection de gènes qui permettront l’obtention de génotypes adaptés aux futures conditions climatiques. / In fruit species, the flowering is a major event which strongly influences fructification. This process tiny controlled by many genetic and environmental factors is still little known. In sweet cherry (Prunus avium), flowers open out only after having satisfied chill and heat requirements. The effects of climate change on the flowering are already notable and could induce important economic losses. Identification of genetic and molecular determinants involved in the flowering will allow the improvement of varietal selection programs to obtain trees adapted to future climate conditions. Objective of this thesis is to increase the knowledge of these determinants and identify genes involved in flowering in sweet cherry. By studying two intraspecific progenies ‘Regina’ × ‘Lapins’ and ‘Regina’ × ‘Garnet’, detection of many quantitative trait loci (QTL) on all linkage groups (LG) has enabled us to confirm the strong involvement of chill requirements in the flowering as well as the complexity of these traits. QTL with major effect was localized on the LG4. In regions covered by all the QTLs controlling flowering date, a hundred candidate genes (CG) for this trait was identified. A subset of these GC was then studied for their expression during development of buds by quantitative PCR (qPCR). In the long term, this work will serve as a basis for the identification and selection of genes that allow obtaining genotypes adapted to future climate conditions.

<p>Systemic lupus erythematosus (SLE) is a complex autoimmune disease with unknown etiology. The aim of this thesis was to identify susceptibility regions through genetic mapping, using model-based linkage analysis on nuclear and extended SLE multicase families.</p><p>In the first paper we performed a genome scan on 19 genetically homogenous Icelandic and Swedish families. One region at 2q37 was identified with a significant linkage with contribution from both populations (Z=4.24). Five other regions 2q11, 4p13, 9p22, 9p13 and 9q13 showed suggestive linkage (Z>2.0).</p><p>In the second paper, 87 families from 10 different countries were analysed only for chromosome 1. One region at 1q31 showed significant linkage (Z=3.79) with contribution from families from all populations, including Mexicans and Europeans. Four other regions 1p36, 1p21, 1q23, and 1q25, showed levels of suggestive linkage. Linkage for most regions was highly dependent on what population was used, which indicated strong genetic heterogeneity in the genetic susceptibility for SLE.</p><p>In the two last papers, we used the positional candidate gene strategy, in order to investigate candidate genes in two regions linked to SLE. For the Bcl-2 gene (at 18q21) we could not detect any association with SLE using three different markers. However, when we investigated the tightly linked low-affinity family of FcγR genes (at 1q23), we could find association for two risk alleles in the FcγRIIA and FcγRIIIA genes. The risk alleles were transmitted to SLE patients on one specific haplotype and therefore are not independent risk alleles.</p><p>The results show that model-based linkage analysis is a strong approach in the search for susceptibility genes behind complex diseases like SLE.</p>

Systemic lupus erythematosus (SLE) is a complex autoimmune disease with unknown etiology. The aim of this thesis was to identify susceptibility regions through genetic mapping, using model-based linkage analysis on nuclear and extended SLE multicase families. In the first paper we performed a genome scan on 19 genetically homogenous Icelandic and Swedish families. One region at 2q37 was identified with a significant linkage with contribution from both populations (Z=4.24). Five other regions 2q11, 4p13, 9p22, 9p13 and 9q13 showed suggestive linkage (Z&gt;2.0). In the second paper, 87 families from 10 different countries were analysed only for chromosome 1. One region at 1q31 showed significant linkage (Z=3.79) with contribution from families from all populations, including Mexicans and Europeans. Four other regions 1p36, 1p21, 1q23, and 1q25, showed levels of suggestive linkage. Linkage for most regions was highly dependent on what population was used, which indicated strong genetic heterogeneity in the genetic susceptibility for SLE. In the two last papers, we used the positional candidate gene strategy, in order to investigate candidate genes in two regions linked to SLE. For the Bcl-2 gene (at 18q21) we could not detect any association with SLE using three different markers. However, when we investigated the tightly linked low-affinity family of FcγR genes (at 1q23), we could find association for two risk alleles in the FcγRIIA and FcγRIIIA genes. The risk alleles were transmitted to SLE patients on one specific haplotype and therefore are not independent risk alleles. The results show that model-based linkage analysis is a strong approach in the search for susceptibility genes behind complex diseases like SLE.

No description available.

This thesis is an investigation of the genetic basis of tocopherol accumulation in soybean (Glycine max [L.] Merrill) seeds. Soybean is the world’s most widely grown protein and oilseed crop and the principle source of vitamin E (tocopherols) as a supplement. Tocopherols (α-, β-, γ- and δ-isomers) are powerful antioxidants that contain human health benefits, including a decrease in the risk of lung cancer, heart disease and osteoporosis. The purpose of this research was to identify genetic and biochemical components affecting tocopherol accumulation in soybean seeds. The objectives were to: 1) investigate location and year effects on soybean seed tocopherol levels in the field; 2) determine environmental factors affecting soybean seed tocopherol levels under controlled conditions; 3) identify simple sequence repeat (SSR) markers that tag quantitative trail loci (QTL) for individual and total tocopherols; and 4) evaluate the potential role of VTE1, VTE3 and VTE4 genes in tocopherol accumulation using the candidate gene approach. Seventy nine recombinant inbred lines (RILs) derived from the cross between OAC Bayfield and OAC Shire were grown in the field at Elora, Woodstock and St. Pauls, ON, in 2009 and 2010. The tocopherol components were quantified using high performance liquid chromatography (HPLC). The results showed a significant (p < 0.001) genotype, environment and genotype x environment effect for each tocopherol component. It was discovered that a 2 x phosphate fertilizer (K2SO4 at 1.0M/150mL) and 30 ˚C temperature treatment increased each tocopherol component, whereas drought had no effects. Single marker analysis identified 42 QTL and interval mapping identified 26 QTL across 17 chromosomes. Significant two-locus epistatic interactions were found with a total of 122 and 152 in the 2009 and 2010 field seasons, respectively. The multiple locus models explained 18.4% to 72.2% with an average of 45.7% of the total phenotypic variation. The candidate gene approach using nucleotide sequences from the coding regions identified two single nucleotide polymorphisms (SNPs) in VTE1, five SNPs in VTE4 and none in VTE3. The SNPs were predicted to cause functional protein changes and the genes co-localized with some of the identified QTL. The results of this study provide a better understanding of the environmental factors and genetic mechanisms that influence the accumulation of tocopherols in soybean seeds. / Grain Farmers of Ontario, Vitamin Research Award

La sténose valvulaire aortique (SVA) est une valvulopathie résultant en l'ouverture incomplète de la valve aortique. La calcification des feuillets associée au vieillissement est la cause la plus importante de la SVA. Sa pathogénèse implique des dépôts de lipoprotéines, de l'inflammation et de la calcification des feuillets. Notre étude vise à identifier les gènes associés à une prédisposition à la SVA afin de mieux comprendre les mécanismes sous-jacents à cette maladie et potentiellement identifier de nouvelles cibles thérapeutiques. Pour ce faire, nous avons recruté 190 patients avec SVA dégénérative et 192 témoins, appariés pour l'âge et le sexe, puis effectué une étude d’association par gènes candidats en utilisant des marqueurs génétiques polymorphiques (SNP). Les gènes candidats choisis incluent (1) ceux dont les polymorphismes ont été présumés associés à la SVA dans des études antérieures (APOB, APOE, ESR1, PTH et VDR) (2) des gènes dont les polymorphismes ont été significativement associés et validés pour quelques maladies inflammatoires (IL-10, TNFAIP3) ou pour le métabolisme lipidique (PCSK9, LDLR) dans des études d’association pangénomiques, et (3) des gènes impliqués dans la pathogénie de la SVA à partir d’études faites sur des modèles animaux en lien avec la calcification (BMP2, CCR5, CTGF, LRP5, MSX2, WNT3), le remodelage tissulaire (CTSS, MMP9) ou le métabolisme lipidique (SMPD1). Pour les gènes des groupes (1) et (2), nous avons utilisé les SNPs rapportés dans la littérature comme étant significativement associés. Pour le groupe (3), nous avons effectué une approche par «tagSNP» qui consiste à sélectionner un groupe de SNP capturant la variabilité génétique dans la région ciblée. Au total, 81 SNPs dans 18 gènes ont été testés. Nous avons trouvé une association nominale avec les gènes BMP2 (OR = 1.55, IC95%: 1.14-2.10, p = 0.004) et LRP5 (OR = 1.47, IC95%: 1.06-2.03, p = 0.023) après ajustement pour la maladie coronarienne. Les gènes BMP2 et LRP5, impliqués dans la calcification selon certains modèles expérimentaux, sont donc associés à la SVA. Ce travail devrait être validé dans une cohorte indépendante plus large dans un avenir rapproché et il pourrait être étendu à d’autres gènes. / Aortic valve stenosis (AVS) is a valvular heart disease caused by calcification leading to incomplete opening of the aortic valve. Calcification of valve leaflets associated with aging is the most common cause of AVS. AVS pathogenesis involves lipoprotein deposits, chronic inflammation and calcification of the aortic valve leaflets. Our study aims to identify genes associated with AVS in order to better understand its mechanisms and potentially identify new therapeutic targets. We recruited 190 cases with AVS of different severity and 192 controls matched for age and sex. Then we conducted a candidate gene association study using single nucleotide polymorphisms (SNPs). The candidate genes selected include: (1) those with polymorphisms putatively implicated in previous genetic association studies of AVS (APOB, APOE, ESR1, PTH and VDR); (2) those with validated associations to inflammatory diseases (IL-10, TNFAIP3) or lipid metabolism (LDLR ,PCSK9) in genome-wide association studies and, (3) genes impliated in AVS pathogenesis from studies with animal models and thought to be involved in calcification (BMP2, CCR5, CTGF, LRP5, MXS2, WNT3); tissue remodeling (CTSS, MMP9) or lipid metabolism (SMPD1). For the first two categories of genes, we tested the SNPs reported to be associated in the literature and, in the third category we used a tag-SNP approach which consists of selecting a subset of SNPs to capture variability in the target region. Finally, 81 SNPs in 18 genes were tested. We found a nominal association of BMP2 (OR=1.55, CI: 1.14 – 2.10, p=0.004) and LRP5 (OR=1.47, CI: 1.06 – 2.03, p=0.023) with presence of AVS after adjustment for coronary heart disease. The genes BMP2 and LRP5, which are known to be involved in calcification based on animal models, are associated with AVS. The result of the current study should be validated in a larger independent cohort in the near future and then, it could also be extended to the study of other genes.

Abstract Osteoporosis is a bone disorder that leads to a reduction in bone volume, deterioration of bone microarchitecture and therefore increased fracture risk. Bone disorders such as osteoporosis commonly have both genetic and environmental components. Family and twin studies have shown the importance of genetics in bone formation and health, but most of the genetic factors contributing to bone formation are still largely unknown. The aim of this thesis was to search for and identify genetic factors that predispose to two different bone disorders manifesting in fractures, namely femoral neck stress fractures and childhood primary osteoporosis without features of OI (i.e. non-OI primary osteoporosis). Furthermore, in vitro studies were performed to elucidate the importance and mechanism of action of identified genetic factors in non-OI primary osteoporosis. By using candidate gene analyses we identified predisposing alleles, haplotypes and their interactions that increased the risk for femoral neck stress fractures in young male military conscripts. The conscripts lacking the CTR C allele and/or VDR C-A haplotype had a three-fold increased risk for femoral neck stress fractures compared to the carriers of both. Furthermore, conscripts carrying the LRP5 A-G-G-C haplotype had a three-fold increased risk for femoral neck stress fractures and in combination with VDR C-A haplotype a four-fold increased risk for stress fractures. These associations were mediated by low body weight and BMI. In the search for genetic factors of non-OI primary osteoporosis in children and adolescent, two novel mutations in LRP5 and two more variants in WNT3A and DKK1 were found in patients. The variants were also observed in the affected family members, but not in the control group. The effects of these variants were examined in in vitro studies and the results showed that some LRP5 mutations and the WNT3A variant might reduce bone formation by decreasing the canonical Wnt signalling activity. / Tiivistelmä Osteoporoosi on luustosairaus, joka alentaa luuntiheyttä ja heikentää luun rakennetta ja siten lisää murtumien riskiä. Osteoporoosin kaltaiset luusairaudet ovat usein monitekijäisiä tauteja, joiden syntyyn vaikuttavat sekä perinnölliset että ympäristölliset tekijät. Perhe- ja kaksostutkimukset ovat osoittaneet perinnöllisten tekijöiden olevan tärkeitä luun muodostuksessa ja terveydessä, mutta nämä tekijät ovat kuitenkin vielä suurelta osin tuntemattomia. Tutkimustyön tavoitteena oli etsiä ja tunnistaa perinnöllisiä tekijöitä, jotka altistavat kahdelle luunmurtumina ilmenevälle sairaudelle: reisiluunkaulan rasitusmurtumille ja lasten primaariselle osteoporoosille. Lisäksi primaariselle osteoporoosille altistavien perinnöllisten tekijöiden merkitystä ja vaikutusmekanismeja tutkittiin in vitro- kokeilla. Reisiluunkaulan rasitusmurtumille altistavien alleelien, haplotyyppien ja näiden vuorovaikutusten tunnistamiseen käytettiin ehdokasgeenianalyysiä nuorten alokkaiden aineistossa. Potilailla, joilta CTR-geenin C-alleeli ja/tai VDR-geenin C-A haplotyyppi puuttuivat, oli kolminkertainen riski rasitusmurtumien syntyyn molempien geenimuotojen kantajiin verrattuna. Myös LRP5-geenin A-G-G-C haplotyypin kantajilla oli kolminkertainen riski rasitusmurtumiin ja VDR-geenin C-A haplotyyppi ja A-G-G-C yhdessä lähes nelinkertaistivat rasitusmurtumien riskin alokkailla. Näiden assosiaatioiden todettiin välittyvän alhaisen painon ja painoindeksin välityksellä. Lapsuudessa tai varhaisnuoruudessa puhkeavan primaarisen osteoporoosin perinnöllisten tekijöiden etsinnässä löydettiin kaksi uutta mutaatiota LRP5-geenistä ja yhteensä kaksi uutta muutosta WNT3A- ja DKK1-geeneistä. Uusien ehdokasgeenilöydösten osuutta primaarisen osteoporoosin syntyyn tukee se, että muutokset löydettiin potilaiden lisäksi heidän sairailta sukulaisiltaan eikä muutoksia havaittu kontrolliaineistoissa. Uusien mutaatioiden mahdollisia vaikutuksia tutkittiin in vitro-kokein, jotka osoittivat, että eräät LRP5-geenin mutaatiot ja WNT3A-geenin muutos alentavat kanonisen Wnt-signalointireitin aktiivisuutta ja voivat siten vähentää luunmuodostusta.

Abstract Meniere’s disease (MD) is an inner ear disorder characterized by vertigo, tinnitus and sensorineural hearing impairment. An inherited form of the disease is called familial Meniere’s disease (FMD). The aim of this thesis was to describe the clinical and genetic features of Finnish FMD and to study its prevalence in Finland. In addition genetic factors previously associated with MD were studied in Finnish MD patients. A total of 38 Meniere-families were analysed in this study. In most of the families the mode of inheritance was found to be autosomal dominant. Meniere-like symptoms such as tinnitus or vertigo were common in these families even in individuals without a full triad of MD. Familial patients were affected earlier, suffered from longer spells of vertigo and had more autoimmune diseases compared to sporadic MD patients. The prevalence of FMD was studied among the patients treated in the Oulu University Hospital and Kainuu Central Hospital during the years 2005-2010. A family history of MD was probable in 23.4% of the cases, but only 9.3% could be confirmed, as it was not possible to gain information from deceased generations. Six candidate genes previously associated with MD were screened for mutations in Finnish MD patients. Two possibly adverse variations were observed in the KCNE1 gene in two patients but in none of the controls. The role of these variations in MD is still unclear and needs further study. The association of MD to the five other genes could not be confirmed, nor was Finnish FMD linked to a previously suggested locus on chromosome 12. / Tiivistelmä Menieren tauti on sisäkorvan sairaus, jolle on tyypillistä huimaus, korvien soiminen ja kuulon heikkeneminen. Tauti voi esiintyä myös perinnöllisenä. Tutkimustyön tavoitteena oli selvittää perinnöllisyyden osuutta Menieren taudissa, kuvata suomalaisen perinnöllisen Menieren taudin tyypilliset piirteet ja tutkia suomalaisessa aineistossa aikaisemmin tautiin yhdistettyjä perinnöllisiä tekijöitä. Tutkimuksessa analysoitiin 38 sukua, joissa Menieren tautia esiintyi perinnöllisenä. Suurimmassa osassa tapauksista periytyminen tapahtui vallitsevasti. Suvuissa esiintyi paljon Meniere-tyypistä oirehdintaa, kuten tinnitusta ja huimausta, ilman Menieren taudin koko taudinkuvaa. Meniere-suvuissa potilaat sairastuivat keskimääräistä aikaisemmin, kärsivät pidemmistä huimauskohtauksista ja sairastivat enemmän autoimmuunitauteja. Perinnöllisen Menieren taudin yleisyyttä tutkittiin Kainuun keskussairaalassa ja Oulun yliopistollisessa sairaalassa vuosina 2005−2010 hoidettujen potilaiden keskuudessa. Potilaista 23,4&#160;%:lla Menieren taudin sukuhistoria oli positiivinen; kuitenkin vain 9,3&#160;% pystyttiin vahvistamaan, sillä tietojen kerääminen edesmenneiltä sukupolvilta ei ollut mahdollista. Kuuden Menieren tautiin aikaisemmin yhdistetyn geenin merkitystä tutkittiin suomalaisessa aineistossa mutaatio- ja ehdokasgeenianalyysillä. KCNE1-geenistä löydettiin kaksi mahdollisesti proteiinia vaurioittavaa sekvenssinvaihtelua, joita ei havaittu kontrollihenkilöillä. Muutosten merkitys Menieren taudin synnyssä jäi kuitenkin epävarmaksi ja vaatii jatkotutkimuksia. Muiden geenien yhteyttä sairauteen ei pystytty vahvistamaan. Suomalainen Menieren tauti ei myöskään kytkeytynyt aikaisemmin ehdotettuun lokukseen kromosomissa 12.

L’amélioration génétique de la luzerne (Medicago sativa), une légumineuse fourragère autotétraploïde, pourrait bénéficier de l’allele mining. Cette méthode consiste à rechercher, dans la diversité naturelle, des allèles ayant potentiellement un effet sur le phénotype. Pour évaluer l’intérêt de cette stratégie qui exploite la diversité naturelle, cinq gènes impliqués dans des caractères sélectionnés ont été retenus : CAD1 et CCoaOMT (digestibilité), CONSTANS-like (rendement fourrager), NHX1 (tolérance à la salinité) et WXP1 (tolérance à la sécheresse). La diversité de ces gènes a été étudiée en séquençant 387 génotypes cultivés et 20 génotypes sauvages. L’analyse des données confirme la présence d’un goulot d’étranglement durant la domestication et la sélection de la luzerne. CONSTANS-like et WXP1 révèlent de nombreux variants alors que CAD1, CCoaOMT et NHX1 sont très peu variables. Des variants ayant un effet potentiel sur le phénotype ont été identifiés dans les zones de la séquence protéique qui sont conservées au sein des Faboideae. L’impact sur le phénotype de deux variants du gène CONSTANS-like a été étudié : Constans-634, à l’origine d’un codon stop prématuré et Constans-4111, situé dans une région conservée du gène. Pour cela des croisements ont été réalisés afin d’obtenir une descendance avec toutes les doses possibles (AAAA, AAAB, AABB, ABBB and BBBB) pour chaque mutation étudiée. Des marqueurs KASPar ont été développés afin de déterminer les doses de mutations chez les descendants. Aucun génotype homozygote muté pour Constans-634 n’a été détecté parmi les 1505 descendants. Ce variant a induit une floraison plus précoce de trois jours pour les génotypes portant trois doses d’allèle muté. Le variant Constans-4111 a induit un effet additif sur la hauteur de tige. Les génotypes homozygotes de type sauvage étaient en moyenne 11,8 cm plus petits que les génotypes homozygotes portant trois ou quatre doses du variant. L’intégration de la stratégie allele mining dans les schémas de sélection des espèces végétales autotétraploïdes hétérozygotes a été discutée. / Lucerne (Medicago sativa) is an autotetraploid forage legume, whose breeding could beneficiate from allele mining. This strategy is based on the natural diversity and consists in seeking alleles with a potential effect on the phenotype. The interest of this approach was evaluated by studying five genes of agronomic interest: CAD1 and CCoaOMT (digestibility), CONSTANS-like (forage yield), NHX1 (salt tolerance) and WXP1 (drought tolerance). The diversity of these five genes was evaluated by sequencing 387 genotypes of cultivated accessions and 20 genotypes of wild accessions. The results confirmed a bottleneck during lucerne domestication and selection. CONSTANS-like and WXP1 were very variable whereas CAD1, CCoaOMT and NHX1 contained very few variants. Variants with a potential strong impact on the phenotype were identified in conserved parts of protein sequence within the Faboideae. The impact on phenotype was studied for two mutations of the CONSTANS-like gene: constans-634, causing a premature stop codon and constans-4111, located in a conserved region of the gene. Genotypes carrying one to three doses of the mutations (AAAB, AABB and ABBB) were polycrossed in order to obtain offsprings with every allele combination (AAAA, AAAB, AABB, ABBB and BBBB). KASPar markers were developed to determine the mutation doses in offspring progeny. No homozygous genotype was found for constans-634 in the 1505 offspring progeny. This mutation induced a premature flowering of three days for the genotypes carrying three doses of the mutation. The mutation constans-4111 induced an additive effect on stem height and the homozygous genotypes without the variant where on average 11.8 cm shorter than homozygous genotypes carrying three or four doses of the variant. The application of allele mining strategy in plant schemes of heterozygous autotetraploid species was discussed.

Erythrocytes infected by mature forms of the Plasmodium falciparum parasite adhere to other components of the vascular space, a behavior considered critical to the pathogenesis of severe malaria. Adhesion is mediated by the P. falciparum erythrocyte membrane protein 1 (PfEMP1), a highly variant antigen expressed by the parasite and subject to switching during the course of an infection. The host ligands of PfEMP1 include CD36, ICAM-1 and the ABO antigens. By employing a series of population- and family-based association studies from multiple African populations, we examined whether variation in the genes underlying these molecules affects susceptibility to severe malaria. Our results suggest that a common frameshift mutation in the ABO glycosyltransferase, responsible for blood group O, is associated with protection from severe malarial phenotypes (P=2x10⁻⁷), particularly severe malarial anaemia. However, we found no significant disease associations with variation in either the ICAM1 or CD36 genes. We focused on two particular functional polymorphisms, the missense ICAM-1Kilifi and the CD36 nonsense mutation T1264G. We genotyped both markers in around 10,000 individuals, but neither demonstrated an association with severe malarial phenotypes. Malaria has been a profound selection pressure shaping human genetic diversity. The last decade has seen the development of several haplotype-based methods to detect signatures of recent positive evolutionary selection. These techniques are potentially invaluable tools in our hunt for genetic variants that protect from life threatening malaria. We used simulations and empirical data from the International HapMap Project to demonstrate the validity of searching for long regions of haplotype homozygosity, as an approach to finding alleles undergoing selective sweeps. We analysed genetic data from a range of populations, particularly those utilized by HapMap, to investigate whether our candidate genes were associated with signals of recent positive selection. We characterized the distribution of a selection event associated with the CD36 1264G allele, focused in Central-West Africa, and demonstrated a novel signal of low population differentiation at the ABO gene, suggestive of longstanding balancing selection. Our work confirms that variation in the host ligands of PfEMP1 modulates severe malaria susceptibility, and highlights the value of using signals of selection, along with functional experiments and genetic association studies, to dissect the biology of severe malaria.