Association studies of up to 1.2 million individuals yield new insights into the genetic etiology of tobacco and alcohol use

Tobacco and alcohol use are leading causes of mortality that influence risk for many complex diseases and disorders 1 . They are heritable 2,3 and etiologically related 4,5 behaviors that have been resistant to gene discovery efforts 6–11 . In sample sizes up to 1.2 million individuals, we discovered 566 genetic variants in 406 loci associated with multiple stages of tobacco use (initiation, cessation, and heaviness) as well as alcohol use, with 150 loci evidencing pleiotropic association. Smoking phenotypes were positively genetically correlated with many health conditions, whereas alcohol use was negatively correlated with these conditions, such that increased genetic risk for alcohol use is associated with lower disease risk. We report evidence for the involvement of many systems in tobacco and alcohol use, including genes involved in nicotinic, dopaminergic, and glutamatergic neurotransmission. The results provide a solid starting point to evaluate the effects of these loci in model organisms and more precise substance use measures

A genetic investigation of sex bias in the prevalence of attention-deficit/hyperactivity disorder

Background Attention-deficit/hyperactivity disorder (ADHD) shows substantial heritability and is 2-7 times more common in males than females. We examined two putative genetic mechanisms underlying this sex bias: sex-specific heterogeneity and higher burden of risk in female cases. Methods We analyzed genome-wide autosomal common variants from the Psychiatric Genomics Consortium and iPSYCH Project (20,183 cases, 35,191 controls) and Swedish populationregister data (N=77,905 cases, N=1,874,637 population controls). Results Genetic correlation analyses using two methods suggested near complete sharing of common variant effects across sexes, with rg estimates close to 1. Analyses of population data, however, indicated that females with ADHD may be at especially high risk of certain comorbid developmental conditions (i.e. autism spectrum disorder and congenital malformations), potentially indicating some clinical and etiological heterogeneity. Polygenic risk score (PRS) analysis did not support a higher burden of ADHD common risk variants in female cases (OR=1.02 [0.98-1.06], p=0.28). In contrast, epidemiological sibling analyses revealed that the siblings of females with ADHD are at higher familial risk of ADHD than siblings of affected males (OR=1.14, [95% CI: 1.11-1.18], p=1.5E-15). Conclusions Overall, this study supports a greater familial burden of risk in females with ADHD and some clinical and etiological heterogeneity, based on epidemiological analyses. However, molecular genetic analyses suggest that autosomal common variants largely do not explain the sex bias in ADHD prevalence

Investigations into malaria infection at the maternal-fetal interface and the characterization of placental polysialic acid

The human placenta is an organ that is derived from the fertilized embryo. It develops in advance of the embryo/fetus and through its specialized trophoblast populations, forms an "anchor" between mother and offspring. It carries out numerous important functions, including maintaining the pregnant state by secreting hormones and other molecules, and promoting tolerance of the genetically foreign (i.e., hemiallogeneic) embryo/fetus. The human placenta is bathed in maternal blood, which allows for nutrient uptake, waste elimination, and gas exchange. Finally, the placenta must defend the embryo/fetus from blood-borne pathogens. In this dissertation, I discuss placental malaria, which is characterized by the accumulation of parasitized erythrocytes at the maternal surface of the placenta. Although placental and congenital infection does not often occur (i.e., parasites are not usually found inside the placenta or embryo/fetus), infant low birth weight and pre-term labor are associated outcomes. Since examination of the placenta usually helps to explain an abnormal neonatal outcome, the characterization of Plasmodium falciparum-infected placental biopsies formed the basis of my studies. I carried out an in-depth histological analysis of samples obtained from pregnant women in Kinshasa, Democratic Republic of the Congo. These placentas, which were severely infected, displayed loss (necrosis) of syncytiotrophoblasts, the cells that cover the chorionic villi and form the primary barrier between maternal and fetal circulations. In parallel, I immunolocalized putative receptors for P. falciparum and my results suggested that histological changes (including syncytiotrophoblast loss) influenced their availability, such that many were only exposed in the infected state. Together, these results suggested that a reexamination of the mechanisms involved in initial adhesion was warranted and prompted me to carry out a binding screen to identify novel glycan receptors. P. falciparum-infected erythrocytes bound Lewis blood group antigens that were spatially and temporally positioned to initiate infection. Finally, I explored the possibility that parasitized erythrocytes might adhere to the uterine arterioles, which channel maternal blood to the intervillous space. Overall, my studies revealed that P. falciparum sequestration involves a complex series of interactions with both fetal and maternal cells, and is influenced by histological changes that expose receptors. As an offshoot, I also examined the role of Hofbauer cells, the fetal macrophage, in relationship to hemozoin, the byproduct of heme digestion by Plasmodium parasites. As my work on placental malaria familiarized me with glycobiology, I undertook a second project investigating the role of polysialic acid during placental development. Previous studies in the nervous and immune systems demonstrated that this cell-surface glycan has an enormous hydrated volume and globally modulates cell-cell interactions. In this dissertation, I showed that it is expressed by human placental trophoblasts and regulated as a function of gestational age--abundant early in pregnancy and barely detectable at term. It promoted cellular migration and invasion. Intriguingly, my results suggested that placental polysialic acid is associated with desmosomes, cell adhesion complexes. Together, these studies demonstrated that polysialic acid influences development of the human placenta

Transcriptional Response of Candida albicans to Nitric Oxide and the Role of the YHB1 Gene in Nitrosative Stress and Virulence

Here, we investigate how Candida albicans, the most prevalent human fungal pathogen, protects itself from nitric oxide ((.)NO), an antimicrobial compound produced by the innate immune system. We show that exposure of C. albicans to (.)NO elicits a reproducible and specific transcriptional response as determined by genome-wide microarray analysis. Many genes are transiently induced or repressed by (.)NO, whereas a set of nine genes remain at elevated levels during (.)NO exposure. The most highly induced gene in this latter category is YHB1, a flavohemoglobin that detoxifies (.)NO in C. albicans and other microbes. We show that C. albicans strains deleted for YHB1 have two phenotypes in vitro; they are hypersensitive to (.)NO and they are hyperfilamentous. In a mouse model of disseminated candidiasis, a YHB1 deleted C. albicans strain shows moderately attenuated virulence, but the virulence defect is not suppressed by deletion of the host NOS2 gene. These results suggest that (.)NO production is not a prime determinant of virulence in the mouse tail vein model of candidiasis and that the attenuated virulence of a yhb1Δ/yhb1Δ strain is attributable to a defect other than its reduced ability to detoxify (.)NO

Histopathologies, Immunolocalization, and a Glycan Binding Screen Provide Insights into Plasmodium falciparum Interactions with the Human Placenta1

During pregnancy, Plasmodium falciparum-infected erythrocytes cytoadhere to the placenta. Infection is likely initiated at two sites where placental trophoblasts contact maternal blood: 1) via syncytiotrophoblast (STB), a multicellular transporting and biosynthetic layer that forms the surface of chorionic villi and lines the intervillous space, and 2) through invasive cytotrophoblasts, which line uterine vessels that divert blood to the placenta. Here, we investigated mechanisms of infected erythrocyte sequestration in relationship to the microanatomy of the maternal-fetal interface. Histological analyses revealed STB denudation in placental malaria, which brought the stromal cores of villi in direct contact with maternal blood. STB denudation was associated with hemozoin deposition (P = 0.01) and leukocyte infiltration (P = 0.001) and appeared to be a feature of chronic placental malaria. Immunolocalization of infected red blood cell receptors (CD36, ICAM1/CD54, and chondroitin sulfate A) in placentas from uncomplicated pregnancies showed that STB did not stain, while the underlying villous stroma was immunopositive. Invasive cytotrophoblasts expressed ICAM1. In malaria, STB denudation exposed CD36 and chondroitin sulfate A in the villous cores to maternal blood, and STB expressed ICAM1. Finally, we investigated infected erythrocyte adherence to novel receptors by screening an array of 377 glycans. Infected erythrocytes bound Lewis antigens that immunolocalized to STB. Our results suggest that P. falciparum interactions with STB-associated Lewis antigens could initiate placental malaria. Subsequent pathologies, which expose CD36, ICAM1, and chondroitin sulfate A, might propagate the infection

Polysialic acid enhances the migration and invasion of human cytotrophoblasts

Polysialic acid (polySia) is a large, cell-surface linear homopolymer composed of α2,8-linked sialic acid residues. Most extensively studied in the nervous system, this unique glycan modulates development by enhancing cell migration and regulating differentiation. PolySia also functions in developing and adult immune systems and is a signature of many cancers. In this study, we demonstrated that human placental trophoblasts, an epithelial lineage, also display this glycan. Cytotrophoblasts and syncytiotrophoblasts expressed polySia in the first trimester and downregulated it during the course of pregnancy. PolySia promoted cytotrophoblast migration in an explant model of chorionic villous growth. Removal of this glycan also reduced cytotrophoblast penetration of basement membranes in an in vitro model of invasion. Finally, we showed that polySia was overexpressed in biopsies from patients with gestational trophoblastic diseases, including benign molar pregnancies and malignant choriocarcinomas. These results demonstrated, for the first time, functional roles for polySia during normal human placental development and implicated these unusual oligosaccharides in the unrestrained invasion of trophoblast tumors

Replication and characterization of CADM2 and MSRA genes on human behavior

Progress identifying the genetic determinants of personality has historically been slow, with candidate gene studies and small-scale genome-wide association studies yielding few reproducible results. In the UK Biobank study, genetic variants in CADM2 and MSRA were recently shown to influence risk taking behavior and irritability respectively, representing some of the first genomic loci to be associated with aspects of personality. We extend this observation by performing a personality “phenome-scan” across 16 traits in up to 140,487 participants from 23andMe for these two genes. Genome-wide heritability estimates for these traits ranged from 5–19%, with both CADM2 and MSRA demonstrating significant effects on multiple personality types. These associations covered all aspects of the big five personality domains, including specific facet traits such as compliance, altruism, anxiety and activity/energy. This study both confirms and extends the original observations, highlighting the role of genetics in aspects of mental health and behavior

Publisher Correction: Multi-trait analysis of genome-wide association summary statistics using MTAG (Nature Genetics, (2018), 50, 2, (229-237), 10.1038/s41588-017-0009-4)

An amendment to this paper has been published and can be accessed via a link at the top of the paper