The pleiotropic contribution of genes in dopaminergic and serotonergic pathways to addiction and related behavioral traits

Introduction: Co-occurrence of substance use disorders (SUD) and other behavioral conditions, such as stress-related, aggressive or risk-taking behaviors, in the same individual has been frequently described. As dopamine (DA) and serotonin (5-HT) have been previously identified as key neurotransmitters for some of these phenotypes, we explored the genetic contribution of these pathways to SUD and these comorbid phenotypes in order to better understand the genetic relationship between them. Methods: We tested the association of 275 dopaminergic genes and 176 serotonergic genes with these phenotypes by performing gene-based, gene-set and transcriptome-wide association studies in 11 genome-wide association studies (GWAS) datasets on SUD and related behaviors. Results: At the gene-wide level, 68 DA and 27 5-HT genes were found to be associated with at least one GWAS on SUD or related behavior. Among them, six genes had a pleiotropic effect, being associated with at least three phenotypes: ADH1C, ARNTL, CHRNA3, HPRT1, HTR1B and DRD2. Additionally, we found nominal associations between the DA gene sets and SUD, opioid use disorder, antisocial behavior, irritability and neuroticism, and between the 5-HT-core gene set and neuroticism. Predicted gene expression correlates in brain were also found for 19 DA or 5-HT genes. Discussion: Our study shows a pleiotropic contribution of dopaminergic and serotonergic genes to addiction and related behaviors such as anxiety, irritability, neuroticism and risk-taking behavior, highlighting a role for DA genes, which could explain, in part, the co-occurrence of these phenotype

Cross-disorder genetic analyses implicate dopaminergic signaling as a biological link between Attention-Deficit/Hyperactivity Disorder and obesity measures

Attention-Deficit/Hyperactivity Disorder (ADHD) and obesity are frequently comorbid, genetically correlated, and share brain substrates. The biological mechanisms driving this association are unclear, but candidate systems, like dopaminergic neurotransmission and circadian rhythm, have been suggested. Our aim was to identify the biological mechanisms underpinning the genetic link between ADHD and obesity measures and investigate associations of overlapping genes with brain volumes. We tested the association of dopaminergic and circadian rhythm gene sets with ADHD, body mass index (BMI), and obesity (using GWAS data of N = 53,293, N = 681,275, and N = 98,697, respectively). We then conducted genome-wide ADHD-BMI and ADHD-obesity gene-based meta-analyses, followed by pathway enrichment analyses. Finally, we tested the association of ADHD-BMI overlapping genes with brain volumes (primary GWAS data N = 10,720-10,928; replication data N = 9428). The dopaminergic gene set was associated with both ADHD (P = 5.81 × 10−3) and BMI (P = 1.63 × 10−5); the circadian rhythm was associated with BMI (P = 1.28 × 10−3). The genome-wide approach also implicated the dopaminergic system, as the Dopamine-DARPP32 Feedback in cAMP Signaling pathway was enriched in both ADHD-BMI and ADHD-obesity results. The ADHD-BMI overlapping genes were associated with putamen volume (P = 7.7 × 10−3; replication data P = 3.9 × 10−2) a brain region with volumetric reductions in ADHD and BMI and linked to inhibitory control. Our findings suggest that dopaminergic neurotransmission, partially through DARPP-32-dependent signaling and involving the putamen, is a key player underlying the genetic overlap between ADHD and obesity measures. Uncovering shared etiological factors underlying the frequently observed ADHD-obesity comorbidity may have important implications in terms of prevention and/or efficient treatment of these conditions

Exploring the contribution to ADHD of genes involved in Mendelian Disorders presenting with hyperactivity and/or inattention

Attention-deficit hyperactivity disorder (ADHD) is a complex neurodevelopmental disorder characterized by hyperactivity, impulsivity, and/or inattention, which are symptoms also observed in many rare genetic disorders. We searched for genes involved in Mendelian disorders presenting with ADHD symptoms in the Online Mendelian Inheritance in Man (OMIM) database, to curate a list of new candidate risk genes for ADHD.We explored the enrichment of functions and pathways in this gene list, and tested whether rare or common variants in these genes are associated with ADHD or with its comorbidities. We identified 139 genes, causal for 137 rare disorders, mainly related to neurodevelopmental and brain function. Most of these Mendelian disorders also present with other psychiatric traits that are often comorbid with ADHD. Using whole exome sequencing (WES) data from 668 ADHD cases, we found rare variants associated with the dimension of the severity of inattention symptoms in three genes: KIF11, WAC, and CRBN. Then, we focused on common variants and identified six genes associated with ADHD (in 19,099 cases and 34,194 controls): MANBA, UQCC2, HIVEP2, FOPX1, KANSL1, and AUH. Furthermore, HIVEP2, FOXP1, and KANSL1 were nominally associated with autism spectrum disorder (ASD) (18,382 cases and 27,969 controls), as well as HIVEP2 with anxiety (7016 cases and 14,475 controls), and FOXP1 with aggression (18,988 individuals), which is in line with the symptomatology of the rare disorders they are responsible for. In conclusion, inspecting Mendelian disorders and the genes responsible for them constitutes a valuable approach for identifying new risk genes and the mechanisms of complex disorders

A Highly Polymorphic Copy Number Variant in the NSF Gene is Associated with Cocaine Dependence

Cocaine dependence is a complex psychiatric disorder involving both genetic and environmental factors. Several neurotransmitter systems mediate cocaine's effects, dependence and relapse, being the components of the neurotransmitter release machinery good candidates for the disorder. Previously, we identified a risk haplotype for cocaine dependence in the NSF gene, encoding the protein N-Ethylmaleimide-Sensitive Factor essential for synaptic vesicle turnover. Here we examined the possible contribution to cocaine dependence of a large copy number variant (CNV) that encompasses part of the NSF gene. We performed a case-control association study in a discovery sample (359 cases and 356 controls) and identified an association between cocaine dependence and the CNV (P=0.013), that was confirmed in the replication sample (508 cases and 569 controls, P=7.1e-03) and in a pooled analysis (P=1.8e-04), with an over-representation of low number of copies in cases. Subsequently, we studied the functional impact of the CNV on gene expression and found thatthe levels of two NSF transcripts were significantly increased in peripheral blood mononuclear cells (PBMC) along with the number of copies of the CNV. These results, together with a previous study from our group, support the role of NSF in the susceptibility to cocaine dependenc

Involvement of the 14-3-3 gene family in autism spectrum disorder and schizophrenia: Genetics, transcriptomics and functional analyses

The 14-3-3 protein family are molecular chaperones involved in several biological functions and neurological diseases. We previously pinpointed YWHAZ (encoding 14-3-3ζ) as a candidate gene for autism spectrum disorder (ASD) through a whole-exome sequencing study, which identified a frameshift variant within the gene (c.659-660insT, p.L220Ffs*18). Here, we explored the contribution of the seven human 14-3-3 family members in ASD and other psychiatric disorders by investigating the: (i) functional impact of the 14-3-3ζ mutation p.L220Ffs*18 by assessing solubility, target binding and dimerization; (ii) contribution of common risk variants in 14-3-3 genes to ASD and additional psychiatric disorders; (iii) burden of rare variants in ASD and schizophrenia; and iv) 14-3-3 gene expression using ASD and schizophrenia transcriptomic data. We found that the mutant 14-3-3ζ protein had decreased solubility and lost its ability to form heterodimers and bind to its target tyrosine hydroxylase. Gene-based analyses using publicly available datasets revealed that common variants in YWHAE contribute to schizophrenia (p = 6.6 × 10-7), whereas ultra-rare variants were found enriched in ASD across the 14-3-3 genes (p = 0.017) and in schizophrenia for YWHAZ (meta-p = 0.017). Furthermore, expression of 14-3-3 genes was altered in post-mortem brains of ASD and schizophrenia patients. Our study supports a role for the 14-3-3 family in ASD and schizophrenia

Genètica molecular de l'autisme: recerca de variants de susceptibilitat i estudis funcionals

[cat] Els trastorns de l’espectre autista (TEA) són trastorns greus del neurodesenvolupament, caracteritzats per una discapacitat en la comunicació, tant verbal com no verbal, la limitació de la interacció social i comportaments i interessos restrictius i repetitius. La seva prevalença s’estima entre el 0,5% i l’1%, amb una mitjana de 4 vegades més homes afectats que dones. Els estudis familiars i de bessons indiquen una àmplia contribució genètica als TEA. Tot i això, el coneixement actual sobre aquests factors genètics és encara limitat, i les causes de la malaltia continuen plantejant una qüestió important. El treball que es presenta en aquesta Tesi Doctoral ha permès identificar variació genètica de risc als TEA. Així, s’ha avaluat la participació en autisme de variants rares del gen candidat PTCHD1, mitjançant el seu cribratge mutacional, i de gens que codifiquen microRNAs, per seqüenciació massiva. També s’ha estudiat la participació de variants genètiques de susceptibilitat, mitjançant estudis d’associació cas-control poblacionals, en el anteriors candidats: PTCHD1 i els gens de microRNA. S’ha dut a terme el primer estudi sistemàtic de la contribució als TEA de variants rares heretades, mitjançant la seqüenciació d’exomes de 10 famílies múltiplex. Aquest estudi va suggerir nous gens candidats, entre els quals destacava el gen de densitat post-sinàptica YWHAZ. A continuació, es va analitzar la família de gens 14-3-3, a la qual pertany YWHAZ, mitjançant un estudi d’associació cas-control amb polimorfismes dels set gens de la família, i el cribratge mutacional dels mateixos a una mostra de pacients per seqüenciació d’alt rendiment, amb l’objectiu d’avaluar la contribució de variants comunes i rares en aquests gens als TEA. S’han realitzat estudis funcionals de dues de les variants rares descrites en aquests treballs: una duplicació de 27 pb a la regió promotora del gen PTCHD1, identificada a tres pacients no emparentats mitjançant el cribratge del gen, i una mutació de canvi de pauta de lectura al gen YWHAZ, identificada a dos germans de l’estudi d’exomes a famílies múltiplex.[eng] Autism Spectrum Disorders (ASD) are a severe group of neurodevelopmental disorders characterized by impairments in both verbal and non-verbal communication, limited social interaction and repetitive and restrictive interests and behaviors. Their prevalence is estimated between 0.5 and 1%, with 4 times more affected males than females. Family and twin studies have shown a large genetic contribution to ASD. However, our current understanding of the specific underlying genetic factors remains largely unknown. The work presented in this Thesis allowed us to identify genetic variation of risk to ASD. We evaluated the involvement of rare genetic variants of the candidate gene PTCHD1 to autism by Sanger sequence analysis, and of genes encoding microRNAs by high-throughput sequencing. We also studied the participation of common susceptibility variants by population-based case-control association studies targeting the former candidates: PTCHD1 and microRNA genes. Additionally, we performed the first systematic study of the contribution to ASD of rare inherited variants by exome sequencing of 10 multiplex families. This study identified new candidate genes, among them the post-synaptic density gene YWHAZ. Subsequently, the 14-3-3 gene family, to which YWHAZ belongs, was analyzed by a case-control association study with polymorphisms covering the different ORFs, and by a mutation screening in a sample of patients using high-throughput sequencing, with the aim to evaluate the contribution of common and rare variants in these genes to ASD. Finally, we performed functional studies of two rare variants described in these works: a 27-bp duplication in the promoter region of PTCHD1, identified in three unrelated patients, and a frameshift mutation in the YWHAZ gene, identified in two affected siblings from one of the multiplex families

Comprehensive exploration of the genetic contribution of the dopaminergic and serotonergic pathways to psychiatric disorders

Psychiatric disorders are highly prevalent and display considerable clinical and genetic overlap. Dopaminergic and serotonergic neurotransmission have been shown to play an important role in many psychiatric disorders. Here we aim to assess the genetic contribution of these systems to eight psychiatric disorders (attention-deficit hyperactivity disorder (ADHD), anorexia nervosa (ANO), autism spectrum disorder (ASD), bipolar disorder (BIP), major depression (MD), obsessive-compulsive disorder (OCD), schizophrenia (SCZ) and Tourette's syndrome (TS)) using publicly available GWAS analyses performed by the Psychiatric Genomics Consortium that include more than 160,000 cases and 275,000 controls. To do so, we elaborated four different gene sets: two 'wide' selections for dopamine (DA) and for serotonin (SERT) using the Gene Ontology and KEGG pathways tools, and two'core' selections for the same systems, manually curated. At the gene level, we found 67 genes from the DA and/or SERT gene sets significantly associated with one of the studied disorders, and 12 of them were associated with two different disorders. Gene-set analysis revealed significant associations for ADHD and ASD with the wide DA gene set, for BIP with the wide SERT gene set, and for MD with the core SERT set. Interestingly, interrogation of a cross-disorder GWAS meta-analysis of the eight psychiatric conditions displayed association with the wide DA gene set. To our knowledge, this is the first systematic examination of genes encoding proteins essential to the function of these two neurotransmitter systems in these disorders. Our results support a pleiotropic contribution of the dopaminergic and serotonergic systems in several psychiatric conditions