Periodic Reporting for period 2 - ATTENTIVE (Distinguishing genetic overlap and causal relationship among attention deficit-hyperactivity disorder and substance use disorders)
Período documentado: 2023-05-01 hasta 2024-04-30
The aim of the project was to understand the genetic basis of the comorbidity between attention deficit-hyperactivity disorder (ADHD) and substance use disorders (SUDs). ADHD and SUDs are complex disorders, hence both genetic and environmental factors contribute to their development. Both ADHD and SUDs present a significant public health burden, especially when they occur concurrently. The risk to develop SUDs increases during the adolescence of patients with ADHD, with a faster progression rate compared to others. Identifying which individuals with ADHD present a higher risk to develop SUDs will ease some of this burden by offering the opportunity for early action and prevention.
Apart from the epidemiological evidence, several previous studies suggested shared genetic architecture between ADHD and SUDs, including cannabis use disorder, nicotine dependence, and alcohol dependence. However, inconsistent findings were observed. In the current study, we aimed to investigate this relationship, using genetic datasets with large sample size, and hence adequate power to detect reliable associations. We included two main SUDs, cannabis use disorder and opioid use disorder, and problematic substance uses problematic alcohol use and problematic tobacco use.
The overall objectives of this project were to investigate a comprehensive genetic relationship between ADHD and SUDs including i) genome-wide genetic correlation, ii) bi-directional genetic causality, iii) shared genetic variants, iiii) the sum of the genetic effects (i.e. polygenic risk) to develop SUDs calculated for patients with ADHD, and iv) validating the molecular function of shared variants in an experimental setting. Apart from the scientific goals, an important objective for the researcher was to develop individual research lines and ideas, and build a network with world-known experts on the field, which were successfully met.
Considering the findings generated by different analytic approaches applied in this study, we hypothesize that horizontal and vertical pleiotropy (shared genetic mechanisms and possible causal effects, respectively) both contribute to ADHD-SUD comorbidities with differences among substances. Specifically, ADHD-CanUD comorbidity could be mainly due to shared genetic mechanisms (horizontal pleiotropy supported by the bidirectional relationship observed in MR analysis and the multiple pleiotropic loci identified by PolarMorphism approach), while ADHD-PAU comorbidity is primarily driven by possible causal effects (vertical pleiotropy supported by PAU→ADHD effect identified by MR and only one locus identified by PolarMorphism approach). The ADHD-PTU relationship seems to be related to a combination of different pleiotropic pathways (supported by results from genomic SEM, MR, and PolarMorphism analyses). While these patterns in ADHD-SUD pleiotropy have to be confirmed by further studies, understanding the genetic factors contributing to ADHD-SUD comorbidity could enhance preventive strategies that alter possible causal relationships and yield more effective treatments based on specific ADHD-SUD molecular targets.
In conclusion, this project highlights the complex genetic relationships underlying the comorbidity between ADHD and SUDs, with differences in pleiotropic mechanisms across specific substances. By uncovering shared genetic pathways and potential causal effects, the findings contribute to a deeper understanding of ADHD-SUD interactions and lay the basis for targeted preventive and therapeutic strategies.
Apart from the epidemiological evidence, several previous studies suggested shared genetic architecture between ADHD and SUDs, including cannabis use disorder, nicotine dependence, and alcohol dependence. However, inconsistent findings were observed. In the current study, we aimed to investigate this relationship, using genetic datasets with large sample size, and hence adequate power to detect reliable associations. We included two main SUDs, cannabis use disorder and opioid use disorder, and problematic substance uses problematic alcohol use and problematic tobacco use.
The overall objectives of this project were to investigate a comprehensive genetic relationship between ADHD and SUDs including i) genome-wide genetic correlation, ii) bi-directional genetic causality, iii) shared genetic variants, iiii) the sum of the genetic effects (i.e. polygenic risk) to develop SUDs calculated for patients with ADHD, and iv) validating the molecular function of shared variants in an experimental setting. Apart from the scientific goals, an important objective for the researcher was to develop individual research lines and ideas, and build a network with world-known experts on the field, which were successfully met.
Considering the findings generated by different analytic approaches applied in this study, we hypothesize that horizontal and vertical pleiotropy (shared genetic mechanisms and possible causal effects, respectively) both contribute to ADHD-SUD comorbidities with differences among substances. Specifically, ADHD-CanUD comorbidity could be mainly due to shared genetic mechanisms (horizontal pleiotropy supported by the bidirectional relationship observed in MR analysis and the multiple pleiotropic loci identified by PolarMorphism approach), while ADHD-PAU comorbidity is primarily driven by possible causal effects (vertical pleiotropy supported by PAU→ADHD effect identified by MR and only one locus identified by PolarMorphism approach). The ADHD-PTU relationship seems to be related to a combination of different pleiotropic pathways (supported by results from genomic SEM, MR, and PolarMorphism analyses). While these patterns in ADHD-SUD pleiotropy have to be confirmed by further studies, understanding the genetic factors contributing to ADHD-SUD comorbidity could enhance preventive strategies that alter possible causal relationships and yield more effective treatments based on specific ADHD-SUD molecular targets.
In conclusion, this project highlights the complex genetic relationships underlying the comorbidity between ADHD and SUDs, with differences in pleiotropic mechanisms across specific substances. By uncovering shared genetic pathways and potential causal effects, the findings contribute to a deeper understanding of ADHD-SUD interactions and lay the basis for targeted preventive and therapeutic strategies.
The project was conducted in three work packages (WPs), addressing the genetic basis of ADHD-SUD comorbidity.
WP1: Identifying genetic variants and analyzing causality in ADHD-SUD comorbidity
The primary aim of WP1 was to identify genetic variants linked to ADHD-SUD comorbidity and analyze causal effects using genome-wide summary statistics. The fellow reviewed the state-of-the-art research, acquired technical skills in shell, bash, R, Python, and C++, and gained expertise in tools such as Linkage Disequilibrium Score Regression, Genomic Structural Equation Modeling, TwoSampleMR, PolarMorphism, and PRS-CS. Key findings included the identification of several variants explaining ADHD-SUD comorbidity, including one shared across all five traits studied and 36 variants associated with ADHD and specific SUDs (7 with cannabis use disorder, 1 with problematic alcohol use, and 28 with problematic tobacco use). Bi-directional causal relationships were identified between ADHD and cannabis use disorder, problematic alcohol use, and problematic tobacco use.
WP2: Untangling the regulatory role of genetic variants
In WP2, the fellow focused on in silico analysis to characterize the regulatory role of shared genetic variants. The variant CADM2 rs62250713 was identified as a functional variant linked to impulsivity, ADHD, and SUDs, as well as a regulator of gene expression in brain regions associated with these traits. The results of WP1 and WP2 were jointly published in Psychiatry Research.
WP3: Functional validation of the CADM2 gene
In the second period of the project, WP3 involved follow-up experiments on CADM2 using CRISPR-Cas9 in induced pluripotent stem cells. The gene was successfully knocked out, and ongoing gene expression studies are exploring its functional effects.
The fellow presented the work at three academic meetings at Yale University and at the World Congress of Psychiatric Genetics in Montreal, Canada, in October 2023. The work resulted from WP1-2 is published in Psychiatry Research (doi: 10.1016/j.psychres.2024.115758). She also mentored lab members, taught genomics courses, and organized events addressing academic mental health and career development.
WP1: Identifying genetic variants and analyzing causality in ADHD-SUD comorbidity
The primary aim of WP1 was to identify genetic variants linked to ADHD-SUD comorbidity and analyze causal effects using genome-wide summary statistics. The fellow reviewed the state-of-the-art research, acquired technical skills in shell, bash, R, Python, and C++, and gained expertise in tools such as Linkage Disequilibrium Score Regression, Genomic Structural Equation Modeling, TwoSampleMR, PolarMorphism, and PRS-CS. Key findings included the identification of several variants explaining ADHD-SUD comorbidity, including one shared across all five traits studied and 36 variants associated with ADHD and specific SUDs (7 with cannabis use disorder, 1 with problematic alcohol use, and 28 with problematic tobacco use). Bi-directional causal relationships were identified between ADHD and cannabis use disorder, problematic alcohol use, and problematic tobacco use.
WP2: Untangling the regulatory role of genetic variants
In WP2, the fellow focused on in silico analysis to characterize the regulatory role of shared genetic variants. The variant CADM2 rs62250713 was identified as a functional variant linked to impulsivity, ADHD, and SUDs, as well as a regulator of gene expression in brain regions associated with these traits. The results of WP1 and WP2 were jointly published in Psychiatry Research.
WP3: Functional validation of the CADM2 gene
In the second period of the project, WP3 involved follow-up experiments on CADM2 using CRISPR-Cas9 in induced pluripotent stem cells. The gene was successfully knocked out, and ongoing gene expression studies are exploring its functional effects.
The fellow presented the work at three academic meetings at Yale University and at the World Congress of Psychiatric Genetics in Montreal, Canada, in October 2023. The work resulted from WP1-2 is published in Psychiatry Research (doi: 10.1016/j.psychres.2024.115758). She also mentored lab members, taught genomics courses, and organized events addressing academic mental health and career development.
Apart from the proposed analyses, the fellow performed additional studies to understand the ADHD-SUD comorbidity better: a horizontal pleiotropy analysis to find genetic variants that can explain the shared genetic architecture between these traits, and a polygenic risk scoring analysis to quantify which individuals with ADHD are more genetically predisposed to develop each SUD. This is the first study to provide comprehensive evidence on the genetic relationship between ADHD and cannabis use disorder, opioid use disorder, problematic alcohol use, and problematic tobacco use. Based on these results and previous evidence, clinical screening of comorbidities in patients with ADHD should include these SUDs. This study could also be the basis to develop preventive strategies and therapeutic approaches in individuals with ADHD, a high risk population for SUDs. Hence, the results from this project may have an immense effect on adolescent health. With our published article in Psychiatry Research, we can raise public awareness about the consequences of non-or not adequately treated ADHD. Furthermore, world-leading experts in ADHD and SUDs are coauthors of the manuscript and carefully assessed the validity of our analyses. Therefore, our study is a reliable source of clinical follow-up.
We are also expecting to show further evidence on the molecular mechanisms behind the shared genetic architecture between ADHD and SUDs by gene expression studies in our CADM2 knockout iPSC model. This has never been studied before, hence we expect groundbreaking results as CADM2 was implicated in ADHD-related traits and SUDs before.
We are also expecting to show further evidence on the molecular mechanisms behind the shared genetic architecture between ADHD and SUDs by gene expression studies in our CADM2 knockout iPSC model. This has never been studied before, hence we expect groundbreaking results as CADM2 was implicated in ADHD-related traits and SUDs before.