Attention-deficit/hyperactivity disorder in a population isolate: linkage to loci at 4q13.2, 5q33.3, 11q22, and 17p11

Genomics of Attention Deficit Hyperactivity Disorder: What the Clinician Needs to Know

This report provides an update on current knowledge and applications of genomic research in attention deficit hyperactivity disorder (ADHD). The history, principles, and underlying assumptions for genetic studies on psychiatric disorders are reviewed. Recent DNA sequencing and genome-wide association studies have revealed common and rare genetic variants associated with ADHD. Communication of genetic knowledge in meetings with patients and their relatives and common misconceptions are addressed. The importance of recognizing genetic syndromes masquerading as ADHD or other common psychiatric disorders is emphasized and how genetic information can be used to improve diagnosis and therapy are discussed.

A Rare Presentation of Hyperphagia and Parasomnias Associated With Chromosome 4q Deletion: A Case Report

Background: Chromosome 4q deletion is a rare genetic disorder affecting an estimated 1 out of 100,000 people. It is characterized by microdeletions of the long arm of chromosome 4 with variable clinical presentations including heart defects, craniofacial and skeletal abnormalities, short stature, and developmental delays. While behavioral and psychiatric symptoms have been reported in a small number of patients with chromosome 4q deletions, none of these reports have described the hyperphagia or parasomnia symptoms that are presented in the current case. Case Presentation: A 7-year-old boy presented with a microdeletion of the long arm of chromosome 4 that resulted in psychiatric symptoms and neurodevelopmental delays. Notable manifestations included hyperphagia and parasomnias, in addition to aggression, functional encopresis, and speech delays. The boy's initial treatment was markedly delayed due to limited genetic testing at the age of 1 year, which led to a misdiagnosis of childhood aggression. This limited the care team involvement for neurologic evaluation and appropriate school interventions that would have otherwise been indicated. At inpatient admission, a multidisciplinary approach to diagnosis and treatment was adopted, encompassing pharmacological and behavioral interventions. The patient's attention-deficit/hyperactivity disorder (ADHD) was treated, and his individualized education plan included a functional behavioral assessment, as well as occupational therapy and speech and language services. Following a 4-day inpatient stay, the patient demonstrated a significant decrease in aggressive behaviors. Conclusion: Chromosome 4q deletion-related behaviors parallel those of children with autism spectrum disorder (ASD), and treatment is primarily focused on behavioral interventions. To successfully manage the psychiatric features of this complex condition, the involvement of a multidisciplinary team is recommended.

Phasic dopamine release in two different rat models of attention-deficit/hyperactivity disorder: Spontaneously hypertensive rats (SHR) versus Lphn3 knockout rats

We examined DA activity in the medial prefrontal cortex (mPFC) and nucleus accumbens core (NAcc) in two Different Rat Models of Attention-Deficit/Hyperactivity Disorder: Spontaneously Hypertensive Rats (SHR) Versus Lphn3 Knockout Rats. We examined baseline stimulation-evoked phasic DA release, half-life, and DA autoreceptor (DAR) functioning in the mPFC and NAcc, as well as the response to nomifensine (10 mg/kg, IP), a DA transporter (DAT) blocker, on these measures in the NAcc. Both rat models were hypodopaminergic, with notable regional and mechanistic differences. The SHRs displayed decreased DA release in the NAcc compared to their control strain (i.e., WKY rats), with no differences in the mPFC, leading a much lower NAcc-to-PFC DA release ratio in SHRs compared to controls suggesting an imbalance in DA transmission between these regions. The Lphn3 KO rats were considered hypodopaminergic based on the reduced summed DA release in the mPFC and NAcc compared to WT controls, although differences were not observed when examining each site independently. Lphn3 KOs displayed increased DA half-life in the mPFC compared with Lphn3 WT rats, an indication of decreased DAT reuptake, with no differences in the NAcc. DAT blockade by nomifensine had a similar effect on DA release in the NAcc of SHRs and WKYs, but increased DA release in the NAcc of Lphn3 KOs to a greater extent than in WTs. These results suggest that the efficacy of pharmacotherapies used to treat externalizing disorders such as ADHD and/or SUD, likely differ between SHRs and Lphn3 KO rats.

The known and unknown about attention deficit hyperactivity disorder (ADHD) genetics: a special emphasis on Arab population

Attention deficit hyperactivity disorder (ADHD) is a clinically and genetically heterogeneous neurodevelopmental syndrome characterized by behavioral appearances such as impulsivity, inattention, and hyperactivity. The prevalence of ADHD is high in childhood when compared to adults. ADHD has been significantly advanced by genetic research over the past 25 years. However, it is logically conceivable that both genetic and/or non-genetic factors, such as postnatal environmental and social influences, are associated with ADHD phenotype in Arab populations. While genetic influences are strongly linked with the etiology of ADHD, it remains obscure how consanguinity which is an underlying factor for many genetic diseases, contributes to ADHD subtypes. Arabian Gulf Nations have one the highest rates of consanguineous marriages, and consanguinity plays an important contributing factor in many genetic diseases that exist in higher percentages in Arabian Gulf Nations. Therefore, the current review aims to shed light on the genetic variants associated with ADHD subtypes in Arabian Gulf nations and Saudi Arabia in particular. It also focuses on the symptoms and the diagnosis of ADHD before turning to the neuropsychological pathways and subgroups of ADHD. The impact of a consanguinity-based understanding of the ADHD subtype will help to understand the genetic variability of the Arabian Gulf population in comparison with the other parts of the world and will provide novel information to develop new avenues for future research in ADHD.

Neuregulin 2 Is a Candidate Gene for Autism Spectrum Disorder

Autism spectrum disorder (ASD) is a complex neurodevelopmental disorder with heterogeneous and complex genetic underpinnings. Our previous microarray gene expression profiling identified significantly different neuregulin-2 gene (NRG2) expression between ASD patients and controls. Thus, we aimed to clarify whether NRG2 is a candidate gene associated with ASD. The study consisted of two stages. First, we used real-time quantitative PCR in 20 ASDs and 20 controls to confirm the microarray gene expression profiling results. The average NRG2 gene expression level in patients with ASD (3.23 ± 2.80) was significantly lower than that in the controls (9.27 ± 4.78, p < 0.001). Next, we conducted resequencing of all the exons of NRG2 in a sample of 349 individuals with ASD, aiming to identify variants of the NRG2 associated with ASD. We identified three variants, including two single nucleotide variants (SNVs), IVS3 + 13A > G (rs889022) and IVS10 + 32T > A (rs182642591), and one small deletion at exon 11 of NRG2 (delGCCCGG, rs933769137). Using data from the Taiwan Biobank as the controls, we found no significant differences in allele frequencies of rs889022 and rs182642591 between two groups. However, there is a significant difference in the genotype and allele frequency distribution of rs933769137 between ASDs and controls (p < 0.0001). The small deletion is located in the EGF-like domain at the C-terminal of the NRG2 precursor protein. Our findings suggest that NRG2 might be a susceptibility gene for ASD.

Differential Effects of ADHD Polygenic Risk on Cognitive Performance in Later Life

OBJECTIVE

Understanding the association between polygenic risk for ADHD and cognition throughout aging has not been widely studied. This study aimed to determine whether ADHD risk influences cognitive performance among individuals at both young-old and middle-old age.

METHOD

Participants from the Health and Retirement Study, a biennial survey of 20,000 Americans, were compared on executive function and delayed recall measures using regression analyses.

RESULTS

There was no significant effect of ADHD risk on memory at both age waves for African-ancestry (AA; n = 403) and European-ancestry (EA; n = 2,286). There was, however, a significant association between ADHD risk and performance on executive function for EA at middle-old age (p = .028), but not young-old age; no such association was observed for AA adults.

CONCLUSION

This finding suggests that ADHD risk may differentially influence cognition among older adults throughout the aging process, with important implications for future research.

Psychopathological Risk in Siblings of Subjects with Attention-Deficit/Hyperactivity Disorder: A cross-Sectional Study

OBJECTIVE

We aim to determine the prevalence of mental disorders in siblings of children with attention deficit hyperactivity disorder (ADHD), and to determine how psychosocial adversity factors relate to this psychopathology, in a low-middle income country (Colombia).

METHODS

We evaluated subjects with ADHD diagnosed according to the DSM-5 criteria, one of their parents and one of their siblings (ages 8-19). We used the ADHD rating scale and a set of instruments to assess the presence of mental disorders as well as psychosocial adversity.

RESULTS

We evaluated 74 trios formed by the index case with ADHD, one sibling and one of the parents. We found that 24.3% of the participating siblings also met the criteria for ADHD and another 24.3% for other psychiatric disorders. The risk of these siblings having ADHD increased further when one of the parents reported a history of ADHD. We also found that 28.3% of the families faced high levels of psychosocial adversity as per their scores in the Rutter Adversity Index.

CONCLUSIONS

Siblings of subjects with ADHD showed a significant risk for ADHD and other mental disorders. That risk increased if a parent reported a history of ADHD and also when two or more psychosocial adversity factors were present. This study supports the importance of early detection in efforts to decrease the risk for other siblings.

Impulsive choice in two different rat models of ADHD-Spontaneously hypertensive and Lphn3 knockout rats

Introduction

Impulsivity is a symptom of attention-deficit/hyperactivity disorder (ADHD) and variants in the Lphn3 (Adgrl3) gene (OMIM 616417) have been linked to ADHD. This project utilized a delay-discounting (DD) task to examine the impact of Lphn3 deletion in rats on impulsive choice. "Positive control" measures were also collected in spontaneously hypertensive rats (SHRs), another animal model of ADHD.

Methods

For Experiment I, rats were given the option to press one lever for a delayed reward of 3 food pellets or the other lever for an immediate reward of 1 pellet. Impulsive choice was measured as the tendency to discount the larger, delayed reward. We hypothesized that impulsive choice would be greater in the SHR and Lphn3 knockout (KO) rats relative to their control strains - Wistar-Kyoto (WKY) and Lphn3 wildtype (WT) rats, respectively.

Results

The results did not completely support the hypothesis, as only the SHRs (but not the Lphn3 KO rats) demonstrated a decrease in the percent choice for the larger reward. Because subsequent trials did not begin until the end of the delay period regardless of which lever was selected, rats were required to wait for the next trial to start even if they picked the immediate lever. Experiment II examined whether the rate of reinforcement influenced impulsive choice by using a DD task that incorporated a 1 s inter-trial interval (ITI) immediately after delivery of either the immediate (1 pellet) or delayed (3 pellet) reinforcer. The results of Experiment II found no difference in the percent choice for the larger reward between Lphn3 KO and WT rats, demonstrating reinforcement rate did not influence impulsive choice in Lphn3 KO rats.

Discussion

Overall, there were impulsivity differences among the ADHD models, as SHRs exhibited deficits in impulsive choice, while the Lphn3 KO rats did not.

Structural insights into adhesion GPCR ADGRL3 activation and Gq, Gs, Gi, and G12 coupling

Adhesion G-protein-coupled receptors (aGPCRs) play key roles in a diversity of physiologies. A hallmark of aGPCR activation is the removal of the inhibitory GAIN domain and the dipping of the cleaved stalk peptide into the ligand-binding pocket of receptors; however, the detailed mechanism remains obscure. Here, we present cryoelectron microscopy (cryo-EM) structures of ADGRL3 in complex with G_q, G_s, G_i, and G₁₂. The structures reveal unique ligand-engaging mode, distinctive activation conformation, and key mechanisms of aGPCR activation. The structures also reveal the uncharted structural information of GPCR/G₁₂ coupling. A comparison of G_q, G_s, G_i, and G₁₂ engagements with ADGRL3 reveals the key determinant of G-protein coupling on the far end of αH5 of Gα. A detailed analysis of the engagements allows us to design mutations that specifically enhance one pathway over others. Taken together, our study lays the groundwork for understanding aGPCR activation and G-protein-coupling selectivity.

[The Genetic Basis of ADHD - An Update]

The Genetic Basis of ADHD - An Update Abstract. Genetic risks play an important role in the etiology of attention-deficit/hyperactivity disorder (ADHD). This review presents the current state of knowledge concerning the genetic basis of the disorder. It discusses the results of twin- and family-based studies, linkage and association studies as well as recent findings resulting from Genome Wide Association Studies (GWAS). Furthermore, it elaborates on the relevance of polygenic risk scores, rare variants, and epigenetic alterations, especially in light of findings on genetic pleiotropy in the context of frequent psychiatric comorbidities in patients with ADHD.

Machine Learning Prediction of ADHD Severity: Association and Linkage to ADGRL3, DRD4, and SNAP25

OBJECTIVE

To investigate whether single nucleotide polymorphisms (SNPs) in the ADGRL3, DRD4, and SNAP25 genes are associated with and predict ADHD severity in families from a Caribbean community.

METHOD

ADHD severity was derived using latent class cluster analysis of DSM-IV symptomatology. Family-based association tests were conducted to detect associations between SNPs and ADHD severity latent phenotypes. Machine learning algorithms were used to build predictive models of ADHD severity based on demographic and genetic data.

RESULTS

Individuals with ADHD exhibited two seemingly independent latent class severity configurations. SNPs harbored in DRD4, SNAP25, and ADGRL3 showed evidence of linkage and association to symptoms severity and a potential pleiotropic effect on distinct domains of ADHD severity. Predictive models discriminate severe from non-severe ADHD in specific symptom domains.

CONCLUSION

This study supports the role of DRD4, SNAP25, and ADGRL3 genes in outlining ADHD severity, and a new prediction framework with potential clinical use.

An assessment of executive function in two different rat models of attention-deficit hyperactivity disorder: Spontaneously hypertensive versus Lphn3 knockout rats

Attention-deficit/hyperactivity disorder (ADHD) a common neurodevelopmental disorder of childhood and often comorbid with other externalizing disorders (EDs). There is evidence that externalizing behaviors share a common genetic etiology. Recently, a genome-wide, multigenerational sample linked variants in the Lphn3 gene to ADHD and other externalizing behaviors. Likewise, limited research in animal models has provided converging evidence that Lphn3 plays a role in EDs. This study examined the impact of Lphn3 deletion (i.e., Lphn3-/- ) in rats on measures of behavioral control associated with externalizing behavior. Impulsivity was assessed for 30 days via a differential reinforcement of low rates (DRL) task and working memory evaluated for 25 days using a delayed spatial alternation (DSA) task. Data from both tasks were averaged into 5-day testing blocks. We analyzed overall performance, as well as response patterns in just the first and last blocks to assess acquisition and steady-state performance, respectively. "Positive control" measures on the same tasks were measured in an accepted animal model of ADHD-the spontaneously hypertensive rat (SHR). Compared with wildtype controls, Lphn3-/- rats exhibited deficits on both the DRL and DSA tasks, indicative of deficits in impulsive action and working memory, respectively. These deficits were less severe than those in the SHRs, who were profoundly impaired on both tasks compared with their control strain, Wistar-Kyoto rats. The results provide evidence supporting a role for Lphn3 in modulating inhibitory control and working memory, and suggest additional research evaluating the role of Lphn3 in the manifestation of EDs more broadly is warranted.

Impulsive and Omission Errors: Potential Temporal Processing Endophenotypes in ADHD

Temporal processing (TP) is associated with functions such as perception, verbal skills, temporal perspective, and future planning, and is intercorrelated with working memory, attention, and inhibitory control, which are highly impaired in individuals with attention deficit hyperactivity disorder (ADHD). Here we evaluate TP measures as potential endophenotypes in Caribbean families ascertained from probands affected by ADHD. A total of 232 individuals were recruited and clinically evaluated using an extensive battery of neuropsychological tasks and reaction time (RT)-based task paradigms. Further, the heritability (genetic variance underpinning phenotype) was estimated as a measure of the genetics apportionment. A predictive framework for ADHD diagnosis was derived using these tasks. We found that individuals with ADHD differed from controls in neuropsychological tasks assessing mental control, visual-verbal memory, verbal fluency, verbal, and semantic fluency. In addition, TP measures such as RT, errors, and variability were also affected in individuals with ADHD. Moreover, we determined that only omission and commission errors had significant heritability. In conclusion, we have disentangled omission and commission errors as possible TP endophenotypes in ADHD, which can be suitable to assess the neurobiological and genetic basis of ADHD. A predictive model using these endophenotypes led to remarkable sensitivity, specificity, precision and classification rate for ADHD diagnosis, and may be a useful tool for patients' diagnosis, follow-up, and longitudinal assessment in the clinical setting.

ADGRL3, FGF1 and DRD4: Linkage and Association with Working Memory and Perceptual Organization Candidate Endophenotypes in ADHD

Attention deficit hyperactivity disorder (ADHD) is a highly heritable neurobehavioral disorder that affects children worldwide, with detrimental long-term consequences in affected individuals. ADHD-affected patients display visual-motor and visuospatial abilities and skills that depart from those exhibited by non-affected individuals and struggle with perceptual organization, which might partially explain impulsive responses. Endophenotypes (quantifiable or dimensional constructs that are closely related to the root cause of the disease) might provide a more powerful and objective framework for dissecting the underlying neurobiology of ADHD than that of categories offered by the syndromic classification. In here, we explore the potential presence of the linkage and association of single-nucleotide polymorphisms (SNPs), harbored in genes implicated in the etiology of ADHD (ADGRL3, DRD4, and FGF1), with cognitive endophenotypes related to working memory and perceptual organization in 113 nuclear families. These families were ascertained from a geographical area of the Caribbean coast, in the north of Colombia, where the community is characterized by its ethnic diversity and differential gene pool. We found a significant association and linkage of markers ADGRL3-rs1565902, DRD4-rs916457 and FGF1-rs2282794 to neuropsychological tasks outlining working memory and perceptual organization such as performance in the digits forward and backward, arithmetic, similarities, the completion of figures and the assembly of objects. Our results provide strong support to understand ADHD as a combination of working memory and perceptual organization deficits and highlight the importance of the genetic background shaping the neurobiology, clinical complexity, and physiopathology of ADHD. Further, this study supplements new information regarding an ethnically diverse community with a vast African American contribution, where ADHD studies are scarce.

Psychopathological Risk in Siblings of Subjects with Attention-Deficit/Hyperactivity Disorder: A cross-Sectional Study

OBJECTIVE

We aim to determine the prevalence of mental disorders in siblings of children with attention deficit hyperactivity disorder (ADHD), and to determine how psychosocial adversity factors relate to this psychopathology, in a low-middle income country (Colombia).

METHODS

We evaluated subjects with ADHD diagnosed according to the DSM-5 criteria, one of their parents and one of their siblings (ages 8-19). We used the ADHD rating scale and a set of instruments to assess the presence of mental disorders as well as psychosocial adversity.

RESULTS

We evaluated 74 trios formed by the index case with ADHD, one sibling and one of the parents. We found that 24.3% of the participating siblings also met the criteria for ADHD and another 24.3% for other psychiatric disorders. The risk of these siblings having ADHD increased further when one of the parents reported a history of ADHD. We also found that 28.3% of the families faced high levels of psychosocial adversity as per their scores in the Rutter Adversity Index.

CONCLUSIONS

Siblings of subjects with ADHD showed a significant risk for ADHD and other mental disorders. That risk increased if a parent reported a history of ADHD and also when two or more psychosocial adversity factors were present. This study supports the importance of early detection in efforts to decrease the risk for other siblings.

Adhesion G protein-coupled receptor L3 gene variants: Statistically significant association observed in the male Indo-caucasoid Attention deficit hyperactivity disorder probands

Primary symptoms of Attention Deficit Hyperactivity Disorder (ADHD) are age inappropriate inattention, hyperactivity and impulsivity. Caucasoid individuals showed increased susceptibility to ADHD and disruptive behaviour in presence of Adhesion G-protein-coupled receptor L3 (ADGRL3) gene variants. We investigated ADGRL3 rs1868790, rs6551665, rs2345039 in Indo-Caucasoid families with ADHD probands (N = 249) and controls (N = 350). Behavioural traits, executive function, and IQ of probands were measured through Conner's Parent Rating Scale-Revised, Parental Account of Children's Symptoms, Barkley Deficit in Executive Functioning-Child & Adolescent Scale, and Wechsler Intelligence Scale for Children-III respectively. After obtaining informed written consent, peripheral blood was collected for genomic DNA isolation and target sites were analyzed by PCR based methods or TaqMan assay. Case-control analysis showed higher frequency of rs2345039 'C' allele, 'CC' genotype and A-A-C haplotype in the ADHD probands, principally due to higher occurrence of the 'C' allele and A-A-C haplotype in the male probands (P < 0.05). Mother of the probands also showed higher occurrence of the 'C' allele and "CC" genotype (P < 0.01). Executive function was better in presence of rs2345039 "GG" (P = 0.04) while IQ score was higher in presence of rs6551665 "AA" (P = 0.06). Linkage disequilibrium between rs6551665 and rs2345039 was stronger in the ADHD cases, chiefly in the male probands. Multifactor dimensionality reduction analysis showed strong interaction between rs6551665 and rs2345039 in the male probands while in the female probands rs1868790 and rs6551665 revealed non-linear interaction. Based on these observations, we infer that ADGRL3 may have a role in the aetiology of ADHD in this population warranting further in depth investigation.

G12/13 is activated by acute tethered agonist exposure in the adhesion GPCR ADGRL3

The adhesion G-protein-coupled receptor (GPCR) latrophilin 3 (ADGRL3) has been associated with increased risk of attention deficit hyperactivity disorder (ADHD) and substance use in human genetic studies. Knockdown in multiple species leads to hyperlocomotion and altered dopamine signaling. Thus, ADGRL3 is a potential target for treatment of neuropsychiatric disorders that involve dopamine dysfunction, but its basic signaling properties are poorly understood. Identification of adhesion GPCR signaling partners has been limited by a lack of tools to acutely activate these receptors in living cells. Here, we design a novel acute activation strategy to characterize ADGRL3 signaling by engineering a receptor construct in which we could trigger acute activation enzymatically. Using this assay, we found that ADGRL3 signals through G12/G13 and Gq, with G12/13 the most robustly activated. Gα12/13 is a new player in ADGRL3 biology, opening up unexplored roles for ADGRL3 in the brain. Our methodological advancements should be broadly useful in adhesion GPCR research.

CDH13 and LPHN3 Gene Polymorphisms in Attention-Deficit/Hyperactivity Disorder: Their Relation to Clinical Characteristics

Genetic factors play a major role in the etiopathogenesis of attention-deficit/hyperactivity disorder (ADHD). In this study, we aimed to investigate the relationship between the CDH13 (rs6565113, rs11150556) and LPHN3 (rs6551665, rs6858066, rs1947274, rs2345039) gene polymorphisms and ADHD. We also sought to examine possible relationships between these polymorphisms and the clinical course and treatment response in ADHD. A total of 120 patients (79% boys), aged 6 to 18 years, newly diagnosed (medication-naïve) with ADHD according to the DSM-5 and a group of 126 controls (74% girls) were enrolled in the study. We examined the association between the aforementioned polymorphisms and ADHD. Univariate and multivariate logistic regression analysis were used to evaluate factors influencing the treatment response of ADHD. A significant difference was found between ADHD and control groups in terms of genotype distribution of the LPHN3 rs6551665 and rs1947274 polymorphisms. The results also showed that having the GG genotype of rs6551665 and CC genotype of rs1947274 of the LPHN3 gene was associated with risk for ADHD, and this relationship was more prominent in male participants. In the multivariate logistic regression model established with variables shown to have a significant relationship with treatment response, the presence of the GG genotype of the LPHN3 rs6551665 polymorphism and high severity of ADHD assessed by CGI-S were associated with poor response to treatment. This study is the first study to investigate the relationship between ADHD and these polymorphisms among Turkish adolescents. Our results imply that the LPHN3 rs6551665 and rs1947274 polymorphisms have a significant effect on ADHD in a Turkish population, and support previous observations that the presence of the GG genotype of the LPHN3 rs6551665 polymorphism may be associated with poor response to treatment in ADHD.

Mutations in sphingolipid metabolism genes are associated with ADHD

Attention deficit hyperactivity disorder (ADHD) is the most prevalent neurodevelopmental disorder in children, with genetic factors accounting for 75-80% of the phenotypic variance. Recent studies have suggested that ADHD patients might present with atypical central myelination that can persist into adulthood. Given the essential role of sphingolipids in myelin formation and maintenance, we explored genetic variation in sphingolipid metabolism genes for association with ADHD risk. Whole-exome genotyping was performed in three independent cohorts from disparate regions of the world, for a total of 1520 genotyped subjects. Cohort 1 (MTA (Multimodal Treatment study of children with ADHD) sample, 371 subjects) was analyzed as the discovery cohort, while cohorts 2 (Paisa sample, 298 subjects) and 3 (US sample, 851 subjects) were used for replication. A set of 58 genes was manually curated based on their roles in sphingolipid metabolism. A targeted exploration for association between ADHD and 137 markers encoding for common and rare potentially functional allelic variants in this set of genes was performed in the screening cohort. Single- and multi-locus additive, dominant and recessive linear mixed-effect models were used. During discovery, we found statistically significant associations between ADHD and variants in eight genes (GALC, CERS6, SMPD1, SMPDL3B, CERS2, FADS3, ELOVL5, and CERK). Successful local replication for associations with variants in GALC, SMPD1, and CERS6 was demonstrated in both replication cohorts. Variants rs35785620, rs143078230, rs398607, and rs1805078, associated with ADHD in the discovery or replication cohorts, correspond to missense mutations with predicted deleterious effects. Expression quantitative trait loci analysis revealed an association between rs398607 and increased GALC expression in the cerebellum.

Proteolytic Processing of Neuregulin 2

Neuregulin 2 (NRG2) belongs to the EGF family of growth factors. Most of this family members require proteolytic cleavage to liberate their ectodomains capable of binding and activating their cognate ErbB receptors. To date, most of the studies investigating proteolytic processing of neuregulins focused on NRG1, which was shown to undergo ectodomain shedding by several ADAM proteases and BACE1 and the remaining fragment was further cleaved by γ-secretase. Recently, NRG2 attracted more attention due to its role in the neurogenesis and modulation of behaviors associated with psychiatric disorders. In this study, we used genetic engineering methods to identify proteases involved in proteolytic processing of murine NRG2. Using non-neuronal cell lines as well as cultures of primary hippocampal neurons, we demonstrated that the major proteases responsible for releasing NRG2 ectodomain are ADAM10 and BACE2. Co-expression of NRG2 and BACE2 in neurons of certain brain structures including medulla oblongata and cerebellar deep nuclei was confirmed via immunohistochemical staining. The cleavage of NRG2 by ADAM10 or BACE2 generates a C-terminal fragment that serves as a substrate for γ-secretase. We also showed that murine NRG2 is subject to post-translational modifications, substantial glycosylation of its extracellular part, and phosphorylation of the cytoplasmic tail.

Genetic Variation Underpinning ADHD Risk in a Caribbean Community

Attention Deficit Hyperactivity Disorder (ADHD) is a highly heritable and prevalent neurodevelopmental disorder that frequently persists into adulthood. Strong evidence from genetic studies indicates that single nucleotide polymorphisms (SNPs) harboured in the ADGRL3 (LPHN3), SNAP25, FGF1, DRD4, and SLC6A2 genes are associated with ADHD. We genotyped 26 SNPs harboured in genes previously reported to be associated with ADHD and evaluated their potential association in 386 individuals belonging to 113 nuclear families from a Caribbean community in Barranquilla, Colombia, using family-based association tests. SNPs rs362990-SNAP25 (T allele; p = 2.46 × 10⁻⁴), rs2282794-FGF1 (A allele; p = 1.33 × 10⁻²), rs2122642-ADGRL3 (C allele, p = 3.5 × 10⁻²), and ADGRL3 haplotype CCC (markers rs1565902-rs10001410-rs2122642, OR = 1.74, P_permuted = 0.021) were significantly associated with ADHD. Our results confirm the susceptibility to ADHD conferred by SNAP25, FGF1, and ADGRL3 variants in a community with a significant African American component, and provide evidence supporting the existence of specific patterns of genetic stratification underpinning the susceptibility to ADHD. Knowledge of population genetics is crucial to define risk and predict susceptibility to disease.

Genetics of attention deficit hyperactivity disorder

Decades of research show that genes play an vital role in the etiology of attention deficit hyperactivity disorder (ADHD) and its comorbidity with other disorders. Family, twin, and adoption studies show that ADHD runs in families. ADHD's high heritability of 74% motivated the search for ADHD susceptibility genes. Genetic linkage studies show that the effects of DNA risk variants on ADHD must, individually, be very small. Genome-wide association studies (GWAS) have implicated several genetic loci at the genome-wide level of statistical significance. These studies also show that about a third of ADHD's heritability is due to a polygenic component comprising many common variants each having small effects. From studies of copy number variants we have also learned that the rare insertions or deletions account for part of ADHD's heritability. These findings have implicated new biological pathways that may eventually have implications for treatment development.

ADGRL3 (LPHN3) variants predict substance use disorder

Genetic factors are strongly implicated in the susceptibility to develop externalizing syndromes such as attention-deficit/hyperactivity disorder (ADHD), oppositional defiant disorder, conduct disorder, and substance use disorder (SUD). Variants in the ADGRL3 (LPHN3) gene predispose to ADHD and predict ADHD severity, disruptive behaviors comorbidity, long-term outcome, and response to treatment. In this study, we investigated whether variants within ADGRL3 are associated with SUD, a disorder that is frequently co-morbid with ADHD. Using family-based, case-control, and longitudinal samples from disparate regions of the world (n = 2698), recruited either for clinical, genetic epidemiological or pharmacogenomic studies of ADHD, we assembled recursive-partitioning frameworks (classification tree analyses) with clinical, demographic, and ADGRL3 genetic information to predict SUD susceptibility. Our results indicate that SUD can be efficiently and robustly predicted in ADHD participants. The genetic models used remained highly efficient in predicting SUD in a large sample of individuals with severe SUD from a psychiatric institution that were not ascertained on the basis of ADHD diagnosis, thus identifying ADGRL3 as a risk gene for SUD. Recursive-partitioning analyses revealed that rs4860437 was the predominant predictive variant. This new methodological approach offers novel insights into higher order predictive interactions and offers a unique opportunity for translational application in the clinical assessment of patients at high risk for SUD.

ADGRL3 rs6551665 as a Common Vulnerability Factor Underlying Attention-Deficit/Hyperactivity Disorder and Autism Spectrum Disorder

Neurodevelopmental disorders are prevalent, frequently occur in comorbidity and share substantial genetic correlation. Previous evidence has suggested a role for the ADGRL3 gene in Attention-Deficit/Hyperactivity Disorder (ADHD) susceptibility in several samples. Considering ADGRL3 functionality in central nervous system development and its previous association with neurodevelopmental disorders, we aimed to assess ADGRL3 influence in early-onset ADHD (before 7 years of age) and Autism Spectrum Disorder (ASD). The sample comprises 187 men diagnosed with early-onset ADHD, 135 boys diagnosed with ASD and 468 male blood donors. We tested the association of an ADGRL3 variant (rs6551665) with both early-onset ADHD and ASD susceptibility. We observed significant associations between ADGRL3-rs6551665 on ADHD and ASD susceptibilities; we found that G-carriers were at increased risk of ADHD and ASD, in accordance with previous studies. The overall evidence from the literature, corroborated by our results, suggests that ADGRL3 might be involved in brain development, and genetic modifications related to it might be part of a shared vulnerability factor associated with the underlying neurobiology of neurodevelopmental disorders such as ADHD and ASD.

Neuregulin-2 ablation results in dopamine dysregulation and severe behavioral phenotypes relevant to psychiatric disorders

Numerous genetic and functional studies implicate variants of Neuregulin-1 (NRG1) and its neuronal receptor ErbB4 in schizophrenia and many of its endophenotypes. Although the neurophysiological and behavioral phenotypes of NRG1 mutant mice have been investigated extensively, practically nothing is known about the function of NRG2, the closest NRG1 homolog. We found that NRG2 expression in the adult rodent brain does not overlap with NRG1 and is more extensive than originally reported, including expression in the striatum and medial prefrontal cortex (mPFC), and therefore generated NRG2 knockout mice (KO) to study its function. NRG2 KOs have higher extracellular dopamine levels in the dorsal striatum but lower levels in the mPFC; a pattern with similarities to dopamine dysbalance in schizophrenia. Like ErbB4 KO mice, NRG2 KOs performed abnormally in a battery of behavioral tasks relevant to psychiatric disorders. NRG2 KOs exhibit hyperactivity in a novelty-induced open field, deficits in prepulse inhibition, hypersensitivity to amphetamine, antisocial behaviors, reduced anxiety-like behavior in the elevated plus maze and deficits in the T-maze alteration reward test-a task dependent on hippocampal and mPFC function. Acute administration of clozapine rapidly increased extracellular dopamine levels in the mPFC and improved alternation T-maze performance. Similar to mice treated chronically with N-methyl-d-aspartate receptor (NMDAR) antagonists, we demonstrate that NMDAR synaptic currents in NRG2 KOs are augmented at hippocampal glutamatergic synapses and are more sensitive to ifenprodil, indicating an increased contribution of GluN2B-containing NMDARs. Our findings reveal a novel role for NRG2 in the modulation of behaviors with relevance to psychiatric disorders.

Familial aggregation and linkage analysis with covariates for metabolic syndrome risk factors

BACKGROUND

Mechanisms of metabolic syndrome (MetS) causation are complex, genetic and environmental factors are important factors for the pathogenesis of MetS In this study, we aimed to evaluate familial and genetic influences on metabolic syndrome risk factor and also assess association between FTO (rs1558902 and rs7202116) and CETP(rs1864163) genes' single nucleotide polymorphisms (SNP) with low HDL_C in the Tehran Lipid and Glucose Study (TLGS).

MATERIALS AND METHODS

The design was a cross-sectional study of 1776 members of 227 randomly-ascertained families. Selected families contained at least one affected metabolic syndrome and at least two members of the family had suffered a loss of HDL_C according to ATP III criteria. In this study, after confirming the familial aggregation with intra-trait correlation coefficients (ICC) of Metabolic syndrome (MetS) and the quantitative lipid traits, the genetic linkage analysis of HDL_C was performed using conditional logistic method with adjusted sex and age.

RESULTS

The results of the aggregation analysis revealed a higher correlation between siblings than between parent-offspring pairs representing the role of genetic factors in MetS. In addition, the conditional logistic model with covariates showed that the linkage results between HDL_C and three marker, rs1558902, rs7202116 and rs1864163 were significant.

CONCLUSIONS

In summary, a high risk of MetS was found in siblings confirming the genetic influences of metabolic syndrome risk factor. Moreover, the power to detect linkage increases in the one parameter conditional logistic model regarding the use of age and sex as covariates.

Deficiency of tumor suppressor NDRG2 leads to attention deficit and hyperactive behavior

Attention-deficit/hyperactivity disorder (ADHD) is a prevalent psychiatric disorder in children. Although an imbalance of excitatory and inhibitory inputs has been proposed as contributing to this disorder, the mechanisms underlying this highly heterogeneous disease remain largely unknown. Here, we show that N-myc downstream-regulated gene 2 (NDRG2) deficiency is involved in the development of ADHD in both mice and humans. Ndrg2-knockout (Ndrg2-/-) mice exhibited ADHD-like symptoms characterized by attention deficits, hyperactivity, impulsivity, and impaired memory. Furthermore, interstitial glutamate levels and excitatory transmission were markedly increased in the brains of Ndrg2-/- mice due to reduced astroglial glutamate clearance. We developed an NDRG2 peptide that rescued astroglial glutamate clearance and reduced excitatory glutamate transmission in NDRG2-deficient astrocytes. Additionally, NDRG2 peptide treatment rescued ADHD-like hyperactivity in the Ndrg2-/- mice, while routine methylphenidate treatment had no effect on hyperactivity in these animals. Finally, children who were heterozygous for rs1998848, a SNP in NDRG2, had a higher risk of ADHD than children who were homozygous for rs1998848. Our results indicate that NDRG2 deficiency leads to ADHD phenotypes and that impaired astroglial glutamate clearance, a mechanism distinct from the well-established dopamine deficit hypothesis for ADHD, underlies the resultant behavioral abnormalities.

Further replication of the synergistic interaction between LPHN3 and the NTAD gene cluster on ADHD and its clinical course throughout adulthood

Attention-Deficit/Hyperactivity Disorder (ADHD) is a common and highly heritable neuropsychiatric disorder. Despite the high heritability, the unraveling of specific genetic factors related to ADHD is hampered by its considerable genetic complexity. Recent evidence suggests that gene-gene interactions can explain part of this complexity. We examined the impact of strongly supported interaction effects between the LPHN3 gene and the NTAD gene cluster (NCAM1-TTC12-ANKK1-DRD2) in a 7-year follow-up of a clinical sample of adults with ADHD, addressing associations with susceptibility, symptomatology and stability of diagnosis. The sample comprises 548 adults with ADHD and 643 controls. Entropy-based analysis indicated a potential interaction between the LPHN3-rs6551665 and TTC12-rs2303380 SNPs influencing ADHD symptom counts. Further analyses revealed significant interaction effects on ADHD total symptoms (p=0.002), and with hyperactivity/impulsivity symptom counts (p=0.005). In the group composed by predominantly hyperactive/impulsive and combined presentation, the presence of LPHN3-rs6551665 G allele was related to increased ADHD risk only in individuals carrying the TTC12-rs2303380 AA genotype (p=0.026). Also, the same allelic constellation is involved in maintenance of ADHD in a predominantly hyperactive/impulsive or combined presentation after a 7-year follow-up (p=0.008). These observations reinforce and replicate previous evidence suggesting that an interaction effect between the LPHN3 gene and the NTAD cluster may have a role in the genetic substrate associated to ADHD also in adults. Moreover, it is possible that the interactions between LPHN3 and NTAD are specific factors contributing to the development of an ADHD phenotype with increased hyperactivity/impulsivity that is maintained throughout adulthood.

An Ultraconserved Brain-Specific Enhancer Within ADGRL3 (LPHN3) Underpins Attention-Deficit/Hyperactivity Disorder Susceptibility

BACKGROUND

Genetic factors predispose individuals to attention-deficit/hyperactivity disorder (ADHD). Previous studies have reported linkage and association to ADHD of gene variants within ADGRL3. In this study, we functionally analyzed noncoding variants in this gene as likely pathological contributors.

METHODS

In silico, in vitro, and in vivo approaches were used to identify and characterize evolutionary conserved elements within the ADGRL3 linkage region (~207 Kb). Family-based genetic analyses of 838 individuals (372 affected and 466 unaffected patients) identified ADHD-associated single nucleotide polymorphisms harbored in some of these conserved elements. Luciferase assays and zebrafish green fluorescent protein transgenesis tested conserved elements for transcriptional enhancer activity. Electromobility shift assays were used to verify transcription factor-binding disruption by ADHD risk alleles.

RESULTS

An ultraconserved element was discovered (evolutionary conserved region 47) that functions as a transcriptional enhancer. A three-variant ADHD risk haplotype in evolutionary conserved region 47, formed by rs17226398, rs56038622, and rs2271338, reduced enhancer activity by 40% in neuroblastoma and astrocytoma cells (p_Bonferroni < .0001). This enhancer also drove green fluorescent protein expression in the zebrafish brain in a tissue-specific manner, sharing aspects of endogenous ADGRL3 expression. The rs2271338 risk allele disrupts binding of YY1 transcription factor, an important factor in the development and function of the central nervous system. Expression quantitative trait loci analysis of postmortem human brain tissues revealed an association between rs2271338 and reduced ADGRL3 expression in the thalamus.

CONCLUSIONS

These results uncover the first functional evidence of common noncoding variants with potential implications for the pathology of ADHD.

Linkage and association analysis of ADHD endophenotypes in extended and multigenerational pedigrees from a genetic isolate

Attention-deficit/hyperactivity disorder (ADHD) is a heritable, chronic, neurodevelopmental disorder with serious long-term repercussions. Despite being one of the most common cognitive disorders, the clinical diagnosis of ADHD is based on subjective assessments of perceived behaviors. Endophenotypes (neurobiological markers that cosegregate and are associated with an illness) are thought to provide a more powerful and objective framework for revealing the underlying neurobiology than syndromic psychiatric classification. Here, we present the results of applying genetic linkage and association analyses to neuropsychological endophenotypes using microsatellite and single nucleotide polymorphisms. We found several new genetic regions linked and/or associated with these endophenotypes, and others previously associated to ADHD, for example, loci harbored in the LPHN3, FGF1, POLR2A, CHRNA4 and ANKFY1 genes. These findings, when compared with those linked and/or associated to ADHD, suggest that these endophenotypes lie on shared pathways. The genetic information provided by this study offers a novel and complementary method of assessing the genetic causes underpinning the susceptibility to behavioral conditions and may offer new insights on the neurobiology of the disorder.

ADGRL3 (LPHN3) variants are associated with a refined phenotype of ADHD in the MTA study

Background

ADHD is the most common neuropsychiatric condition affecting individuals of all ages. Long‐term outcomes of affected individuals and association with severe comorbidities as SUD or conduct disorders are the main concern. Genetic associations have been extensively described. Multiple studies show that intronic variants harbored in the ADGRL3 (LPHN3) gene are associated with ADHD, especially associated with poor outcomes.

Methods

In this study, we evaluated this association in the Multimodal Treatment Study of children with ADHD (MTA), initiated as a 14‐month randomized clinical trial of 579 children diagnosed with DSM‐IV ADHD‐Combined Type (ADHD‐C), that transitioned to a 16‐year prospective observational follow‐up, and 289 classmates added at the 2‐year assessment to serve as a local normative comparison group (LNCG). Diagnostic evaluations at entry were based on the Diagnostic Interview Schedule for Children‐Parent (DISC‐P), which was repeated at several points over the years. For an add‐on genetic study, blood samples were collected from 232 in the MTA group and 139 in the LNCG.

Results

For the 205 MTA participants, 14.6% retained the DISC‐P diagnosis of ADHD‐C in adolescence. For 127 LNCG participants, 88.2% remained undiagnosed by the DISC‐P. We genotyped 15 polymorphic SNP markers harbored in the ADGRL3 gene, and compared allele frequencies for the 30 cases with continued diagnosis of ADHD‐C in adolescence to the other participants. Replication of the association of rs2345039 ADGRL3 variant was observed (P value = 0.004, FDR corrected = 0.03; Odds ratio = 2.25, upper CI 1.28–3.97).

Conclusion

The detection of susceptibility conferred by ADGRL3 variants in the extreme phenotype of continued diagnosis of ADHD‐C from childhood to adolescence provides additional support that the association of ADGRL3 and ADHD is not spurious. Exploring genetic effects in longitudinal cohorts, in which refined, age‐dependent phenotypes are documented, is crucial to understand the natural history of ADHD.

LPHN3 and attention-deficit/hyperactivity disorder: a susceptibility and pharmacogenetic study

Latrophilin 3 (LPHN3) is a brain-specific member of the G-protein coupled receptor family associated to both attention-deficit/hyperactivity disorder (ADHD) genetic susceptibility and methylphenidate (MPH) pharmacogenetics. Interactions of LPHN3 variants with variants harbored in the 11q chromosome improve the prediction of ADHD development and medication response. The aim of this study was to evaluate the role of LPHN3 variants in childhood ADHD susceptibility and treatment response in a naturalistic clinical cohort. The association between LPHN3 and ADHD was evaluated in 523 children and adolescents with ADHD and 132 controls. In the pharmacogenetic study, 172 children with ADHD were investigated. The primary outcome measure was the parent-rated Swanson, Nolan and Pelham Scale - version IV applied at baseline, first and third months of treatment with MPH. The results reported herein suggest the CGC haplotype derived from single nucleotide polymorphisms (SNPs) rs6813183, rs1355368 and rs734644 as an ADHD risk haplotype (P = 0.02, OR = 1.46). Although non-significant after multiple testing correction, its interaction with the 11q chromosome SNP rs965560 slightly increases risk (P = 0.03, OR = 1.55). Homozygous individuals for the CGC haplotype showed faster response to MPH treatment as a significant interaction effect between CGC haplotype and treatment over time was observed (P < 0.001). Homozygous individuals for the GT haplotype derived from SNPs rs6551665 and rs1947275 showed a nominally significant interaction with treatment over time (P = 0.04). Our findings replicate previous findings reporting that LPHN3 confers ADHD susceptibility, and moderates MPH treatment response in children and adolescents with ADHD.

Hot and Cool Executive Functions in Children with Attention-Deficit/Hyperactivity Disorder and Comorbid Oppositional Defiant Disorder

While neuropsychological deficits in both "hot" and "cool" executive functions (EFs) have been documented among individuals with attention-deficit/hyperactivity disorder (ADHD), these EF deficits are not universal across all individuals with this diagnosis. One potential moderator of executive dysfunction may be the presence of comorbid oppositional defiant disorder (ODD). This study examined the association between "hot" and "cool" EFs and comorbid ODD in children with ADHD. Thirty-three children with ADHD and comorbid ODD (ADHD+ODD), 67 with ADHD without ODD (ADHD-ODD), and 30 typically developing controls participated. Children were 7-12 years of age. "Cool" EFs were assessed with a spatial span task and a card sorting test. "Hot" EFs were assessed using a delay discounting task and a gambling task. ADHD-ODD and ADHD+ODD groups performed more poorly on "cool" EF tasks than controls, but did not differ from each other. Furthermore, the number of ADHD symptoms, but not ODD symptoms, was associated with "cool" EF scores. The three groups did not differ on "hot" EF tasks and the number of ADHD or ODD symptoms was unrelated to "hot" EF scores. In sum, children with ADHD presented with "cool" EF deficits which appear to be unrelated to ODD comorbidity. However, "hot" EF deficits were not present among children with ADHD, irrespective of comorbid ODD status.

Neuropsychological and dimensional behavioral trait profiles in Costa Rican ADHD sib pairs: Potential intermediate phenotypes for genetic studies

Attention deficit hyperactivity disorder (ADHD) is associated with substantial functional impairment in children and in adults. Many individuals with ADHD have clear neurocognitive deficits, including problems with visual attention, processing speed, and set shifting. ADHD is etiologically complex, and although genetic factors play a role in its development, much of the genetic contribution to ADHD remains unidentified. We conducted clinical and neuropsychological assessments of 294 individuals (269 with ADHD) from 163 families (48 multigenerational families created using genealogical reconstruction, 78 affected sib pair families, and 37 trios) from the Central Valley of Costa Rica (CVCR). We used principal components analysis (PCA) to group neurocognitive and behavioral variables using the subscales of the Child Behavior Checklist (CBCL) and 15 neuropsychological measures, and created quantitative traits for heritability analyses. We identified seven cognitive and two behavioral domains. Individuals with ADHD were significantly more impaired than their unaffected siblings on most behavioral and cognitive domains. The verbal IQ domain had the highest heritability (92%), followed by auditory attention (87%), visual processing speed and problem solving (85%), and externalizing symptoms (81%). The quantitative traits identified here have high heritabilities, similar to the reported heritability of ADHD (70-90%), and may represent appropriate alternative phenotypes for genetic studies. The use of multigenerational families from a genetically isolated population may facilitate the identification of ADHD risk genes in the face of phenotypic and genetic heterogeneity.

Genetics in child and adolescent psychiatry: methodological advances and conceptual issues

Discovering the genetic basis of early-onset psychiatric disorders has been the aim of intensive research during the last decade. We will first selectively summarize results of genetic research in child and adolescent psychiatry by using examples from different disorders and discuss methodological issues, emerging questions and future directions. In the second part of this review, we will focus on how to link genetic causes of disorders with physiological pathways, discuss the impact of genetic findings on diagnostic systems, prevention and therapeutic interventions. Finally we will highlight some ethical aspects connected to genetic research in child and adolescent psychiatry. Advances in molecular genetic methods have led to insights into the genetic architecture of psychiatric disorders, but not yet provided definite pathways to pathophysiology. If replicated, promising findings from genetic studies might in some cases lead to personalized treatments. On the one hand, knowledge of the genetic basis of disorders may influence diagnostic categories. On the other hand, models also suggest studying the genetic architecture of psychiatric disorders across diagnoses and clinical groups.

Attention-Deficit/Hyperactivity Disorder: Focus upon Aberrant N-Methyl-D-Aspartate Receptors Systems

Attention-deficit/hyperactivity disorder (ADHD) pathophysiology persists in an obscure manner with complex interactions between symptoms, staging, interventions, genes, and environments. Only on the basis of increasing incidence of the disorder, the need for understanding is greater than ever. The notion of an imbalance between central inhibitory/excitatory neurotransmitters is considered to exert an essential role. In this chapter, we first review how the default mode network functions and dysfunction in individuals diagnosed with ADHD. We also present and briefly review some of the animal models used to examine the neurobiological aspects of ADHD. There is much evidence indicating that compounds/interventions that antagonize/block glutamic acid receptors and/or block the glutamate signal during the "brain growth spurt" or in the adult animal may induce functional and biomarker deficits. Additionally, we present evidence suggesting that animals treated with glutamate blockers at the period of the "brain growth spurt" fail to perform the exploratory activity, observed invariably with control mice, that is associated with introduction to a novel environment (the test cages). Later, when the control animals show less locomotor and rearing activity, i.e., interest in the test cages, the MK-801, ketamine and ethanol treated mice showed successively greater levels of locomotion and rearing (interest), i.e., they fail to "habituate" effectively, implying a cognitive dysfunction. These disturbances of glutamate signaling during a critical period of brain development may contribute to the ADHD pathophysiology. As a final addition, we have briefly identified new research venues in the interaction between ADHD, molecular studies, and personality research.

Attention Deficit Hyperactivity Disorder in the Light of the Epigenetic Paradigm

Attention deficit hyperactivity disorder (ADHD) is a highly prevalent neurodevelopmental disorder characterized by a definite behavioral pattern that might lead to performance problems in the social, educational, or work environments. In the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition, the symptoms of ADHD were restricted to those associated with cognitive (attention deficit) and behavioral (hyperactivity/impulsivity) deficits, while deficient emotional self-regulation, a relevant source of morbidity, was left out. The etiology of it is complex, as its exact causes have not yet been fully elucidated. ADHD seems to arise from a combination of various genetic and environmental factors that alter the developing brain, resulting in structural and functional abnormalities. The aim of this paper was to review epigenetics and ADHD focused on how multidimensional mechanisms influence the behavioral phenotype.

The serotonin transporter gene polymorphism 5-HTTLPR moderates the effects of stress on attention-deficit/hyperactivity disorder

INTRODUCTION

The role of the serotonin transporter gene polymorphism 5-HTTLPR in attention-deficit/hyperactivity disorder (ADHD) is unclear. Heterogeneity of findings may be explained by gene-environment interactions (GxE), as it has been suggested that S-allele carriers are more reactive to psychosocial stress than L-allele homozygotes. This study aimed to investigate whether 5-HTTLPR genotype moderates the effects of stress on ADHD in a multisite prospective ADHD cohort study.

METHODS

5-HTTLPR genotype, as well as the number of stressful life events in the past 5 years and ongoing long-term difficulties, was determined in 671 adolescents and young adults with ADHD, their siblings, and healthy controls (57.4% male, average age 17.3 years). Linear mixed models, accounting for family relatedness, were applied to investigate the effects of genotype, experienced stress, and their interaction on ADHD severity at time point T2, while controlling for ADHD severity at T1 (mean follow-up time 5.9 years) and for comorbid internalizing problems at T2.

RESULTS

The interaction between genotype and stress significantly predicted ADHD severity at T2 (p = .006), which was driven by the effect on hyperactivity-impulsivity (p = .004). Probing of the interaction effect made clear that S-allele carriers had a significantly more positive correlation between stress and ADHD severity than L-allele homozygotes.

CONCLUSION

The results show that the interaction between 5-HTTLPR and stress is a mechanism involved particularly in the hyperactivity/impulsivity dimension of ADHD, and that this is independent of comorbid internalizing problems. Further research into the neurobiological mechanisms underlying this interaction effect is warranted.

Molecular genetic studies of ADHD and its candidate genes: a review

Attention-deficit/hyperactivity disorder (ADHD) is a common childhood-onset psychiatric disorder with high heritability. In recent years, numerous molecular genetic studies have been published to investigate susceptibility loci for ADHD. These results brought valuable candidates for further research, but they also presented great challenge for profound understanding of genetic data and general patterns of current molecular genetic studies of ADHD since they are scattered and heterogeneous. In this review, we presented a retrospective review of more than 300 molecular genetic studies for ADHD from two aspects: (1) the main achievements of various studies were summarized, including linkage studies, candidate-gene association studies, genome-wide association studies and genome-wide copy number variation studies, with a special focus on general patterns of study design and common sample features; (2) candidate genes for ADHD have been systematically evaluated in three ways for better utilization. The thorough summary of the achievements from various studies will provide an overview of the research status of molecular genetics studies for ADHD. Meanwhile, the analysis of general patterns and sample characteristics on the basis of these studies, as well as the integrative review of candidate ADHD genes, will propose new clues and directions for future experiment design.

The neurobiological link between OCD and ADHD

Obsessive compulsive disorder (OCD) and attention deficit hyperactivity disorder (ADHD) are two of the most common neuropsychiatric diseases in paediatric populations. The high comorbidity of ADHD and OCD with each other, especially of ADHD in paediatric OCD, is well described. OCD and ADHD often follow a chronic course with persistent rates of at least 40–50 %. Family studies showed high heritability in ADHD and OCD, and some genetic findings showed similar variants for both disorders of the same pathogenetic mechanisms, whereas other genetic findings may differentiate between ADHD and OCD. Neuropsychological and neuroimaging studies suggest that partly similar executive functions are affected in both disorders. The deficits in the corresponding brain networks may be responsible for the perseverative, compulsive symptoms in OCD but also for the disinhibited and impulsive symptoms characterizing ADHD. This article reviews the current literature of neuroimaging, neurochemical circuitry, neuropsychological and genetic findings considering similarities as well as differences between OCD and ADHD.

Association of the KCNJ5 gene with Tourette Syndrome and Attention-Deficit/Hyperactivity Disorder

Linkage and association of Tourette Syndrome (TS) and Attention-Deficit/Hyperactivity Disorder (ADHD) have previously been reported in the 11q24 chromosomal region. To identify the risk gene within the region we studied the potassium inwardly-rectifying channel J5 (KCNJ5) gene in a sample of 170 nuclear families with TS. We genotyped eight markers across the gene and observed biased transmission of haplotypes from parents to probands in this sample. We then tested these markers in an independent sample of 242 nuclear families with ADHD and found the same haplotype was significantly over transmitted to ADHD probands. Screening of the coding region of KCNJ5 in 48 probands with TS did not identify any variation that could explain the association of the haplotype. We also genotyped two microsatellite markers, one in the promoter and the other in the 3' region and found no evidence for association for either marker for TS, however, we found significant evidence for association with the 3' repeat and ADHD. A small gene (c11orf45) of unknown function lies within the first intron of KCNJ5 that is transcribed in the opposite orientation and this gene may regulate the expression of KCNJ5. We studied the correlation of the expression of KCNJ5 and the antisense transcript in brain tissues from control individuals and found that the antisense transcript and the short KCNJ5 isoform are co-expressed in three brain regions. The results of this study indicate that KCNJ5 is associated with TS and ADHD in our samples, however, the functional variant(s) remain to be identified.

Genetic Variants in the FADS Gene: Implications for Dietary Recommendations for Fatty Acid Intake

Unequivocally, genetic variants within the fatty acid desaturase (FADS) cluster are determinants of long chain polyunsaturated fatty acid (LC-PUFA) levels in circulation, cells and tissues. A recent series of papers have addressed these associations in the context of ancestry; evidence clearly supports that the associations are robust to ethnicity. However ∼80% of African Americans carry two copies of the alleles associated with increased levels of arachidonic acid, compared to only ∼45% of European Americans raising important questions of whether gene-PUFA interactions induced by a modern western diet are differentially driving the risk of diseases of inflammation in diverse populations, and are these interactions leading to health disparities. We highlight an important aspect thus far missing in the debate regarding dietary recommendations; we content that current evidence from genetics strongly suggest that an individual's, or at the very least the population from which an individual is sampled, genetic architecture must be factored into dietary recommendations currently in place.

Imaging genetics in adult attention-deficit/hyperactivity disorder (ADHD): a way towards pathophysiological understanding?

Attention-deficit/hyperactivity disorder (ADHD) is a common, early-onset and enduring developmental disorder whose underlying etiological and neurobiological processes are the current focus of major research. Research strategies have made considerable effort in elucidating the complex genetic architecture of ADHD and indicate various pathways from genotype to phenotype. Understanding ADHD as a neuropsychiatric disorder enabled to investigate markers of neural activity as endophenotypes to better explain the link from gene to symptomatology (the so-called imaging genetics approach). Overcoming the originally rather restrictive requirements for an endophenotype, imaging genetics studies are supposed to offer a much more flexible and hypothesis-driven approach towards the etiology of ADHD. Although 1) ADHD often persists into adulthood, thus remaining a prevalent disorder, and 2) imaging genetics provides a promising research approach, a review on imaging genetics in adult ADHD - as available for childhood ADHD (Durston 2010) - is lacking. In this review, therefore, findings from the few available imaging genetics studies in adult ADHD will be summarized and complemented by relevant findings from healthy controls and children with ADHD that are considered important for the adult ADHD imaging genetics approach. The studies will be reviewed regarding implications for basic research and possible practical applications. Imaging genetics studies in adult ADHD have the potential to further clarify pathophysiological pathways and mechanisms, to derive new testable hypotheses, to investigate genetic interaction effects and to partly influence practical applications. In combination with other research strategies, they can incrementally foster the understanding of relevant processes in a more comprehensive way. Current limitations comprise the incapability to discover new genes, a high genetic load in patients potentially obscuring the effect of single candidate genes, the mostly unknown heritability of the endophenotype and the heterogeneous manifestation of ADHD.

The null distribution of likelihood-ratio statistics in the conditional-logistic linkage model

Olson's conditional-logistic model retains the nice property of the LOD score formulation and has advantages over other methods that make it an appropriate choice for complex trait linkage mapping. However, the asymptotic distribution of the conditional-logistic likelihood-ratio (CL-LR) statistic with genetic constraints on the model parameters is unknown for some analysis models, even in the case of samples comprising only independent sib pairs. We derive approximations to the asymptotic null distributions of the CL-LR statistics and compare them with the empirical null distributions by simulation using independent affected sib pairs. Generally, the empirical null distributions of the CL-LR statistics match well the known or approximated asymptotic distributions for all analysis models considered except for the covariate model with a minimum-adjusted binary covariate. This work will provide useful guidelines for linkage analysis of real data sets for the genetic analysis of complex traits, thereby contributing to the identification of genes for disease traits.

Haplotype co-segregation with attention deficit-hyperactivity disorder in unrelated German multi-generation families

Complex disorders have proved to be elusive in the search for underlying genetic causes. In the presence of large multi-generation pedigrees with multiple affected individuals, heritable familial forms of the disorders can be postulated. Observations of particular chromosomal haplotypes shared among all affected individuals within pedigrees may reveal chromosomal regions, in which the disease-related genes may be located. Hence, the biochemical pathways involved in pathogenesis can be exposed. We have recruited eight large Attention Deficit-Hyperactivity Disorder (ADHD, OMIM: #143465) families of German descent. Densely spaced informative microsatellite markers with high heterozygosity rates were used to fine-map and haplotype chromosomal regions of interest in these families. In three subsets and one full family of the eight ADHD families, haplotypes co-segregating with ADHD-affected individuals were identified at chromosomes 1q25, 5q11-5q13, 9q31-9q32, and 18q11-18q21. Positive LOD scores supported these co-segregations. The existence of haplotypes co-segregating among affected individuals in large ADHD pedigrees suggests the existence of Mendelian forms of the disorder and that ADHD-related genes are located within these haplotypes. In depth sequencing of these haplotype regions can identify causative genetic mechanisms and will allow further insights into the clinico-genetics of this complex disorder.