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

adgrl3.1-deficient zebrafish show noradrenaline-mediated externalizing behaviors, and altered expression of externalizing disorder-candidate genes, suggesting functional targets for treatment

Externalizing disorders (ED) are a cause of concern for public health, and their high heritability makes genetic risk factors a priority for research. Adhesion G-Protein-Coupled Receptor L3 (ADGRL3) is strongly linked to several EDs, and loss-of-function models have shown the impacts of this gene on several core ED-related behaviors. For example, adgrl3.1-/- zebrafish show high levels of hyperactivity. However, our understanding of the mechanisms by which this gene influences behavior is incomplete. Here we characterized, for the first time, externalizing behavioral phenotypes of adgrl3.1-/- zebrafish and found them to be highly impulsive, show risk-taking in a novel environment, have attentional deficits, and show high levels of hyperactivity. All of these phenotypes were rescued by atomoxetine, demonstrating noradrenergic mediation of the externalizing effects of adgrl3.1. Transcriptomic analyses of the brains of adgrl3.1-/- vs. wild-type fish revealed several differentially expressed genes and enriched gene clusters that were independent of noradrenergic manipulation. This suggests new putative functional pathways underlying ED-related behaviors, and potential targets for the treatment of ED.

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.

Matricellular proteins in cutaneous wound healing

Cutaneous wound healing is a complex process that encompasses alterations in all aspects of the skin including the extracellular matrix (ECM). ECM consist of large structural proteins such as collagens and elastin as well as smaller proteins with mainly regulative properties called matricellular proteins. Matricellular proteins bind to structural proteins and their functions include but are not limited to interaction with cell surface receptors, cytokines, or protease and evoking a cellular response. The signaling initiated by matricellular proteins modulates differentiation and proliferation of cells having an impact on the tissue regeneration. In this review we give an overview of the matricellular proteins that have been found to be involved in cutaneous wound healing and summarize the information known to date about their functions in this process.

ADGRL3 genomic variation implicated in neurogenesis and ADHD links functional effects to the incretin polypeptide GIP

Attention deficit/hyperactivity disorder (ADHD) is the most common childhood neurodevelopmental disorder. Single nucleotide polymorphisms (SNPs) in the Adhesion G Protein-Coupled Receptor L3 (ADGRL3) gene are associated with increased susceptibility to developing ADHD worldwide. However, the effect of ADGRL3 non-synonymous SNPs (nsSNPs) on the ADGRL3 protein function is vastly unknown. Using several bioinformatics tools to evaluate the impact of mutations, we found that nsSNPs rs35106420, rs61747658, and rs734644, previously reported to be associated and in linkage with ADHD in disparate populations from the world over, are predicted as pathogenic variants. Docking analysis of rs35106420, harbored in the ADGLR3-hormone receptor domain (HRM, a common extracellular domain of the secretin-like GPCRs family), showed that HRM interacts with the Glucose-dependent insulinotropic polypeptide (GIP), part of the incretin hormones family. GIP has been linked to the pathogenesis of diabetes mellitus, and our analyses suggest a potential link to ADHD. Overall, the comprehensive application of bioinformatics tools showed that functional mutations in the ADGLR3 gene disrupt the standard and wild ADGRL3 structure, most likely affecting its metabolic regulation. Further in vitro experiments are granted to evaluate these in silico predictions of the ADGRL3-GIP interaction and dissect the complexity underlying the development of ADHD.

Case Report of a Juvenile Patient with Autism Spectrum Disorder with a Novel Combination of Copy Number Variants in ADGRL3 (LPHN3) and Two Pseudogenes

We report the finding of two copy number variants (CNVs) in a 12-year-old boy presenting both with autism spectrum disorder (ASD) and attention deficit/hyperactivity disorder (ADHD). Clinical features included aggressive behavior, mood instability, suicidal statements, repetitive and restrictive behavior, sensitivity to noise, learning problems and dyslexia, though no intellectual disability was present. Using array-based comparative genomic hybridization (array-CGH), we identified two CNVs, both triplex duplications of 324 kb on 3p26.3, and 284 kb on 4q13.1, respectively. One of the CNVs is located on chromosome 4q13.1 in the region of the gene encoding for adhesion G protein-coupled receptor L3 (ADGRL3, former name: latrophilin-3, LPHN3), the other on chromosome 3p26.3 in the region of the two pseudogenes AC090043.1 and RPL23AP39. The patient described in the present study showed increased symptoms under methylphenidate treatment but responded positively to 3 mg per day of the atypical neuroleptic drug aripiprazole. To our knowledge, this is the first report of a CNV in the ADGRL3 gene and its first association with ASD in humans.

Adhesion G protein-coupled receptor gluing action guides tissue development and disease

Phylogenetic analysis of human G protein-coupled receptors (GPCRs) divides these transmembrane signaling proteins into five groups: glutamate, rhodopsin, adhesion, frizzled, and secretin families, commonly abbreviated as the GRAFS classification system. The adhesion GPCR (aGPCR) sub-family comprises 33 different receptors in humans. Majority of the aGPCRs are orphan receptors with unknown ligands, structures, and tissue expression profiles. They have a long N-terminal extracellular domain (ECD) with several adhesion sites similar to integrin receptors. Many aGPCRs undergo autoproteolysis at the GPCR proteolysis site (GPS), enclosed within the larger GPCR autoproteolysis inducing (GAIN) domain. Recent breakthroughs in aGPCR research have created new paradigms for understanding their roles in organogenesis. They play crucial roles in multiple aspects of organ development through cell signaling, intercellular adhesion, and cell-matrix associations. They are involved in essential physiological processes like regulation of cell polarity, mitotic spindle orientation, cell adhesion, and migration. Multiple aGPCRs have been associated with the development of the brain, musculoskeletal system, kidneys, cardiovascular system, hormone secretion, and regulation of immune functions. Since aGPCRs have crucial roles in tissue patterning and organogenesis, mutations in these receptors are often associated with diseases with loss of tissue integrity. Thus, aGPCRs include a group of enigmatic receptors with untapped potential for elucidating novel signaling pathways leading to drug discovery. We summarized the current knowledge on how aGPCRs play critical roles in organ development and discussed how aGPCR mutations/genetic variants cause diseases.

ADGRL1 haploinsufficiency causes a variable spectrum of neurodevelopmental disorders in humans and alters synaptic activity and behavior in a mouse model

ADGRL1 (latrophilin 1), a well-characterized adhesion G protein-coupled receptor, has been implicated in synaptic development, maturation, and activity. However, the role of ADGRL1 in human disease has been elusive. Here, we describe ten individuals with variable neurodevelopmental features including developmental delay, intellectual disability, attention deficit hyperactivity and autism spectrum disorders, and epilepsy, all heterozygous for variants in ADGRL1. In vitro, human ADGRL1 variants expressed in neuroblastoma cells showed faulty ligand-induced regulation of intracellular Ca²⁺ influx, consistent with haploinsufficiency. In vivo, Adgrl1 was knocked out in mice and studied on two genetic backgrounds. On a non-permissive background, mice carrying a heterozygous Adgrl1 null allele exhibited neurological and developmental abnormalities, while homozygous mice were non-viable. On a permissive background, knockout animals were also born at sub-Mendelian ratios, but many Adgrl1 null mice survived gestation and reached adulthood. Adgrl1^-/- mice demonstrated stereotypic behaviors, sexual dysfunction, bimodal extremes of locomotion, augmented startle reflex, and attenuated pre-pulse inhibition, which responded to risperidone. Ex vivo synaptic preparations displayed increased spontaneous exocytosis of dopamine, acetylcholine, and glutamate, but Adgrl1^-/- neurons formed synapses in vitro poorly. Overall, our findings demonstrate that ADGRL1 haploinsufficiency leads to consistent developmental, neurological, and behavioral abnormalities in mice and humans.

Gene expression profiles in the brain of phenylketonuria mouse model reversed by the low phenylalanine diet therapy

To gain insight into the potential protective mechanisms of low phenylalanine diet (LPD) in phenylketonuria (PKU), gene expression profiles were studied in the cerebral cortex and hippocampus of a PKU mouse model (BTBR-Pah^enu2). PKU mice were fed with low Phe diet (LPD-PKU group) and normal diet (PKU group). Wild-type mice were treated with normal diet (WT group) as control. After 12 weeks, we detected gene expression in the cerebral cortex and hippocampus of the three groups by RNA-sequencing, and then screened the differentially-expressed genes (DEGs) among the groups by bioinformatics analyses. We found that the transcriptional profiles of both cerebral cortex and hippocampus changed markedly between PKU and WT mice. Furthermore, LPD changed the transcriptional profiles of the cerebral cortex and the hippocampus of PKU mice significantly, especially in the cerebral cortex, with overlaps of genes that changed with the disease and altered by LPD treatment. In the cerebral cortex, hundreds of DEGs enriched in a wide spectrum of biological processes, molecular function, and cellular component, including nervous system development, axon development and guidance, calcium ion binding, modulation of chemical synaptic transmission, and regulation of protein kinase activity. In the hippocampus, the overlapping genes were enriched in positive regulation of long term synaptic, negative regulation of excitatory postsynaptic potential, positive regulation of synapse assembly. Our results showed that genes impaired in PKU and then rescued by LPD might indicate the potential protective capability of LPD in the PKU brain.

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.

Chromosomal Microarray Analysis as First-Tier Genetic Test for Schizophrenia

Schizophrenia is a chronic, devastating mental disorder with complex genetic components. Given the advancements in the molecular genetic research of schizophrenia in recent years, there is still a lack of genetic tests that can be used in clinical settings. Chromosomal microarray analysis (CMA) has been used as first-tier genetic testing for congenital abnormalities, developmental delay, and autism spectrum disorders. This study attempted to gain some experience in applying chromosomal microarray analysis as a first-tier genetic test for patients with schizophrenia. We consecutively enrolled patients with schizophrenia spectrum disorder from a clinical setting and conducted genome-wide copy number variation (CNV) analysis using a chromosomal microarray platform. We followed the 2020 “Technical Standards for the interpretation and reporting of constitutional copy-number variants: a joint consensus recommendation of the American College of Medical Genetics and Genomics (ACMG) and the Clinical Genome Resource (ClinGen)” to interpret the clinical significance of CNVs detected from patients. We recruited a total of 60 patients (36 females and 24 males) into this study. We detected three pathogenic CNVs and one likely pathogenic CNV in four patients, respectively. The detection rate was 6.7% (4/60, 95% CI: 0.004–0.13), comparable with previous studies in the literature. Also, we detected thirteen CNVs classified as uncertain clinical significance in nine patients. Detecting these CNVs can help establish the molecular genetic diagnosis of schizophrenia patients and provide helpful information for genetic counseling and clinical management. Also, it can increase our understanding of the pathogenesis of schizophrenia. Hence, we suggest CMA is a valuable genetic tool and considered first-tier genetic testing for schizophrenia spectrum disorders in clinical settings.

Expression of the adult ADHD-associated gene ADGRL3 is dysregulated by risk variants and environmental risk factors

OBJECTIVES

ADGRL3 is a well-replicated risk gene for adult ADHD, encoding the G protein-coupled receptor latrophilin-3 (LPHN3). However, LPHN3's potential role in pathogenesis is unclear. We aimed to determine whether ADGRL3 expression could be dysregulated by genetic risk variants and/or ADHD-associated environmental risk factors.

METHODS

Eighteen adult ADHD patients and healthy controls were genotyped for rs734644, rs1397547, rs1397548, rs2271338, rs2305339, rs2345039 and rs6551665 ADGRL3 SNPs, and fibroblast cells were derived from skin punches. The environmental ADHD risk factors 'low birthweight' and 'maternal smoking' were modelled in fibroblast cell culture using starvation and nicotine exposure, respectively. Quantitative real-time PCR and western blotting were performed to quantify ADGRL3 gene and protein expression under control, starvation and nicotine-exposed conditions.

RESULTS

Starvation was found to significantly decrease ADGRL3 expression, whereas nicotine exposure significantly increased ADGRL3 expression. rs1397547 significantly elevated ADGRL3 transcription and protein expression. rs6551665 and rs2345039 interacted with environment to modulate ADGRL3 transcription. ADGRL3 SNPs were significantly able to predict its transcription under both baseline and starvation conditions, and rs1397547 was identified as a significant independent predictor.

CONCLUSIONS

ADGRL3 SNPs and environmental risk factors can regulate ADGRL3 expression, providing a potential functional mechanism by which LPHN3 may play a role in ADHD pathogenesis.

Understanding ADHD: Toward an Innovative Therapeutic Intervention

Attention deficit hyperactivity disorder (ADHD) is a pervasive condition affecting persons across all age groups, although it is primarily diagnosed in children. This neurological condition affects behavior, learning, and social adjustment and requires specific symptomatic criteria to be fulfilled for diagnosis. ADHD may be treated with a combination of psychological or psychiatric therapeutic interventions, but it often goes unattended. People with ADHD face societal bias challenges that impact how they manage the disorder and how they view themselves. This paper summarizes the present state of understanding of this disorder, with particular attention to early diagnosis and innovative therapeutic intervention. Contemporary understanding of the mind-brain duality allows for innovative therapeutic interventions based on neurological stimulation. This paper introduces the concept of neurostimulation as a therapeutic intervention for ADHD and poses the question of the relationship between patient adherence to self-administered therapy and the aesthetic design features of the neurostimulation device. By fabricating devices that go beyond safety and efficacy to embrace the aesthetic preferences of the patient, it is proposed that there will be improvements in patient adherence to a device intended to address ADHD.

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.

Enhanced Transient Striatal Dopamine Release and Reuptake in Lphn3 Knockout Rats

Latrophilin-3 (LPHN3) is an adhesion G protein coupled receptor involved in regulating neuroplasticity. Variants of LPHN3 are associated with increased risk of attention-deficit hyperactivity disorder. Data from mouse, zebrafish, Drosophila, and rat show that disruption of LPHN3 results in hyperactivity, and in the Sprague-Dawley Lphn3 knockout rat, exhibit deficits in learning and memory and changes in dopamine (DA) markers in the neostriatum. To determine the effects of Lphn3 deletion on DA neurotransmission, we compared the concentration, duration, and frequency of DA transients in KO and wild-type rats using fast-scan cyclic voltammetry in brain slices. Lphn3 KO rats showed higher release of DA, and the duration and interevent time were markedly decreased compared with wild-type rats. The data demonstrate that LPHN3 plays a heretofore unrecognized role in DA signaling and may represent a new target for small molecule regulation of DA neurotransmission with translational implications.

Previously Identified Genetic Variants in ADGRL3 Are not Associated with Risk for Equine Degenerative Myeloencephalopathy across Breeds

Equine neuroaxonal dystrophy/equine degenerative myeloencephalopathy (eNAD/EDM) is a neurologic disease that has been reported in young horses from a wide range of breeds. The disease is inherited and associated with vitamin E deficiency during the first two years of life, resulting in bilateral symmetric ataxia. A missense mutation (chr3:71,917,591 C > T) within adhesion G protein-coupled receptor L3 (ADGRL3) was recently associated with risk for EDM in the Caspian breed. In order to confirm these findings, genotyping of this missense mutation, along with the three other associated single nucleotide polymorphisms (SNPs) in the genomic region, was carried out on 31 postmortem-confirmed eNAD/EDM cases and 43 clinically phenotyped controls from various breeds. No significant association was found between eNAD/EDM confirmed cases and genotype at any of the four identified SNPs (P > 0.05), including the nonsynonymous variant (EquCab2.0 chr3:71,917,591; allelic P = 0.85). These findings suggest that the four SNPs, including the missense variant in the ADGRL3 region, are not associated with risk for eNAD/EDM across multiple breeds of horses.

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.