Association of Rare Genetic Variants in Opioid Receptors with Tourette Syndrome

Oligogenic risk score for Gilles de la Tourette syndrome reveals a genetic continuum of tic disorders

Gilles de la Tourette syndrome (GTS) and other tic disorders (TDs) have a substantial genetic component with their heritability estimated at between 60 and 80%. Here we propose an oligogenic risk score of TDs using whole-genome sequencing (WGS) data from a group of Polish GTS patients, their families, and control samples (n = 278). In this study, we first reviewed the literature to obtain a preliminary list of 84 GTS/TD candidate genes. From this list, 10 final risk score genes were selected based on single-gene burden tests (SKAT p < 0.05) between unrelated GTS cases (n = 37) and synthetic control samples based on a database of local allele frequencies. These 10 genes were CHADL, DRD2, MAOA, PCDH10, HTR2A, SLITRK5, SORCS3, KCNQ5, CDH9, and CHD8. Variants in and in the vicinity (± 20 kbp) of the ten risk genes (n = 7654) with a median minor allele frequency in the non-Finnish European population of 0.02 were integrated into an additive classifier. This risk score was then applied to healthy and GTS-affected individuals from 23 families and 100 unrelated healthy samples from the Polish population (AUC-ROC = 0.62, p = 0.02). Application of the algorithm to a group of patients with other tic disorders revealed a continuous increase of the oligogenic score with healthy individuals with the lowest mean, then patients with other tic disorders, then GTS patients, and finally with severe GTS cases with the highest oligogenic score. We have further compared our WGS results with the summary statistics of the Psychiatric Genomics Consortium genome-wide association study (PGC GWAS) of TDs and found no signal overlap except for the CHADL gene locus. Polygenic risk scores from common variants of GTS GWAS show no difference between patient and control groups, except for the comparison between patients with non-GTS TDs and patients with severe GTS. Overall, we leveraged WGS data to construct a GTS/TD risk score based on variants that may cooperatively contribute to the aetiology of these disorders. This study provides evidence that typical and severe adult GTS as well as other tic disorders may exist on a single spectrum in terms of their genetic background.

Developing a phenotype risk score for tic disorders in a large, clinical biobank

Tics are a common feature of early-onset neurodevelopmental disorders, characterized by involuntary and repetitive movements or sounds. Despite affecting up to 2% of children and having a genetic contribution, the underlying causes remain poorly understood. In this study, we leverage dense phenotype information to identify features (i.e., symptoms and comorbid diagnoses) of tic disorders within the context of a clinical biobank. Using de-identified electronic health records (EHRs), we identified individuals with tic disorder diagnosis codes. We performed a phenome-wide association study (PheWAS) to identify the EHR features enriched in tic cases versus controls (n = 1406 and 7030; respectively) and found highly comorbid neuropsychiatric phenotypes, including: obsessive-compulsive disorder, attention-deficit/hyperactivity disorder, autism spectrum disorder, and anxiety (p < 7.396 × 10-5). These features (among others) were then used to generate a phenotype risk score (PheRS) for tic disorder, which was applied across an independent set of 90,051 individuals. A gold standard set of tic disorder cases identified by an EHR algorithm and confirmed by clinician chart review was then used to validate the tic disorder PheRS; the tic disorder PheRS was significantly higher among clinician-validated tic cases versus non-cases (p = 4.787 × 10-151; β = 1.68; SE = 0.06). Our findings provide support for the use of large-scale medical databases to better understand phenotypically complex and underdiagnosed conditions, such as tic disorders.

Correction: Association of Rare Genetic Variants in Opioid Receptors with Tourette Syndrome

[This corrects the article DOI: 10.5334/tohm.464.].

What Have We Learned About the Genetics of Obsessive-Compulsive and Related Disorders in Recent Years?

Obsessive-compulsive disorder (OCD) is a complex, multifactorial disorder with onset in either childhood or early adulthood. Lifetime prevalence has been estimated to be around 2%-3%. DSM-5 groups OCD together with closely related disorders-body dysmorphic disorder, trichotillomania (hair-pulling disorder), hoarding disorder, and excoriation disorder (skin-picking disorder)-as obsessive-compulsive and related disorders (OCRDs). In addition, DSM-5 includes a "tic-related" specifier, recognizing that OCD and Tourette syndrome/chronic tics are frequently comorbid. In recent years, the first large-scale genome-wide studies of OCRDs have emerged. These studies confirmed results from earlier twin and family studies that have demonstrated a strong genetic component to OCRDs. Furthermore, from analyses of common genetic variation, these studies offered a first insight into how the genetic risk of developing an OCRD might be connected to the genetic risk of developing another OCRD. This article is an update of the authors' previous report; it summarizes recent findings on the genetics of OCRDs and highlights some of the recent directions in OCRD genetics that will pave the way for new insights into OCRD pathophysiology.

Recent progress on Tourette syndrome

Tic disorders and Tourette syndrome are the most common movement disorders in children and are characterized by movements or vocalizations. Clinically, Tourette syndrome is frequently associated with comorbid psychiatric symptoms. Although dysfunction of cortical–striatal–thalamic–cortical circuits with aberrant neurotransmitter function has been considered the proximate cause of tics, the mechanism underlying this association is unclear. Recently, many studies have been conducted to elucidate the epidemiology, clinical course, comorbid symptoms, and pathophysiology of tic disorders by using laboratory studies, neuroimaging, electrophysiological testing, environmental exposure, and genetic testing. In addition, many researchers have focused on treatment for tics, including behavioral therapy, pharmacological treatment, and surgical treatment. Here, we provide an overview of recent progress on Tourette syndrome.

Candidate Genes and Pathways Associated with Gilles de la Tourette Syndrome-Where Are We?

Gilles de la Tourette syndrome (GTS) is a childhood-onset neurodevelopmental and -psychiatric tic-disorder of complex etiology which is often comorbid with obsessive-compulsive disorder (OCD) and/or attention deficit hyperactivity disorder (ADHD). Twin and family studies of GTS individuals have shown a high level of heritability suggesting, that genetic risk factors play an important role in disease etiology. However, the identification of major GTS susceptibility genes has been challenging, presumably due to the complex interplay between several genetic factors and environmental influences, low penetrance of each individual factor, genetic diversity in populations, and the presence of comorbid disorders. To understand the genetic components of GTS etiopathology, we conducted an extensive review of the literature, compiling the candidate susceptibility genes identified through various genetic approaches. Even though several strong candidate genes have hitherto been identified, none of these have turned out to be major susceptibility genes yet.

A Comprehensive Review of Tic Disorders in Children

Tics are characterized by sudden, rapid, recurrent, nonrhythmic movement or vocalization, and are the most common movement disorders in children. Their onset is usually in childhood and tics often will diminish within one year. However, some of the tics can persist and cause various problems such as social embarrassment, physical discomfort, or emotional impairments, which could interfere with daily activities and school performance. Furthermore, tic disorders are frequently associated with comorbid neuropsychiatric symptoms, which can become more problematic than tic symptoms. Unfortunately, misunderstanding and misconceptions of tic disorders still exist among the general population. Understanding tic disorders and their comorbidities is important to deliver appropriate care to patients with tics. Several studies have been conducted to elucidate the clinical course, epidemiology, and pathophysiology of tics, but they are still not well understood. This article aims to provide an overview about tics and tic disorders, and recent findings on tic disorders including history, definition, diagnosis, epidemiology, etiology, diagnostic approach, comorbidities, treatment and management, and differential diagnosis.

Tourette syndrome research highlights from 2019

This is the sixth yearly article in the Tourette Syndrome Research Highlights series, summarizing research from 2019 relevant to Tourette syndrome and other tic disorders. The highlights from 2020 is being drafted on the Authorea online authoring platform; readers are encouraged to add references or give feedback on our selections comments feature on this page. After the calendar year ends, this article is submitted as the annual update for the Tics collection F1000Research.

[Tics and Tourette's syndrome in children]

The article represents a review of modern literature on tics and Tourette's syndrome in paediatric population and describes recent advances in neurogenetics, neuroanatomy and neurotransmitter heterogeneity of the disease pathogenesis. The analysis of the literature supports the plausibility of transformation of tics and Tourette's syndrome from psychiatric disorders into neurological disorders (according to ICD-11) based on recent data on neurophysiology and functional neuroanatomy. Neuroanatomy of motor behaviour is described as the most complex self-regulating neural network of thalamo-cortical loop, basal ganglia in combination with the limbic system, insular and cingulate cortex with involvement of hippocampus, subthalamic region and cerebellum. The evaluation of pharmaceutical treatment options has been carried out, including a review of successful local experience in treating tics in paediatric patients with hopantenic acid, topiramate and neuropeptides of cortexin.