The genetics of Tourette syndrome

Convergent imaging-transcriptomic evidence for disturbed iron homeostasis in Gilles de la Tourette syndrome

Gilles de la Tourette syndrome (GTS) is a neuropsychiatric movement disorder with reported abnormalities in various neurotransmitter systems. Considering the integral role of iron in neurotransmitter synthesis and transport, it is hypothesized that iron exhibits a role in GTS pathophysiology. As a surrogate measure of brain iron, quantitative susceptibility mapping (QSM) was performed in 28 patients with GTS and 26 matched controls. Significant susceptibility reductions in the patients, consistent with reduced local iron content, were obtained in subcortical regions known to be implicated in GTS. Regression analysis revealed a significant negative association of tic scores and striatal susceptibility. To interrogate genetic mechanisms that may drive these reductions, spatially specific relationships between susceptibility and gene-expression patterns from the Allen Human Brain Atlas were assessed. Correlations in the striatum were enriched for excitatory, inhibitory, and modulatory neurochemical signaling mechanisms in the motor regions, mitochondrial processes driving ATP production and iron‑sulfur cluster biogenesis in the executive subdivision, and phosphorylation-related mechanisms affecting receptor expression and long-term potentiation in the limbic subdivision. This link between susceptibility reductions and normative transcriptional profiles suggests that disruptions in iron regulatory mechanisms are involved in GTS pathophysiology and may lead to pervasive abnormalities in mechanisms regulated by iron-containing enzymes.

Convergent imaging-transcriptomic evidence for disturbed iron homeostasis in Gilles de la Tourette syndrome

Gilles de la Tourette syndrome (GTS) is a neuropsychiatric movement disorder with reported abnormalities in various neurotransmitter systems. Considering the integral role of iron in neurotransmitter synthesis and transport, it is hypothesized that iron exhibits a role in GTS pathophysiology. As a surrogate measure of brain iron, quantitative susceptibility mapping (QSM) was performed in 28 patients with GTS and 26 matched controls. Significant susceptibility reductions in the patient cohort, consistent with reduced local iron content, were obtained in subcortical regions known to be implicated in GTS. Regression analysis revealed a significant negative association of tic scores and striatal susceptibility. To interrogate genetic mechanisms that may drive these reductions, spatially specific relationships between susceptibility and gene-expression patterns extracted from the Allen Human Brain Atlas were assessed. Correlations in the striatum were enriched for excitatory, inhibitory, and modulatory neurochemical signaling mechanisms in the motor regions, mitochondrial processes driving ATP production and iron-sulfur cluster biogenesis in the executive subdivision, and phosphorylation-related mechanisms that affect receptor expression and long-term potentiation. This link between susceptibility reductions and normative transcriptional profiles suggests that disruptions in iron regulatory mechanisms are involved in GTS pathophysiology and may lead to pervasive abnormalities in mechanisms regulated by iron-containing enzymes.

Exonic deletions in IMMP2L in schizophrenia with enhanced glycation stress subtype

We previously identified a subtype of schizophrenia (SCZ) characterized by increased plasma pentosidine, a marker of glycation and oxidative stress (PEN-SCZ). However, the genetic factors associated with PEN-SCZ have not been fully clarified. We performed a genome-wide copy number variation (CNV) analysis to identify CNVs associated with PEN-SCZ to provide an insight into the novel therapeutic targets for PEN-SCZ. Plasma pentosidine was measured by high-performance liquid chromatography in 185 patients with SCZ harboring rare CNVs detected by array comparative genomic hybridization. In three patients with PEN-SCZ showing additional autistic features, we detected a novel deletion at 7q31.1 within exons 2 and 3 of IMMP2L, which encodes the inner mitochondrial membrane peptidase subunit 2. The deletion was neither observed in non-PEN-SCZ nor in public database of control subjects. IMMP2L is one of the SCZ risk loci genes identified in a previous SCZ genome-wide association study, and its trans-populational association was recently described. Interestingly, deletions in IMMP2L have been previously linked with autism spectrum disorder. Disrupted IMMP2L function has been shown to cause glycation/oxidative stress in neuronal cells in an age-dependent manner. To our knowledge, this is the first genome-wide CNV study to suggest the involvement of IMMP2L exons 2 and 3 in the etiology of PEN-SCZ. The combination of genomic information with plasma pentosidine levels may contribute to the classification of biological SCZ subtypes that show additional autistic features. Modifying IMMP2L functions may be useful for treating PEN-SCZ if the underlying biological mechanism can be clarified in further studies.

Elevated common variant genetic risk for tourette syndrome in a densely-affected pedigree

Tourette syndrome (TS) is a highly heritable neuropsychiatric disorder with complex patterns of genetic inheritance. Recent genetic findings in TS have highlighted both numerous common variants with small effects and a few rare variants with moderate or large effects. Here we searched for genetic causes of TS in a large, densely-affected British pedigree using a systematic genomic approach. This pedigree spans six generations and includes 122 members, 85 of whom were individually interviewed, and 53 of whom were diagnosed as "cases" (consisting of 28 with definite or probable TS, 20 with chronic multiple tics [CMT], and five with obsessive-compulsive behaviors [OCB]). A total of 66 DNA samples were available (25 TS, 15 CMT, 4 OCB cases, and 22 unaffecteds) and all were genotyped using a dense single nucleotide polymorphism (SNP) array to identify shared segments, copy number variants (CNVs), and to calculate genetic risk scores. Eight cases were also whole genome sequenced to test whether any rare variants were shared identical by descent. While we did not identify any notable CNVs, single nucleotide variants, indels or repeat expansions of near-Mendelian effect, the most distinctive feature of this family proved to be an unusually high load of common risk alleles for TS. We found that cases within this family carried a higher load of TS common variant risk similar to that previously found in unrelated TS cases. Thus far, the strongest evidence from genetic data for contribution to TS risk in this family comes from multiple common risk variants rather than one or a few variants of strong effect.

Whole-exome sequencing identifies genes associated with Tourette's disorder in multiplex families

Tourette's Disorder (TD) is a neurodevelopmental disorder (NDD) that affects about 0.7% of the population and is one of the most heritable NDDs. Nevertheless, because of its polygenic nature and genetic heterogeneity, the genetic etiology of TD is not well understood. In this study, we combined the segregation information in 13 TD multiplex families with high-throughput sequencing and genotyping to identify genes associated with TD. Using whole-exome sequencing and genotyping array data, we identified both small and large genetic variants within the individuals. We then combined multiple types of evidence to prioritize candidate genes for TD, including variant segregation pattern, variant function prediction, candidate gene expression, protein-protein interaction network, candidate genes from previous studies, etc. From the 13 families, 71 strong candidate genes were identified, including both known genes for NDDs and novel genes, such as HtrA Serine Peptidase 3 (HTRA3), Cadherin-Related Family Member 1 (CDHR1), and Zinc Finger DHHC-Type Palmitoyltransferase 17 (ZDHHC17). The candidate genes are enriched in several Gene Ontology categories, such as dynein complex and synaptic membrane. Candidate genes and pathways identified in this study provide biological insight into TD etiology and potential targets for future studies.

Tics, tremors and other movement disorders in childhood

Movement disorders presenting in childhood include tics, dystonia, chorea, tremor, stereotypy, myoclonus, and parkinsonism, each of which can be part of various clinical syndromes with distinct etiologies.  Some of these conditions are benign and require only reassurance; others are bothersome and require treatment, or may be clues that herald underlying pathology.  Answers lie in the inherent characteristics of the movements themselves, together with the clinical context provided in the history obtained by the examiner.  The aim of this review is to present an overview of the categories of involuntary movements, along with examples of common acquired and genetic causes, and an approach to history-taking, examination, and treatment.

Tic Disorders and PANDAS

Tics are the most common movement disorder in childhood and are a frequent reason for referral to child neurology clinics. The purpose of this review is to examine the phenomenology of tics, discuss what is known regarding their genetic and pathophysiological causes and to evaluate current treatment options. The evidence for the evaluation and treatment of the controversial diagnosis of pediatric autoimmune neuropsychiatric disorders associated with group A streptococci (PANDAS) will also be reviewed. With improved understanding of tic disorders, their etiology and response to current treatment options, we may be able to more effectively diagnose them and identify novel treatment strategies.

Social cognition and self-other distinctions in neuropsychiatry: Insights from schizophrenia and Tourette syndrome

Impairments in social cognition may reflect dysfunction of disorder specific or disorder general mechanisms. Although cross-disorder comparison may prove insightful, few studies have compared social cognition in different neuropsychiatric disorders. Parallel investigation of schizophrenia and Tourette syndrome (TS) is encouraged by similarities including the presence of problematic social behavior, echophenomena, emotional dysregulation and dopamine dysfunction. Focusing on tests of social cognition administered in both disorders, this review aims to summarize behavioral, neurophysiological and neuroimaging findings, before exploring how these may contribute to clinical symptoms. Studies investigating social cognition (imitation, emotion recognition, and understanding of beliefs or intentions) in patients with schizophrenia or TS were identified through Web of Science and PubMed searches. Although findings indicate that social cognitive deficits are more apparent in schizophrenia, adults with TS can exhibit similar task performance to patients with paranoia. In both disorders, behavioral and neuroimaging findings raise the possibility of increased internal simulation of others' actions and emotions, in combination with a relative under-application of mentalizing. More specifically, dysfunction in neurobiological substrates such as temporo-parietal junction and inferior frontal gyrus may underlie problems with self-other distinctions in both schizophrenia and TS. Difficulties in distinguishing between actions and mental states linked to the self and other may contribute to a range of psychiatric symptoms, including emotional dysregulation, paranoia, social anhedonia and socially disruptive urges. Comparing different patient populations could therefore reveal common neuro-cognitive risk factors for the development of problematic social behaviors, in addition to markers of resilience, coping strategies and potential neuro-compensation mechanisms.

Association of the AADAC gene and Tourette syndrome in a Han Chinese cohort

Tourette syndrome (TS) is a complex neuropsychiatric disorder with chronic motor and vocal tics. Though the etiology is elusive, strong evidence for a genetic contribution to TS has been established. To date, various chromosomal or genetic alterations have been implicated in its pathogenesis. Recently, the deletion in the arylacetamide deacetylase gene (AADAC) was reported to be associated with TS. To investigate the association between the AADAC gene variants and TS, we conducted genetic analysis of the AADAC gene in 200 Han Chinese patients and 300 ethnicity-matched normal controls. Two variants, including a heterozygous splice-site variant, c.361 + 1G > A (rs762169706), and a missense variant, c.744A > T (p.R248S, rs186388618), were identified in two unrelated patients. The c.361 + 1G > A variant, absent in 300 ethnicity-matched controls, led to the deletion of exon 2 in AADAC mRNA, probably associated with development of TS. The c.744A > T variant, predicted to be damaging, was identified in two normal controls. The findings indicate that the AADAC gene c.361 + 1G > A variant may be a potential candidate factor for TS development, though further investigations are warranted.

A Review of the Neuropsychological Dimensions of Tourette Syndrome

Neurocognitive functioning in Tourette syndrome (TS) has been the subject of intensive research in the past 30 years. A variety of impairments, presumably related to frontal and frontostriatal dysfunctions, have been observed. These impairments were found in various domains, such as attention, memory, executive functions, language, motor and visuomotor functions, among others. In line with contemporary research, other neurocognitive domains have recently been explored in TS, bringing evidence of altered social reasoning, for instance. Therefore, the aims of this review are to give an overview of the neuropsychological dimensions of TS, to report how neuropsychological functions evolve from childhood to adulthood, and to explain how various confounding factors can affect TS patients' performance in neuropsychological tasks. Finally, an important contribution of this review is to show how recent research has confirmed or changed our beliefs about neuropsychological functioning in TS.

Association between the polymorphism of C861G (rs6296) in the serotonin 1B receptor gene and Tourette syndrome in Han Chinese people

INTRODUCTION

Clinical, neuroimaging and other studies provided evidence that the dysfunction of the serotonin neurotransmitter system were found in Tourette syndrome (TS). This study is to explore the association between the polymorphism of C861G (rs6296) in HTR1B and TS in Han Chinese people.

METHODS

Two hundred ninety-nine TS patients (260 TS trios and 39 TS patients) and 388 healthy controls were collected. The genotype of HTR1B C861G was detected using Taqman probes. The case-control study and family-based study was used separately to study association between HTR1B C861G and TS in Han Chinese people.

RESULTS

In case-control study, no statistically significant difference was found in the distribution of HTR1B C861G polymorphism between TS patients and controls (for genotype: χ²  = 3.408, P = 0.182; for allele: χ²  = 0.395, P = 0.530, OR = 0.934, 95%CI: 0.754-1.156). In family-based study, we observed nonsignificant over-transmission of the G861 allele in HTR1B to TS offspring using the transmission disequilibrium test (TDT), haplotype relative risk (HRR) and haplotype-based HRR (HHRR) (TDT χ²  = 0.410, P = 0.560; HRR = 1.151, χ²  = 0.421, P = 0.517, 95% CI: 0.753-1.759; HHRR = 0.919, χ²  = 0.467, P = 0.495, 95%CI: 0.720-1.172).

DISCUSSION

Our study suggested that the polymorphism of HTR1B C861G is not a risk factor for TS in Han Chinese population. However, the result should be replicated in larger sample and different population.

Increased Risk of Tics in Children Infected with Enterovirus: A Nationwide Population-Based Study

OBJECTIVE

Both tics and enterovirus (EV) infections are common in children. The association between EV infections and tics has been seldom evaluated. The aim of this study was to evaluate the risk of diagnosed tics after EV infections in children.

METHODS

A nationwide retrospective cohort study was conducted to determine the risk of tics after EV infections by analyzing data from the National Health Insurance Research Database in Taiwan. Children aged < 18 years with EV infection during 2000 to 2007 were enrolled. For comparison, non-EV-infected children were randomly selected and matched with EV-infected children at a 1:1 ratio according to sex, age, urbanization level, parental occupation, and the year of EV infection. All patients were followed up until the diagnosis of tics, death, loss to follow-up, withdrawal from the insurance system, or December 31, 2008.

RESULTS

A total of 282,321 EV-infected and 282,317 non-EV-infected children were included in this study. The mean age was 2.39 years in both cohorts. The overall incidences of tics were 9.12 and 6.21 per 10,000 person-years in the EV-infected and non-EV-infected cohorts, respectively. Children with EV infection were significantly associated with an increased risk of tics compared with those without EV infection (adjusted hazard ratio, 1.38; 95% confidence interval, 1.27-1.5). Multivariable analyses showed that boys, children living in urbanized areas, children whose parents had white-collar jobs, and children with allergic rhinitis or bronchial asthma exhibited a significantly increased risk of tics.

CONCLUSION

This study revealed an increased risk of tics after EV infection in children.

Parental Psychopathology and Tourette Syndrome/Chronic Tic Disorder in Offspring: A Nationwide Case-Control Study

OBJECTIVE

To determine the associations between maternal and paternal psychiatric diagnoses and Tourette syndrome (TS)/chronic tic disorder (CT) in a nationwide study.

METHOD

This nested case-control study linked data derived from three national registers. All singletons born and diagnosed with TS/CT in Finland between January 1991 and December 2010 were identified (n = 1,120) and matched to four controls (n = 4,299). Conditional logistic regression was used to examine the associations between parental psychopathology and TS/CT.

RESULTS

Altogether, 24.9% of patients with TS/CT and 12.0% of controls had a mother with a psychiatric diagnosis. Similarly, 17.9% and 12.9% had a father with a psychiatric diagnosis. Any maternal and any paternal psychiatric diagnosis was associated with offspring TS/CT (odds ratio [OR] 2.3; 95% CI 1.9-2.7 and OR 1.2; 95% CI 1.01-1.5, respectively). The association between maternal psychiatric diagnosis and TS/CT was stronger than that between paternal psychiatric diagnosis and TS/CT (p < .001). Maternal personality disorders (OR 3.1, 95% CI 1.9-5.1), anxiety disorders (OR 2.6, 95% CI 1.9-3.5), affective disorders (OR 2.3, 95% CI 1.8-2.9), psychotic disorders (OR 2.0, 95% CI 1.2-3.3), and addiction disorders (OR 1.8, 95% CI 1.1-2.8) were associated with TS/CT. Paternal OCD (OR 6.5, 95% CI 1.1-39.5) and anxiety disorders (OR 1.5, 95% CI 1.1-2.3) were associated with TS/CT.

CONCLUSION

Parental psychiatric diagnoses (especially in the mother) are associated with diagnosed offspring TS/CT. Further studies are required before the results can be generalized to all children with TS/CT. The associations between maternal psychiatric disorders and TS may reflect both maternal specific environmental and/or genetic influences.

A search for the common ground between Tic; Obsessive-compulsive and Autism Spectrum Disorders: part I, Tic disorders

This article is the first of four articles designed to explore the complex interrelationship between Autism Spectrum Disorders (ASD); Obsessive compulsive and Related Disorders (OCRD) and Tic Disorders/Tourette's Syndrome (TD/TS). We begin with an overview TD/TS and follow-up with reviews of OCRD and ASD. The final article in this series represents a synthesis of the neurobiological and genetic markers shared by patients presenting with all three syndromes. The goal is to describe the complex endophenotype of these patients in an effort to better define gene markers that underlie these heterogeneous clinical syndromes. Tic disorders (TD) are a collection of hyperkinetic movements that begin in early childhood. Tics are transient for most affected preschool children but a subgroup development persistent movements or progress to develop Tourette Syndrome (TS). TDs as a group display high heritability rates but definitive gene markers still elude us. The difficulty defining genetic markers is in large part due to the diverse neurodevelopmental trajectory, changing topography and typology, development of a broad spectrum of neurocognitive and behavioral complications, and a mixed pattern of psychiatric comorbidities.

Tourette Syndrome and Comorbid Neuropsychiatric Conditions

Tourette syndrome is a neuropsychiatric condition characterized by both motor and phonic tics over a period of at least 1 year with the onset in childhood or adolescence. Apart from the tics, most of the patients with Tourette syndrome have associated neuropsychiatric comorbidities consisting of attention deficit hyperactivity disorder, obsessive compulsive disorder, rage attacks, sleep issues, depression, and migraine. Patients may also have physical complications directly from violent motor tics which can rarely include cervical myelopathy, arterial dissection, and stroke. The purpose of this article is to review the associated neuropsychiatric comorbidities of Tourette syndrome with emphasis on recent research.

A Review and Update on Tourette Syndrome: Where Is the Field Headed?

Tourette syndrome (TS) is a childhood onset neurologic disorder with manifestations including multiple motor and phonic tics, and in most cases a variety of behavioral comorbidities such as attention deficit hyperactivity disorder, obsessive compulsive disorder, and other impulse control disorders. Although it is considered a hereditary disorder, likely modified by environmental factors, genetic studies have yet to uncover relevant causative genes and there is no animal model that mimics the broad clinical phenomenology of TS. There has been a marked increase in the number of neurophysiological, neuroimaging, and other studies on TS. The findings from these studies, however, have been difficult to interpret because of small sample sizes, variability of symptoms across patients, and comorbidities. Although anti-dopaminergic drugs are the most widely used medications in the treatment of TS, there has been increasing interest in other drugs, behavioral therapies, and surgical approaches including deep brain stimulation. Herein, we review the current literature and discuss the complexities of TS and the challenges in understanding its pathophysiology and in selecting the most appropriate treatment. We also offer an expert's view of where the field of TS may be headed.

The Genetic Etiology of Tourette Syndrome: Large-Scale Collaborative Efforts on the Precipice of Discovery

Gilles de la Tourette Syndrome (TS) is a childhood-onset neurodevelopmental disorder that is characterized by multiple motor and phonic tics. It has a complex etiology with multiple genes likely interacting with environmental factors to lead to the onset of symptoms. The genetic basis of the disorder remains elusive. However, multiple resources and large-scale projects are coming together, launching a new era in the field and bringing us on the verge of discovery. The large-scale efforts outlined in this report are complementary and represent a range of different approaches to the study of disorders with complex inheritance. The Tourette Syndrome Association International Consortium for Genetics (TSAICG) has focused on large families, parent-proband trios and cases for large case-control designs such as genomewide association studies (GWAS), copy number variation (CNV) scans, and exome/genome sequencing. TIC Genetics targets rare, large effect size mutations in simplex trios, and multigenerational families. The European Multicentre Tics in Children Study (EMTICS) seeks to elucidate gene-environment interactions including the involvement of infection and immune mechanisms in TS etiology. Finally, TS-EUROTRAIN, a Marie Curie Initial Training Network, aims to act as a platform to unify large-scale projects in the field and to educate the next generation of experts. Importantly, these complementary large-scale efforts are joining forces to uncover the full range of genetic variation and environmental risk factors for TS, holding great promise for identifying definitive TS susceptibility genes and shedding light into the complex pathophysiology of this disorder.

Social disinhibition is a heritable subphenotype of tics in Tourette syndrome

OBJECTIVE

To identify heritable symptom-based subtypes of Tourette syndrome (TS).

METHODS

Forty-nine motor and phonic tics were examined in 3,494 individuals (1,191 TS probands and 2,303 first-degree relatives). Item-level exploratory factor and latent class analyses (LCA) were used to identify tic-based subtypes. Heritabilities of the subtypes were estimated, and associations with clinical characteristics were examined.

RESULTS

A 6-factor exploratory factor analysis model provided the best fit, which paralleled the somatotopic representation of the basal ganglia, distinguished simple from complex tics, and separated out socially disinhibited and compulsive tics. The 5-class LCA model best distinguished among the following groups: unaffected, simple tics, intermediate tics without social disinhibition, intermediate with social disinhibition, and high rates of all tic types. Across models, a phenotype characterized by high rates of social disinhibition emerged. This phenotype was associated with increased odds of comorbid psychiatric disorders, in particular, obsessive-compulsive disorder and attention-deficit/hyperactivity disorder, earlier age at TS onset, and increased tic severity. The heritability estimate for this phenotype based on the LCA was 0.53 (SE 0.08, p 1.7 × 10(-18)).

CONCLUSIONS

Expanding on previous modeling approaches, a series of TS-related phenotypes, including one characterized by high rates of social disinhibition, were identified. These phenotypes were highly heritable and may reflect underlying biological networks more accurately than traditional diagnoses, thus potentially aiding future genetic, imaging, and treatment studies.

Selective activation of D1 dopamine receptors impairs sensorimotor gating in Long-Evans rats

BACKGROUND AND PURPOSE

Sensorimotor gating is a perceptual process aimed at filtering out irrelevant information. In humans and animal models, this function can be operationally measured through the prepulse inhibition (PPI) of the acoustic startle reflex. Notably, PPI deficits are associated with numerous neuropsychiatric conditions characterized by gating disturbances, including schizophrenia and Tourette syndrome. Ample evidence has shown that dopamine plays a key role in PPI regulation and, in particular, rodent studies indicate that this neurotransmitter modulates PPI through D1 and D2 dopamine receptors. In mice, the relative contributions of these two families of receptors are strain-dependent. Conversely, the role of D1 receptors in the regulation of PPI across different rat strains remains unclear.

EXPERIMENTAL APPROACH

We tested the effects of selective D1 and D2 receptor agonists and antagonists on the startle reflex and PPI of Sprague-Dawley, Wistar and Long-Evans rats.

KEY RESULTS

In contrast with Sprague-Dawley and Wistar rats, the full D1 receptor agonist SKF82958 elicited significant PPI deficits in Long-Evans rats, an effect sensitive to the selective D1 antagonist SCH23390.

CONCLUSIONS AND IMPLICATIONS

Our results suggest that, in Long-Evans rats, D1 receptor activation may be sufficient to significantly impair PPI. These data emphasize the role of D1 receptors in the pathophysiology of neuropsychiatric disorders featuring alterations in sensorimotor gating, and uphold the importance of the genetic background in shaping the role of dopamine receptors in the regulation of this key information-processing function.

LINKED ARTICLES

This article is part of a themed section on Updating Neuropathology and Neuropharmacology of Monoaminergic Systems. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v173.13/issuetoc.

Pediatric Autoimmune Disorders Associated with Streptococcal Infections and Tourette's Syndrome in Preclinical Studies

Accumulating evidence suggests that Tourette's Syndrome (TS) - a multifactorial pediatric disorder characterized by the recurrent exhibition of motor tics and/or vocal utterances - can partly depend on immune dysregulation provoked by early repeated streptococcal infections. The natural and adaptive antibody-mediated reaction to streptococcus has been proposed to potentially turn into a pathological autoimmune response in vulnerable individuals. Specifically, in conditions of increased permeability of the blood brain barrier (BBB), streptococcus-induced antibodies have been proposed to: (i) reach neuronal targets located in brain areas responsible for motion control; and (ii) contribute to the exhibition of symptoms. This theoretical framework is supported by indirect evidence indicating that a subset of TS patients exhibit elevated streptococcal antibody titers upon tic relapses. A systematic evaluation of this hypothesis entails preclinical studies providing a proof of concept of the aforementioned pathological sequelae. These studies shall rest upon individuals characterized by a vulnerable immune system, repeatedly exposed to streptococcus, and carefully screened for phenotypes isomorphic to the pathological signs of TS observed in patients. Preclinical animal models may thus constitute an informative, useful tool upon which conducting targeted, hypothesis-driven experiments. In the present review we discuss the available evidence in preclinical models in support of the link between TS and pediatric autoimmune neuropsychiatric disorders associated with streptococcus infections (PANDAS), and the existing gaps that future research shall bridge. Specifically, we report recent preclinical evidence indicating that the immune responses to repeated streptococcal immunizations relate to the occurrence of behavioral and neurological phenotypes reminiscent of TS. By the same token, we discuss the limitations of these studies: limited evidence of behavioral phenotypes isomorphic to tics and scarce knowledge about the immunological phenomena favoring the transition from natural adaptive immunity to pathological outcomes.

Safety and efficacy of aripiprazole for the treatment of pediatric Tourette syndrome and other chronic tic disorders

Tourette syndrome is a childhood-onset chronic tic disorder characterized by multiple motor and vocal tics and often accompanied by specific behavioral symptoms ranging from obsessionality to impulsivity. A considerable proportion of patients report significant impairment in health-related quality of life caused by the severity of their tics and behavioral symptoms and require medical intervention. The most commonly used medications are antidopaminergic agents, which have been consistently shown to be effective for tic control, but are also associated with poor tolerability because of their adverse effects. The newer antipsychotic medication aripiprazole is characterized by a unique mechanism of action (D2 partial agonism), and over the last decade has increasingly been used for the treatment of tics. We conducted a systematic literature review to assess the available evidence on the efficacy and safety of aripiprazole in pediatric patients with Tourette syndrome and other chronic tic disorders (age range: 4–18 years). Our search identified two randomized controlled trials (involving 60 and 61 participants) and ten open-label studies (involving between six and 81 participants). The majority of these studies used two validated clinician-rated instruments (Yale Global Tic Severity Scale and Clinical Global Impression scale) as primary outcome measures. The combined results from randomized controlled trials and open-label studies showed that aripiprazole is an effective, safe, and well-tolerated medication for the treatment of tics. Aripiprazole-related adverse effects (nausea, sedation, and weight gain) were less frequent compared to other antidopaminergic medications used for tic management and, when present, were mostly transient and mild. The reviewed studies were conducted on small samples and had relatively short follow-up periods, thus highlighting a need for further trials to assess the long-term use of aripiprazole in pediatric patients with Tourette syndrome and other chronic tic disorders with measurement of its efficacy using both clinician-rated and self-report scales.

Obstetric and Neonatal Adversities, Parity, and Tourette Syndrome: A Nationwide Registry

OBJECTIVE

To determine the relationships between parity, obstetric adversities, neonatal factors, and Tourette syndrome in a large nationwide cohort.

STUDY DESIGN

This nationwide, register-based, nested case-control study identified all children diagnosed with Tourette syndrome born between 1991 and 2010 from the Finnish Hospital Discharge Register (n = 767). Each case was matched to 4 controls. Information on parity, obstetric, and neonatal factors was obtained from the Finnish Medical Birth Register. Conditional logistic regression was used to determine the relationship between parity, obstetric, and neonatal factors, and Tourette syndrome.

RESULTS

Nulliparity was associated with increased odds for Tourette syndrome (OR 1.7, 95% CI 1.4-2.2), and 3 or more previous births was associated with decreased odds for Tourette syndrome (OR 0.5, 95% CI 0.3-0.9) compared with parity 1-2. Birth weight 4000-4499 g was associated with decreased odds for Tourette syndrome (OR 0.7, 95% CI 0.5-0.9). Low birth weight, gestational age, weight for gestational age, Apgar score at 1 minute, induced labor, birth type or presentation, neonatal treatment, or maternal blood pressure were not associated with Tourette syndrome.

CONCLUSIONS

Increasing parity and high birth weight are associated with decreased odds for Tourette syndrome.

Recent Advances in Understanding and Managing Tourette Syndrome

Tourette syndrome (TS) is a neurologic and behavioral disorder consisting of motor and phonic tics with onset in childhood or adolescence. The severity of tics can range from barely perceptible to severely impairing due to social embarrassment, discomfort, self-injury, and interference with daily functioning and school or work performance. In addition to tics, most patients with TS have a variety of behavioral comorbidities, including attention deficit hyperactivity disorder and obsessive-compulsive disorder. Studies evaluating the pathophysiology of tics have pointed towards dysfunction of the cortico-striato-thalamo-cortical circuit, but the mechanism of this hyperkinetic movement disorder is not well understood. Treatment of TS is multidisciplinary, typically involving behavioral therapy, oral medications, and botulinum toxin injections. Deep brain stimulation may be considered for “malignant” TS that is refractory to conventional therapy. In this review, we will highlight recent developments in the understanding and management strategies of TS.

Prenatal Maternal Smoking and Tourette Syndrome: A Nationwide Register Study

This is the first nationwide register-based study to examine the relationship between prenatal maternal smoking and Tourette syndrome. A total of 767 children diagnosed with Tourette syndrome were identified from the Finnish Hospital Discharge Register. Each case was matched to four controls. Information on maternal smoking during pregnancy was obtained from the Finnish Medical Birth Register. Conditional logistic regression models were used for statistical analyses. Prenatal maternal smoking was associated with Tourette syndrome when comorbid with ADHD (OR 4.0, 95 % CI 1.2-13.5, p = 0.027 for exposure during first trimester, OR 1.7, 95 % CI, 1.05-2.7, p = 0.031 for exposure for the whole pregnancy). There was no association between maternal smoking during pregnancy and Tourette syndrome without comorbid ADHD (OR 0.5, 95 % CI 0.2-1.3, p = 0.166, OR 0.9, 95 % CI 0.7-1.3, p = 0.567). Further research is needed to elucidate the mechanisms behind the association between prenatal maternal smoking and Tourette syndrome with comorbid ADHD.

Involvement of astrocyte metabolic coupling in Tourette syndrome pathogenesis

Tourette syndrome is a heritable neurodevelopmental disorder whose pathophysiology remains unknown. Recent genome-wide association studies suggest that it is a polygenic disorder influenced by many genes of small effect. We tested whether these genes cluster in cellular function by applying gene-set analysis using expert curated sets of brain-expressed genes in the current largest available Tourette syndrome genome-wide association data set, involving 1285 cases and 4964 controls. The gene sets included specific synaptic, astrocytic, oligodendrocyte and microglial functions. We report association of Tourette syndrome with a set of genes involved in astrocyte function, specifically in astrocyte carbohydrate metabolism. This association is driven primarily by a subset of 33 genes involved in glycolysis and glutamate metabolism through which astrocytes support synaptic function. Our results indicate for the first time that the process of astrocyte-neuron metabolic coupling may be an important contributor to Tourette syndrome pathogenesis.

Association of ADORA1 rs2228079 and ADORA2A rs5751876 Polymorphisms with Gilles de la Tourette Syndrome in the Polish Population

BACKGROUND

Gilles de la Tourette syndrome (GTS) is a neurodevelopmental disorder characterized by motor and vocal tics. Hyperactivity of dopaminergic transmission is considered a prime abnormality in the pathophysiology of tics. There are reciprocal antagonistic interactions between adenosine and dopamine transmission. The aim of the study was to analyze the association of two polymorphisms, rs2228079 in ADORA1 and rs5751876 in ADORA2A, with the risk of GTS and co-morbid disorders.

MATERIAL AND METHODS

A total of 162 Polish GTS patients and 270 healthy persons were enrolled in the study. Two polymorphisms were selected on the basis of knowledge of SNPs frequencies in ADORA1 and ADORA2A. Chi-square test was used for allelic and genotypic association studies. Association of genotypes with age of tic onset was analyzed with Mann-Whitney test. Multivariate logistic regression was used to find independent predictors of GTS risk.

RESULTS

We found that the risk of GTS was associated with rs2228079 and rs5751876 polymorphisms. The GG+GT genotypes of rs2228079 in ADORA1 were underrepresented in GTS patients (p = 0.011), whereas T allele of rs5751876 in ADORA2A was overrepresented (p = 0.017). The GG genotype of rs2228079 was associated with earlier age of tic onset (p = 0.046). We found also that the minor allele G of rs2228079 was more frequent in GTS patients with depression as compared to the patients without depression (p = 0.015). Also the genotype GG was significantly more frequent in patients with obsessive compulsive disorder/behavior (OCD/OCB, p = 0.021) and depression (p = 0.032), as compared to the patients without these co-morbidities. The minor allele T frequency of rs5751876 was lower in GTS patients with co-morbid attention deficit hyperactivity disorder (p = 0.022), and TT+TC genotypes were less frequent in the non-OCD anxiety disorder group (p = 0.045).

CONCLUSION

ADORA1 and ADORA2A variants are associated with the risk of GTS, co-morbid disorders, and may affect the age of tic onset.

Genetic predisposition increases the tic severity, rate of comorbidities, and psychosocial and educational difficulties in children with Tourette syndrome

This study aimed to examine whether there are differences in tic severity, comorbidities, and psychosocial and educational consequences in children with Tourette syndrome and genetic predisposition to Tourette syndrome compared with children with Tourette syndrome without genetic predisposition to Tourette syndrome. A total of 314 children diagnosed with Tourette syndrome participated in this study. Validated diagnostic tools were used to assess tic severity, comorbidities, and cognitive performance. A structured interview was used to evaluate psychosocial and educational consequences related to Tourette syndrome. The children with Tourette syndrome and genetic predisposition present with statistically significant differences in terms of severity of tics, comorbidities, and a range of psychosocial and educational factors compared with the children with Tourette syndrome without genetic predisposition. Professionals need to be aware of genetic predisposition to Tourette syndrome, as children with Tourette syndrome and genetic predisposition have more severe symptoms than those children with Tourette syndrome who are without genetic predisposition.

Tourette syndrome and comorbid ADHD: causes and consequences

Attention deficit hyperactivity disorder (ADHD) is the most common comorbid condition in patients with Tourette syndrome (TS). The co-occurrence of ADHD and TS is in most cases associated with a higher social and psychopathological impairment. Comorbidity between Tourette and ADHD appears to have a complex and partially known pathogenesis in which genetic, environmental, and neurobiological factors can be implicated. Genetic studies have revealed an involvement of dopaminergic, catecholaminergic, and GABAergic genes that modulated the activity of neurotransmitters. Furthermore, there are a lot of networks implicated in the development of ADHD and TS, involving cortical and striatal areas and basal ganglia. Although a large number of studies tried to find a common pathogenesis, the complex pathways responsible are not clear. The genes implicated in both disorders are currently unidentified, but it is probable that epigenetic factors associated with neural modifications can represent a substrate for the development of the diseases.

CONCLUSION

In this paper, recent advances in neurobiology of ADHD and TS are reviewed, providing a basis for understanding the complex common pathogenesis underlying the frequent co-occurrence of the two conditions and the therapeutic choices.

A t(3;9)(q25.1;q34.3) translocation leading to OLFM1 fusion transcripts in Gilles de la Tourette syndrome, OCD and ADHD

Gilles de la Tourette syndrome (GTS) is a neuropsychiatric disorder with a strong genetic etiology; however, finding of candidate genes is hampered by its genetic heterogeneity and the influence of non-genetic factors on disease pathogenesis. We report a case of a male patient with GTS, obsessive compulsive disorder, attention-deficit/hyperactivity-disorder, as well as other comorbidities, and a translocation t(3;9)(q25.1;q34.3) inherited from a mother with tics. Mate-pair sequencing revealed that the translocation breakpoints truncated the olfactomedin 1 (OLFM1) gene and two uncharacterized transcripts. Reverse-transcription PCR identified several fusion transcripts in the carriers, and OLFM1 expression was found to be high in GTS-related human brain regions. As OLFM1 plays a role in neuronal development it is a likely candidate gene for neuropsychiatric disorders and haploinsufficiency of OLFM1 could be a contributing risk factor to the phenotype of the carriers. In addition, one of the fusion transcripts may exert a dominant-negative or gain-of-function effect. OLFM1 is unlikely to be a major GTS susceptibility gene as no point mutations or copy number variants affecting OLFM1 were identified in 175 additional patients. The translocation described is thus a unique event, but further studies in larger cohorts are required to elucidate involvement of OLFM1 in GTS pathogenesis.

The Tourette International Collaborative Genetics (TIC Genetics) study, finding the genes causing Tourette syndrome: objectives and methods

Tourette syndrome (TS) is a neuropsychiatric disorder characterized by recurrent motor and vocal tics, often accompanied by obsessive-compulsive disorder and/or attention-deficit/hyperactivity disorder. While the evidence for a genetic contribution is strong, its exact nature has yet to be clarified fully. There is now mounting evidence that the genetic risks for TS include both common and rare variants and may involve complex multigenic inheritance or, in rare cases, a single major gene. Based on recent progress in many other common disorders with apparently similar genetic architectures, it is clear that large patient cohorts and open-access repositories will be essential to further advance the field. To that end, the large multicenter Tourette International Collaborative Genetics (TIC Genetics) study was established. The goal of the TIC Genetics study is to undertake a comprehensive gene discovery effort, focusing both on familial genetic variants with large effects within multiply affected pedigrees and on de novo mutations ascertained through the analysis of apparently simplex parent-child trios with non-familial tics. The clinical data and biomaterials (DNA, transformed cell lines, RNA) are part of a sharing repository located within the National Institute for Mental Health Center for Collaborative Genomics Research on Mental Disorders, USA, and will be made available to the broad scientific community. This resource will ultimately facilitate better understanding of the pathophysiology of TS and related disorders and the development of novel therapies. Here, we describe the objectives and methods of the TIC Genetics study as a reference for future studies from our group and to facilitate collaboration between genetics consortia in the field of TS.

Progress in research on Tourette syndrome

Tourette syndrome (TS) is a heritable neuropsychiatric disorder commonly complicated by obsessions and compulsions, but defined by frequent unwanted movements (motor tics) and vocalizations (phonic tics) that develop in childhood or adolescence. In recent years, research on TS has progressed rapidly on several fronts. Inspired by the Fifth International Scientific Symposium on Tourette Syndrome, the articles in this special issue review advances in the phenomenology, epidemiology, genetics, pathophysiology, and treatment of TS.

Rabbit genome analysis reveals a polygenic basis for phenotypic change during domestication

The genetic changes underlying the initial steps of animal domestication are still poorly understood. We generated a high-quality reference genome for the rabbit and compared it to resequencing data from populations of wild and domestic rabbits. We identified more than 100 selective sweeps specific to domestic rabbits but only a relatively small number of fixed (or nearly fixed) single-nucleotide polymorphisms (SNPs) for derived alleles. SNPs with marked allele frequency differences between wild and domestic rabbits were enriched for conserved noncoding sites. Enrichment analyses suggest that genes affecting brain and neuronal development have often been targeted during domestication. We propose that because of a truly complex genetic background, tame behavior in rabbits and other domestic animals evolved by shifts in allele frequencies at many loci, rather than by critical changes at only a few domestication loci.

The X-Linked Hypothesis of Brain Disorders

In this article, we propose an X-linked hypothesis of brain disorders that postulates a neuronal origin of those neurodegenerative and psychiatric disorders with a greater male prevalence. The hypothesis is based on the accumulated genetics and genomic evidence linking X chromosome genes and transcripts to neuronal cells. The behavioral genetics literature has long pointed to the link between postsynaptic protein complexes coded on chromosome X and mental retardation. More recently, novel genomic evidence has emerged of X-linked mRNA overexpression of neuronal source in the human brain. We review the evidence for this hypothesis and its consistency with the distribution across genders of brain disorders of known aetiology. We then provide examples of the utilization of this hypothesis in the investigation of the pathophysiology of complex brain disorders in both the stratification of disease cohorts and the development of realistic preclinical models. We conclude by providing a general framework for testing its validity, which will be exploited in future studies, and provide future directions for research.

Tic disorders

PURPOSE OF REVIEW

Primary tic disorders are complex, multifactorial disorders in which tics are accompanied by other sensory features and an array of comorbid behavioral disorders. Secondary tics are proportionally much less frequent, but their etiology is diverse. This review aims to guide clinicians in the recognition of the phenomenology, pathophysiology, and treatment of these disorders.

RECENT FINDINGS

Advances include greater phenomenologic insights, particularly of nonmotor (sensory) features; increased knowledge of disease mechanisms, particularly coming from neuropsychological, functional imaging, pathologic, and animal model studies; growing evidence on the efficacy of alpha-2 agonists and the newer generation of dopamine-modulating agents; and recent strides in the evaluation of cognitive-behavioral therapy and deep brain stimulation surgery.

SUMMARY

The correct diagnostic approach to tic disorders requires accurate historical gathering, a thorough neurologic examination, and detailed definition of the patient's psychopathologic profile. Treatment should always begin with individualized psychoeducational strategies. Although pharmacologic treatments remain beneficial for most patients, cognitive-behavioral treatments have thus far shown promising efficacy. Deep brain stimulation surgery should still be limited to adult patients refractory to pharmacotherapy and cognitive-behavioral therapy.

Genetic variants and animal models in SNCA and Parkinson disease

Parkinson disease (PD; MIM 168600) is the second most common progressive neurodegenerative disorder characterized by a variety of motor and non-motor features. To date, at least 20 loci and 15 disease-causing genes for parkinsonism have been identified. Among them, the α-synuclein (SNCA) gene was associated with PARK1/PARK4. Point mutations, duplications and triplications in the SNCA gene cause a rare dominant form of PD in familial and sporadic PD cases. The α-synuclein protein, a member of the synuclein family, is abundantly expressed in the brain. The protein is the major component of Lewy bodies and Lewy neurites in dopaminergic neurons in PD. Further understanding of its role in the pathogenesis of PD through various genetic techniques and animal models will likely provide new insights into our understanding, therapy and prevention of PD.

Mouse models of neurodevelopmental disease of the basal ganglia and associated circuits

This chapter focuses on neurodevelopmental diseases that are tightly linked to abnormal function of the striatum and connected structures. We begin with an overview of three representative diseases in which striatal dysfunction plays a key role--Tourette syndrome and obsessive-compulsive disorder, Rett's syndrome, and primary dystonia. These diseases highlight distinct etiologies that disrupt striatal integrity and function during development, and showcase the varied clinical manifestations of striatal dysfunction. We then review striatal organization and function, including evidence for striatal roles in online motor control/action selection, reinforcement learning, habit formation, and action sequencing. A key barrier to progress has been the relative lack of animal models of these diseases, though recently there has been considerable progress. We review these efforts, including their relative merits providing insight into disease pathogenesis, disease symptomatology, and basal ganglia function.

The implication of neuroactive steroids in Tourette's syndrome pathogenesis: A role for 5α-reductase?

Tourette's syndrome (TS) is a neurodevelopmental disorder characterised by recurring motor and phonic tics. The pathogenesis of TS is considered to reflect dysregulations in the signalling of dopamine (DA) and other neurotransmitters, which lead to excitation/inhibition imbalances in cortico-striato-thalamocortical circuits. The causes of these deficits may reflect complex gene × environment × sex (G × E × S) interactions; indeed, the disorder is markedly predominant in males, with a male-to-female prevalence ratio of approximately 4 : 1. Converging lines of evidence point to neuroactive steroids as being likely molecular candidates to account for G × E × S interactions in TS. Building on these premises, our group has begun examining the possibility that alterations in the steroid biosynthetic process may be directly implicated in TS pathophysiology; in particular, our research has focused on 5α-reductase (5αR), the enzyme catalysing the key rate-limiting step in the synthesis of pregnane and androstane neurosteroids. In clinical and preclinical studies, we found that 5αR inhibitors exerted marked anti-DAergic and tic-suppressing properties, suggesting a central role for this enzyme in TS pathogenesis. Based on these data, we hypothesise that enhancements in 5αR activity in early developmental stages may lead to an inappropriate activation of the 'backdoor' pathway for androgen synthesis from adrenarche until the end of puberty. We predict that the ensuing imbalances in steroid homeostasis may impair the signalling of DA and other neurotransmitters, ultimately resulting in the facilitation of tics and other behavioural abnormalities in TS.

Long-term efficacy and safety of fluphenazine in patients with Tourette syndrome

OBJECTIVES

Haloperidol and pimozide are the only drugs currently approved by the U.S. Food and Drug Administration for treatment of Tourette syndrome (TS), but their potential side effects, which include tardive dyskinesia (TD), limit their use.

METHODS

We performed a retrospective chart review of patients with TS treated with fluphenazine over a 26-year period.

RESULTS

Among 268 patients with TS, fluphenazine was initiated at a mean age of 15.8 ± 10.7 years (range, 4.1-70.2) and titrated to an optimal dose of 3.24 ± 2.3 mg/day (range, 0.5-12.0), which was continued for an average of 2.6 ± 3.2 years (range, 0.01-16.8). Marked to moderate improvement was noted in 211 (80.5%). The most common side effects included drowsiness, fatigue, or both, observed in 70 (26.1%) patients. There were no cases of TD.

CONCLUSIONS

Fluphenazine appears to be safe and effective in the treatment of TS, and there were no cases of TD in this cohort treated up to 16.8 years.

Personalized genomic disease risk of volunteers

Next-generation sequencing (NGS) is commonly used for researching the causes of genetic disorders. However, its usefulness in clinical practice for medical diagnosis is in early development. In this report, we demonstrate the value of NGS for genetic risk assessment and evaluate the limitations and barriers for the adoption of this technology into medical practice. We performed whole exome sequencing (WES) on 81 volunteers, and for each volunteer, we requested personal medical histories, constructed a three-generation pedigree, and required their participation in a comprehensive educational program. We limited our clinical reporting to disease risks based on only rare damaging mutations and known pathogenic variations in genes previously reported to be associated with human disorders. We identified 271 recessive risk alleles (214 genes), 126 dominant risk alleles (101 genes), and 3 X-recessive risk alleles (3 genes). We linked personal disease histories with causative disease genes in 18 volunteers. Furthermore, by incorporating family histories into our genetic analyses, we identified an additional five heritable diseases. Traditional genetic counseling and disease education were provided in verbal and written reports to all volunteers. Our report demonstrates that when genome results are carefully interpreted and integrated with an individual's medical records and pedigree data, NGS is a valuable diagnostic tool for genetic disease risk.

Genetic analysis of the fused in sarcoma gene in Chinese Han patients with Parkinson's disease

BACKGROUND AND PURPOSE

Exome sequencing in a large essential tremor (ET) family identified a novel nonsense mutation (p.Q290X) in the fused in sarcoma gene (FUS) as the cause of this family. Because of the clinical overlap between ET and Parkinson's disease (PD), the role of FUS in an independent cohort of PD patients from China mainland was evaluated.

METHODS

The entire coding region of FUS in 508 Chinese Han patients with PD and the identified variants in 633 normal controls were evaluated. A variant was further screened in an additional 382 controls for the frequency in our population.

RESULTS

A novel variant c.696C > T (p.Y232Y) in 2 sporadic patients with PD and six variants (c.52C > A, p.P18T; c.52C > T, p.P18S; c.147C > A, p.G49G; c.291C > T, p.Y97Y; c.684C > T, p.G228G; c.1176G > A, p.M392I) without significant difference in genotypic and allelic distributions in our PD cohort were identified.

CONCLUSION

The FUS gene is not a genetic risk factor for PD in the population of Chinese Han ethnicity.

The molecular biology of genetic-based epilepsies

Epilepsy is one of the most common neurological disorders characterized by abnormal electrical activity in the central nervous system. The clinical features of this disorder are recurrent seizures, difference in age onset, type, and frequency, leading to motor, sensory, cognitive, psychic, or autonomic disturbances. Since the discovery of the first monogenic gene mutation in 1995, it is proposed that genetic factor plays an important role in the mechanism of epilepsy. Genes discovered in idiopathic epilepsies encode for ion channel or neurotransmitter receptor proteins, whereas syndromes with epilepsy as a main feature are caused by genes that are involved in functions such as cortical development, mitochondrial function, and cell metabolism. The identification of these monogenic epilepsy-causing genes provides new insight into the pathogenesis of epilepsies. Although most of the identified gene mutations present a monogenic inheritance, most of idiopathic epilepsies are complex genetic diseases exhibiting a polygenic or oligogenic inheritance. This article reviews recent genetic and molecular progresses in exploring the pathogenesis of epilepsy, with special emphasis on monogenic epilepsy-causing genes, including voltage-gated channels (Na(+), K(+), Ca(2+), Cl(-), and HCN), ligand-gated channels (nicotinic acetylcholine and GABAA receptors), non-ion channel genes as well as the mitochondrial DNA genes. These progresses have improved our understanding of the complex neurological disorder.

Common and rare alleles of the serotonin transporter gene, SLC6A4, associated with Tourette's disorder

To evaluate the hypothesis that functionally over-expressing alleles of the serotonin transporter (SERT) gene (solute carrier family 6, member 4, SLC6A4) are present in Tourette's disorder (TD), just as we previously observed in obsessive compulsive disorder (OCD), we evaluated TD probands (N = 151) and controls (N = 858). We genotyped the refined SERT-linked polymorphic region 5-HTTLPR/rs25531 and the associated rs25532 variant in the SLC6A4 promoter plus the rare coding variant SERT isoleucine-to-valine at position 425 (I425V). The higher expressing 5-HTTLPR/rs25531 LA allele was more prevalent in TD probands than in controls (χ(2)  = 5.75; P = 0.017; odds ratio [OR], 1.35); and, in a secondary analysis, surprisingly, it was significantly more frequent in probands who had TD alone than in those who had TD plus OCD (Fisher's exact test; P = 0.0006; OR, 2.29). Likewise, the higher expressing LAC haplotype (5-HTTLPR/rs25531/rs25532) was more frequent in TD probands than in controls (P = 0.024; OR, 1.33) and also in the TD alone group versus the TD plus OCD group (P = 0.0013; OR, 2.14). Furthermore, the rare gain-of-function SERT I425V variant was observed in 3 male siblings with TD and/or OCD and in their father. Thus, the cumulative count of SERT I425V becomes 1.57% in OCD/TD spectrum conditions versus 0.15% in controls, with a recalculated, family-adjusted significance of χ(2) = 15.03 (P < 0.0001; OR, 9.0; total worldwide genotyped, 2914). This report provides a unique combination of common and rare variants in one gene in TD, all of which are associated with SERT gain of function. Thus, altered SERT activity represents a potential contributor to serotonergic abnormalities in TD. The present results call for replication in a similarly intensively evaluated sample. © 2013 Movement Disorder Society.

Theoretical and practical considerations behind the use of laboratory animals for the study of Tourette syndrome

In the present manuscript we review a substantial body of literature describing several pre-clinical animal models designed and developed with the purpose of investigating the biological determinants of Tourette syndrome (TS). In order to map the animal models onto the theoretical background upon which they have been devised, we first define phenomenological and etiological aspects of TS and then match this information to the available pre-clinical models. Thus, we first describe the characteristic symptoms exhibited by TS patients and then a series of hypotheses attempting to identify the multifactorial causes of TS. With respect to the former, we detail the phenomenology of abnormal repetitive behaviors (tics and stereotypies), obsessive-compulsive behaviors and aberrant sensory-motor gating. With respect to the latter, we describe both potential candidate vulnerability genes and environmental factors (difficult pregnancies, psychosocial stressors and infections). We then discuss how this evidence has been translated in pre-clinical research with respect to both dependent (symptoms) and independent (etiological factors) variables. Thus, while, on the one hand, we detail the methodologies adopted to measure abnormal repetitive and obsessive-compulsive behaviors, and sensory-motor gating, on the other hand, we describe genetic engineering studies and environmental modulations aimed at reproducing the proposed biological determinants in laboratory rodents. A special emphasis is placed upon "programming" events, occurring during critical stages of early development and exerting organizational delayed consequences. In the final section, we outline a heuristic model with the purpose of integrating clinical and pre-clinical evidence in the study of TS.