Genome scan for linkage to Gilles de la Tourette syndrome

Tourette disorder and other tic disorders

Tourette disorder is a developmental neuropsychiatric condition characterized by vocal and motor tics that can range in severity from mild to disabling. It represents one end of a spectrum of tic disorders and is estimated to affect 0.5-0.7% of the population. Accumulated evidence supports a substantial genetic contribution to disease risk, but the identification of genetic variants that confer risk has been challenging. Positive findings in candidate gene association studies have not replicated, and genomewide association studies have not generated signals of genomewide significance, in large part because of inadequate sample sizes. Rare mutations in several genes have been identified, but their causality is difficult to establish. As in other complex neuropsychiatric disorders, it is likely that Tourette disorder risk involves a combination of common, low-effect and rare, larger-effect variants in multiple genes acting together with environmental factors. With the ongoing collection of larger patient cohorts and the emergence of affordable high-throughput genomewide sequencing, progress is expected to accelerate in coming years.

Jian-Pi-Zhi-Dong-Decoction regulates the expression of glutamate transporters to attenuate glutamate excitotoxicity and exerts anti-tics effects in Tourette syndrome model rats

PURPOSE

This study explored whether Jian-Pi-Zhi-Dong-Decoction (JPZDD) could regulate the metabolism of glutamate (GLU) and its transporters in the striatum to exert anti-tics effects in Tourette syndrome (TS) rats.

MATERIALS AND METHODS

We randomly assigned 56 Sprague Dawley rats into four groups, each with 14 rats: control, model, tiapride (Tia), and JPZDD. TS groups (model, Tia, and JPZDD) received intraperitoneal injection of 3,3'-iminodipropionitrile for 7 days to establish TS model. Thereafter, rats in the four groups were treated differently once a day for 6 weeks. Behavioral evaluation was performed each week by using stereotypy recording and autonomic activity test. The level of GLU in the striatum was examined by high-performance liquid chromatography. Expression of EAAT1 and VGLUT1 were measured by quantitative real-time PCR (qRT-PCR) and laser scanning confocal microscope.

RESULTS

Compared with the model group, the stereotypy score and autonomic activity were decreased in Tia and JPZDD groups. Notably, the model group had increased concentration of GLU, which decreased after JPZDD and Tia treatments. In the model group, EAAT1 and glial cells were highly co-expressed and the relative fluorescence intensity (FI) of EAAT1 was significantly lower than that in the control group. Treatment with JPZDD and Tia increased the relative FI of EAAT1. The mRNA level of EAAT1 decreased in the model group compared to that in the control group, although it was significantly elevated following JPZDD or Tia treatment. In the model group, there was low co-expression of VGLUT1 and axon cells and the FI of VGLUT1 was remarkably increased relative to that in the control group and reduced following treatment with JPZDD and Tia. A similar trend was observed in the mRNA and protein expression of VGLUT1, although it was not statistically significant.

CONCLUSION

The mechanism by which JPZDD alleviated behavioral dysfunction of TS rats may be associated with maintaining normal GLU transport by upregulating EAAT1 and down-regulating VGLUT1 in the striatum.

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.

Tourette Syndrome: Bridging the Gap between Genetics and Biology

Tourette syndrome is a childhood neuropsychiatric disorder, which presents with disruptive motor and vocal tics. The disease also has a high comorbidity with obsessive-compulsive disorder and attention deficit hyperactivity disorder, which may further increase the distress experienced by patients. Current treatments act with varying efficacies in alleviating symptoms, as the underlying biology of the disease is not fully understood to provide precise therapeutic targets. Moreover, the genetic complexity of the disorder presents a substantial challenge to the identification of genetic alterations that contribute to the Tourette's phenotype. Nevertheless, genetic studies have suggested involvement of dopaminergic, serotonergic, glutamatergic, and histaminergic pathways in the pathophysiology of at least some cases. In addition, genetic overlaps with other neuropsychiatric disorders may point toward a shared biology. The findings that are emerging from genetic studies will allow researchers to piece together the underlying components of the disease, in the hopes that a deeper understanding of Tourette's can lead to improved treatments for those affected by it.

GDNF gene is associated with tourette syndrome in a family study

BACKGROUND

Tourette syndrome is a disorder characterized by persistent motor and vocal tics, and frequently accompanied by the comorbidities attention deficit hyperactivity disorder and obsessive-compulsive disorder. Impaired synaptic neurotransmission has been implicated in its pathogenesis. Our aim was to investigate the association of 28 candidate genes, including genes related to synaptic neurotransmission and neurotrophic factors, with Tourette syndrome.

METHODS

We genotyped 506 polymorphisms in a discovery cohort from the United States composed of 112 families and 47 unrelated singletons with Tourette syndrome (201 cases and 253 controls). Genes containing significant polymorphisms were imputed to fine-map the signal(s) to potential causal variants. Allelic analyses in Tourette syndrome cases were performed to check the role in attention deficit hyperactivity disorder and obsessive-compulsive disorder comorbidities. Target polymorphisms were further studied in a replication cohort from southern Spain composed of 37 families and three unrelated singletons (44 cases and 73 controls).

RESULTS

The polymorphism rs3096140 in glial cell line-derived neurotrophic factor gene (GDNF) was significant in the discovery cohort after correction (P = 1.5 × 10(-4) ). No linkage disequilibrium was found between rs3096140 and other functional variants in the gene. We selected rs3096140 as target polymorphism, and the association was confirmed in the replication cohort (P = 0.01). No association with any comorbidity was found.

CONCLUSIONS

As a conclusion, a common genetic variant in GDNF is associated with Tourette syndrome. A defect in the production of GDNF could compromise the survival of parvalbumin interneurons, thus altering the excitatory/inhibitory balance in the corticostriatal circuitry. Validation of this variant in other family cohorts is necessary.

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.

Neurobiology of tourette syndrome: current status and need for further investigation

Tourette syndrome (TS) is a common, chronic neuropsychiatric disorder characterized by the presence of fluctuating motor and phonic tics. The typical age of onset is ∼5-7 years, and the majority of children improve by their late teens or early adulthood. Affected individuals are at increased risk for the development of various comorbid conditions, such as obsessive-compulsive disorder, attention deficit hyperactivity disorder, school problems, depression, and anxiety. There is no cure for tics, and symptomatic therapy includes behavioral and pharmacological approaches. Evidence supports TS being an inherited disorder; however, the precise genetic abnormality remains unknown. Pathologic involvement of cortico-striatal-thalamo-cortical (CSTC) pathways is supported by neurophysiological, brain imaging, and postmortem studies, but results are often confounded by small numbers, age differences, severity of symptoms, comorbidity, use of pharmacotherapy, and other factors. The primary site of abnormality remains controversial. Although numerous neurotransmitters participate in the transmission of messages through CSTC circuits, a dopaminergic dysfunction is considered a leading candidate. Several animal models have been used to study behaviors similar to tics as well as to pursue potential pathophysiological deficits. TS is a complex disorder with features overlapping a variety of scientific fields. Despite description of this syndrome in the late 19th century, there remain numerous unanswered neurobiological questions.

Tourette disorder spectrum maps to chromosome 14q31.1 in an Italian kindred

Tourette syndrome (TS) is a frequent neuropsychiatric disorder of unknown etiology. A number of chromosomal regions have been nominated as TS loci in linkage studies, but confirmation has met with limited success and causative mutations have not yet been definitely identified. Furthermore, TS, chronic tics, and obsessive–compulsive disorder (OCD) occur at increased frequencies among TS relatives, supporting the view that these phenotypes represent parts of the same genetically determined spectrum. We ascertained a four-generation Italian kindred segregating TS, chronic multiple motor tics (CMT), and OCD, and we performed a ten-centimorgan (cM) genome-wide linkage scan in order to map the underlying genetic defect. Suggestive linkage to chromosome 14q31.1 (multipoint LOD = 2.4) was detected by affected-only analysis under an autosomal dominant model and a narrower phenotype definition (only the subjects with TS and CMT were considered as affected). The linkage peak increased and it approached genome-wide significance (LOD = 3.29) when a broader phenotype definition was adopted (subjects with TS, CMT, and OCD considered as affected). Haplotype analysis defined a ∼2.3 cM critical region, shared by all the relatives with TS, CMT, or OCD. In conclusion, we provide strong evidence for linkage of TS spectrum to chromosome 14q31.1. Suggestive linkage to an overlapping region of chromosome 14q was reported in a recent scan of TS sibling pairs. This region might therefore contain an important gene for TS, and it should be prioritized for further study.

Polymorphisms of interleukin 1 gene IL1RN are associated with Tourette syndrome

Tourette syndrome has a multifactorial etiology in which genetic, environmental, and immunologic factors interact to establish vulnerability. Various interleukin 1 genes are associated with several immunoinflammatory diseases. It is not known whether polymorphisms in those genes are involved in the pathogenesis of Tourette syndrome. In this association study, single nucleotide polymorphisms were used to investigate the distribution of genotypes of the interleukin 1 receptor antagonist gene (IL1RN; alias IL1RA) and of the interleukin 1beta gene (IL1B) in patients with Tourette syndrome. A total of 159 children with Tourette syndrome and 175 healthy control subjects were included in the study. There was no significant difference between patients and control subjects in the distribution of genotype and allele frequencies for IL1B exon 5 and promoter region; however, the number of individuals homozygotic for IL1RN( *)1 was significantly greater (P < 0.0001), and the IL1RN( *)1 allele frequency was significantly higher (P < 0.0001), among patients than among control subjects. The odds ratio for developing Tourette syndrome in individuals with the IL1RN( *)1 allele, compared with IL1RN( *)2, was 7.65. Thus, the IL1RN gene may be a useful marker for prediction of the susceptibility to Tourette syndrome.

Linkage analysis of Tourette syndrome in a large Utah pedigree

Tourette syndrome (TS) is a neuropsychiatric disorder characterized by multiple motor and phonic tics. The heritability of TS has been well established, yet there is a lack of consensus in genome-wide linkage studies. The purpose of this study was to conduct a genome-wide linkage analysis on a unique, large, high-risk TS Utah pedigree. We examined a qualitative trait (TS1) where cases had a definitive diagnosis of TS as observed by a clinical interviewer (n = 66) and a quantitative phenotype based on the total Yale global motor and phonic tic severity scores (n = 102). Both parametric and non-parametric multipoint linkage analyses based on MCMC methods were performed using a 10 cM spaced micro-satellite autosomal marker set. Two regions of interest were identified under affecteds-only recessive models; a LOD score of 3.3 on chromosome 1p for Yale tic severity and a LOD score of 3.1 on chromosome 3p for the TS1 phenotype. Twenty-seven individuals shared linked segregating haplotypes for the 1p region. They had significantly higher Yale tic phonic scores than non-sharers (P = 0.01). There were 46 haplotype sharers on chromosome 3p with significantly higher percentage of females among these individuals compared to the non-sharers (P = 0.03). The significant linkage peaks on chromosomes 1p and 3p are in new areas of the genome for TS, and replication of these findings is necessary.

Glutamatergic modulatory therapy for Tourette syndrome

Tourette syndrome (TS) is a neuropsychiatric disorder characterized by the presence of chronic, fluctuating motor and vocal (phonic) tics. The disorder is commonly associated with a variety of comorbidities including obsessive-compulsive disorder (OCD), attention deficit hyperactivity disorder (ADHD), school problems, anxiety, and depression. Therapeutically, if tics are causing psychosocial or physical problems, symptomatic medications are often prescribed, typically alpha-adrenergic agonists or dopamine antagonists. Recognizing that therapy is often ineffective and frequently associated with unacceptable side-effects, there is an ongoing effort to identify new tic-suppressing therapies. Several lines of evidence are presented that support the use of glutamate modulators in TS including glutamate's major role in cortico-striatal-thalamo-cortical circuits (CSTC), the recognized extensive interaction between glutamate and dopamine systems, results of familial genetic studies, and data from neurochemical analyses of postmortem brain samples. Since insufficient data is available to determine whether TS is definitively associated with a hyper- or hypo-glutamatergic state, potential treatment options using either glutamate antagonists or agonists are reviewed. Data from studies using these agents in the treatment of OCD are presented. If validated, modulation of the glutamate system could provide a valuable new pharmacological approach in the treatment of tics associated with Tourette syndrome.

The genetics of Tourette syndrome: a review

OBJECTIVES

This article summarizes and evaluates recent advances in the genetics of Gilles de la Tourette syndrome (GTS).

METHODS

This is a review of recent literature focusing on (1) the genetic etiology of GTS; (2) common genetic components of GTS, attention deficit hyperactivity disorder (ADHD), and obsessive compulsive disorder (OCD); (3) recent linkage studies of GTS; (4) chromosomal translocations in GTS; and (5) candidate gene studies.

RESULTS

Family, twin, and segregation studies provide strong evidence for the genetic nature of GTS. GTS is a heterogeneous disorder with complex inheritance patterns and phenotypic manifestations. Family studies of GTS and OCD indicate that an early-onset form of OCD is likely to share common genetic factors with GTS. While there apparently is an etiological relationship between GTS and ADHD, it appears that the common form of ADHD does not share genetic factors with GTS. The largest genome wide linkage study to date observed evidence for linkage on chromosome 2p23.2 (P=3.8x10(-5)). No causative candidate genes have been identified, and recent studies suggest that the newly identified candidate gene SLITRK1 is not a significant risk gene for the majority of individuals with GTS.

CONCLUSION

The genetics of GTS are complex and not well understood. The Genome Wide Association Study (GWAS) design can hopefully overcome the limitations of linkage and candidate gene studies. However, large-scale collaborations are needed to provide enough power to utilize the GWAS design for discovery of causative mutations. Knowledge of susceptibility mutations and biological pathways involved should eventually lead to new treatment paradigms for GTS.

Chromosome 5 and Gilles de la Tourette syndrome: Linkage in a large pedigree and association study of six candidates in the region

Gilles de la Tourette Syndrome (TS) is a neuropsychiatric disorder characterized by both motor and vocal tics. In our previous genome scan for TS we identified evidence for linkage to the centromeric region of chromosome 5 in a single large family of 32 individuals with 10 family members with TS or chronic multiple tics (CMT). In this paper we report further analyses of the 5p-centromeric region in this pedigree. An additional 11 family members were identified and screened for TS. Using a set of 14 microsatellite markers we refined the linked region to a approximately 28 Mb interval between the markers D5S1506 and D5S76. A set of six candidate genes located in this region were selected to be tested for genetic association with TS. These genes were GDNF, ITGA1, ISL1, FGF10, HCN1 and SLC1A3. The TDT statistic was used for the association tests in a sample of 171 independent nuclear families with 241 affected children with TS. We found no evidence for an association between TS and markers in these genes in this sample of families. This study represents the first efforts to narrow the linkage region in the extended pedigree and the first tests of candidate genes in the chromosome 5 region linked to TS.

Principal components analysis of a large cohort with Tourette syndrome

BACKGROUND

Tourette syndrome is a heterogeneous familial disorder for which the genetic mechanisms are unknown. A better characterisation of the phenotype may help identify susceptibility genes.

AIMS

To extend previous factor-analytic studies of the syndrome.

METHOD

Symptom data from 410 people with Tourette syndrome were included in agglomerative hierarchical cluster and principal components analyses.

RESULTS

Five factors were observed, characterised by: (1) socially inappropriate behaviours and other complex vocal tics; (2) complex motor tics; (3) simple tics; (4) compulsive behaviours; and (5) touching self. Individuals with co-occurring attention-deficit hyperactivity disorder had significantly higher factor scores on Factors 1 and 3, whereas individuals with co-occurring obsessive-compulsive disorder and behaviours had significantly higher factor scores for Factors 1-4.

CONCLUSIONS

These findings add to the growing body of evidence that Tourette syndrome is not a unitary condition and can be disaggregated into more homogeneous symptom components.

Tourette's syndrome is not associated with interleukin-10 receptor 1 variants on chromosome 11q23.3

Interleukin-10 receptor 1 (IL-10R1) single nucleotide polymorphisms, located on chromosome 11q23 - a strong candidate for linkage with Tourette's syndrome (TS) - have been investigated for association with TS. DNA of 77 patients with a DSM-IV (Diagnostic and Statistical Manual IV) diagnosis of TS and 250 healthy controls was genotyped. IL-10R1 was not associated with TS.

Association study between Gilles de la Tourette Syndrome and two genes in the Robo-Slit pathway located in the chromosome 11q24 linked/associated region

Gilles de la Tourette Syndrome (GTS) is an inherited neuropsychiatric disorder characterized by the presence of motor and phonic tics. Previous genetic studies have identified linkage and association between GTS and the 11q24 chromosomal region. We selected for study, within this region, two possible susceptibility genes for GTS, the ROBO3 and ROBO4 genes. These two genes were selected because of the recent identification of SLITRK1 as a potential susceptibility gene for GTS based on a translocation breakpoint and the further finding of two mutations in the SLITRK1 gene in three patients with GTS. While thus far, the SLITRK1 gene appears to account for only a few cases of GTS, these findings, if confirmed, point to other genes in these pathways that may contribute to GTS. Based on this, we examined two genes in the Slit-Robo pathway involved in cell migration, axonal pathfinding, and/or neuronal differentiation because of their location in 11q24, a region previously identified as linked and associated with GTS. We selected six haplotype tagging single nucleotide polymorphisms (SNPs) for ROBO3 and four for ROBO4 and genotyped them in our sample of trios and sibpair families diagnosed with GTS. Based on 155 nuclear families with 255 affected children, we did not find evidence for association between GTS and either the ROBO3 or ROBO4 genes. Thus, these two genes are unlikely to be the susceptibility genes contributing to GTS on 11q24.

Tourette's syndrome: clinical features, pathophysiology, and therapeutic approaches

Tourette's syndrome (TS) is a disorder characterized by simple and complex motor tics, vocal tics, and frequently obsessive-compulsive symptoms, its onset occurs before the age of 21. Typically, TS shows a waxing and waning course, but a chronification of the tics, even during later life, is often observed, TS mainly occurs in boys, and shows genetic heritability with differing penetrance. The pathological mechanism is still unclear. Neuroanatomical and neuroimaging studies, as well as effective treatment using antipsychotics, suggest that a disturbance of the dopaminergic system in the basal ganglia plays an important role in the pathogenesis of TS, Several possibly causative mechanisms of the disturbed dopaminergic neurotransmission are discussed, with the main emphasis on the-infection-triggered- inflammatory immune process, Extrapyramidal movement disorders are known to occur as a symptom of poststreptococcal disease, such as in Sydenham's chorea. Cases of childhood TS are proposed to be caused by such a post-streptococcal mechanism, being part of a spectrum of childhood neurobehavioral disorders termed pediatric autoimmune neuropsychiatric disorder associated with streptococcal infection (PANDAS), The overlap between TS and PANDAS is discussed, and a critical view of the PANDAS concept is presenter], The therapeutic implications of the different pathological mechanisms are described, taking into consideration not only the acute or chronic natures of different infections, but also an autoimmune process, Moreover, therapeutic strategies using typical and atypical antipsychotics, and also experimental therapies such as repetitive transcranial magnetic stimulation and deep brain stimulation, are critically discussed.

A subgroup of Tourette's patients overexpress specific natural killer cell genes in blood: a preliminary report

Gilles de la Tourette Syndrome (TS) is a heritable, neurodevelopmental disorder characterized by motor and vocal tics. As no single gene or region has emerged from standard linkage approaches, TS may result from several as-yet-unidentified genetic factors, and may also occur due to infection-triggered, autoimmune processes. Etiological or pathogenic differences might result in clinically indistinguishable TS subgroups. We have previously used whole genome human oligonucleotide microarrays in an attempt to identify patterns of gene expression in blood linked with TS. In this proof-of-principle study, we applied Principal Components Analysis to a previously collected set of 16 familial TS and 16 control blood samples to identify subgroups. Fourteen genes, primarily Natural Killer Cell (NK) genes, discriminated between TS and all controls. Granzyme B and NKG7 were confirmed using RT-PCR. Five probesets (four genes) reside in chromosomal regions previously linked to familial TS or obsessive-compulsive disorder. Using the 14 genes, a Principal Components Analysis as well as a cluster analysis identified a TS subgroup (n = 10/16) that overexpressed the NK genes. 7/10 subjects within this subgroup were diagnosed with attention-deficit hyperactivity disorder (ADHD), suggesting that this expression profile might be associated with TS and co-morbid ADHD. Principal Components Analysis of gene expression in blood may be useful for identifying subgroups of other complex neurodevelopmental diseases, and the gene expression profile identified in this study may provide a biomarker for at least one subgroup of heritable TS.

The Gilles de la Tourette syndrome: a principal component factor analytic study of a large pedigree

BACKGROUND

The genetics and phenotypes of Gilles de la Tourette syndrome are complicated. Once indicated to be inherited as a single major autosomal dominant condition, several areas of interest on many chromosomes and one gene have been identified for Gilles de la Tourette syndrome, but no results have been replicated. Factor analytic studies suggest that there are more than one Gilles de la Tourette syndrome phenotype and it is not a unitary condition.

OBJECTIVE

To characterize Gilles de la Tourette syndrome phenotypes in a group of individuals who underwent a complete genome scan.

METHODS

We studied 85 members of a multiply affected multigenerational kindred, of whom 69 displayed Gilles de la Tourette syndrome-related symptoms (tics, obsessive-compulsive behaviours, obsessive-compulsive symptoms, attention deficit hyperactivity symptoms), using first a hierarchical cluster analysis followed by a principal component factor analysis.

RESULTS

Three significant factors resulted from our analysis, accounting for approximately 42% of the symptomatic variance: Factor 1 (predominantly 'pure tics'), Factor 2 (predominantly 'attention deficit hyperactivity disorder and aggressive behaviours') and Factor 3 (predominantly 'depression-anxiety-obsessional symptoms and self-injurious behaviours'). Different kinds of tics occurred in all three factors. Only frowning/raising eyebrows and sniffing/smelling loaded significantly on both Factors 1 and 3.

CONCLUSION

Our results give further evidence that the genetics of Gilles de la Tourette syndrome is complex and suggest that Gilles de la Tourette syndrome is not a unitary condition, thus confirming the results of earlier studies which have described several Gilles de la Tourette syndrome phenotypes. Although a genome scan on the pedigree reported three areas of interest and the present study found three factors, further studies would have to be undertaken to elucidate whether the three factors 'mapped' with the genetic data. Possible reasons for our findings and suggestions for future research are discussed.

Neurobiologie bei Tic- und Zwangsstörungen

Zusammenfassung. Erst in den letzten Jahren wird auch in der Forschung vermehrtes Augenmerk auf die Überschneidung von Tic- und Zwangsstörungen gerichtet. Während in Übersichtsarbeiten zum gemeinsamen Auftreten von Tic- und Zwangsstörungen die zahlreichen Befunde zu Phänomenologie, begleitender Psychopathologie, Epidemiologie und daraus resultierenden Therapieimplikationen breiten Raum einnehmen, sind die Untersuchungsergebnisse hinsichtlich ätiologischer und pathophysiologischer Gemeinsamkeiten in entsprechenden Arbeiten unterrepräsentiert. Daher wird mit dieser Arbeit ein Überblick über den aktuellen neurobiologischen Forschungsstand zu den Gemeinsamkeiten und Unterschieden von Tic- und Zwangsstörungen gegeben.

Tic symptom profiles in subjects with Tourette Syndrome from two genetically isolated populations

BACKGROUND

Tourette Syndrome (TS) has a complex etiology and wide variability in phenotypic expression. Identifying underlying symptom patterns may be useful for etiological and outcome studies of TS.

METHODS

Lifetime tic and related symptom data were collected between 1996 and 2001 in 121 TS subjects from the Central Valley of Costa Rica and 133 TS subjects from the Ashkenazi Jewish (AS) population in the US. Subjects were grouped by tic symptoms using an agglomerative hierarchical cluster analysis. Cluster membership was tested for association with available ancillary information (age of onset, tic severity, comorbid disorders, medication treatment and family history).

RESULTS

Cluster analysis identified two distinct groups in each sample, those with predominantly simple tics (cluster 1), and those with multiple complex tics (cluster 2). Membership in cluster 2 was correlated with increased tic severity, global impairment, medication treatment, and presence of comorbid obsessive-compulsive symptoms in both samples, and with family history of tics, lower verbal IQ, earlier age of onset, and comorbid obsessive-compulsive disorder and attention-deficit/hyperactivity disorder in the AS sample.

CONCLUSIONS

This study provides evidence for consistent and reproducible symptom profiles in two independent TS study samples. These findings have implications for etiological studies of TS.

Genome scan for Tourette disorder in affected-sibling-pair and multigenerational families

Tourette disorder (TD) is a neuropsychiatric disorder with a complex mode of inheritance and is characterized by multiple waxing and waning motor and phonic tics. This article reports the results of the largest genetic linkage study yet undertaken for TD. The sample analyzed includes 238 nuclear families yielding 304 "independent" sibling pairs and 18 separate multigenerational families, for a total of 2,040 individuals. A whole-genome screen with the use of 390 microsatellite markers was completed. Analyses were completed using two diagnostic classifications: (1) only individuals with TD were included as affected and (2) individuals with either TD or chronic-tic (CT) disorder were included as affected. Strong evidence of linkage was observed for a region on chromosome 2p (-log P = 4.42, P = 3.8 x 10(-5) in the analyses that included individuals with TD or CT disorder as affected. Results in several other regions also provide moderate evidence (-log P >2.0) of additional susceptibility loci for TD.

Genetic and clinical analysis of a large Dutch Gilles de la Tourette family

Gilles de la Tourette syndrome is a complex neuropsychiatric disorder, which becomes evident in childhood between the ages of 2 and 15 years. Tourette syndrome is defined by the occurrence of a large range and variable number of unwanted repetitive simple or complex motor and vocal tics that start in childhood and follow a waxing and waning course. A major gene for this syndrome has not yet been identified, probably owing to both genetic and phenotypic heterogeneity of this disease. This article describes the clinical evaluation of patients and family members in a large Dutch Gilles de la Tourette Syndrome pedigree and the decisions encountered with respect to phenotyping. The importance of an accurate definition of the Tourette phenotype is discussed, which is highly important for reliable genetic linkage and association studies. Subsequent linkage analysis resulted in three linkage peaks on different chromosomes 3q, 9q, and 13q. Multipoint analysis resulted in a single linkage peak with logarithm of odds score 2.55 with marker D3S1311 on chromosome 3q.

Analysis of the dopamine beta hydroxylase gene in Gilles de la Tourette syndrome

Numerous lines of evidence support the role of the catecholamines in the development of tics and Gilles de la Tourette syndrome (GTS). Dopamine-beta-hydroxylase (DBH) is the key enzyme in the conversion of dopamine to norepinephrine and the alleles of several polymorphisms of the DBH gene are correlated with individual variation in serum levels of the enzyme. We investigated the genetic relationship of the gene for DBH to GTS in two samples, one collected in Canada and one collected in Turkey. In total 106 affected probands and siblings in 71 nuclear pedigrees and 40 affected individuals and 71 family members in five multi-generational pedigrees were genotyped for three polymorphisms in the DBH locus. In the Canadian pedigrees we found no convincing evidence for linkage either in the multi-generational pedigrees or association in the nuclear families. We found significant evidence for association in the Turkish pedigrees (n = 29) for the 19 bp insertion/deletion markers; however, there was no supporting evidence for association with the other two markers. Based on the small sample size and low number of informative transmissions, we conclude that the results from the 19 bp insertion/deletion markers may be a chance false positive finding. These findings, in total, suggest that the DBH locus is unlikely to be a major gene influencing the susceptibility to DBH.

Genetics and epidemiology of Tourette syndrome

Although the genetic basis of Tourette syndrome is well established, uncertainty about how best to define and assess the Tourette syndrome phenotype has hampered efforts to identify the genes responsible for susceptibility to the disorder. In addition, such efforts have typically been underpowered or were undertaken before the technology was available to perform systematic genome-wide genetic investigations. The Tourette Syndrome Association International Consortium on Genetics was formed by more than a dozen research groups from around the world to develop common approaches to phenotyping Tourette syndrome and to pool samples for uniform, well-powered genetic investigations. Several recent advances, including the completion of genome-wide scans of affected sib-pairs and large families, show real promise for identifying Tourette syndrome susceptibility genes. In this review, we describe the key epidemiologic, linkage, and association studies in Tourette syndrome and illustrate the strategies currently being used to identify Tourette syndrome genes.

Tourette's Syndrome

This article has focused on TS, and the relationship between TS and OCD has been addressed from different perspectives. In patients who have OCD, the presence of TS seems to have some impact in the clinical manifestation of OCD symptoms. One of the main features of tic-related OCD is the frequent presence of sensory phenomena preceding the compulsions, in the absence of obsessions. Genetic epidemiologic studies provide consistent evidence for the association between TS and OCD. Although no major loci have been identified so far, family and segregation analysis studies support the assumption that genes play a major role in the etiology of TS and related disorders. Genes interact with environmental factors,which can modulate the expression of TS or OCD and determine the onset of these disorders. Neuroimaging studies suggest that the pathophysiology of TS encompasses projections of primary, secondary, and somato sensory cortex to the putamen, dorsolateral caudate nucleus, and globus pallidus,whereas the pathophysiology of OCD involves more ventral structures,such as orbitofrontal-caudate-thalamic-cortical areas. Current treatment strategies for TS include education, behavioral therapy, pharmacotherapy,and support from patients associations. Alfa-adrenergic agents such as guanfacine and clonidine are first-choice treatments for TS; typical antipsychotics are more effective but are troublesome because of their long-term side-effect profiles. For comorbid TS plus OCD, each condition should be treated with its respective first-line option. Nonetheless, for patients who have tic-related OCD who are unresponsive to monotherapy with serotonin reuptake inhibitors, augmentation of serotonin reuptake inhibitors with atypical antipsychotics may be of benefit. Despite important advances, re-search is needed to clarify further the biologic and behavioral aspects of TS and its relationship with the frequently associated conditions, with particular attention to their management and prognosis.

Indications of linkage and association of Gilles de la Tourette syndrome in two independent family samples: 17q25 is a putative susceptibility region

Gilles de la Tourette syndrome (GTS) is characterized by multiple motor and phonic tics and high comorbidity rates with other neurobehavioral disorders. It is hypothesized that frontal-subcortical pathways and a complex genetic background are involved in the etiopathogenesis of the disorder. The genetic basis of GTS remains elusive. However, several genomic regions have been implicated. Among them, 17q25 appears to be of special interest, as suggested by various independent investigators. In the present study, we explored the possibility that 17q25 contributes to the genetic component of GTS. The initial scan of chromosome 17 performed on two large pedigrees provided a nonparametric LOD score of 2.41 near D17S928. Fine mapping with 17 additional microsatellite markers increased the peak to 2.61 (P=.002). The original families, as well as two additional pedigrees, were genotyped for 25 single-nucleotide polymorphisms (SNPs), with a focus on three genes in the indicated region that could play a role in the development of GTS, on the basis of their function and expression profile. Multiple three-marker haplotypes spanning all three genes studied provided highly significant association results (P<.001). An independent sample of 96 small families with one or two children affected with GTS was also studied. Of the 25 SNPs, 3 were associated with GTS at a statistically significant level. The transmission/disequilibrium test for a three-site haplotype moving window again provided multiple positive results. The background linkage disequilibrium (LD) of the region was studied in eight populations of European origin. A complicated pattern was revealed, with the pairwise tests producing unexpectedly high LD values at the telomeric TBCD gene. In conclusion, our findings warrant the further investigation of 17q25 as a candidate susceptibility region for GTS.

Genome scan of Tourette syndrome in a single large pedigree shows some support for linkage to regions of chromosomes 5, 10 and 13

OBJECTIVES

To localize genes influencing the susceptibility to Gilles de la Tourette syndrome (GTS) and associated chronic multiple tics (CMT).

METHOD

A single, large, multiple affected pedigree containing 35 subjects diagnosed with GTS and a further 14 with CMT was genotyped for markers spanning the autosomes. Linkage analysis was carried out using classical lod score analysis and model-free lod score analysis. All markers were subjected to two-point analysis, and markers producing a two-point result significant at P<0.005 were subjected to three-point analysis using adjacent markers.

RESULTS

The following markers produced at least one result significant at 0.005 using two-point analysis: D5S1981, D5S2050, D10S591, D10S189, D13S217, and D14S288. Three-point analysis with D5S2050 and D5S400 produced a lod of 2.9 with CMT. Three-point analysis of D10S591 and D10S189 produced lods of 1.9 with GTS and CMT. Three-point analysis of D13S217 and D13S171 produced a lod of 2.7 with GTS. No single haplotype appeared to account for the majority of cases within the pedigree.

CONCLUSIONS

It seems likely that more than one susceptibility allele is present in the pedigree. Although none of the three positive regions is conclusively implicated, it seems probable that at least one contains a susceptibility locus. We recommend that association-based studies be carried out in these three regions to produce further evidence for a localization and to carry out fine-mapping.

Children at familial risk for Tourette's disorder: Child and parent diagnoses

Tourette's disorder (TD) is a neuropsychiatric disorder that onsets in childhood and appears to result from an interaction of genetic and environmental factors. The goal of the current prospective longitudinal study is to examine the onset of TD in offspring of parents with TD. At-risk children and control children were enrolled between the ages of 3 and 6 years and prospectively studied with yearly structured assessments over intervals of 2-5 years. Of 34 at-risk children free of tics at baseline, 10 (29%) subsequently developed a tic disorder, including 3 with TD. None of the 13 control children developed a tic disorder (P = 0.045). OCD or subclinical OCD emerged in 11 cases but no controls (P = 0.021). Finally, ADHD occurred in 14 at-risk children but no controls (P = 0.005). When at-risk families were dichotomized into bilineal or unilineal categories, rates of TD in children with two affected parents were three times the rate observed for children with one affected parent. These findings support the hypothesis that at least some cases of TD result from a complex genetic etiology. TD, OCD, and ADHD are significantly increased in children with TD parents. Furthermore, the risk is even greater when both parents are affected. Finally, our diagnosis of tic disorders in 21% of subjects initially reported by parents to be unaffected affirms the value of structured clinical assessments.

An update on the genetics of Gilles de la Tourette syndrome

OBJECTIVES

To summarize the current data suggesting that Gilles de la Tourette syndrome (GTS) is inherited and genetic.

METHODS

The extant literature on family studies, segregation analyses, candidate genes studies and linkage studies of GTS was reviewed and summarized.

RESULTS AND CONCLUSIONS

There is considerable data that suggests that: (1). genetic factors play an important role in the manifestation of GTS; (2). several genes are important with some possibly having major effect; and (3). several regions of the genome have been identified as potential locations of these susceptibility genes.

CNTNAP2 is disrupted in a family with Gilles de la Tourette syndrome and obsessive compulsive disorder

Gilles de la Tourette syndrome (GTS) is a sporadic or inherited complex neuropsychiatric disorder characterized by involuntary motor and vocal tics. There is comorbidity with disorders like obsessive compulsive disorder and attention deficit hyperactivity disorder. Until now linkage analysis has pointed to a number of chromosomal locations, but has failed to identify a clear candidate gene(s). We have investigated a GTS family with a complex chromosomal insertion/translocation involving chromosomes 2 and 7. The affected father [46,XY,inv(2) (p23q22),ins(7;2) (q35-q36;p21p23)] and two affected children [46,XX,der(7)ins(7;2)(q35-q36;p21p23) and 46,XY,der(7)ins(7;2)(q35-q36;p213p23)] share a chromosome 2p21-p23 insertion on chromosome 7q35-q36, thereby interrupting the contactin-associated protein 2 gene (CNTNAP2). This gene encodes a membrane protein located in a specific compartment at the nodes of Ranvier of axons. We hypothesize that disruption or decreased expression of CNTNAP2 could lead to a disturbed distribution of the K(+) channels in the nervous system, thereby influencing conduction and/or repolarization of action potentials, causing unwanted actions or movements in GTS.

Translocation breakpoint in two unrelated Tourette syndrome cases, within a region previously linked to the disorder

Tourette syndrome (TS) is a complex neuropsychiatric disorder characterized by both motor and vocal tics. The etiology of TS is poorly understood; however, evidence of genetic transmission arises from family and twin studies. A complex mode of inheritance has been suggested, likely involving contributions of several genes with different effect size. We describe here two unrelated families wherein balanced t(6;8) chromosomal translocations occur in individuals diagnosed with TS. In one of these families, the transmission of the translocation is associated with learning and behavioral difficulties; in the other family, one parent is unaffected and the other cannot be traced, thus transmission cannot be demonstrated and it is possible that the translocation may have occurred de novo. The breakpoint on chromosome 8 occurs within the q13 band in both families, suggesting that a gene or genes in this region might contribute to the TS phenotype. Existing linkage and cytogenetic data, suggesting involvement of chromosome 8 in TS families and individuals, further support this hypothesis. We have identified two YAC clones mapping distal and proximal to the chromosome 8 translocation site, as determined by fluorescent in situ hybridization (FISH). PCR amplification of genetic markers in this region, using isolated chromosomes from one of the patients, followed by BAC screening with the closest flanking genetic markers, has identified a 200-kb BAC, which, by FISH, we have demonstrated encompasses the chromosome 8 breakpoint in both families. The fact that the chromosomal breaks in the TS cases from both families occur within such a small region of chromosome 8 further supports the hypothesis that disruption of a gene or genes in this part of chromosome 8 contributes to the clinical phenotype.

Evaluation of the genes for the adrenergic receptors alpha 2A and alpha 1C and Gilles de la Tourette Syndrome

Gilles de la Tourette Syndrome (GTS) has long been known to be familial, and evidence from twin studies indicates that it has a substantial genetic component. Our genome scan of sibling pair families with GTS found evidence suggestive of linkage to several chromosomal locations. On the basis of these findings, we have begun to study additional markers in these regions, with some of the markers located in candidate genes. Two candidate genes stand out in these regions: the adrenergic receptor alpha 1C(1A) (ADRA1C) located on chromosome 8p and the adrenergic receptor alpha 2A (ADRA2A) located on chromosome 10q. The adrenergic system has been suggested to play a role in GTS based on the reduction of symptoms with the adrenergic receptor agonists, clonidine and guanfacine. We examined the inheritance of polymorphisms in the ADRA2A and ADRA1C genes in 113 nuclear families identified through a GTS proband. We found no significant evidence for linkage using the transmission disequilibrium test for these two genes. Based on our families, we conclude that these genes are not major genetic factors contributing to the susceptibility to GTS.

Is Tourette's syndrome an autoimmune disease?

We provide a review of recent research findings which support the involvement of autoimmunity in childhood-onset tic disorders, in particular the presence of antineuronal autoantibodies, D8/17 B lymphocyte overexpression, a marker of chorea associated with streptococcal infection, and possible beneficial effects of immunomodulatory intervention. One of the most controversial areas in this field is the validity of the proposed PANDAS concept. Some researchers have delineated a putatively unique subgroup of patients, from the spectrum of illness encompassing Tourette's syndrome and obsessive-compulsive disorder (OCD), whose tics and obsessive-compulsive symptoms are shown to arise in response to beta-hemolytic streptococcal infections. They designated it by the term pediatric autoimmune neuropsychiatric disorders associated with streptococcal infections (PANDAS). Herein we additionally present pros and cons concerning the concept of PANDAS. Finally, recommendations for future research directions are given.

Genome-wide linkage analysis of families with obsessive-compulsive disorder ascertained through pediatric probands

The goal of this study was to identify chromosomal regions likely to contain susceptibility alleles for early-onset obsessive-compulsive disorder (OCD). A genome scan was done in 56 individuals from seven families ascertained through pediatric OCD probands; 27 of the 56 subjects had a lifetime diagnosis of definite OCD. Denser mapping of regions on chromosomes 2, 9, and 16 was subsequently done with those subjects and ten additional subjects from the largest family in the study. Direct interviews were completed with 65 of the 66 genotyped individuals. Relatives were interviewed blind to proband status. Of the 65 interviewed individuals, 32 had a lifetime diagnosis of definite OCD. Three of the seven probands had a history of Tourette disorder. Two of the 25 relatives with OCD had a tic history, whereas none of the 33 relatives without OCD had tics. The genome scan consisted of 349 microsatellite markers with an average between-marker distance of 11.3 centiMorgan (cM). Fine mapping was done with 24 additional markers at an average spacing of 1.6 cM. Parametric and nonparametric linkage analyses were conducted using GENEHUNTER(+). The maximum multipoint LOD score with a dominant model was 2.25 on 9p. However, with fine mapping and additional subjects, that LOD score decreased to 1.97. The maximum multipoint nonparametric LOD* score was 1.73 on 19q. The maximum multipoint LOD score with a recessive model was 1.40 on 6p. The results provide suggestive evidence for linkage on 9p and identify regions requiring further study with much larger samples.

The familial phenotype of obsessive-compulsive disorder in relation to tic disorders: the Hopkins OCD family study

BACKGROUND

Obsessive-compulsive disorder (OCD) and tic disorders have phenomenological and familial-genetic overlaps. An OCD family study sample that excludes Tourette's syndrome in probands is used to examine whether tic disorders are part of the familial phenotype of OCD.

METHODS

Eighty case and 73 control probands and their first-degree relatives were examined by experienced clinicians using the Schedule for Affective Disorders and Schizophrenia-Lifetime Anxiety version. DSM-IV psychiatric diagnoses were ascertained by a best-estimate consensus procedure. The prevalence and severity of tic disorders, age-at-onset of OCD symptoms, and transmission of OCD and tic disorders by characteristics and type of proband (OCD + tic disorder, OCD - tic disorder) were examined in relatives.

RESULTS

Case probands and case relatives had a greater lifetime prevalence of tic disorders compared to control subjects. Tic disorders spanning a wide severity range were seen in case relatives; only mild severity was seen in control relatives. Younger age-at-onset of OCD symptoms and possibly male gender in case probands were associated with increased tic disorders in relatives. Although relatives of OCD + tic disorder and OCD - tic disorder probands had similar prevalences of tic disorders, this result is not conclusive.

CONCLUSIONS

Tic disorders constitute an alternate expression of the familial OCD phenotype.

Tourette syndrome: clinical characteristics and current management strategies

Tourette Syndrome (TS) is a disorder comprised of involuntary motor and phonic tics often associated with psychiatric conditions. The etiology for TS is unclear, with both genetic and immunological theories being studied to date. When pharmacotherapy is considered by the patient and physician to be required, owing to either functional impairment from tics or comorbid psychiatric illness, dopamine receptor antagonists are commonly used. Our first-line agents for tic suppression include clonidine, guanfacine, clonazepam and baclofen. Should these agents be ineffective, we would recommend pimozide, fluphenazine, risperidone or haloperidol. The potential benefit of other agents, such as olanzapine, ziprasidone, pergolide and botulinum toxin, is encouraging. Despite many years of concern, we have found little exacerbation of tics with stimulant medications for attention deficit hyperactivity disorder, but clearly clonidine and guanfacine can ameliorate both comorbid conditions. Obsessive compulsive disorder, when associated with TS, may be treated with either a selective serotonin reuptake inhibitor in association with a dopamine receptor antagonist or risperidone alone. New therapies for all aspects of TS and its comorbid conditions are in active clinical trials.

Imprinted genes and mental dysfunction

There is a rapidly accumulating body of evidence from family, adoption and twin studies suggestive of a genetic component to many common mental disorders. In some cases, the transmission of abnormalities has been shown to be dependent upon the sex of the parent from whom they are inherited. Such 'parent-of-origin effects' may be explained by a number of genetic mechanisms, one of which is 'genomic imprinting'. In imprinted genes one allele is silenced according to its parental origin. This in turn means that imprinted traits are passed down the maternal or paternal line, in contrast to the more frequent Mendelian mode of inheritance that is indifferent to the parental origin of the allele. In the present review, we survey the evidence for the influence of imprinted genes on a number of mental disorders, ranging from explicit imprinted conditions, where in some cases abnormalities have been mapped to particular gene candidates, to examples where the evidence for parent-of-origin effects is less strong. We also consider, briefly, the wider implications of imprinted effects on mental dysfunction, in particular with respect to evolutionary pressures on mammalian brain development and function.

A family study of Tourette syndrome in Japan

Although the mode of inheritance remains in doubt, twin and family studies conducted mostly in the United States and western Europe suggest that genetic factors play an important role in the transmission and expression of Tourette syndrome (TS). In an effort to evaluate population-based genetic differences, we generated risk estimates for first-degree relatives of TS probands in Japan using methods similar to those utilized in recent Western studies. The subjects were 52 TS probands seen at an outpatient clinic of Tokyo University Hospital and their 165 first-degree relatives. All probands and one or more first-degree relatives in each family were interviewed concerning the presence of tic and obsessive-compulsive symptoms by expert clinicians. The age-corrected rates of TS, chronic motor tics, obsessive-compulsive disorder, and subclinical obsessive-compulsive symptoms in the first-degree relatives were 2.0%, 12.0%, 1.6%, and 7.0%, respectively. Rates of TS and related disorders in Japan appear to be much lower than those in recent Western family studies. If replicated, these data suggest that there may be differences in the nature and frequency of vulnerable alleles for TS and related disorders in the Japanese compared to European populations.

Neuropsychiatric genetics: misclassification in linkage studies of phenotype-genotype research

Research on neuropsychiatric disorders has produced a number of very important findings in the last few decades. However, several problems continue to hinder research in this area. One problem area has been the appropriate classification of disease status for probands and extended family members in linkage studies. In this article, we examine rates of misclassification in a 12-year follow-up study of children previously diagnosed with Tourette syndrome. At the 12-year follow-up, we found a 5 to 12% rate of misclassification of previously diagnosed cases. We present a model of a linkage study with three classification steps. The model demonstrates that an error rate of 5% would result in misclassification of 20% of true cases by step three. Adding additional steps to improve diagnostic accuracy may increase rather than decrease classification error.