Cross-disorder genome-wide analyses suggest a complex genetic relationship between Tourette's syndrome and OCD

OBJECTIVE

Obsessive-compulsive disorder (OCD) and Tourette's syndrome are highly heritable neurodevelopmental disorders that are thought to share genetic risk factors. However, the identification of definitive susceptibility genes for these etiologically complex disorders remains elusive. The authors report a combined genome-wide association study (GWAS) of Tourette's syndrome and OCD.

METHOD

The authors conducted a GWAS in 2,723 cases (1,310 with OCD, 834 with Tourette's syndrome, 579 with OCD plus Tourette's syndrome/chronic tics), 5,667 ancestry-matched controls, and 290 OCD parent-child trios. GWAS summary statistics were examined for enrichment of functional variants associated with gene expression levels in brain regions. Polygenic score analyses were conducted to investigate the genetic architecture within and across the two disorders.

RESULTS

Although no individual single-nucleotide polymorphisms (SNPs) achieved genome-wide significance, the GWAS signals were enriched for SNPs strongly associated with variations in brain gene expression levels (expression quantitative loci, or eQTLs), suggesting the presence of true functional variants that contribute to risk of these disorders. Polygenic score analyses identified a significant polygenic component for OCD (p=2×10(-4)), predicting 3.2% of the phenotypic variance in an independent data set. In contrast, Tourette's syndrome had a smaller, nonsignificant polygenic component, predicting only 0.6% of the phenotypic variance (p=0.06). No significant polygenic signal was detected across the two disorders, although the sample is likely underpowered to detect a modest shared signal. Furthermore, the OCD polygenic signal was significantly attenuated when cases with both OCD and co-occurring Tourette's syndrome/chronic tics were included in the analysis (p=0.01).

CONCLUSIONS

Previous work has shown that Tourette's syndrome and OCD have some degree of shared genetic variation. However, the data from this study suggest that there are also distinct components to the genetic architectures of these two disorders. Furthermore, OCD with co-occurring Tourette's syndrome/chronic tics may have different underlying genetic susceptibility compared with OCD alone.

Copy number variation in obsessive-compulsive disorder and tourette syndrome: a cross-disorder study

OBJECTIVE

Obsessive-compulsive disorder (OCD) and Tourette syndrome (TS) are heritable neurodevelopmental disorders with a partially shared genetic etiology. This study represents the first genome-wide investigation of large (>500 kb), rare (<1%) copy number variants (CNVs) in OCD and the largest genome-wide CNV analysis in TS to date.

METHOD

The primary analyses used a cross-disorder design for 2,699 case patients (1,613 ascertained for OCD, 1,086 ascertained for TS) and 1,789 controls. Parental data facilitated a de novo analysis in 348 OCD trios.

RESULTS

Although no global CNV burden was detected in the cross-disorder analysis or in secondary, disease-specific analyses, there was a 3.3-fold increased burden of large deletions previously associated with other neurodevelopmental disorders (p = .09). Half of these neurodevelopmental deletions were located in a single locus, 16p13.11 (5 case patient deletions: 0 control deletions, p = .08 in the current study, p = .025 compared to published controls). Three 16p13.11 deletions were confirmed de novo, providing further support for the etiological significance of this region. The overall OCD de novo rate was 1.4%, which is intermediate between published rates in controls (0.7%) and in individuals with autism or schizophrenia (2-4%).

CONCLUSION

Several converging lines of evidence implicate 16p13.11 deletions in OCD, with weaker evidence for a role in TS. The trend toward increased overall neurodevelopmental CNV burden in TS and OCD suggests that deletions previously associated with other neurodevelopmental disorders may also contribute to these phenotypes.

Partitioning the heritability of Tourette syndrome and obsessive compulsive disorder reveals differences in genetic architecture

The direct estimation of heritability from genome-wide common variant data as implemented in the program Genome-wide Complex Trait Analysis (GCTA) has provided a means to quantify heritability attributable to all interrogated variants. We have quantified the variance in liability to disease explained by all SNPs for two phenotypically-related neurobehavioral disorders, obsessive-compulsive disorder (OCD) and Tourette Syndrome (TS), using GCTA. Our analysis yielded a heritability point estimate of 0.58 (se = 0.09, p = 5.64e-12) for TS, and 0.37 (se = 0.07, p = 1.5e-07) for OCD. In addition, we conducted multiple genomic partitioning analyses to identify genomic elements that concentrate this heritability. We examined genomic architectures of TS and OCD by chromosome, MAF bin, and functional annotations. In addition, we assessed heritability for early onset and adult onset OCD. Among other notable results, we found that SNPs with a minor allele frequency of less than 5% accounted for 21% of the TS heritability and 0% of the OCD heritability. Additionally, we identified a significant contribution to TS and OCD heritability by variants significantly associated with gene expression in two regions of the brain (parietal cortex and cerebellum) for which we had available expression quantitative trait loci (eQTLs). Finally we analyzed the genetic correlation between TS and OCD, revealing a genetic correlation of 0.41 (se = 0.15, p = 0.002). These results are very close to previous heritability estimates for TS and OCD based on twin and family studies, suggesting that very little, if any, heritability is truly missing (i.e., unassayed) from TS and OCD GWAS studies of common variation. The results also indicate that there is some genetic overlap between these two phenotypically-related neuropsychiatric disorders, but suggest that the two disorders have distinct genetic architectures.

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.

Overrepresentation of rare variants in a specific ethnic group may confuse interpretation of association analyses

Rare sequence variants may be important in understanding the biology of common diseases, but clearly establishing their association with disease is often difficult. Association studies of such variants are becoming increasingly common as large-scale sequence analysis of candidate genes has become feasible. A recent report suggested SLITRK1 (Slit and Trk-like 1) as a candidate gene for Tourette Syndrome (TS). The statistical evidence for this suggestion came from association analyses of a rare 3'-UTR variant, var321, which was observed in two patients but not observed in more than 2000 controls. We genotyped 307 Costa Rican and 515 Ashkenazi individuals (TS probands and their parents) and observed var321 in five independent Ashkenazi parents, two of whom did not transmit this variant to their affected child. Furthermore, we identified var321 in one subject from an Ashkenazi control sample. Our findings do not support the previously reported association and suggest that var321 is overrepresented among Ashkenazi Jews compared with other populations of European origin. The results further suggest that overrepresentation of rare variants in a specific ethnic group may complicate the interpretation of association analyses of such variants, highlighting the particular importance of precisely matching case and control populations for association analyses of rare variants.

Association between maternal smoking and increased symptom severity in Tourette's syndrome

OBJECTIVE

Substantial evidence suggests that both environmental and genetic factors contribute to the development and clinical expression of Tourette's syndrome. Although genetic studies of Tourette's syndrome are common, studies of environmental factors are relatively few and have not identified consistent risk factors across studies. This study examines in a large cohort of subjects (N=180) the relationship between prenatal/perinatal adverse events with Tourette's syndrome severity as determined by tic severity and rates of commonly comorbid disorders such as obsessive-compulsive disorder (OCD), attention deficit hyperactivity disorder (ADHD), and self-injurious behavior.

METHOD

Tic severity, OCD, ADHD, self-injurious behavior, and exposure to a variety of prenatal/perinatal events were systematically assessed in all subjects enrolled in three genetic studies of Tourette's syndrome. Using linear and logistic regression, a best-fit model was determined for each outcome of interest.

RESULTS

Prenatal maternal smoking was strongly correlated with increased tic severity and with the presence of comorbid OCD in these Tourette's syndrome subjects. Other variables, such as paternal age and subject's birth weight, were significantly but less strongly associated with increased symptom severity. The authors found no association between symptom severity and hypoxia, forceps delivery, or hyperemesis during pregnancy, which have been previously identified as risk factors.

CONCLUSIONS

This study identifies prenatal maternal smoking as a strong risk factor for increased symptom severity in Tourette's syndrome.

Self injurious behaviour in Tourette syndrome: correlates with impulsivity and impulse control

BACKGROUND

Self injurious behaviour (SIB), the deliberate, repetitive infliction of self harm, is present in a wide variety of neuropsychiatric disorders, including Tourette syndrome (TS). Although SIB occurs in up to 60% of individuals with TS, and can cause significant clinical impairment and distress, little is known about its aetiology.

OBJECTIVE

This study examined the relationship between SIB and other behavioural features that commonly co-occur with TS in nearly 300 subjects with TS participating in three genetic studies. SIB, obsessions, compulsions, tic severity, attention deficit hyperactivity disorder related impulsivity, risk taking behaviours, and rages were systematically assessed in all subjects.

METHODS

Using logistic regression, a best fit model was determined for both mild to moderate SIB and severe SIB.

RESULTS

Mild/moderate SIB in TS was correlated with the presence of obsessive and compulsive symptoms such as the presence of aggressive obsessions or violent or aggressive compulsions, and with the presence of obsessive-compulsive disorder and overall number of obsessions. Severe SIB in TS was correlated with variables related to affect or impulse dysregulation; in particular, with the presence of episodic rages and risk taking behaviours. Both mild/moderate and severe SIB were also correlated with tic severity.

CONCLUSIONS

This study suggests that mild/moderate and severe SIB in TS may represent different phenomena, which has implications for clinical management of these symptoms.

An open-label study of the treatment efficacy of olanzapine for Tourette's disorder

BACKGROUND

An open-label trial was performed to explore efficacy and safety of olanzapine, an atypical neuroleptic with diverse receptor activity including both dopamine-2 and serotonin-2A and -2C antagonism, for treatment of Tourette's disorder.

METHOD

Ten adult patients aged 20 to 44 years with Tourette's disorder were treated using an open-label, flexible dosing schedule for 8 weeks. Three patients who continued olanzapine were reevaluated after 6 months. Three subjects were psychotropic medication naive, 5 patients experienced intolerable side effects with conventional neuroleptics, and 2 patients had remote (> or = 10 years) successful response to conventional neuroleptics. Tic severity was rated by the Yale Global Tic Severity Scale; weight, vital signs, and adverse effects were assessed weekly. Electrocardiogram, laboratory studies, and comorbid symptoms, assessed by the Yale-Brown Obsessive Compulsive Scale and ADHD Behavior Checklist for Adults, were measured at baseline and at week 8.

RESULTS

Two of 10 patients prematurely discontinued olanzapine owing to excessive sedation. Of 8 patients who completed the 8-week trial, 4 (50%) demonstrated reduction of global tic severity scores by > or = 20 points, and 6 (75%) demonstrated reductions by > or = 10 points. No significant changes in comorbid symptoms were demonstrated. Sedation, weight gain, increased appetite, dry mouth, and transient asymptomatic hypoglycemia were the most common side effects. Tic improvements were maintained in 3 patients reassessed 6 months later. Final olanzapine dosages ranged from 2.5 mg to 20 mg daily (mean = 10.9 mg/day).

CONCLUSION

This open-label study suggests that olanzapine should be explored as a potential alternative to conventional neuroleptic medications for treatment of motor tics and Tourette's disorder.

Explosive outbursts in children with Tourette's disorder

OBJECTIVE

Sudden, explosive outbursts of behavior occur in some children with Tourette's disorder (TD). The etiology of these symptoms is unknown. This study investigated the relationship between explosive outbursts, TD, and its comorbid disorders.

METHOD

Tic type and severity and the presence of specific comorbid disorders were compared in 37 children with TD and explosive outbursts and 31 children with TD who did not have such symptoms.

RESULTS

Children with TD and explosive outbursts were more likely to demonstrate significant comorbid conditions, particularly attention-deficit/hyperactivity disorder, obsessive-compulsive disorder, and oppositional defiant disorder. Tic type and severity did not appear related to the presence of explosive outbursts. A highly significant relationship was demonstrated between the number of comorbid psychiatric diagnoses and explosive outbursts.

CONCLUSIONS

Explosive outbursts in children with TD resemble intermittent explosive disorder and may reflect dysregulation of diverse domains of brain function. The presence of such symptoms should alert the clinician to underlying comorbid conditions.

Paroxetine treatment of episodic rages associated with Tourette's disorder

BACKGROUND

Episodic rages have been estimated to occur in as many as 30% of patients with Tourette's syndrome (Tourette's disorder), but their treatment has never been systematically investigated. We report on the results of an open-label pilot study using paroxetine for the treatment of Tourette's disorder-associated rage episodes.

METHOD

Forty-five Tourette's/rage patients (DSM-IV) were treated with paroxetine, specifically to control their rages. Other symptoms such as tics, attention-deficit/hyperactivity disorder (ADHD) and obsessive-compulsive disorder (OCD) were not targeted by this study. Treatment was deemed to be therapeutic when rage symptoms were diminished by 75% or more by patient report and were diminished in frequency by at least 1 point on a 4-point scale devised by the authors.

RESULTS

After 8 weeks on paroxetine treatment, 29 patients (76% of those who completed the study) reported that rages were significantly diminished or completely absent. Nine patients reported no significant change in rages. Seven patients did not complete the study (3 because of side effects and 4 whose rage frequency increased). The mean dose of paroxetine was 33 mg/day; minimum effective dose was 15 mg/day.

CONCLUSION

We were unable to determine any factors that significantly altered the efficacy of paroxetine for treatment of Tourette's disorder-associated rage episodes. The great majority (87%) of the patients had both ADHD and OCD in addition to Tourette's disorder. The age, sex, and concomitant use of other medications revealed no significant differences in treatment outcome. The results suggest that paroxetine may have an important role in the clinical treatment of episodic rages in Tourette's disorder patients.

Rage attacks in children and adolescents with Tourette's disorder: a pilot study

BACKGROUND

Sudden, explosive episodes of rage occur in a significant number of clinically referred children with Tourette's disorder and cause considerable psychosocial morbidity. The etiology of these symptoms is unknown. We conducted a pilot study of 12 consecutive children with Tourette's disorder and rage attacks to determine whether comorbidity of Tourette's-associated disorders is related to these symptoms.

METHOD

Twelve consecutive children with Tourette's disorder who presented with rage attacks were evaluated, including 2 females and 10 males. Tourette's disorder diagnosis, presence of comorbid disorders, and tic severity were assessed using DSM-IV diagnostic criteria and standardized rating scales.

RESULTS

All 12 children met diagnostic criteria for Tourette's disorder, obsessive-compulsive disorder (OCD), and attention-deficit/hyperactivity disorder (ADHD). Two children were also diagnosed with comorbid oppositional defiant disorder, and 4 children were diagnosed with comorbid conduct disorder. None of the subjects met diagnostic criteria for a mood disorder. All subjects had only mild tic severity.

CONCLUSION

The clinical phenomenon of rage attacks in children with Tourette's disorder resembles intermittent explosive disorder and may reflect specific underlying neurologic disturbances. This pilot study suggests that rage attacks in Tourette's disorder may be related to the presence of comorbid disorders.

The course and prognosis of Tourette syndrome

The view of Tourette syndrome as a lifelong disorder, once held as a certainty, has changed considerably in the past two decades. It is now known that in the majority of cases, tics will ebb in severity and will no longer be problematic in the adult years. This discovery, however, has been accompanied by the realization that Tourette syndrome is a far more complex disorder than was originally discerned and that it has many unanswered questions.

Risperidone as a treatment for Tourette's syndrome

BACKGROUND

An open-label trial was performed to assess the efficacy and safety of risperidone, a benzisoxazole derivative with potent D2 and 5-HT2 antagonism, for treatment of Tourette's syndrome.

METHOD

Thirty-eight patients with Tourette's syndrome volunteered to take risperidone for treatment of their tics. All patients had failed to respond adequately to conventional treatments (with neuroleptics such as haloperidol and/or with the alpha 2-adrenergic agonist clonidine) or had suffered from intolerable side effects from such treatments. Patients were rated for tic severity by the Yale Global Tic Severity Scale (YGTSS) before treatment and after 1 month of treatment with risperidone. Patients were monitored carefully for side effects and clinical response.

RESULTS

Of the 38 patients, 8 discontinued risperidone treatment before the end of the trial because of intolerable side effects. At the end of the 4-week trial, 22 patients (58%) were improved, 7 patients (18%) had no appreciable change in their symptoms, and 1 patient (3%) had a documented worsening of tics. Doses of risperidone at the end of the trial ranged from 0.5 mg to 9 mg/day (mean = 2.7 mg/day).

CONCLUSION

This open clinical trial suggests that risperidone may be a promising alternative to conventional medications used for treating the symptoms of Tourette's syndrome.

Subtle and underrecognized side effects of neuroleptic treatment in children with Tourette's disorder

A variety of side effects developed in children treated with neuroleptics for Tourette's disorder. Of 208 children, 34 manifested dose-related symptoms of dysphoria, nine experienced a worsening of symptoms of Tourette's disorder that was attributed to akathisia, five became hostile and aggressive, three developed "fog states" that disappeared with discontinuation of neuroleptics or treatment with primidone, and three experienced symptoms of tardive dyskinesia that resolved with time. This data base of neuroleptic-treated children with Tourette's disorder demonstrates a variety of subtle and underrecognized side effects that may not be as readily discernible in children receiving neuroleptics for a primary psychiatric disorder.

A follow-up of 78 patients with Gilles de la Tourette's syndrome

The authors conducted a follow-up study of 78 patients with Gilles de la Tourette's syndrome. Four of the patients were in spontaneous remission; 59 patients taking haloperidol showed an average improvement of 79.3% and the remaining patients, 3 of whom were taking medication other than haloperidol and 12 of whom were not taking any medication, showed an average improvement of 24.7%. Side effects were the main cause of discontinuing haloperidol. The authors found that response to haloperidol was unrelated to family history of tics, age at onset, type or severity of symptoms, or signs of organicity.