Tourette syndrome research highlights from 2020

We present here research from 2020 relevant to Tourette syndrome (TS). The authors briefly summarize a few reports they consider most important or interesting.

Inhibitory Control in Children with Tourette Syndrome Is Impaired in Everyday Life but Intact during a Stop Signal Task

Tourette Syndrome (TS) has previously been associated with deficits in inhibitory control (IC). However, studies on IC in individuals with TS have produced conflicting results. In the present study, we investigated IC, comparing the Stop Signal Reaction Time (SSRT) measure with parent and teacher ratings of daily life IC in 169 children aged 8–12 (60 with TS, 60 typically developing controls, 27 with attention-deficit/hyperactivity disorder (ADHD), and 22 with TS + ADHD). We further investigated associations of IC with TS and ADHD symptom severity. Children with TS showed intact SSRT performance, but impairments in daily life IC, as reported by parents and teachers. For the latter, we observed a staircase distribution of groups, with the healthy controls presenting with the best IC, followed by TS, TS + ADHD, and finally ADHD. Dimensional analyses indicated a strong association between ADHD severity and both measures of IC. Our results indicate that children with TS are not impaired in a laboratory-based measure of IC, although some difficulties were evident from measures of everyday behaviour, which may in part be due to parents and teachers interpreting tics as disinhibited behaviour. Comorbid ADHD or the severity of subthreshold ADHD symptomatology appeared to account for IC deficits.

The Gilles de la Tourette Syndrome-Quality of Life Scale (GTS-QOL): A Validation in Japanese Patients

Background: Though Gilles de la Tourette's syndrome (GTS) has significant impact on the quality of life of its patients, measures of health-related quality of life (HR-QOL) specific to adolescents and adults with GTS were not developed until recently. The present study provides evidence on the validity of the Gilles de la Tourette Syndrome-Quality of Life Scale (GTS-QOL), the first disease-specific HR-QOL instrument for GTS patients, for the first time in an East Asian sample.Methods: One hundred and two Japanese individuals aged 13 and above with GTS were included in our study. Internal consistency was evaluated using Cronbach's alpha. The 4-factor structure of the GTS-QOL was assessed using confirmatory factor analysis, using goodness of fit indices, factor loadings of each questionnaire item, and covariances between factors. Validity was assessed using interscale correlations. Convergent and discriminate construct validity was evaluated using correlations with other scales such as the 28-item General Health Questionnaire, the Yale Global Tic Severity Scale, and the short version of the Padua Inventory.Results: Scaling assumptions were met. Internal consistency reliability was high, with a Cronbach's alpha of 0.96. Confirmatory factor analysis revealed sufficient factor loadings and goodness of fit. All measures of goodness of fit corroborated the fit of the 4-factor model. Standardized covariances between factors in the confirmatory factor analysis were >0.8. There were significant correlations with other well-validated scales, and thus convergent and discriminate construct validity was sufficient.Conclusion: The GTS-QOL is a valid and reliable instrument to measure disease-specific HR-QOL of GTS patients in Japan.

LRRTM4 Terminal Exon Duplicated in Family with Tourette Syndrome, Autism and ADHD

Tourette syndrome (TS) is a neurodevelopmental disorder characterised by motor and vocal tics and strong association with autistic deficits, obsessive–compulsive disorder (OCD) and attention-deficit/hyperactivity disorder (ADHD). The genetic overlap between TS and autism spectrum disorder (ASD) includes those genes that encode the neurexin trans-synaptic connexus (NTSC) inclusive of the presynaptic neurexins (NRXNs) and postsynaptic neuroligins (NLGNs), cerebellin precursors (CBLNs in complex with the glutamate ionotropic receptor deltas (GRIDs)) and the leucine-rich repeat transmembrane proteins (LRRTMs). In this study, we report the first evidence of a TS and ASD association with yet another NTSC gene family member, namely LRRTM4. Duplication of the terminal exon of LRRTM4 was found in two females with TS from the same family (mother and daughter) in association with autistic traits and ASD.

Genome-wide Association Study identifies two novel loci for Gilles de la Tourette Syndrome

Tourette Syndrome (TS) is a childhood-onset neurodevelopmental disorder of complex genetic architecture, characterized by multiple motor tics and at least one vocal tic persisting for more than one year. We performed a genome-wide meta-analysis integrating a novel TS cohort with previously published data, resulting in a sample size of 6,133 TS individuals and 13,565 ancestry-matched controls. We identified a genome-wide significant locus on chromosome 5q15 and one array-wide significant locus on chromosome 2q24.2. Integration of eQTL, Hi-C and GWAS data implicated the NR2F1 gene and associated lncRNAs within the 5q15 locus, and the RBMS1 gene within the 2q24.2 locus. Polygenic risk scoring using previous GWAS results demonstrated statistically significant ability to predict TS status in the novel cohort. Heritability partitioning identified statistically significant enrichment in brain tissue histone marks, while polygenic risk scoring on brain volume data identified statistically significant associations with right and left putamen volumes. Our work presents novel insights in the neurobiology of TS opening up new directions for future studies.

An oligogenic risk model for Gilles de la Tourette syndrome based on whole-genome sequencing data

Gilles de la Tourette syndrome (GTS) is a neurodevelopmental disorder from the spectrum of tic disorders (TDs). GTS and other TDs have a substantial genetic component with the heritability estimated at between 60 and 80%. Here we propose an oligogenic risk model of GTS and other TDs using whole-genome sequencing (WGS) data from a group of Polish GTS patients and their families (n=185). The model is based on the overrepresentation of putatively pathogenic coding and non-coding genetic variants in genes selected from a set of 86 genes previously suggested to be associated with GTS. Based on the variant overrepresentation (SKAT test results) between unrelated GTS patients and controls based on gnomAD database allele frequencies five genes (HDC, CHADL, MAOA, NAA11, and PCDH10) were selected for the risk model. Putatively pathogenic variants (n = 98) with the median allele frequency of ~0.04 in and near these genes were used to build an additive classifier which was then validated on the GTS patients and their families. This risk model successfully assigned individuals from 22 families to either healthy or GTS groups (AUC-ROC = 0.6, p < 0.00001). These results were additionally validated using the GTS GWAS data from the Psychiatric Genomic Consortium. To investigate the GTS genetics further we identified 32 genes from the list of 86 genes as candidate genes in 14 multiplex families, including NEGR1 and NRXN with variants overrepresented in multiple families. WGS data allowed the construction of an oligogenic risk model of GTS based on possibly pathogenic variants likely contributing to the risk of GTS and TDs. The model includes putatively deleterious rare and non-coding variants in and near GTS candidate genes that may cooperatively contribute to GTS etiology and provides a novel approach to the analysis of clinical WGS data.