Cognitive function and decision-making in Tourette syndrome
Morand-Beaulieu et al., (Brain Sci. 2017) provide updated (the previous review was published in 2009 by Eddy et al.) and exhaustive review of neuropsychological aspects of TS. The review highlighted the slight alteration of social cognition as well as more frequent learning difficulties and disabilities in children with TS. Recent data seem also confirm the deficit in executive function in TS as indexed by poor performance in continuous performance test and Stroop tests. Interestingly, using longitudinal evaluation of executive function in children with TS, Yaniv et al. (Psychiatry Research 2017) showed that tic reduction was related to the development of the executive functions components associated with response inhibition and that patients with remitted TS performed at normal or even higher levels. In contrast, the attentional and memory capacity seems to be impacted by co-morbid conditions more than TS per se. Sample size or the healthy control group may explain different results obtained by \citet{Abramovitch2017}.
In a recent meta-anlaysis, Morand-Beaulieu et al. returned to the puzzling question of inhibitory control in TS \citep{Morand-Beaulieu2017}. The authors showed larger inhibitory deficits in TS + ADHD patients. However, this deficit was still present in pure TS. This deficit in TS was most prominent in verbal responses, was associated with tics severity as assessed with YGTSS total tics score and was larger in studies that included medicated TS patients.
Salvador et al. (Scientific Reports 2017) studies the decisional capacities in TS and specifically ability to learn from the outcomes of alternative courses of action (known as a counterfactual learning). The results showed normal performance in the task in unmedicated TS whereas alteration was found in TS patients treated with the dopamine D2-like partial agonist aripiprazole, suggesting this medication may impair certain aspects of human reinforcement learning.
Brandt et al. (Scientific Reports, 2017) reported on enhanced multi-component behaviour in TS, which was also reflected in a smaller P3 event related potential measured by EEG and potentially related to chronic tic control in these patients.
The Committee on Research of the American Neuropsychiatric Association published a systematic review on the neurobiology of the premonitory urge in TS \citep{28121259}. Conceição and colleagues proposed a computational model that attempts to link urge and tic phenomenology with functional anatomical evidence implicating somatosensory cortex and insula \citep{29017141}.
Other
An underexplored comorbidity of TD are autism spectrum disorders (ASD). There are few epidemiological studies on the subject but the prevalence of ASD in children with tic disorers is estimated at 20% \citep{17075357}. In a large study including patients with TD (n=535) and their family members (n=234), \citet{28647013a} used the Social Responsiveness Scale Second Edition (SRS) to characterize ASD symptoms, and compared them to historial ASD samples. SRS scores in participants with TD were similar to those observed in other clinical samples but lower than in ASD samples. This is mostly but not entirely explained by elevations in the RRB (restricted interests and repetitive behaviors) subscale, which may be indicating tics rather than other stereotypic movements. The presence of OCD was associated with higher scores on the social cognition and RRB subscales. Complex tics and OCD symptoms (repetitive behaviors) can also be hard to discriminate from core ASD symptoms, especially those related to social communication.
In a sample of 811 TS subjects recruited for a genetics study, hair pulling (3.8%) and skin picking (13.0%) disorders by DSM-5 were surprisingly common \citep{29098466}.
\citet{28071825} review screening instruments and rating scales for tic disorders; see also \citep{28436544,28436554}.
Data from 122 adults with TS: "change in symptoms, and treatment response were not associated with neuropsychological performance on tests of inhibitory control, intellectual ability, or motor function, regardless of type of treatment. The finding that significant change in symptom severity of TS/CTD patients is not associated with impairment or change in inhibitory control regardless of treatment type suggests that inhibitory control [as measured by these tests] may not be a clinically relevant facet of these disorders in adults" \citep{27864156}. Sample size or the healthy control group may explain different results from \citet{28039814}.
Etiology
A national database study of parental psychopathology \citep{28335873}.
Genetics
Large mixed genetic sample yielded two heritable collections of symptoms that cross diagnostic boundaries, here named symmetry (including some other O-C symptoms) and disinhibition (including complex verbal tics) \citep{27809572}.
Whole exome sequencing from over 500 trios
\citep{Willsey2017}. Whole exome sequencing in a 3-generation family with TS,
PNKD gene, iPSCs and neuronal cells
\citep{28894297}. News release
here.
Epigenetics
Environmental risk factors