https://www.mdpi.com/2073-4425/12/10/1510

Epigenetics

Investigation of gene–environment interactions in relation to tic severity \citep{34389898}.

Environmental risk factors

The EMTICS study published its results testing the PANDAS hypothesis \citep{33568537}. This study followed 715 children with TS or persistent (chronic) tic disorder (TS/CTD) for an average of 16 months. Tic severity was measured thrice annually, and infection with group A beta-hemolytic streptococcus (GAS) was monitored carefully using pharyngeal swabs and serologic testing. The study identified 405 tic exacerbations in 308 participants, but these exacerbations did not correspond significantly to GAS exposure. The authors conclude that their "study does not support GAS exposures as contributing factors for tic exacerbations in children with CTD. Specific work-up or active management of GAS infections is unlikely to help modifying the course of tics in CTD and is therefore not recommended." These results and conclusion support those of previous studies \citep*{31111754}
Social contagion as a possible cause of tic-like symptoms: 
 

Pathophysiology

Animal models

Benzodiazepines and ethanol are among the well-known positive allosteric modulators (PAMs) of GABA-A receptors. A PAM highly selective for GABA-A receptors containing α6 subunits showed efficacy in the D1CT-7 transgenic mouse model of tics \citep{33525455}. Dopamine antagonists show similar effects but induce catalepsy, whereas this PAM did not. These results suggest strategies for future human studies including for treatment of tic disorders.

Pathological studies

Electrophysiology

\citep{33949779}
A patient was treated for major depressive disorder with bilateral ventral internal capsule and ventral striatum DBS and developed dose-dependent (voltage-dependent) coprolalia and limb movements, along with changes in affect, mood and memory \citep{33568978}. Inpatient observation supported the conclusion that these symptoms were most likely caused by the focal electrical stimulation. Although a single case, this report adds to previous data implicating primarily subcortical nuclei in secondary tic disorders. 
Dual-site TMS and diffusion tensor imaging showed loss of normal prefrontal (pre-SMA) inhibition of motor cortex in 12 children with TS/CTD compared to 14 control participants \citep{33462641}. The decreased inhibition correlated to impairment of tic inhibition. Increased fractional anisotropy was also observed in several white matter pathways in TS/CTD. These results support similar previous findings in adults with TS and support a plausible pathophysiological mechanism relevant to tic persistence.
Two articles here from early 2021

Neuroimaging studies

 

Pharmacological studies

Interesting hypothesis, "Allopregnanolone: The missing link to explain the effects of stress on tic exacerbation?" \citep{34423500}.
Report on valbenazine development \citep{33682568}.

Clinical and neuropsychological studies

"Inhibitory Control in Youth with Tourette's Disorder, Attention-Deficit/Hyperactivity Disorder and their Combination and Predictors of Objective Tic Suppressibility" \citep{34411767}.

Other

 

Treatment

Renewed European clinical guidelines for tic disorders \citep{34244849}.

Psychological interventions

A group therapy study compared CBIT to a control condition with education about tics \citep{33415472}. Group CBIT better reduced tics, especially at 3 months after the intervention. Children with behavioral problems had less improvement, whereas higher intellectual functioning portended better results. This report adds to previous suggestions that group therapy—which can reach more patients at lower cost—is an effective way to deliver CBIT.
Homework compliance predicts CBIT treatment success \citep{33770556}.
Mechanisms Underlying Behavior Therapy for Tourette’s Disorder \citep{Essoe_2021}
(include?) A pilot study of online mindfulness-based group therapy for adults with tic disorders showed that it was feasible, but with lower adherence to prescribed homework than expected, and only 2 of 5 showed any meaningful improvement \citep{33757602}.

Medication

https://www.neurologyadvisor.com/conference-highlights/mds-2021/ecopipam-shows-promise-in-tic-reduction-in-children-with-tourette-syndrome/

Neurosurgery

A collaborative study across several sites revealed several brain regions whose activity, based on fMRI functional connectivity in a healthy population, predicted success of DBS for OCD (10.1016/j.biopsych.2021.04.006). 
Thalamic DBS https://www.mdlinx.com/journal-summary/thalamic-deep-brain-stimulation-for-tourette-syndrome-a-naturalistic-trial-with-brief-randomized/35OXgvYZMOeHEfUvHr1u3s