Abstract
Tourette’s Syndrome (TS) is a complex disorder characterized by repetitive, sudden, and involuntary movements or vocalizations, called tics. Tics usually appear in childhood, and their severity varies over time. In addition to frequent tics, people with TS are at risk for associated problems including attention deficit hyperactivity disorder (ADHD), obsessive-compulsive disorder (OCD), anxiety, depression, and problems with sleep. TS occurs in most populations and ethnic groups worldwide, and it is more common in males than in females. Previous family and twin studies have shown that the majority of cases of TS are inherited. TS was previously thought to have an autosomal dominant pattern of inheritance. However, several decades of research have shown that this is unlikely the case. Instead TS most likely results from a variety of genetic and environmental factors, not changes in a single gene. In the past decade, there has been a rapid development of innovative genetic technologies and methodologies, as well as significant progresses in genetic studies of psychiatric disorders. In this review, we will briefly summarize previous genetic epidemiological studies of TS and related disorders. We will also review previous genetic studies based on genome-wide linkage analyses and candidate gene association studies to comment on problems of previous methodological and strategic issues. Our main purpose for this review will be to summarize the new genetic discoveries of TS based on novel genetic methods and strategies, such as genome-wide association studies (GWASs), whole exome sequencing (WES) and whole genome sequencing (WGS). We will also compare the new genetic discoveries of TS with other major psychiatric disorders in order to understand the current status of TS genetics and its relationship with other psychiatric disorders.
Highlights
The results suggested that genetic correlations accounted 0.56 of heritability, with concordance rate of 0.38 for MZ pairs and 0.11 for DZ pairs for tic disorder
Candidate genes studies have shown that multiple genes (DRD2, DRD4, 5-HT2C, SERT) in multiple neural systems, including dopaminergic, serotonergic, histaminergic pathways, might be associated with pathogenesis of Tourette’s Syndrome (TS), but results are not yet convincing enough
Several new candidate genes, e.g., SLITRK1, Inner mitochondrial membrane protein 2L (IMMP2L), Contactin associated protein-like 2 gene (CNTNAP2), NLGN4, have been identified through linkage studies and structural genomic aberrations, in which very rare genetic variants with large effects were found in TS patients and families
Summary
Tourette’s Syndrome (TS) is a complex neuropsychiatric and developmental disorder characterized by repetitive, sudden, involuntary movements and vocalizations, called tics. Tic symptoms increase during times of stress, anxiety, fatigue and decrease with focused concentration, such as processing fine motor movements [5]. Poor fine-motor skills and smaller caudate volume in childhood were found to be associated with increased adulthood tic severity [10,11]. These may represent different subtypes of TS, and need to be taken into consideration when planning genetic studies to identify the underlying causes
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