Causes and origins of Tourette syndrome have not been fully elucidated. Tourette syndrome (also called "Tourette's syndrome", "Tourette's disorder", "Gilles de la Tourette syndrome", "GTS" or "TS") is an inherited neurological disorder with onset in childhood, characterized by the presence of multiple motor tics and at least one phonic tic, which characteristically wax and wane. Tourette's syndrome occurs along a spectrum of tic disorders, which includes transient tics and chronic tics. Contemporary prevalence estimates of the condition range from 1 to 3 per 1,000^[1] to 10 per 1,000.^[2] Tourette syndrome (also called Tourettes syndrome, Tourettes disorder, Gilles de la Tourette syndrome, GTS or TS) is an inherited neurological disorder with onset in childhood, characterized by the presence of multiple motor tics and at least one phonic tic, which characteristically wax and wane. ... To inherit something is to get it from ones ancestors. ... Neurology is a branch of medicine dealing with disorders of the central and peripheral nervous systems. ... A tic is a repeated, impulsive action, almost reflexive in nature, which the actor feels powerless to control or avoid. ... A tic is a repeated, impulsive action, almost reflexive in nature, which the actor feels powerless to control or avoid. ...

Genetic factors

Genetic studies have proven that the overwhelming majority of cases of Tourette's syndrome are inherited, although the exact mode of inheritance is not yet known.^[3] Tic disorders have long been thought to be inherited as an autosomal dominant gene. Recent research challenges the autosomal dominant hypothesis, and suggests an additive model involving multiple genes.^[4][5] According to Roger Freeman, M.D., "Genes that cause tics have not yet been identified; it's very unlikely there's just one. Tics are very familial, but not in a Mendelian pattern (dominant, recessive, etc.). You can't 'inherit' the committee decision to define a problem in a specific way, so TS can't itself be inherited. It's a tic disorder that is inherited." ^[6] An autosome is a non-sex chromosome. ... In genetics, the term dominant gene refers to the allele that causes a phenotype that is seen in a heterozygous genotype. ...

The inherited vulnerability to tic disorders may produce varying symptoms in different family members: Tourette's is a condition of incomplete penetrance, meaning not everyone who inherits the genetic vulnerability will show symptoms; Tourette's also shows variable expression — even family members with the same genetic makeup may show different levels of symptom severity. Inheriting the gene or genes does not necessarily mean that symptoms will be displayed. The gene(s) may express as TS, as a milder tic disorder (transient or chronic tics), or as obsessive compulsive symptoms with no tics at all. Only a minority of the children who inherit the gene(s) will have symptoms severe enough to ever require medical attention.^[7] Penetrance is a term used in genetics that describes the extent to which the properties controlled by a gene, its phenotype, will be expressed. ... Expressivity refers to variations of a phenotype in genetics. ... Genetics (from the Greek genno γεννώ= give birth) is the science of genes, heredity, and the variation of organisms. ...

A person with TS has about a 50% chance of passing the gene(s) to one of his/her children. Gender appears to have a role in the expression of the genetic vulnerability, with males more likely to express tics than females.^[4] There is currently no way to predict the symptoms a child may display, even if the gene(s) are inherited. The word gender describes the state of being male, female, or neither. ...

Recent research suggests that a small number of Tourette syndrome cases may be caused by a defect on chromosome 13 of gene SLITRK1. Some cases of tourettism (tics due to reasons other than inherited Tourette's syndrome) can be caused by mutation.^[8] The finding of a chromosomal abnormality appears to apply to a very small minority of cases (1 - 2%). Studies to locate all of the genes implicated in Tourette's syndrome are ongoing.^[9] Chromosome 13 is one of the 23 pairs of chromosomes in humans. ... SLITRK1 (SLIT and NTRK-like family, member 1) is a human gene on chromosome 13q31. ... In biology, mutations are changes to the genetic material (usually DNA or RNA). ...

Factors of vulnerability

While it is known that Tourette's is genetic, the exact mechanism affecting the inherited vulnerability has not been established. Research presents considerable evidence that abnormal activity of the brain chemical, or neurotransmitter, dopamine, is involved. Other neurotransmitters may also be involved.^[7] Neuroanatomic models implicate failures in circuits connecting the brain's cortex and subcortex.^[4] Neurotransmitters are chemicals that are used to relay, amplify and modulate electrical signals between a neuron and another cell. ... Dopamine is a chemical naturally produced in the body. ... Neuroanatomy is the anatomy of the nervous system. ...

Again, in some cases, tics may not be inherited; these cases are identified as "sporadic" TS (also known as tourettism) because a genetic link is missing.^[8]

Non-genetic influences

Studies suggest that non-genetic, environmental, infectious, or psychosocial factors — while not causing Tourette's — can impact upon the expression of the severity of the disorder.^[4] As one example of non-genetic factors, twin studies have shown that the lower birth weight twin is the one more likely to display more symptoms.^[10] Other perinatal events, such as maternal stress^[11] and obstetric complications,^[12] may also impact upon the severity of the expression of the inherited genetic vulnerability. Autoimmune processes may affect tic onset and exacerbation in some cases: the unproven and contentious hypothesis that pediatric autoimmune neuropsychiatric disorders associated with streptococcal infections, P.A.N.D.A.S., plays a role in the onset of tic disorders and OCD is a current focus of research. An environment is a complex of external factors that acts on a system and determines its course and form of existence. ... Infection is also the title of an episode of the television series Babylon 5; see Infection (Babylon 5). ... Psychosocial pertains to ones psychological development in the context of ones social environment. ... Twin study - Wikipedia /**/ @import /skins-1. ... Perinatal defines the period occurring around the time of birth (5 months before and 1 month after). ... This article needs cleanup. ... Autoimmune diseases arise from an overactive immune response of the body against substances and tissues normally present in the body. ... P.A.N.D.A.S. is an abbreviation for Pediatric Autoimmune Neuropsychiatric Disorders Associated with Streptococcal infections, a term used to describe a subset of children who have Obsessive Compulsive Disorder (OCD) and/or tic disorders such as Tourette Syndrome, and in whom symptoms typically worsen following strep infections...

Relation with OCD and ADHD

Some forms of obsessive-compulsive disorder (OCD) may be genetically linked to Tourette's.^[13] Genetic studies show an increased rate of tics and obsessive-compulsive behaviors or OCD in relatives of patients with Tourette's, and "reinforce the idea that at least some forms of OCD are etiologically related to TS, and may, therefore, be a variant expression of the same etiologic factors that are important for the expression of tics." ^[14] Further evidence supporting that OCD and Tourette's are alternative expressions of a common genetic vulnerability is that males inheriting the genetic vulnerability are more likely to display tics, while females are more likely to display obsessive-compulsive traits.^[5] Etiology (alternately aetiology, aitiology) is the study of causation. ...

The genetic relationship of attention-deficit hyperactivity disorder (ADHD) to Tourette's syndrome is less clear, with some evidence to suggest no genetic linkage, and some evidence to suggest that some forms of Tourette's syndrome may be genetically related to ADHD.^[15] Not all persons with Tourette's syndrome will have ADHD or OCD, although in clinical populations, a high percentage of patients presenting for care do have ADHD. ^[5] The high co-occurrence of ADHD observed in tertiary, referred populations may be an artifact of clinical ascertainment bias. Further study is needed to elucidate the genetic relationship between ADHD and Tourette's.^[15] To meet Wikipedias quality standards, this article or section may require cleanup. ... Ascertainment bias describes the incorrect results of a study due to the way in which the data were collected. ...

See also

• Tic
• Tic disorder
• Tourette syndrome

A tic is a repeated, impulsive action, almost reflexive in nature, which the actor feels powerless to control or avoid. ... A tic is a repeated, impulsive action, almost reflexive in nature, which the actor feels powerless to control or avoid. ... Tourette syndrome (also called Tourettes syndrome, Tourettes disorder, Gilles de la Tourette syndrome, GTS or TS) is an inherited neurological disorder with onset in childhood, characterized by the presence of multiple motor tics and at least one phonic tic, which characteristically wax and wane. ...

Notes

1. ^ Scahill L, Tanner C, Dure L. The epidemiology of tics and Tourette syndrome in children and adolescents. Adv Neurol. 2001;85:261-71. PMID 11530433
2. ^ Kadesjo B, Gillberg C. Tourette's disorder: epidemiology and comorbidity in primary school children. J Am Acad Child Adolesc Psychiatry. 2000 May;39(5):548-55. PMID 10802971
3. ^ Robertson MM. Tourette syndrome, associated conditions and the complexities of treatment. Brain. 2000;123 Pt 3:425-462. PMID 10686169
4. ^ ^a b c d Zinner SH. Tourette disorder. Pediatr Rev. 2000;21(11):372-383. PMID 11077021
5. ^ ^a b c Bagheri MM, Kerbeshian J, Burd L. Recognition and management of Tourette's syndrome and tic disorders. Am Fam Physician. 1999; 59:2263-2274.
6. ^ Freeman, RD. Tourette's Syndrome: minimizing confusion. Accessed 8 February 2006.
7. ^ ^a b Tourette Syndrome Association. Tourette Syndrome: Frequently Asked Questions Accessed 8 Feb 2006.
8. ^ ^a b Mejia NI, Jankovic J. Secondary tics and tourettism. Rev Bras Psiquiatr. 2005;27(1):11-7. PMID 15867978
9. ^ Schmidt, William (19 Oct 2005). Genetic mutation is linked to Tourette's. Yale Daily News.
10. ^ Hyde TM, Aaronson BA, Randolph C, et al. Relationship of birth weight to the phenotypic expression of Gilles de la Tourette's syndrome in monozygotic twins. Neurology. 1992 Mar;42 (3 Pt 1):652-8. PMID 1549232
11. ^ Leckman JF, Dolnansky ES, Hardin MT, et al. Perinatal factors in the expression of Tourette's syndrome: an exploratory study. J Am Acad Child Adolesc Psychiatry. 1990 Mar;29(2):220-6. PMID 1969861
12. ^ Santangelo SL, Pauls DL, Goldstein JM, et al. Tourette's syndrome: what are the influences of gender and comorbid obsessive-compulsive disorder? J Am Acad Child Adolesc Psychiatry. 1994 Jul-Aug;33(6):795-804. PMID 8083136
13. ^ Pauls DL, Towbin KE, Leckman JF, et al. Gilles de la Tourette's syndrome and obsessive-compulsive disorder. Evidence supporting a genetic relationship. Arch Gen Psychiatry. 1986 Dec;43(12):1180-2. PMID 3465280
14. ^ Cohen, DJ, Jankovic J, Goetz CG, (eds). Advances in Neurology, Vol. 85, Tourette Syndrome. Lippincott, Williams & Wilkins, Philadelphia, PA, 2001.
15. ^ ^a b Leckman JF, Cohen DJ. Tourette's Syndrome—Tics, Obsessions, Compulsions: Developmental Psychopathology and Clinical Care. John Wiley & Sons, Inc., New York, 1999.