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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.〔Black, KJ. (Tourette Syndrome and Other Tic Disorders. ) ''eMedicine'' (March 22, 2006). Retrieved on June 27, 2006.〕 The exact cause of Tourette's is unknown, but it is well established that both genetic and environmental factors are involved.〔Walkup JT, Mink JW, Hollenback PJ, (eds). ''Advances in Neurology, Vol. 99, Tourette Syndrome.'' Lippincott Williams & Wilkins, Philadelphia, PA, 2006, p. xv. ISBN 0-7817-9970-8〕 Genetic studies have proved that the overwhelming majority of cases of Tourette's are inherited, although the exact mode of inheritance is not yet known,〔Robertson MM. Tourette syndrome, associated conditions and the complexities of treatment. ''Brain''. 2000;123 Pt 3:425–62. p. 425. PMID 10686169〕 and no gene has been identified.〔 Tics are believed to result from dysfunction in the thalamus, basal ganglia, and frontal cortex of the brain,〔 involving abnormal activity of the brain chemical, or neurotransmitter, dopamine. Non-genetic factors—while not causing Tourette's—can influence the severity of the disorder. Some forms of Tourette's may be genetically linked to obsessive-compulsive disorder (OCD), while the relationship between Tourette's and attention-deficit hyperactivity disorder (ADHD) is not yet fully understood. == Genetic factors== Genetic studies, including twin studies,〔Pauls DL. The genetics of Tourette syndrome. ''Curr Psychiatry Rep.'' 2001 Apr;3(2):152-7. PMID 11276411〕 have proven that the overwhelming majority of cases of Tourette syndrome are inherited, although the exact mode of inheritance is not yet known.〔Robertson MM. Tourette syndrome, associated conditions and the complexities of treatment. ''Brain''. 2000;123 Pt 3:425–462. p. 425. PMID 10686169〕 Tic disorders have long been thought to be inherited as an autosomal dominant gene, but recent research challenges the autosomal dominant hypothesis, and suggests an additive model involving multiple genes.〔Zinner SH. Tourette disorder. ''Pediatr Rev''. 2000;21(11):372. PMID 11077021〕〔Bagheri MM, Kerbeshian J, Burd L. Recognition and management of Tourette's syndrome and tic disorders. ''Am Fam Physician''. 1999; 59:2263–2274. PMID 10221310(Full text. )〕 According to Roger Freeman, MD, "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 itself can't be inherited. It's a tic disorder that is inherited."〔Freeman, RD. (Tourette's Syndrome: minimizing confusion ). Retrieved on February 8, 2006.〕 In some cases, tics may not be inherited; these cases are identified as "sporadic" Tourette syndrome (also known as tourettism) because a genetic link is missing.〔Mejia NI, Jankovic J. Secondary tics and tourettism. ''Rev Bras Psiquiatr''. 2005;27(1):11-7. PMID 15867978 (Full-text PDF )〕 A person with Tourette syndrome 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.〔 Tourette syndrome 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. The gene(s) may express as Tourette syndrome, as a milder tic disorder (transient or chronic tics), or as obsessive compulsive symptoms with no tics at all.〔van de Wetering BJ, Heutink P. The genetics of the Gilles de la Tourette syndrome: a review. ''J Lab Clin Med.'' 1993 May;121(5):638–45. PMID 8478592〕 Only a minority of the children who inherit the gene(s) will have symptoms severe enough to require medical attention.〔 Tourette Syndrome Association. (Tourette Syndrome: Frequently Asked Questions. ) Retrieved on February 8, 2005.〕 There is currently no way to predict the symptoms a child may display, even if the gene(s) are inherited. 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.〔 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.〔Schmidt, William (October 19, 2005). (Genetic mutation is linked to Tourette's. ) ''Yale Daily News.'' 〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Causes and origins of Tourette syndrome」の詳細全文を読む スポンサード リンク
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