Tourette's "Genetic Breakthrough" - The SLITRK1 Gene

"Genetic Breakthrough Yields Clue to Tourette Syndrome"

Putting the new findings about the SLITRK1 Tourette's Gene Into Perspective

There was a big splash in the media about a "genetic breakthrough" with respect to Tourette's syndrome. Some of the media reports went so far as to leave the impression that *the gene* for Tourette's had been found, and that, consequently, a "cure" might be forthcoming.

In order to put this Tourette's gene finding into perspective, it may be instructive to look at some of the more serious, official press releases and articles about the SLITRK1 genetic finding.

"Pursuing genetic analysis of one boy with TS with a known chromosomal abnormality, the group was able to pinpoint a gene (SLITRK1) on Chromosome 13 that is associated with some forms of TS." (1)

"A bad break that apparently gave a young boy Tourette syndrome ... a boy who had an inversion in chromosome 13: A portion of his chromosome had an orientation opposite that of normal chromosomes. The boy was the only member of his family with Tourette syndrome and the only one with the inversion." (2)

" ... the researchers focused on identifying an individual with both TS and a chromosomal abnormality." (4)

"They compared the gene to a wider TS population of 174 people. The team found an abnormal DNA sequence in one family and the identical, very rare change in the DNA sequence in two unrelated people." (3)

"Searching for the same gene in the genome of 174 other individuals with TS revealed three individuals with the same mutation. " (4)

"Taken together, these converging results suggest that this gene is associated with some forms of TS in some families." (1)

"The researchers stressed that the discovery only explains one in 100 people who have Tourette's Syndrome." (8)

" ... the gene is responsible for at most a small fraction of Tourette cases. Other researchers warn that the findings, although interesting, remain tentative. 'Each piece of the evidence is intriguing but not on its own conclusive,' says UCLA geneticistNelson Freimer. 'To what degree can the pieces be combined to make a persuasive case? Opinions will differ on that.' " (2)

"Scientists remain uncertain of the ultimate impact of the research. 'In terms of how characteristic it is of the Tourette's population as a whole, the jury is still out,' King said." (4)

Summarizing this information from "official" sources:

A. The identified boy had a chromosomal abnormality.

B. No one else in his family had Tourette's syndrome.

C. Of 174 people studied, the chromosomal mutation was found in a total of 3 people (1 percent to 2 percent).

D. Tourette's syndrome researchers and experts ackowledge that the findings pertain to some individuals, some families, and a small fraction of Tourette's syndrome cases (about 1 in a hundred).

E. Opinions among Tourette's experts and researchers vary as to the relevance and significance of this finding.

A more confusing aspect of the way this finding has been presented has to do with what is known as "tourettism," which refers to secondary causes of tics, that may mimic Tourette's syndrome. We find indications throughout the medical literature that chromosomal mutations are a known cause of tourettism, which mimics Tourette's, but may be different from primary, inherited, genetic Tourette syndrome.

Here is some information about tourettism:

"Motor and phonic tics are most frequently due to Tourette syndrome, but there are many other causes of tics ... Genetic and chromosomal disorders, such as Down's syndrome, neuroacanthocytosis, and Huntington's disease were associated with tics ... To understand the physiopathology of tics and Tourette syndrome, it is important to recognize that these may be caused or associated with other disorders." (7)

"Pathologic tics (secondary [tourettism]) * Infections - Encephalitis, Creutzfeldt-Jakob disease * Sydenham chorea * Drugs - Stimulants, levodopa, carbamazepine, phenytoin, phenobarbital, antipsychotics (tardive tics) * Toxins - Carbon monoxide * Developmental - Static encephalopathy, mental retardation syndromes, chromosomal abnormalities * Other - Head trauma, stroke, neurocutaneous syndromes, chromosomal abnormalities, schizophrenia, neuroacanthocytosis degenerative disorders." (5)

"Several conditions, termed tourettism, may mimic Tourette's syndrome. Drugs, including stimulants, levodopa (Dopar, Larodopa), and antiepileptic medications (eg, phenytoin [Dilantin], carbamazepine [Atretol, Epitol, Tegretol], lamotrigine [Lamictal]), may cause tourettism. ... Neuroleptic medications with potent dopamine2 (D2) antagonist activity (eg, haloperidol [Haldol]) may cause tardive tourettism, which presents with delayed and often permanent tics identical to Tourette's syndrome. Other causes of tourettism include infections (eg, Creutzfeld-Jakob disease, encephalitis), toxins (eg, carbon monoxide), Huntington's disease, head trauma, stroke, neuroacanthocytosis, chromosomal abnormalities, cerebral palsy, neurocutaneous syndromes, and schizophrenia. " (6)

This information may help put this Tourette's genetic finding into perspective. It is likely that the boy's chromosomal mutation is unrelated to the Tourette's gene(s) that most people with tics have inherited, particularly since no one else in his family has Tourette's, and the SLITRK1 gene was not found in 98% of the study sample of people with tics. Whether or not this finding is related to tourettism and will ultimately be helpful in identifying the gene(s) associated with Tourette's syndrome remains to be discovered.

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SOURCES
(1) TSA: Genetic Breakthrough Yields Clue to Tourette Syndrome
(2) TSA: Teenager’s Odd Chromosome Points To Possible Tourette Syndrome Gene
(3) Researchers at Yale Identify a Genetic Link to Tourette's Syndrome
(4) Yale Daily News: Genetic mutation is linked to Tourette's
(5) e-medicine article on Tourette Syndrome
(6) PostGraduate Medicine: Is It a Tic or Tourette's?
(7) Secondary tics and tourettism
(8) Science Daily

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