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RECHERCHES ET AVANCEES SCIENTIFIQUES
Autisme : nouvelle percée
Une anomalie dans la réponse cérébrale à la perception de la voix humaine dans l’autisme
Des marqueurs sanguins pour l’autisme
Autisme : nouvelle percée
http://radio-canada.ca/nouvelles/Santeeducation/nouvelles/200404/01/001-autisme.shtml
Mise à jour le jeudi 1 avril 2004, 12 h 05 . .
Une équipe américaine a identifié deux variantes du même gène qui multiplieraient au moins par deux les risques de développer l'autisme, cet état caractérisé par un détachement de la réalité et un repli sur soi.
Les chercheurs de l'école de médecine Mount Sinaï de New York estiment que les variantes sont assez fréquentes mais ne peuvent pas à elles seules déclencher la maladie. Ils pensent que plusieurs gènes doivent être actifs simultanément pour que l'autisme se développe. En mars 2003 (voir hyperliens), des chercheurs français et suédois de l'Institut Pasteur et de l'hôpital de l'université de Göteborg ont annoncé l'identification de gènes associés à l'autisme.
La présente étude apporte d'autres preuves qu'un gène peut avoir une influence sur le déclenchement d'un autisme. Des études supplémentaires sont toutefois indispensables pour confirmer ce lien.
La piste génétique se concrétise
Plusieurs observations tendent à démontrer qu'une prédisposition génétique serait à l'origine de l'autisme. Par exemple, le risque de développer la maladie dans les familles d'autistes est 45 fois plus élevé que dans la population générale.
Également, les études menées chez des jumeaux monozygotes (issu d'un seul oeuf) montrent que lorsqu'un des enfants est atteint d'autisme, le deuxième a une probabilité de 60% d'être également autiste, alors que ce risque est quasiment nul chez les jumeaux dizygotes (deux ovules).
Les résultats complets sont publiés selon une étude publiée dans l'American Journal of Psychiatry.
Scientists say they have identified a gene which may increase the risk of developing autism.
The gene is involved in the production of ATP, a molecule that provides the energy cells need to function.
Researchers in the United States said the risk only applied to people with a certain genetic make-up.
Writing in the American Journal of Psychiatry, they said as many as 10 different genes might be involved in the development of autism.
Autism affects about one in every 1,000 people. It is a developmental disability that affects the way a person communicates and interacts with other people.
People with autism can have problems relating to other people and to the world at large. They can have problems understanding people's feelings or making friends.
Having one of these variants appears to approximately double an individuals risk for the disorder
Dr Joseph Buxbaum
There is growing evidence that the condition may be inherited. Studies suggest parents with one child with autism are 100 times more likely to have another child with the condition compared with other families.
However, scientists agree that the condition is complex and that more than one gene is involved.
Gene tests
Dr Joseph Buxbaum and colleagues at Mount Sinai School of Medicine in New York carried out genetic tests on 411 families, who have members with autism.
They found that they all had variations in the SLC25A12 gene, which is involved in the production of ATP.
The researchers suggested this flaw could disrupt the production of the fuel needed by cells. They said even minor disruptions could affect the ability of cells to function properly.
However, the researchers said the genetic variations they identified in this study appeared to be quite common.
By themselves, they do not cause autism. They said people with autism probably had this and other genetic mutations.
"Having one of these variants appears to approximately double an individuals risk for the disorder, but it is an accumulation of genetic factors that cause the disease," Dr Buxbaum said. "Our current challenge is to identify more of these genes."
He added: "Identifying all or most of the genes involved will lead to new diagnostic tools and new approaches to treatment."
The National Autistic Society in the UK welcomed the study.
"Scientists over the world are engaged in looking for the genetic roots of autism," a spokeswoman said.
"Some are looking at other chromosomes as loci for possible genes. The NAS welcomes any research which furthers our understanding of the cause and possible treatment of autism."
Linkage and Association of the Mitochondrial Aspartate/Glutamate Carrier SLC25A12 Gene
With Autism
Am J Psychiatry 161:662-669, April 2004
© 2004 American Psychiatric Association
Nicolas Ramoz, Ph.D., Jennifer G. Reichert, B.Sc., Christopher J. Smith, Ph.D., Jeremy M. Silverman, Ph.D., Irina N. Bespalova, Ph.D., Kenneth L. Davis, M.D., and Joseph D. Buxbaum, Ph.D.
OBJECTIVE: Autism/autistic disorder (MIM number 209850) is a complex, largely genetic psychiatric disorder. The authors recently mapped a susceptibility locus for autism to chromosome region 2q24-q33 (MIM number 606053). In the present study, genes across the 2q24-q33 interval were analyzed to identify an autism susceptibility gene in this region.
METHOD: Mutation screening of positional candidate genes was performed in two stages. The first stage involved identifying, in unrelated subjects showing linkage to 2q24-q33, genetic variants in exons and flanking sequence within candidate genes and comparing the frequency of the variants between autistic and unrelated nonautistic subjects. Two single nucleotide polymorphisms (SNPs) that showed evidence for divergent distribution between autistic and nonautistic subjects were identified, both within SLC25A12, a gene encoding the mitochondrial aspartate/glutamate carrier (AGC1). In the second stage, the two SNPs in SLC25A12 were further genotyped in 411 autistic families, and linkage and association tests were carried out in the 197 informative families.
RESULTS: Linkage and association were observed between autistic disorder and the two SNPs, rs2056202 and rs2292813, found in SLC25A12. Using either a single affected subject per family or all affected subjects, evidence for excess transmission was found by the Transmission Disequilibrium Test for rs2056202, rs2292813, and a two-locus G*G haplotype. Similar results were observed using TRANSMIT for the analyses. Evidence for linkage was supported by linkage analysis with the two SNPs, with a maximal multipoint nonparametric linkage score of 1.57 and a maximal multipoint heterogeneity lod score of 2.11. Genotype relative risk could be estimated to be between 2.4 and 4.8 for persons homozygous at these loci.
CONCLUSIONS: A strong association of autism with SNPs within the SLC25A12 gene was demonstrated. Further studies are needed to confirm this association and to decipher any potential etiological role of AGC1 in autism.
Peter Zwack,Ph.D.
Professeur titulaire
Département des Sciences de la Terre et de l'atmosphère
Université du Québec à Montréal
B.P. 8888, Succ. "Centre-ville"
Canada Montréal, (Québec) H3C 3P8 Canada
Messagerie: Salle PK-6125
201, ouest Président Kennedy
Montréal, (Québec) H2X 3Y7 Canada
Fax 1-514-987-7749
E-Mail zwack.peter@uqam.ca
Page Web Page http://people.sca.uqam.ca/~peter/peter_home.html
RETOUR
Une anomalie dans la réponse cérébrale à la perception de la voix humaine dans l’autisme
la voix humaine est riche en informations verbales mais aussi non-verbales : elle constitue un véritable "visage auditif" que nous savons interpréter. Nos capacités à percevoir ces informations vocales jouent un rôle crucial dans nos interactions sociales. De plus, une équipe de chercheurs a mis en évidence, par l’imagerie cérébrale fonctionnelle, que la perception vocale implique des régions corticales spécifiques appelées "aires de la voix", situées chez la plupart des individus le long du sillon temporal supérieur.
