Pubmed du 21/05/09

lundi 25 mai 2009

1. International Society for Autism Research News. Autism Res ;2009 (May 19) ;2(2):123.

2. Allen-Brady K, Robison R, Cannon D, Varvil T, Villalobos M, Pingree C, Leppert MF, Miller J, McMahon WM, Coon H. Genome-wide linkage in Utah autism pedigrees. Mol Psychiatry ;2009 (May 19)

Genetic studies of autism over the past decade suggest a complex landscape of multiple genes. In the face of this heterogeneity, studies that include large extended pedigrees may offer valuable insights, as the relatively few susceptibility genes within single large families may be more easily discerned. This genome-wide screen of 70 families includes 20 large extended pedigrees of 6-9 generations, 6 moderate-sized families of 4-5 generations and 44 smaller families of 2-3 generations. The Center for Inherited Disease Research (CIDR) provided genotyping using the Illumina Linkage Panel 12, a 6K single-nucleotide polymorphism (SNP) platform. Results from 192 subjects with an autism spectrum disorder (ASD) and 461 of their relatives revealed genome-wide significance on chromosome 15q, with three possibly distinct peaks : 15q13.1-q14 (heterogeneity LOD (HLOD)=4.09 at 29 459 872 bp) ; 15q14-q21.1 (HLOD=3.59 at 36 837 208 bp) ; and 15q21.1-q22.2 (HLOD=5.31 at 55 629 733 bp). Two of these peaks replicate earlier findings. There were additional suggestive results on chromosomes 2p25.3-p24.1 (HLOD=1.87), 7q31.31-q32.3 (HLOD=1.97) and 13q12.11-q12.3 (HLOD=1.93). Affected subjects in families supporting the linkage peaks found in this study did not reveal strong evidence for distinct phenotypic subgroups.Molecular Psychiatry advance online publication, 19 May 2009 ; doi:10.1038/mp.2009.42.

3. Farley MA, McMahon WM, Fombonne E, Jenson WR, Miller J, Gardner M, Block H, Pingree CB, Ritvo ER, Ritvo RA, Coon H. Twenty-year outcome for individuals with autism and average or near-average cognitive abilities. Autism Res ;2009 (Mar 18) ;2(2):109-118.

Previous studies found substantial variability in adult outcome for people with autism whose cognitive functioning was within the near-average and average ranges. This study examined adult outcome for 41 such individuals (38 men and 3 women) originally identified through an epidemiological survey of autism in Utah. Mean age at the time of their previous cognitive assessment was 7.2 years (SD=4.1, range=3.1-25.9 years) and at follow-up was 32.5 years (SD=5.7 years, range=22.3-46.4 years). Outcome measures included standardized assessments of diagnostic status, cognitive ability, and adaptive behavior. Additional information collected concerned demographic variables, indicators of independence, social relationships, medical and psychiatric conditions, and social service use. Outcomes for this sample were better than outcomes described in previous work on individuals with similar cognitive functioning. For example, half of the participants were rated as "Very Good" or "Good" on a global outcome measure. As in previous studies, there was considerable variability in measured cognitive ability over time. Over half of the sample had large gains or losses of cognitive ability of greater than 1 standard deviation. Cognitive gain was associated with better outcome, as was better adaptive functioning. While all participants had baseline IQs in the nonimpaired range, there was limited evidence to support the use of other early childhood variables to predict adult outcome.

4. Goin-Kochel RP, Porter AE, Peters SU, Shinawi M, Sahoo T, Beaudet AL. The MTHFR 677C—>T polymorphism and behaviors in children with autism : exploratory genotype-phenotype correlations. Autism Res ;2009 (Mar 30) ;2(2):98-108.

New evidence suggests that autism may be associated with (a) varied behavioral responses to folate therapy and (b) metabolic anomalies, including those in folate metabolism, that contribute to hypomethylation of DNA. We hypothesized that children with autism who are homozygous for the MTHFR 677 T allele (TT) and, to a lesser extent those with the CT variant, would exhibit more behavioral problems and/or more severe problematic behaviors than homozygous wild-type (CC) individuals because of difficulties in effectively converting 5,10-MTHF to 5-MTHF. Data from the Autism Genetic Resource Exchange (AGRE) collection were analyzed for all children who met strict criteria for autism per the Autism Diagnostic Interview-Revised (ADI-R) and the Autism Diagnostic Observation Schedule (ADOS) and who had been genotyped for the 677 C to T MTHFR polymorphism (n=147). Chi-square tests, logistic regression, and one-way ANOVAs were used to determine whether differences existed among MTHFR genotypes for specific behaviors on the ADI-R and indices for level of functioning. Exploratory results indicated four behaviors from the ADI-R that were more common and problematic (95% CI) among those with at least one copy of the T allele as compared to homozygous wild-type individuals : direct gaze, current complex body movements, a history of self-injurious behavior, and current overactivity (ORs=2.72, 2.33, 2.12, 2.47, respectively). No differences existed among genotypes for level of functioning as measured with the Peabody Picture Vocabulary Test-Third Edition, Ravens Colored Progressive Matrices, or the Vineland Adaptive Behavior Scales. Findings call for further investigation of the relationship between folate metabolism and problem behaviors among children with autism.

5. Hu VW, Steinberg ME. Novel clustering of items from the Autism Diagnostic Interview-Revised to define phenotypes within autism spectrum disorders. Autism Res ;2009 (Mar 26) ;2(2):67-77.

Heterogeneity in phenotypic presentation of Autism spectrum disorders has been cited as one explanation for the difficulty in pinpointing specific genes involved in autism. Recent studies have attempted to reduce the "noise" in genetic and other biological data by reducing the phenotypic heterogeneity of the sample population. The current study employs multiple clustering algorithms on 123 item scores from the Autism Diagnostic Interview-Revised (ADI-R) diagnostic instrument of nearly 2,000 autistic individuals to identify subgroups of autistic probands with clinically relevant behavioral phenotypes in order to isolate more homogeneous groups of subjects for gene expression analyses. Our combined cluster analyses suggest optimal division of the autistic probands into four phenotypic clusters based on similarity of symptom severity across the 123 selected item scores. One cluster is characterized by severe language deficits, while another exhibits milder symptoms across the domains. A third group possesses a higher frequency of savant skills while the fourth group exhibited intermediate severity across all domains. Grouping autistic individuals by multivariate cluster analysis of ADI-R scores reveals meaningful phenotypes of subgroups within the autistic spectrum, which we show, in a related (accompanying) study, to be associated with distinct gene expression profiles.

6. Kilpinen H, Ylisaukko-Oja T, Rehnstrom K, Gaal E, Turunen JA, Kempas E, von Wendt L, Varilo T, Peltonen L. Linkage and Linkage Disequilibrium Scan for Autism Loci in an Extended Pedigree from Finland. Hum Mol Genet ;2009 (May 19)

Population isolates, such as Finland, have proved beneficial in mapping rare causative genetic variants due to a limited number of founders resulting in reduced genetic heterogeneity and extensive linkage disequilibrium. We have here used this special opportunity to identify rare alleles in autism by genealogically tracing 20 autism families into one extended pedigree with verified genealogical links reaching back to the 17(th) century. In this unique pedigree we performed a dense microsatellite marker genome-wide scan of linkage and linkage disequilibrium, and followed initial findings with extensive fine-mapping. We identified a putative autism susceptibility locus at 19p13.3, and obtained further evidence for previously identified loci at 1q23 and 15q11-13. Most promising candidate genes were TLE2 and TLE6 genes clustered at 19p13 and ATP1A2 at 1q23.

7. Spence SJ, Schneider MT. The role of epilepsy and epileptiform EEGs in autism spectrum disorders. Pediatr Res ;2009 (Jun) ;65(6):599-606.

Autism is a neurodevelopmental disorder of unknown etiology characterized by social and communication deficits and the presence of restricted interests/repetitive behaviors. Higher rates of epilepsy have long been reported, but prevalence estimates vary from as little as 5% to as much as 46%. This variation is probably the result of sample characteristics that increase epilepsy risk such as sample ascertainment, lower intelligence quotient (IQ), the inclusion of patients with nonidiopathic autism, age, and gender. However, critical review of the literature reveals that the rate in idiopathic cases with normal IQ is still significantly above the population risk suggesting that autism itself is associated with an increased risk of epilepsy. Recently, there has been interest in the occurrence of epileptiform electroencephalograms (EEGs) even in the absence of epilepsy. Rates as high as 60% have been reported and some investigators propose that these abnormalities may play a causal role in the autism phenotype. Although this phenomenon is still not well understood and risk factors have yet to be determined, the treatment implications are increasingly important. We review the recent literature to elucidate possible risk factors for both epilepsy and epileptiform EEGs. We then review existing data and discuss controversies surrounding treatment of EEG abnormalities.

8. Strom SP, Stone JL, Ten Bosch JR, Merriman B, Cantor RM, Geschwind DH, Nelson SF. High-density SNP association study of the 17q21 chromosomal region linked to autism identifies CACNA1G as a novel candidate gene. Mol Psychiatry ;2009 (May 19)

Chromosome 17q11-q21 is a region of the genome likely to harbor susceptibility to autism (MIM(209850)) based on earlier evidence of linkage to the disorder. This linkage is specific to multiplex pedigrees containing only male probands (MO) within the Autism Genetic Resource Exchange (AGRE). Earlier, Stone et al.(1) completed a high-density single nucleotide polymorphism association study of 13.7 Mb within this interval, but common variant association was not sufficient to account for the linkage signal. Here, we extend this single nucleotide polymorphism-based association study to complete the coverage of the two-LOD support interval around the chromosome 17q linkage peak by testing the majority of common alleles in 284 MO trios. Markers within an interval containing the gene, CACNA1G, were found to be associated with Autism Spectrum Disorder at a locally significant level (P=1.9 x 10(-5)). While establishing CACNA1G as a novel candidate gene for autism, these alleles do not contribute a sufficient genetic effect to explain the observed linkage, indicating that there is substantial genetic heterogeneity despite the clear linkage signal. The region thus likely harbors a combination of multiple common and rare alleles contributing to the genetic risk. These data, along with earlier studies of chromosomes 5 and 7q3, suggest few if any major common risk alleles account for Autism Spectrum Disorder risk under major linkage peaks in the AGRE sample. This provides important evidence for strategies to identify Autism Spectrum Disorder genes, suggesting that they should focus on identifying rare variants and common variants of small effect.Molecular Psychiatry advance online publication, 19 May 2009 ; doi:10.1038/mp.2009.41.


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