New autism loci discovered

Two large-scale genetic analyses have turned up a trio of new sites associated with autism, including a large-effect allele that seems to reduce the risk of developing the debilitating brain disorder, researchers reported today (Nov. 12) at the__ linkurl:American Society of Human Genetics__ meeting;http://www.ashg.org/2008meeting/ in Philadelphia. Last year, the Autism Genome Project Consortium performed the largest genome-wide linkage scan to date with around 10,000 SNPs in 1,181 families with at least two affected individuals. The group flagged a handful of genomic regions harboring linkurl:autism;http://www.the-scientist.com/2008/6/1/26/1/ susceptibility genes, although none of the linkage results were statistically significant linkurl:(__Nat Genet__, 39:319-328, 2007).;http://www.nature.com/ng/journal/v39/n3/abs/ng1985.html Now, a team led by linkurl:Dan Arking,;http://www.hopkinsmedicine.org/geneticmedicine/People/Faculty/Arking.html a geneticist at Johns Hopkins University, has ramped up the SNP count to include around 500,000 markers in 802 affected pairs of siblings. They then eliminated all the error-prone or uninformative SNPs to amass a collection of 180,000 high-quality markers for their analysis. "It's the cleanest best set of markers you can imagine," Arking said at a press conference. This enhanced genome-wide scan proved effective. Arking's team discovered two regions of significant linkage that had not been implicated before with the disease -- one at the tip of chromosome 20's short arm, and one at the end of chromosome 6's long arm. Arking, together with linkurl:Lauren Weiss,;http://psych.ucsf.edu/faculty.aspx?id=2774 a molecular geneticist at the University of California, San Francisco, also used the SNP dataset to perform familial association mapping in 1,594 parent-offspring trios to hunt for common variants of major effect linked to the disorder. At first, they did not find any genome-wide significant results. Additional assays, however, revealed a hitherto unidentified site on chromosome 5 where one particular allele was transmitted less often than expected to autistic individuals whose parents carried the allele. Thus, this allele, although only found in 4% of the population as a whole, likely confers some protection against autism, Arking and Weiss argued. This "protective allele" fell near the linkurl:semaphorin;http://www.the-scientist.com/article/display/21491/ 5A (__SEMA5A__) gene, which is involved in axonal guidance during neural development. The researchers compared brain slices of 20 autistic individuals with 10 controls and found that __SEMA5A__ had much lower expression levels in the autistic brains, further implicating this novel locus with autism. Arking and Weiss will present their findings in a linkurl:talk;http://www.ashg.org/2008meeting/abstracts/fulltext/f22475.htm on Saturday (Nov. 15) and in a linkurl:poster;http://www.ashg.org/cgi-bin/2008/ashg08s?author=weiss%20l&sort=ptimes&sbutton=Detail&absno=22118&sid=338373 on Friday (Nov. 14).

New autism loci discovered

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