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Genome scan finds new genetic links to autism

Feb. 18, 2007
Courtesy UCLA
and World Science staff

The first re­sults from a scan of the world’s larg­est col­lec­tion of DNA from fam­i­lies af­fect­ed by au­tism point to two new ge­net­ic links that may pre­dis­pose peo­ple to the brain dis­or­der. The re­search jour­nal Na­ture Ge­net­ics re­ported the find­ings in its Feb. 18 on­line edi­tion. 

The five-year study was led by the Au­tism Ge­nome Proj­ect, an in­ter­na­tion­al con­sor­ti­um of sci­en­tists from 19 coun­tries.

“This large-scale study re­veals that au­tism is an ex­treme­ly di­verse con­di­tion… [with] nu­mer­ous ge­net­ic ori­gins, rath­er than a sin­gle or few ma­jor caus­es,” said Dan­iel Gesch­wind of the Uni­ver­si­ty of Cal­i­for­nia, Los An­ge­les, site of one of the stu­dy’s 13 re­search cen­ters.

Au­tism is a com­plex dis­or­der that strikes as early as 2 or 3 years of age. It dis­rupts a child’s abil­i­ty to com­mu­ni­cate and de­vel­op so­cial re­la­tion­ships. Sci­en­tists sus­pect the dis­ease is high­ly he­red­i­tary. 

The U.S. Cen­ters for Dis­ease Con­trol and Pre­vention re­ports that one in 150 Amer­i­can chil­dren is di­ag­nosed with au­tism or one of its re­lat­ed con­di­tions. Af­fect­ing four times as many boys as girls, au­tism di­ag­noses have mul­ti­plied ten­fold in the last dec­ade, for un­clear rea­sons.

The con­sor­ti­um searched for ge­net­ic com­mon­al­i­ties in au­tis­tic peo­ple from near­ly 1,200 fam­i­lies. The sci­en­tists scanned the DNA for vari­a­tions in gene copy num­ber­s—tiny tracts of ex­tra or de­let­ed genes thought to be pos­si­bly tied to au­tism. 

The large num­ber of fam­i­lies “per­mit­ted us to or­gan­ize au­tis­tic chil­dren with si­m­i­lar fea­tures of this dis­or­der in­to smaller groups, where gene link­ages may be more eas­i­ly de­tect­ed,” said the uni­ver­si­ty’s Rita Can­tor.

The re­sults im­pli­cat­ed a pre­vi­ously un­i­den­ti­fied re­gion of chro­mo­some 11; and neurexin 1, a mem­ber of a gene fam­i­ly be­lieved to play a key role in com­mu­ni­ca­tion be­tween brain cells. 

The neurexin find­ing al­so high­light­ed a group of brain cells called glu­ta­mate neu­rons and the genes af­fect­ing their de­vel­op­ment and func­tion, sug­gest­ing these are crit­i­cal­ly in­volved in au­tism and re­lat­ed dis­or­ders, re­search­ers said. 

Sci­en­tists cau­tioned that more stud­ies with even more sub­jects will be needed to full ex­plain hered­i­ty’s role in au­tism. “We are op­ti­mis­tic” that this ap­proach will lead to im­proved treat­ments, Gesch­wind said.

Fam­i­lies who par­ti­ci­pated had more than one mem­ber di­ag­nosed with one of three ge­net­ically re­lat­ed dis­eases: au­tism, per­va­sive de­vel­op­mental dis­or­der or As­perg­er’s syn­drome. 

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The first results from a scan of the world’s largest collection of DNA from families affected by autism point to two new genetic links that may predispose people to the brain disorder. The research journal Nature Genetics reported the findings in its Feb. 18 online edition. The five-year study was led by the Autism Genome Project, an inter national consortium involving scientists from 50 institutions in 19 countries. “This large-scale study reveals that autism is an extremely diverse condition… [with] numerous genetic origins, rather than a single or few major causes,” said Daniel Geschwind of the University of California, Los Angeles, site of one of the study’s 13 research centers. The consortium searched for genetic commonalities in autistic people from nearly 1,200 families. The scientists scanned the DNA for variations in gene copy numbers—tiny tracts of extra or deleted genes thought to be possibly tied to autism. “The large number of families in this study permitted us to organize autistic children with similar features of this disorder into smaller groups, where gene linkages may be more easily detected,” said the university’s Rita Cantor. The results implicated a previously unidentified region of chromosome 11; and neurexin 1, a member of a gene family believed to play a key role in com munication between brain cells. The neurexin finding also highlighted a group of brain cells called glutamate neurons and the genes affecting their development and function, suggesting that these are critically involved in autism and related disorders, researchers said. Scientists cautioned that more studies with even more subjects will be needed to full explain heredity’s role in autism. “We are optimistic that this approach will lead to improved interventions for autistic children,” Geschwind said. Families who partici pated had more than one member diagnosed with one of three genetically related diseases: autism, pervasive developmental disorder or Asperger’s syndrome. Autism is a complex disorder that strikes in early childhood, often as young as 2 or 3. It disrupts a child’s ability to com municate and develop social relationships. Scientists suspect the disease is highly hereditary. The U.S. Centers for Disease Control and Prevention reports that one in 150 American children is diagnosed with an autism or its related conditions. Affecting four times as many boys as girls, autism diagnoses have multiplied tenfold in the last decade.