More pieces in the complex autism inheritance puzzle are emerging in the latest study from a research team including geneticists from The Children's Hospital of Philadelphia, the University of Pennsylvania School of Medicine and several collaborating institutions. This study identified 27 different genetic regions where rare copy number variations – missing or extra copies of DNA segments – were found in the genes of children with autism spectrum disorders (ASDs), but not in the healthy controls. The complex combination of multiple genetic duplications and deletions is thought to interfere with gene function, which can disrupt the production of proteins necessary for normal neurological development.
"We focused on changes in the exons of DNA—protein-coding areas in which deletions or duplications are more likely to directly disrupt biological functions," said study leader Hakon Hakonarson, M.D., Ph.D., director of the Center for Applied Genomics at The Children's Hospital of Philadelphia and associate professor of Pediatrics at the University of Pennsylvania School of Medicine. "We identified additional autism susceptibility genes, many of which, as we previously found, belong to the neuronal cell adhesion molecule family involved in the development of brain circuitry in early childhood." He added that the team discovered many "private" gene mutations, those found only in one or a few individuals or families—an indication of genetic complexity, in which many different gene changes may contribute to an autism spectrum disorder.
"We are finding that both inherited and new, or de novo, genetic mutations are scattered throughout the genome and we suspect that different combinations of these variations contribute to autism susceptibility," said Maja Bucan, Ph.D., professor of Genetics at the University of Pennsylvania School of Medicine and Chair of the Steering committee for Autism Speaks' Autism Genetic Resource Exchange (AGRE). "We are grateful to families of children with autism spectrum disorders for their willingness to participate in genetic studies because family-based studies have many advantages. We have learned a lot both from genetic analyses of children with autism as well as analyses of their patents and their unaffected siblings."
The researchers compared genetic samples of 3,832 individuals from 912 families with multiple children with ASDs from the AGRE cohort against genetic samples of 1,070 disease-free children from The Children's Hospital of Philadelphia. This study also uncovered two novel genes in which variations were found, BZRAP1 and MDGA2 – thought to be important in synaptic function and neurological development, respectively. Interestingly, key variants of these genes were transmitted in some, but not all, of the affected individuals in families.
The findings were published in the June 26 edition of the journal PloS Genetics.
By further refining the genetic landscape of ASDs, the current study expands the findings of two large autism gene studies published in April, led by Hakonarson and co-authored by Gerard Schellenberg, Ph.D., professor of Pathology and Laboratory Medicine at the University of Pennsylvania School of Medicine, Bucan and others. One study was the first to report common gene variants in ASDs. The other identified copy number variants that raise the risk of having an ASD. Both studies found gene changes on two biological pathways with crucial roles in early central nervous system development. Hakonarson and Bucan said the latest findings reinforce the view that multiple gene variants, both common and rare, may be interacting to cause the heterogeneous group of disorders included under autism spectrum disorders.
AGRE, a program of Autism Speaks, provided genetic biomaterials and clinical data from families having more than one member diagnosed with an ASD. Blood samples donated by children and their families at Children's Hospital were used as healthy controls. AGRE makes data publicly available to qualified researchers worldwide.
About The Children's Hospital of Philadelphia
The Children's Hospital of Philadelphia was founded in 1855 as the nation's first pediatric hospital. Through its long-standing commitment to providing exceptional patient care, training new generations of pediatric healthcare professionals and pioneering major research initiatives, Children's Hospital has fostered many discoveries that have benefited children worldwide. Its pediatric research program is among the largest in the country, ranking second in National Institutes of Health funding. In addition, its unique family-centered care and public service programs have brought the 430-bed hospital recognition as a leading advocate for children and adolescents. For more information, visit http://www.chop.edu.
About Autism Speaks
Autism Speaks is the nation's largest autism science and advocacy organization, dedicated to funding research into the causes, prevention, treatments and a cure for autism; increasing awareness of autism spectrum disorders; and advocating for the needs of individuals with autism and their families. Autism Speaks funds more than $30 million each year in new autism research, in addition to supporting the Autism Treatment Network, Autism Genetic Resource Exchange, Autism Clinical Trials Network, Autism Tissue Program and a range of other scientific and medical programs. To learn more about the Autism Genome Resource Exchange (AGRE), please visit http://www.autismspeaks.org/science/programs/agre/index.php. To learn more about Autism Speaks, please visit www.AutismSpeaks.org.