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Study finds pregnancy and birth environment may affect development of autism in twins

Genetics alone cannot account for the high rates of autism among fraternal, or non-identical, twins

Autism Speaks, the world's largest autism science and advocacy organization, joined in announcing significant findings from the largest known study of twins with autism spectrum disorder (ASD). This work, conducted by a consortium of renowned researchers and using material from Autism Speaks Autism Genetic Resource Exchange (AGRE) was published online today in the Archives of General Psychiatry.

The California Autism Twins Study suggests environmental influences, which could include parental age, low birth weight, multiple births, and maternal infections during pregnancy may greatly increase risk for ASD. The study suggested that both genetic and shared environmental factors significantly increase risk for ASD: an estimated 38 percent of risk being associated with genetic heritability and 58 percent with the environment that twins share during pregnancy and perhaps early infancy. The study also found that the relative contributions of shared genes and shared environment are similar for males and females.

"It has been well-established that genetic factors contribute to risk for autism," says Clara Lajonchere, Ph.D., a study co-author and vice president of clinical programs for Autism Speaks. "We now have strong evidence that, on top of genetic heritability, a shared prenatal environment may have a greater than previously realized role in the development of autism."

The study involved 192 pairs of twins, both identical and non-identical, where at least one of the twins in the pair had autism. This approach allowed the researchers to look at how often both children in the twin pair received a diagnosis of autism. Study of identical twins, who share 100 percent of their genes, helps researchers determine the degree to which a disorder is inherited, or genetic; and comparison to fraternal twins, who share around 50 percent of their DNA, allows researchers to understand how environmental influences add to the risk of ASD.

The finding that shared environment is of significant influence in twins has important implications for future research. Because the prenatal environment and early postnatal environment are shared between twins, it is believed that at least some of the environmental factors affecting susceptibility to autism exert their effect during these critical periods of life. Future studies that investigate such twin-shared experiences and their role in enhancing or suppressing genetic susceptibility are likely to advance the understanding of autism.

The study could not pinpoint the specific time period (i.e. early pregnancy, late pregnancy or birth), nor the specific risk factors (i.e. parental age, maternal nutrition, maternal infections during pregnancy, premature and/or underweight birth, etc.) that contribute to the increased risk notes Dr. Lajonchere. "Indeed, multiple-birth pregnancies are themselves associated with increased risk of developmental disorders such as cerebral palsy and autism. This speaks to the importance of further study on what prenatal and perinatal factors increase risk beyond that of inherited genes," she concludes.

AGRE, which Dr. Lajonchere heads, was instrumental in this study. AGRE clinical staff recruited twins to participate and performed the home-based testing of many of the study participants, using scientifically validated research measures for diagnosing autism spectrum disorders. Other institutes involved in the study include: Stanford University, Environmental Health Investigations Branch, California Department of Public Health, Kaiser Permanente Northern California, University of California Davis, MIND Institute, and the Institute for Human Genetics and Department of Epidemiology and Biostatistics, University of California, San Francisco

About Autism

Autism is a complex neurobiological disorder that inhibits a person's ability to communicate and develop social relationships, and is often accompanied by behavioral challenges. Autism spectrum disorders are diagnosed in one in 110 children in the United States, and one in 70 boys. The prevalence of autism has increased 600 percent in the past two decades. The Centers for Disease Control and Prevention have called autism a national public health crisis whose cause and cure remain unknown.

About Autism Speaks

Autism Speaks is North America's largest autism science and advocacy organization. Since its inception in 2005, Autism Speaks has made enormous strides, committing over $160 million to research and developing innovative new resources for families. The organization is 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. In addition to funding research, Autism Speaks has created resources and programs including the Autism Speaks Autism Treatment Network, Autism Speaks' Autism Genetic Resource Exchange and several other scientific and clinical programs. Notable awareness initiatives include the establishment of the annual United Nations-sanctioned World Autism Awareness Day on April 2, which Autism Speaks celebrates through its Light it Up Blue initiative. Also, Autism Speaks award-winning "Learn the Signs" campaign with the Ad Council has received over $272 million in donated media. Autism Speaks' family resources include the Autism Video Glossary, a 100 Day Kit for newly-diagnosed families, a School Community Tool Kit and a community grant program. Autism Speaks has played a critical role in securing federal legislation to advance the government's response to autism, and has successfully advocated for insurance reform to cover behavioral treatments in 26 states thus far, with bills pending in an additional 12 states. Each year Walk Now for Autism Speaks events are held in more than 80 cities across North America. To learn more about Autism Speaks, please visit

About the Co-Founders

Autism Speaks was founded in February 2005 by Suzanne and Bob Wright, the grandparents of a child with autism. Bob Wright is Senior Advisor at Lee Equity Partners and Chairman and CEO of the Palm Beach Civic Association. He served as Vice Chairman of General Electric; and as the Chief Executive Officer of NBC and NBC Universal for more than twenty years. He also serves on the boards of the Polo Ralph Lauren Corporation, Mission Product, LLC, EMI Group Global Ltd. and the New York Presbyterian Hospital. Suzanne Wright is a Trustee Emeritus of Sarah Lawrence College, her alma mater. Suzanne has received numerous awards, the Women of Distinction Award from Palm Beach Atlantic University, the CHILD Magazine Children's Champions Award, Luella Bennack Volunteer Award, Spirit of Achievement award by the Albert Einstein College of Medicine's National Women's Division and The Women of Vision Award from the Weizmann Institute of Science. In 2008, the Wrights were named to the Time 100 Heroes and Pioneers category, a list of the most influential people in the world, for their commitment to global autism advocacy. They have also received numerous awards such as the first ever Double Helix Award for Corporate Leadership, NYU Child Advocacy Award, Castle Connolly National Health Leadership Award and The American Ireland Fund Humanitarian Award. In May of 2010 they received Honorary Doctor of Humane Letters Degrees from St. John's University in Queens and delivered the commencement address as the first married couple to be bestowed such an honor.

Jane E. Rubinstein | EurekAlert!
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