Fetuses found to be vulnerable in 24th to 28th week

      Margaret Munro

      National Post
      Pregnant women who suffer a major stressful event -- such as the death of a loved one, loss of a job or a long-distance move -- seem to have a greater chance of having a child with autism, researchers say.
      Fetuses 24 to 28 weeks old appear to be particularly vulnerable to the ill effects of maternal stress, which may deform their developing brains, according to a study led by David Beversdorf, a neuroscientist at Ohio State University Medical Center.
      He and his colleagues charted the stress experienced by 500 women during their pregnancies. They found the 188 mothers in the group who had children with autism experienced much more major stress during the 24th through 28th weeks of their pregnancy than those with normal children.
      Stress levels during pregnancy for the mothers of children with autism were nearly twice those of other mothers in the study. Dr. Beversdorf says the results indicate there is much more than genes at work in the baffling disorder.
      "Researchers have been examining the genetic component of the disease for years, but there is now evidence through this study that autism is also linked to external factors, such as prenatal stress," says Dr. Beversdorf, who issued a statement on the findings this week after reporting the results at the annual meeting of the Society for Neuroscience in San Diego.
      Autism is a neurological disorder that usually appears before a child's third birthday.
      Autism is being diagnosed in increasing numbers among children in the industrialized world. About one in 1,000 children has autism, using the term's most narrow definition, but as many as one in 200 suffers from autism-related conditions. The children typically have trouble interacting and communicating with others, suffer language delays and demonstrate repetitive patterns of behaviour.
      Parents and researchers have been searching for explanations for decades. Environmental toxins and childhood vaccinations have been implicated. And scientists have linked more than a dozen different genes -- many of them involved in brain development -- to autism.
      Several findings "are difficult to reconcile with a purely genetic cause of autism, such as the consistent finding of an increased incidence of March birthdays among autistic children," Dr. Beversdorf and his colleagues say. They also note that twin studies have shown autism can occur in just one identical twin, making it clear that more than genes is involved.
      The researchers asked almost 500 mothers to recall their stress levels during pregnancy. The study included the 188 mothers of children with autism, 212 women who had normal children and 92 women who had children with Down's syndrome, a neurological disorder caused by chromosomal abnormality. Life-altering events, such as the death of a spouse or losing a job, qualified as "major stressors."
      The researchers found stress levels for the mothers of children with autism were nearly twice those of the other mothers. "A significant difference was detected for the autism group, with a peak at weeks 24 to 28," they report. They say the timing seems to correlate with the periods of development of the fetal cerebellum -- a portion of the brain that is structurally different in autistic children.
      The findings are "certainly provocative" and worthy of more research, says Susan Bryson, a chair of research for autism at Dalhousie University in Halifax.
      Dr. Bryson's research suggests brain damage much earlier in pregnancy -- toward the end of the first month -- can cause autism. But she says there may be many other factors, both genetic and environmental, at work. Complicating things even more, the multiple factors may be interacting.

      reprinted from Nationa Post Online November 25, 2001