As scientists strive to find what's behind a spike in autism, especially in boys, a new study has raised the possibility that antidepressants taken by their mother may be one of the culprits, a finding that has set off fear and concern among women and their doctors.
Rodents exposed to the antidepressant Celexa displayed autism-like changes in both the structure of their brains and the behavior of their pups, especially the males, according to the study published last month in the Proceedings of the National Academies of Sciences. Celexa is a commonly prescribed antidepressant in a class that includes Lexapro, Zoloft and Prozac.
Another study has found that autistic children were twice as likely as other children to have been exposed to antidepressants before birth. First-trimester exposure created nearly four times the risk, according to the report published in July in the journal Archives of General Psychiatry.
But rats are not humans. The authors caution that years of research are ahead before a cause of autism is known. In 1998, a small study in the medical journal Lancet, since retracted, had wrongly suggested a childhood vaccine might be a cause of the syndrome. Millions of dollars were spent disproving that connection. Meanwhile, mistrust of vaccines surged and the true causes of autism have gone undiscovered.
Antidepressants on rise
The number of pregnant and nursing women taking antidepressants has surged in the past decade, from one half of 1 percent in the mid-1990s to about 10 percent today, the authors reported. Doctors have favored treating the depression as studies mount showing infants of severely depressed women fare worse on most measures of learning and development.
And as the numbers of women taking antidepressants has risen, the number of children diagnosed with autism has increased dramatically.
In the early 1990s, scientists estimated 1 in 1,500 children had a disorder that placed them on the autism spectrum. By 2002, the estimate had increased to 1 in 150, and more recent research suggests that 1 in 90 children may have an autism-spectrum disorder.
While genetics likely play a role, many researchers suspect something in the environment. Whether mothers' exposure to the SSRI (selective serotonin reuptake inhibitor) class of drugs is that trigger, whether it's unrelenting stress or something else is a question that requires much more research, scientists said.
Another drug that acts on the brain, sodium valporate, used to treat seizures, has also shown a possible link to autism.
The uncertainty puts doctors such as Natalie Sohn, a West Palm Beach obstetrician-gynecologist, in a quandary.
Sohn remembers watching a fellow doctor take a pregnant patient off antidepressants only to learn the woman later committed suicide.
”Depression needs to be treated. Women with depression can be suicidal; they can be nonfunctional in major depression,” Sohn said. ”The real problem with psychiatric disease in pregnancy is all these medications have never really been studied.”
Sohn said she'd be hesitant to stop prescribing the medications if she believes a woman's depression is severe, a decision in keeping with advice from the National Institutes of Health's director, Dr. Thomas Insel.
The studies show an elevated risk, but they were done on rats. Were the loner rats really autistic or simply lost and confused? Plus, the rat mothers started from normal baseline serotonin levels, a chemical messenger in the brain. People who are severely depressed may have abnormally low serotonin. Selective serotonin reuptake inhibitors keep the brain from clearing out the neurotransmitter, so that larger amounts remain in the space between neurons for longer periods of time.
”These studies will help to balance the mental health needs of pregnant mothers with possible increased risk to their offspring,” Insel said.
Affecting development
The study showed that altering serotonin levels can affect how the fetal brain develops, and in ways that mimic autism, said Dr. Rick Lin, professor of neurobiology and anatomical sciences at University of Mississippi Medical Center.
Lin has spent more than a decade researching both the stress hormone norepinephrine and serotonin. Many things can affect serotonin, not just taking SSRIs, Lin said. Stress is a major factor, he said.
”SSRIs are still the best drugs for depression, and there is no way we can stop treating the mothers right now,” Lin said. ”My opinion? All mothers should try to do their best to reduce stress. Kid around — take a walk, get husbands and grandparents to chip in and help, exercise, talk to another person. Try biofeedback, massage, yoga.”
Lin and colleagues Kimberly Simpson and Ian Paul conducted the study with researchers at the University of California, San Francisco.
For the study, Lin said rat pups born to normal parents were exposed to either saline injections or the SSRI drug for two weeks after birth, in an amount comparable to human doses. Since rats are born less developed than human babies, the timing of their exposure correlated to the last trimester of pregnancy and first three months of postnatal development in humans.
The researchers found the SSRI-exposed rat pups behaved differently from ones given only saline injections. They were fearful of new sounds and experiences, and avoided the play and company of other pups, even into adulthood — behavior that's similar to that of autistic children.
The rats' brains had a malformed structure where left-right brain networking takes place. The insulation on the neurons was thick in some areas, thin in others. Similar malformations have been documented in autistic children's brains.
The rat pups also had damage to other parts of their brains, especially sensory-processing areas including the area used to process sound.
What's more, the malformations were seen three times more frequently in the male rat pups exposed to SSRIs shortly after birth than female rat pups. That, too, is a hallmark of autism in humans. In children, autism is three to four times more frequent in boys than girls.
Opportunity for study
When asked to comment on the NIH-funded research, the NIH's Insel chose his words carefully.
”While one must always be cautious extrapolating from medication effects in rats to medication effects in people, these new results suggest an opportunity to study the mechanisms by which antidepressants influence brain and behavioral development,” he said.
0 comments:
Post a Comment