点击显示 收起
June 11, 2007 -- Federal courts are now set to decide whether there is a link between autism and childhood vaccines. But what do medical experts think?
Parents are suing the federal government, claiming that a preservative in childhood vaccines led to autism in their children.
Typically, symptoms of autism are first noted by parents as their child begins to have delays in speaking after age 1, around the same time a child typically receives the MMR (measles-mumps-rubella) vaccine. This has led some to suggest a link between the vaccine and autism.
Autism is a pervasive development disorder (PDD), a group of illnesses that involve delays in the development of many basic skills, most notably the ability to socialize or form relationships with others as well as the ability to communicate and to use imagination (including fantasy play). Children with these disorders often are confused in their thinking and generally have problems understanding the world around them.
In addition to problems with social interaction, imagination, and communication, children with autism also have a limited range of interests. Many children with autism (nearly 75%) also have mental retardation. In many cases, children with autism are unable to emotionally bond with their parents or other family members.
In years past, experts believed autism affected four to five out of every 10,000 children. But a new CDC report released earlier this year showed about one in 150 8-year-old children had autism. Since that study involved just 14 states, it’s unclear if those numbers reflect national statistics.
If there is indeed a rise, what could be fueling this increase? The question is whether this possible rise is due to doctors doing a better job at identifying kids with autism or to some other reason.
What could that reason be? One theory is children’s vaccines. The MMR vaccine – measles, mumps, and rubella -- has gotten the most attention, mainly linked to the mercury-based preservative thimerosal.
Several medical studies have shown no link between autism and the MMR vaccine. And several premier medical organizations have concluded that there is no link between autism and thimerosal.
The CDC says there is no evidence to suggest a link. The Institute of Medicine, a nonprofit, nongovernment organization, takes it one step further and says the MMR vaccine absolutely does not cause autism.
Since 1999, when the American Academy of Pediatrics recommended that thimerosal be taken out of vaccines as a precautionary measure, kids’ exposure to the preservative has dropped significantly.
Thimerosal has been removed from or reduced to trace amounts in all vaccines routinely recommended for children 6 years of age and younger. The exception is the flu vaccine. A preservative-free version of the flu vaccine (contains trace amounts of thimerosal) is available in limited supply for infants, children, and pregnant women.
Some vaccines, such as the tetanus-diphtheria booster for older children and adults, are also available in formulations that are free of thimerosal or contain only trace amounts.
The exact cause of autism is not known, but research has pointed to several possible factors, including genetics, certain types of infections, and problems occurring at birth.
Recent studies strongly suggest that some people have a genetic predisposition to autism, meaning that a susceptibility to develop the condition may be passed on from parents to children.
Researchers are looking for clues about which genes contribute to this increased vulnerability. In some children, environmental factors may also play a role. Studies of people with autism have found abnormalities in several regions of the brain, which suggest that autism results from a disruption of early brain development while still in utero.