SAN FRANCISCO, Nov. 8 (UPI) -- Thus far, research looking at mercury levels in children with and without autism has produced mixed results.
Studies that measured concentrations of the metal in the blood, urine and stools of 40 full-term infants 6 months and younger inoculated with vaccines containing the mercury-based preservative thimerosal, which some parents and doctors link to autism and other neurodevelopmental disorders, showed the levels stayed within the recommended guidelines and that the toxin was rapidly flushed in the baby's feces.
However, studies of preterm infants indicated their mercury blood level after just one hepatitis B shot rose ten-fold, passing the safety line set by the Environmental Protection Agency, researchers said.
Other tests detected high mercury totals retained in autistic babies' hair, excretions and blood. Researchers said this result points to these children's inability to effectively eliminate the metal from their bodies.
In another study, which analyzed samples from babies' first haircuts, Mark Blaxill of the anti-mercury advocacy group SafeMinds, Boyd Haley, chemistry chairman at the University of Kentucky in Lexington from 1996 to 2005, and Amy Holmes, a Louisiana physician and mother of a child with autism, found locks from 45 healthy youngsters contained eight times more mercury than those from 94 of their autistic peers.
The researchers said they observed that the lower the amount of mercury in the hair, the more severe the autistic symptoms in the child. This suggests the neurotoxin might be retained in a youngster's brain and other organs, the study authors said.
Because mercury crosses the placental barrier, the investigators also examined the mothers' exposure to the toxin through food, dental fillings and a thimerosal-containing blood product called Rho D immunoglobulin.
This medicine is typically injected into pregnant women with rare Rh negative blood, which is found in 15 percent of the population and which could prove harmful, even fatal, should the newborn, or any future babies, be Rh positive.
In that case, if even tiny amounts of the mom's and baby's incompatible blood mix -- say, after amniocentesis -- the mother could develop an allergic reaction to her child. This could potentially lead to anemia, brain damage or even death in the child.
The investigators found nearly half of the autistic youngsters' mothers had received the shots, compared with only 9 percent in the non-autistic group.
But other researchers found no such difference.
"The hypothesis for this study was if mercury is causing a problem, we would expect the earlier you got exposed to it, the more problematic it would be," said pediatrician Dr. Judith Miles of the University of Columbia in Missouri who conducted a separate study of 600 families with autistic children.
The work was supported by Johnson & Johnson, maker of the immunoglobulin medicine RhoGAM, which contained thimerosal until 2001.
Miles said she knows the grant will taint the results of her research in some people's eyes, but she approached the drug company for funding because "otherwise we wouldn't be able to do the study."
Her team found no evidence Rh negative mothers are any more likely than those with the more common blood type to have autistic children.
The researchers also reported the moms had similar exposure to the thimerosal-containing product while pregnant with children later diagnosed with autism as during pregnancies that delivered their non-autistic brothers and sisters.
"If thimerosal was causing problems, we'd expect our 600 families (with autistic children) to have a higher proportion of families who had gotten thimerosal-containing vaccines (than in the general population)," Miles said. "But we haven't found that."
Nevertheless, she said she recognizes the concerns many parents have and tries to accommodate them.
"I work with families who are worried, and we split the vaccines and make sure there's (no thimerosal) in them, and we work with not giving all the vaccines at the same time if they're worried because we don't have all the answers," Miles said.
(Note: In this multi-part installment, based on dozens of reports, conferences and interviews, Ped Med is keeping an eye on autism, taking a backward glance at its history and surrounding controversies, facing facts revealed by research and looking forward to treatment enhancements and expansions.)
Next: What doctors do and do not know about autism
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