Intense and even fanatical resistance to vaccination against childhood diseases is itself a significant public health problem. Opponents have blamed vaccines for everything from allergies and diabetes to cancer and autism.
A recent study of abnormalities in the DNA of children with autism spectrum disorders (ASDs) should finally put to rest the claims of some activists, mainly parents of affected children, that vaccines cause these conditions.
An international group of scientists reported in June in the journal Nature that patients suffering from ASDs had in their genes a higher incidence of mutations in the form of deletions, insertions or duplications of segments of DNA than unaffected control subjects. These findings offer the possibility of both early detection and the development of drugs to target and neutralize the specific biochemical abnormalities caused by the mutations.
Autism is a developmental disorder characterized by deficits in social interaction and communication; a limited range of activities and interests; and often the presence of repetitive, stereotyped behaviors. Cognitive development can range from above-average to profound intellectual disability. Autism disorders are diagnosed in 1 in 110 children in the U.S. and are found in four times as many boys as girls.
Although it has been known that ASDs run in families the underlying genetic determinants have been elusive, but the Nature article offers some new insights. Drawing on data from 60 research institutions in 12 countries, the researchers analyzed the genes of 996 children with ASDs and 1,287 children without the condition. They found that each affected individual carried his or her own unique assortment of mutations.
This contrasts with the situation in sickle-cell anemia, for example, where the disease is most commonly caused by a unique mutation -- a change in one specific nucleotide of DNA, which in turn causes a single amino acid change -- in a gene that codes for the protein of hemoglobin. (Genes comprise DNA, which is a template that, after an intermediate step, directs the ordering of various amino acids into proteins.)
Where and when do these ASD mutations arise? Professor Daniel Geschwind, chief of human genetics and director of the Center for Autism Research and Treatment at the UCLA School of Medicine, said the findings suggest that the "tiny genetic errors may occur during formation of the parents' eggs and sperm," and that these mutations are conveyed into the DNA of offspring. "The autistic child is the first in their family to carry that variant. The parents do not have it."
If ASDs arise spontaneously in this way, still unresolved is why they appear to be so heritable: The occurrence of ASDs in siblings is about 100 times greater than the rate at which the disorders affect unrelated people in the population. Perhaps there is a predilection in some people toward the tiny genetic errors in eggs and sperm that give rise to ASDs and that would tend to affect all their offspring.
It is unclear how the beleaguered parents of autistic children will react to this new information about the genetic basis of autism spectrum disorders. In the past many have resisted such explanations, preferring instead to blame adverse reactions to vaccines as the cause in spite of persuasive evidence to the contrary.
The basis for this misapprehension is a 1998 article by a British physician that claimed a link between the measles-mumps-rubella (MMR) vaccine and the autistic symptoms. However, the findings were never duplicated and were subsequently discredited in the medical community worldwide, and the article was withdrawn by the journal that had published it.
Last month's article in Nature offers important new scientific insights into the molecular basis of autism spectrum disorders. One of the lead researchers predicted, "Just knowing about these genetic changes can help the families come to terms with why their child has autism." That remains to be seen. But equally important are the broader implications of this research -- namely, the alleviation of misplaced concerns in the broader community about childhood vaccines, and greater awareness of the public health benefits of wider immunization.
Dr. Henry Miller, a physician and molecular biologist, is a fellow at Stanford University's Hoover Institution. Dr. Elizabeth Whelan is president of the American Council on Science and Health.
