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TESTIMONY ON "MERCURY IN MEDICINE"
BY MARIE M. BRISTOL-POWER, Ph.D., COORDINATOR,
NETWORK ON THE NEUROBIOLOGY AND AND GENETICS OF AUTISM
NATIONAL INSTITUTE OF CHILD HEALTH AND HUMAN DEVELOPMENT
NATIONAL INSTIUTES OF HEALTH
U.S. DEPARMENT OF HEALTH AND HUMAN SERVICES
HOUSE COMMITTEE ON GOVERNMENT REFORM
JUNE 18, 2000
Mr. Chairman and Members of the Committee, I am Marie Bristol-Power, Ph.D., the Coordinator of the Network on the Neurobiology and Genetics of Autism for the National Institute of Child Health and Human Development (NICHD) at the National Institutes of Health (NIH). In addition, I am the NICHD program staff representative to the NIH Autism Coordinating Committee (NIH/ACC). At your invitation, I am pleased to address this Committee on the topic of NIH autism research and vaccines.
Autism is a developmental disorder that affects the most central of human behaviors—the ability to communicate, to interact socially and emotionally with others, and to have the broad repertoire of skills and knowledge needed to easily take one’s place in the worlds of work and leisure. The great variability in expression of autism and related disorders indicates the complexity of the puzzle this disorder presents. Genetic, infectious, metabolic, immunologic, and possible environmental influences have been implicated as possible causes or triggers of autism.
We believe that no single cause will account for all cases of autism (and the range of Autism Spectrum Disorders), nor will any one intervention or treatment prevent or "cure" all its manifestations. Autism might be better understood as a class of disorders. Solving the puzzle of autism will be like peeling an onion, one layer at a time. To date, the gene, protein product, and some understanding of mechanisms have been found for Fragile X, once defined as a form of autism. This past year, a major gene for Rett’s syndrome, one of the Autism Spectrum Disorders, was identified. Genetic "hotspots" for autism have been discovered by independent, international groups of researchers using common diagnostic criteria. Promising work also continues on candidate genes such as on chromosome 15q11-13, and the serotonin transporter gene. The current consensus is that autism probably involves multiple genes that interact in some complex way to make individuals genetically susceptible to Autism Spectrum Disorders. The scientific challenge is to identify both the genetic basis for the disorder and the other influences that might lead to or precipitate autism in susceptible individuals.
REGRESSION IN AUTISM
There are two modes of presentation of autism—one, thought to be true for the majority of children with autism, in which the child has symptoms from birth, and a second, historically considered to constitute 20-30% of all cases, in which the child apparently develops normally and then loses functional communication and social skills, usually between 18-24 months. Recent reports suggest that the relative proportion of early onset to later onset regressive autism may be changing. Further research is needed to verify these reports. In any case, at this time, there is not a proven explanation why some children appear to develop normally and then regress. As with the overall etiology of autism, there is likely to be a variety of causes of autistic regression. In fact, a number of other developmental disorders, caused by a number of different mechanisms—genetic, metabolic, neurologic, immunologic and combinations of these mechanisms—are characterized by periods of normal development followed by regression. At the NIH, scientifically defensible mechanisms will be investigated so that the tragedy of various forms of regressive autism can be understood and ultimately prevented. The NIH supports research in these areas, and encourages the submission of research applications on these different mechanisms. Currently supported studies in these areas include research at the University of Utah/Utah State on a possible immuno-genetic basis for autism and at the University of Rochester on the interaction of genes and environment in at least a subset of cases of autism.
VACCINES AND AUTISM
Recent reports in the literature and testimony before this Committee have raised the possibility of a link between vaccines, especially the MMR vaccine, and regressive autism, a particular concern given the importance of vaccines to the health of America’s children. A related concern has been raised about the possibility of a link between mercury and autism resulting from exposure to preservatives such as thimersol in cumulative infant vaccinations. Since it is clear that vaccines are safe and effective for the vast majority of children, such reports raise the question of whether or not some children may suffer adverse events from vaccines that are helpful to the vast majority of children who receive them.
Even before recent letters to the Secretary of Health and Human Services were received from the Chairman and Ranking Member of this Committee, the NIH was looking very carefully at the suggestions raised by congressional witnesses and others on what causes autistic regression. The results of current studies are inadequate to draw conclusions that would have far-reaching effects on children’s vaccination programs. However, these results are of sufficient concern that they must be addressed. The NIH is taking a number of different approaches to get information needed as rapidly as possible to determine the merit of these recent concerns.
In addition to pursuing ongoing research on the various causes of autism, the NICHD, with co-funding from CDC, has begun a study of regression in 1,000 persons with autism through the Network on the Neurobiology and Genetics of Autism of the Collaborative Programs of Excellence in Autism supported by the NICHD and the National Institute on Deafness and Other Communication Disorders. A minimum of 200 children with documented regressive autism will be compared with matched groups of children with early onset autism and 200 normally developing control children. Group comparisons (early onset autism, regressive autism, and normal development) will include presence/absence/duration of normal development, age at regression, vaccination histories of children and of mothers (i.e., maternal vaccination before, during, or after pregnancy), measles antibody levels, and association of vaccine additives and autism. The study provides for independent, blind assessment of laboratory samples. Analyses will re-examine the hypotheses of Drs. Singh, Wakefield, and O’Leary. Initial laboratory assessments will include comparisons of immunity to measles using ELISA and other related tests of antibody levels and presence of measles virus nucleic acids in peripheral white blood cells using Real Time (RT) PCR. Subsequent assessments may include immunity to other components of the MMR vaccine, immune responses to DTP vaccine (including thimerosal), immune responses to host proteins, and transcript profiling using expression arrays representing infectious agents.
Since no one study will be definitive, the NIH is also eagerly awaiting the reports and research recommendations on this topic expected to come from an established blue ribbon panel at the American Academy of Pediatrics, and another panel of experts about to be established by the National Academy of Sciences/Institute of Medicine.
Retrospective research and literature reviews will provide valuable information. However, a prospective, longitudinal study is ultimately needed to determine the contributions of both genes and environments to healthy development and to the onset of developmental disorders such as autism. A national initiative, involving the NICHD and other NIH institutes, CDC, EPA, other federal agencies, and independent research laboratories is needed to study the developmental course of autism and other disorders in the context of normal development. Such an effort would involve following a minimum of 100,000 to 150,000 children and youth from pregnancy through at least 21-years of age, collecting both biological and behavioral measures, including vaccination history and exposure to other environmental toxins, diet, and other influences. The NICHD is working with the other agencies to initiate the planning for such a study. The recent announcement of the imminent completion of the description of the human genome signals the beginning of a new era of genetic medicine. We must pursue knowledge of the role of environmental influences in the course of autism and other developmental disorders with the same diligence we are applying to understand the underlying genetic susceptibility to autism.
At the same time, we must be vigilant that we do not overlook alternative explanations for autism and for regression. For example, recent research by Dr. Karin Nelson of the National Institute of Neurological Disorders and Stroke has identified potential biological markers present at birth that distinguish infants with autism or mental retardation from infants with cerebral palsy and from normal infants. This research, as well as work by Dr. Patricia Rodier at the University of Rochester that suggests onset of autism as early as the first three weeks of gestation, raises questions about the impact of postnatal influences on the onset of autism. Similarly, possible metabolic or other infectious sources of autism etiology must also be explored. All hypotheses must be open to independent testing and researchers held accountable to the rules of evidence and peer review.
The NIH is committed to working with the Congress, parent advocacy groups, other federal agencies, scientists, and individual families so that no stone will go unturned in our search for the causes of autism, including the causes of autistic regression after normal development.
I will be pleased to respond to your questions.
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