RICHARD GRINKER, George Washington University: It's where somebody who previously had the identical symptoms now is conceptualized differently. And so, if you went back 30, 40 years, and you looked at people who were diagnosed with mental retardation or who were diagnosed with what was then called childhood schizophrenia, you would find that those people, 30 years ago, would qualify for the diagnosis of autism today. And I suspect that we may see the prevalence of autism continue to increase, not because there are more cases. They were there all along, perhaps, but because we're getting better at locating them, finding them and delivering services to these children and adults who really need help.
ROBERT MACNEIL: But a majority of the researchers we talked to believe that wider diagnosis explains only part of the increase in autism numbers. The rest remains the object of much scientific speculation. Among others, Dr. Irva Hertz-Picciotto, who heads the Division of Environmental and Occupational Health at UC-Davis, sees many possible environmental factors.
IRVA HERTZ-PICCIOTTO, University of California, Davis: There is a group that did look at the diagnostic substitution explanation. They thought that maybe explained a quarter to a third. But in addition to that, there has probably been an environmental contribution for a long time. We, in fact, know that some of the potential environmental causes do include, for example, infectious agents.
ROBERT MACNEIL: Do you have candidate factors for those factors that may be fresh in the environment?
IRVA HERTZ-PICCOTTO: I have a lot of candidate factors, actually. And they include nutritional factors, infectious agents, chemicals in our environment, including chemicals in the household products that we use every day. There are a variety of factors that could be influencing development, and they may play a role at different points in development. But I think multiple factors contribute not just across the population but within any one individual. So when I say that I think autism is multifactorial in its causation, I think that applies to even at the individual level so that it might take two or three susceptibility genes combined with two or three environmental factors at critical junctures.
ROBERT MACNEIL: Which might explain why individuals with autism are so different, even though they share some obvious symptoms.
IRVA HERTZ -PICCOTTO: Exactly. Exactly.
RICHARD GRINKER: And I say, "OK, there's this big prevalence increase in autism. That's undeniable. There's a prevalence increase." Whether it means that there's an increase in the real number of people with autism or not, there's a prevalence increase. But I see it as progress. I really see it as an achievement to be able to identify these kids who previously were either misdiagnosed or maybe had no diagnosis at all.