SFARI.org: Can epidemiological studies explain the increase in autism rates?
Maureen Durkin: Epidemiology is good at capturing autism’s rise, but not necessarily explaining it. The reasons have been tough to capture using epidemiologic studies, because they’re only as good as the data available. The studies cannot easily separate out whether the rising rates stem from changes in awareness or other reasons.
S: What progress have you made so far in explaining the rise?
MD: Traditional epidemiologic efforts have identified risk factors and causes. We then see how much of the increase in autism prevalence could be attributed to those factors. So far, nothing that we can identify and measure would be enough to account for the magnitude of the increase we’ve seen.
As an example, the age of parents has increased pretty dramatically in the past four decades. The average age of first birth for mothers has increased by about five years, for example. That trend is coincident with the rise in autism. But when you do the numbers, at most, 1 percent of the increase in autism prevalence could be attributed to parental age, perhaps even less.
One thing we wondered: Because older parents are usually more educated and have more resources than younger parents, maybe they’re better able to get an autism diagnosis for their child. So the contribution of parental age might be more than just the numbers of older parents. It might also come from tSheir ability to advocate and raise awareness. That’s difficult to capture in epidemiological data.
We’ve also measured perinatal factors. Improvements in the survival of very premature babies have probably contributed to autism prevalence becausethese babies are at greater risk for autism. But again, these factors cannot explain the dramatic increase.
Other issues involve diagnosis, including ‘autism’ expanding to a spectrum and other changes in diagnostic criteria. But from 2000 to 2010, when there were no such changes, we still saw more than a doubling in the prevalence of autism.
S: Is autism on the upswing worldwide?
MD: We see disparities in autism prevalence worldwide. But that is largely because we lack information for most of the world, not because autism is changing at different rates in different places. But everywhere that prevalence has been measured over time, it seems to be increasing. Those areas are mostly restricted to Western Europe, the U.S. and a few Asian countries. That’s changing, however; the map is filling in as more studies come out.