Autism Epidemic? More Likely We're Just Better At 
Diagnosis
By John Timmer
Ars Technica
May 5, 2011
http://arstechnica.com/science/news/2011/05/autism-epidemic-more-likely-were-just-better-at-diagnosis.ars

In the developed world, rates of autism spectrum
diagnoses have skyrocketed in recent years, raising the
specter that a new environmental factor has been
altering the developmental trajectory of the youngest
children. Searches for putative environmental
influences, however, have generally come up empty, even
as researchers have identified very strong genetic
influence on the disorders. The disparate rates of
progress provide some support for an alternate
interpretation: autism has always been around at roughly
this level; we've just gotten much better at diagnosing
it.

A study in the UK now provides a bit more support for
this argument. Researchers have performed a large-scale
survey of adults, looking for indications of autism
spectrum disorders where none had ever been diagnosed.
And they found cases, enough to suggest that the rates
haven't changed considerably.

The report starts out by describing the evidence for a
rising tide of autism spectrum disorders (ASDs). Surveys
prior to the 1990s had indicated an incidence of about
4.4 cases per 10,000 individuals. By the '90s, that rate
had risen to 12.7, and more recent surveys suggest an
incidence of 10 per every 1,000, or roughly one percent.
This startling rise, if it's real, suggests a recent
uptick in an environmental exposure is altering neural
development in early childhood.

Based on that suggestion, the British team started with
a few simple hypotheses. If the prevalence of ASDs has
been increasing, then the youngest adults would have
rates similar to the ones seen in the oldest children,
with the rates dropping with age. They also hypothesized
that any adults they did find would share features with
the other ASD individuals, including poor social
integration; like the current generation, they'd be more
likely to be male.

They then set about an enormous undertaking: diagnosing
a representative population of UK adults. As a first
pass, they selected a population based on postal codes
and employment statistics. With over 14,000 households
identified, interviewers fanned out, ultimately
completing over 7,000 interviews that provided a first
level of screening for ASD diagnoses. From that pool,
850 individuals were chosen for a second, more in-depth
interview; 630 people completed that, and the authors
adjusted their data to take a failure to respond into
account, leaving them with a population that was largely
representative of the English population over 16 years
of age.

As the authors note, however, this population excludes
those who have been institutionalized or have severe
disabilities, so it's not fully representative. There
was, however, no indication that ASD issues made anyone
less likely to participate in the survey.

Based on the scores obtained using the Autism Diagnostic
Observation Schedule (a standard diagnostic test), the
authors identified 19 adults who qualify as autistic.
That's a rate of 9.8 per 1,000, or roughly the same rate
as its appearance in children. Unfortunately, because of
the small sample size, the 95 percent confidence
interval is pretty broad, ranging from three to 17.

The small sample size also makes it difficult to say
much about the population as a whole. Males are far more
likely to have ASD symptoms, and the group as a whole
was less likely to have completed university education
or have gotten married, and more likely to be living in
government-run housing. Beyond that, none of the
measures were statistically significant.

This lack of statistical robustness also keeps the
authors from evaluating one of their hypotheses, that
apparent rates would drop with age. There is a slight
drop of ASD diagnoses in older individuals, but the
study is so small that the trend is statistically
consistent with rates actually increasing. Nevertheless,
the authors note that the trend is in no way consistent
with a sudden upswing in ASD prevalence.

Overall, this looks like a very solid preliminary study.
From a practical point of view, it suggests that there
is a substantial population of economically and
educationally disadvantaged people with ASD who are
undiagnosed. Better recognition of and support for this
group would seem to be a significant public health
concern, given its apparent size.

The rate of apparent diagnosis also suggests that autism
has been historically under-diagnosed, and may have been
present at roughly its current rates for a long time.
The small size of the population in the study, however,
limits the confidence in these results. Unfortunately,
given the effort and expense that were required to
generate this small survey-two rounds of in-person
interviews-we're not likely to see a larger study that's
equally thorough.

Archives of General Psychoatry, 2011. DOI:
10.1001/archgenpsychiatry.2011.38  (About DOIs).

___________________________________________

Portside aims to provide material of interest to people
on the left that will help them to interpret the world
and to change it.

Submit via email: [log in to unmask]

Submit via the Web: http://portside.org/submittous3

Frequently asked questions: http://portside.org/faq

Sub/Unsub: http://portside.org/subscribe-and-unsubscribe

Search Portside archives: http://portside.org/archive

Contribute to Portside: https://portside.org/donate