[acb-hsp] Autism Epidemic

[peter altschul]

Autism Epidemic? More Likely We're Just Better At Diagnosis
  By John Timmer Ars Technica May 5, 2011
  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 (ASD's).  Surveys prior to the 
1990's had indicated an incidence of about 4.4 cases per 10,000 
individuals.  By the '90's, 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 ASD's 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 ASAID 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 ASAID 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 ASAID 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 
ASAID 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 ASAID 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 ASAID 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 ASAID 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: 
10.1001starchgenpsychiatrydd2011.38
  (About DOI's).