"Is Autism Really on the Rise?"
In 1943, a famous paper was published in which
a child psychiatrist at Hopkins described
a series of children with so-called “fascinating peculiarities.”
He thought these characteristics formed
a unique “syndrome” he called autism,
which seemed rare at the time,
but who knew how many were out there undiagnosed.
What causes it?
Autism is currently “considered a multi-factorial disorder
resulting from [both] genetic and non-genetic risk factors.”
Yes, it can run in families,
but genetic factors may account
for only 10 to 20% of autism cases.
This is based in part on the fact
that you can have identical twins,
with identical DNA— the same genes,
and one identical twin may have autism and the other not.
So, while genetic susceptibility
may be a key contributor to these autism spectrum disorders,
it may just “load the gun,” so to speak,
with prenatal, perinatal, and postnatal environmental exposures,
some kind of exposures during, around, or after pregnancy,
being the events that “pull the trigger”
and may actually give rise to the disease.
This is good news.
The larger role these non-genetic factors play in causing autism,
the more modifiable the risk factors may be,
potentially opening up avenues for the primary prevention
of autism in the first place.
Since autism as a medical condition was first described,
the prevalence of autism has apparently exploded
from like 1 in 5000 individuals to 1 in 68,
more than 1% of the population.
That would be like a 7,000% increase,
and indeed, you’ll see graphs like this:
showing an exponential increase in the prevalence of autism,
from like no diagnosed cases in the early 1900s,
to the prevalence shooting through the roof in the 80s and 90s.
And so, that immediately gets you thinking:
what happened around that time
that could account for the explosion?
But, wait a second...
Of course, there were no diagnosed cases
in the early 1900s;
it didn’t even have a name until 1943.
As Canner said in the original paper,
there’s probably more cases out there,
but they just hadn’t been looking.
So, this isn’t a graph of the prevalence of autism;
it’s a graph of the prevalence of autism diagnoses,
and that depends on what diagnostic criteria you’re using,
and whether you’re out there looking for it or not.
Put another way, historical prevalence estimates for autism
and its rarity might well have been underestimates
of the true prevalence back then,
may have just been missing lots of cases.
The increased recognition among doctors and society at large,
the broadening of the diagnostic concept over time,
and different studies using different criteria
may account for much of the apparent increase in prevalence,
although this can’t be quantified.
So,before we start speculating
about the reason for the explosive increase,
maybe we should first make sure the explosion is real.
The bottom line is that, while we may never really know
what the prevalence was a half century ago,
we do have decent data over the last few decades
that really does point to a considerable increase
in the true prevalence.
So yeah, maybe there wasn’t actually a 22-fold increase
in autism in the 80s and 90s;
maybe there was actually only an 8-fold increase.
So yeah, we may quibble whether their increase
was 800% or closer to 2000%,
but the bottom line seems to be autism rates
are really increasing.
And so, the question legitimately then turns to why...
which we’ll explore, next.