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Sally, Ann, and Danny 123
The most striking data on the increase in prevalence come from the
state of California, which keeps good records on children with developmental
disabilities. California has reported a dramatic increase in the
number of children with autism but also a dramatic decrease in children
receiving a diagnosis of mental retardation (though to be fair, this finding
has been challenged as well). It’s certainly possible that children
who in the past would have received a diagnosis of mental retardation
are today receiving a diagnosis of ASD, especially since in many jurisdictions
it’s easier to get services with an autism diagnosis than with a
mental retardation diagnosis.
Ron and Carol raised a fourth problem in our discussion. They
rightly point out that no one else in their family has autism, no uncles
or cousins. In their case the other children in the family are completely
normal and there are no extended relatives with the diagnosis. How is
this possible, if the disorder is inherited? I explained to them that, in
fact, there are several inherited disorders where there is little family history
(like breast cancer and senile dementia), even though some of the
genes that cause these disorders have now been identified. In addition,
other studies have shown that single autistic-like traits, that are not
severe enough to warrant a formal diagnosis, are found more commonly
among relatives of children with ASD than in the general population.
Traits such as social isolation, intense interests and hobbies, rigidity, unusual
ways of communicating, and perhaps learning problems are not
uncommonly seen in relatives from both sides of the family; about
twenty percent of relatives are affected with these traits. So, although
autism may be very rare among extended family members, there is some
evidence that individuals with unusual personalities are found in the
family tree.
Now, it may be that once a diagnosis of autism is given, parents
search their family tree and perhaps overidentify ASD-like traits in individuals
that they might otherwise not recognize. People often look at
their relatives with a new perspective and wonder if they might have a
mild form of ASD. “It was from your side of the family.” “No, it was
from yours—just think of your cousin William!” parents will sometimes
argue. On the other hand, these data may indicate that the genes
for autism/ASD are not uncommon in isolation and that the full disorder
occurs when certain genes combine or when genes interact with
certain intrauterine environments.
So, no genes for autism have yet been identified, but several promising
leads have turned up. Progress has been rapid in the last few years,