GENETICS STUDY
the role of genes in autism
and pervasive developmental disorder (pdd)
There is clear evidence that genetic factors
play a role in autism. The risk of autism
to siblings
of children with autism has been found
to be between 2% and 8% or 50-200 times
the
general
population
rate. Meanwhile, four twin studies have
reported that the rate of autism is much
higher among
identical twins than non-identical twins,
which would point
to a genetic base.
Families of children
with autism also show higher rates of other
forms of pervasive
developmental disorder (PDD). For example,
the co-twins of
an identical twin with autism can have
atypical autism
or Asperger syndrome, and the risk of Asperger
syndrome and atypical autism in the non-twin
siblings of individuals with autism is
2.8%.
Another type of impairment that has
recently been reported to occur in first degree
relatives is
a lesser variant of PDD characterized
by similar impairments in reciprocal social
interaction,
communication and interests but not enough
to merit a diagnosis
of PDD. For example, a recent family
history study found that roughly 20% of siblings
of children with autism have social or
communication impairments
or a restricted pattern of interests.
This
is much
higher than the 3% found in a control
group of children with Down syndrome, indicating
that
the genes for autism also confer susceptibility
to
milder forms of PDD.
We do not know why
there is such a large variation in clinical expression.
Complications
during
birth have been suggested as a factor
that may contribute
to the severity among genetically susceptible
individuals. In fact, a genetics study
currently being led by
Dr. Peter Szatmari of the Offord Centre
for Child Studies in Hamilton, Ontario,
has found
that
affected siblings within a family are
very similarly affected
in terms of IQ and severity of impairment.
This suggests that genetic factors
are probably responsible
for the variation in clinical expression
among PDD children.
Understanding
autism – It’s mainly in the
genes
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