An unknown external factor, rather than better diagnosis,
appears to be behind a large rise in autism in the United States, writes
Scientists in California have discovered that an almost
three-fold increase in cases in the state is not the result of improved
diagnosis or better recognition of cases, as had been suggested by health
The findings have been published as the controversy continues
over whether Britain is seeing a similar rise in autism. A survey
by the National Autistic Society earlier this year suggested that more than
one in 80 primary school children may now have autism.
A genetic predisposition in the children affected, triggered by
something yet unknown in the environment, was the most likely explanation for
the rise in California, said a British expert.
Dr Fiona Scott, of the Autism Research Centre in Cambridge,
told BBC Radio 4's Today programme: "The rise is such that you couldn't
explain it just by genetics, there would have to be something else going on.
"Much likelier is there is some kind of genetic
predisposition or susceptibility and there may be groups of children who are
being triggered somehow to actually develop autism."
The results of the California study have been described as
"sobering" by doctors there. Robert Byrd, a paediatrician, said:
"Speculation about the increase in autism in California has led some to try
to explain it away as a statistical issue: instead we found that autism is on
the rise in the state and we don't know why."
The analysis was ordered by the Californian state legislature
after pressure from parents who feared that the rise could be have been
triggered by the introduction of the three-in-one measles, mumps and rubella
vaccine (MMR), introduced in California in the late 1970s.
in Britain, the American authorities have reassured parents that there is no
need to be concerned about MMR.