IT SEEMS clear that autism is caused by something that either damages the
brain or prevents it developing properly. But what?
According to one of the most widely accepted theories, autism is at least
partly a genetic disorder. But the picture emerging from genetic studies is very
complicated, with autism being linked to many different locations on the
genome.
And while many autistic children show signs of autism from birth, some seem
to develop normally but then regress after their first year. That suggests it is
triggered by something in the environment. It may well be both: something in the
environment may trigger the disease in children who are genetically
susceptible.
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There is no shortage of theories on the identity of that trigger. Everything
from mercury poisoning to vitamin A deficiency has been blamed. Paul Shattock, a
British biochemist, has found evidence that digestive problems in a child may
set off autism
(快猫短视频, 20 June 1998, p 42).
He proposes that
some children can鈥檛 break down cow鈥檚 milk and wheat into amino acids, leaving
鈥渞ogue鈥� peptides in their systems that wreak havoc by mimicking the brain鈥檚
opiates and neurotransmitters.
In Andrew Wakefield鈥檚 controversial version of this theory the MMR vaccine
causes inflammation of the gut, making it 鈥渓eaky鈥� and allowing these rogue
peptides into the body. But while he claims that the measles virus from MMR can
be found in inflamed gut tissue, other studies using more sensitive methods have
failed to find the virus. A Japanese team has evidence that Wakefield鈥檚 methods
are actually detecting a human protein that resembles a measles protein.
Another theory is that autism is an autoimmune disease, in which the body
starts attacking a key substance in the brain. Vijendra Singh, a
neuroimmunologist at Utah State University in Logan, has found high levels of
鈥渁utoantibodies鈥� against myelin basic protein in autistic children. Myelin is
the fatty sheath that protects and insulates nerve fibres in the brain and is
installed at record rate during early childhood brain development.
Singh doesn鈥檛 stop there. He thinks measles triggers the autoimmune reaction.
He says that autistic children tend to have a very strong reaction to the
measles virus, producing seven times more antibodies than normal. In a study
that has been submitted for publication, he claims that 53 per cent of 80
autistic children but none of 60 other children had abnormal antibodies to the
measles component of MMR.
鈥淲hat we鈥檙e finding is that many autistic children have an inappropriate
response to MMR,鈥� he says. Singh thinks that an atypical measles infection,
perhaps in children with a particular genetic vulnerability, might lead to
autism. He believes it might be possible to identify children who shouldn鈥檛 be
given the vaccine.
Elizabeth Miller of the Public Health Laboratory Service in London says that
it鈥檚 impossible to know which antigens in the vaccine supposedly trigger
production of antibodies in patients. She points out that an exhaustive study by
Phil Minor of the US National Institute for Biological Standards and Control has
shown that there鈥檚 nothing resembling myelin basic protein in the MMR
vaccine.
鈥淎 dispassionate look at the published scientific evidence says there鈥檚
overwhelming safety of the vaccine and no link to autism,鈥� she says. Even Singh
isn鈥檛 suggesting that vaccination be stopped. 鈥淚t鈥檚 the best preventative
medicine we have today,鈥� says Singh.
