The causes of autism, the fast-growing disorder that has struck fear into the middle classes and has been linked with the MMR vaccination, may be less mysterious than has been thought, scientists report today.

The causes of autism, the fast-growing disorder that has struck fear into the middle classes and has been linked with the MMR vaccination, may be less mysterious than has been thought, scientists report today.

The developmental disorder characterised by "extreme autistic loneliness" and "an obsessional desire for the maintenance of sameness" according to Leo Kanner, who first described it in 1943, has risen seven-fold in the UK in the last decade but no biological reason for the rise has been found.

Now a new study has discovered that in up to a third of cases it may be possible to identify the cause of the condition. Researchers in the Netherlands who ran detailed tests on 25 adults with autism found definite or probable causes of the disorder in nine of them.

The 25 adults were all living in a home for mentally retarded people in Baarn, in the Netherlands. Over three-quarters of people with autism are mentally retarded and the condition is three times as common in boys as in girls.

All the adults were aged from 22 to 45 and were given a thorough physical examination including eye, ear, nose and throat investigations, plus a brain scan, blood tests and a full genetic analysis.

The results showed a definitive cause of autism in five cases. In one, there was a strong link with alcoholism in the mother – the child was born with foetal alcohol syndrome (suffering from withdrawal symptoms).

A second case was probably linked to alcoholism in the mother. Alcohol is thought to affect the migration of neuronal and glia cells in the foetus's developing brain. A third case was linked to anti-convulsant drugs taken by a woman with epilepsy.

Eight patients were found to have abnormally large or small heads and neurological examination showed signs of drowsiness, tremor or similar problems in three of them. Two had signs of brain atrophy on being scanned.

In all, physical examination showed abnormalities in 20 patients and in seven of these the findings contributed to establishing a diagnosis. Genetic studies showed chromosomal defects in several patients.

The authors of the study, from the department of paediatrics at Emma Children's Hospital, Amsterdam, reveal their findings in the Journal of Medical Genetics. They say: "Autism poses an extremely heavy burden for affected subjects, their families and society.

"Research focusing on biological causes and on guidelines for these studies in each specific person is important both in diagnostics, management and genetic counselling."

Previous research has suggested that the single most consistent physical characteristic of people with autism is the size of their heads. There is also a greater incidence of minor physical abnormalities, indicating that something may have gone wrong during development of the foetus in the womb.

Autism is known to run in families, indicating a strong genetic component. However many cases also appear to result from an early "environmental insult", such as an infection or exposure to a toxic substance such as alcohol.

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