— LONDON (Reuters) - Causes of autism can be detected in about a third of cases and genetic factors may play an important role, Dutch researchers said on Thursday.

Doctors at the Emma Children's Hospital in Amsterdam said the chronic disorder which causes sufferers to lose their mental functions and become withdrawn and self-absorbed are due to a genetic predisposition to the syndrome and environmental factors.

"The causes underlying autism are very variable but with a state-of-the art diagnostic workup it is possible to find a cause in up to a third of patients," said pediatrician Dr. Clara van Karnebeek.

In a study reported in the Journal of Medical Genetics, she and her colleagues studied 25 adults with autism and by using a battery of tests found the cause in nine of them.

Abuse of alcohol or drugs during pregnancy, different genetic defects and metabolic disturbances were among the causes they found. All of them in some way damaged the brain, they said.

"Autism should be considered a symptom, caused by a variety of underlying disorders," Van Karnebeek said in the study.

Fears that the measles, mumps and rubella (MMR) vaccine can cause autism and bowel problems have led to a steep drop in the number of children being vaccinated and outbreaks of the measles in some parts of Britain.

Despite reassurances from scientists many parents have demanded single immunizations as an alternative to the triple jab.

Autism usually occurs before the age of 30 months. The condition is more prevalent among boys than girls. A minority of people with the disorder, who are known as autistic savants, show remarkable artistic, musical or mathematical skills.

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