BERLIN (September 27, 2012)--A new European study may provide some hope to parents of children born with severe mental disabilities who are worried about having another baby with the same condition.

The small-scale study found that more than half the cases of severe mental disability caused by genetic defects are the result of random mutations, not inherited.

Anita Rauch, a researcher at the Institute of Medical Genetics in Zurich, who was one of the study's lead authors, said if the disability is caused by a random mutation, "the chances of recurrence drop dramatically" from the usual estimate of eight percent.

A scientist who was not part of the research cautions, however,that if there were a larger study that included subjects from parts of the world where marriage between blood relatives is more common, it could produce different results.

The study was published online by the journal Lancet.