Gene variations hinder mental illness tests-study

* Huge number of gene variations may underlie illnesses

* Genetic tests and more targeted drugs still long way off

By Kate Kelland

LONDON, July 1 (Reuters) - As many as 30,000 different gene variations may underlie schizophrenia and bipolar disease, meaning any kind of quick test to predict either disease is a long way off, scientists said on Wednesday.

Three studies by a multinational group of researchers analysed the DNA of 10,000 people with schizophrenia, and 20,000 without, and found 30,000 common gene variations linked with the mental illness.

They also show just how complex such diseases are, the researchers told a news conference.

"It's like we've got a 'join-the-dots picture', and we now know we have several thousands of dots to be joined," Mick O'Donovan of London's Institute of Psychiatry, who worked on one of the studies, told reporters.

"But we don't even have numbers on them yet so we don't know in what order to connect them up."

The scientists stressed that although the large scale of the combined studies meant their results were robust as building blocks, they could not be used yet to predict an individual's risk of developing the disease.

"We are far away from being able to tell a family: 'Your child will develop schizophrenia' or not," said Pablo Gejman of North Shore University Health System Research Institute in Evanston, Illinois, who worked on one study.

O'Donovan said it would be "entirely unscrupulous" for the studies' findings to be used to offer any kind of genetic test.

DEVASTATING DISEASES

Schizophrenia is a chronic and often devastating psychiatric disorder that affects about one in 100 people.

Patients experience hallucinations and disordered thinking and although some antipsychotic drugs, such as AstraZeneca's (AZN.L) Seroquel and Eli Lilly's (LLY.N) Zyprexa, can ease symptoms, they do not offer a cure and may have side-effects.