It will be some time before the specific genes that are responsible will be identified

Debbie Tsuang, University of Washington

Scientists at the University of Washington examined four specific chromosomes to determine if they contained genes that contribute to schizophrenia.

Like previous studies, they found an association between the chromosomes, 13 and 15.

However, the found no such link with the other two chromosomes, 12 and 16.

Ethnic differences

Their study is among the first to include large samples of Americans with both European and African backgrounds.

They found that the association between chromosome 15 and schizophrenia in European-American families was positive while there was no such link in African-American families.

Speaking at the American College of Neuropsychopharmacology annual meeting in Hawaii on Sunday, Debby Tsuang who headed the study said: "This was one of the strongest results of our analysis.

"It means that different combinations of genes may contribute to schizophrenia in different groups."

The work of scientists if complicated further by the fact that the two chromosomes that show a positive linkage to schizophrenia contain hundreds of genes that could contribute to the condition.

"Currently, there is no good way to decipher which of these genes is directly responsible," said Tsuang.

"Due to the complex genetic characteristics of schizophrenia, it will likely be some time before the specific genes that are responsible will be identified and even longer before treatments based on these findings become possible."

A spokesman for the National Schizophrenia Fellowship said the condition may be caused by a range of other factors.

"Anyone looking for a single 'Big Bang' theory for the development of schizophrenia is likely to be disappointed. Schizophrenia is a very complex and poorly understood condition.

"Its causes, and there may be many, involve an interaction of various genes and environmental factors in ways that have not been defined."