Disease gene linked to evolution.

• Position: Schizophrenia

Approximately two percent of Caucasians have a gene segment variation that can cause a certain form of schizophrenia. Most people with the variation, known as a polymorphism, do not have the disease. A University of Iowa, Iowa City, study reveals a good prognosis for those who do have this form of schizophrenia. The researchers also found that this polymorphism is associated with overall benefits for human survival, and the initial mutation occurred in a single common ancestor about 100,000 years ago.

This has implications for finding better ways to treat this particular type of schizophrenia and possibly augmenting the positive influences of the polymorphism on human survival, as well as studying other gene defects.

"While this polymorphism [known as HOPA12pb] makes us more vulnerable to a certain illness, in this case schizophrenia, overall it is evolutionarily beneficial," notes Robert Philibert, associate professor of psychiatry in the Roy J. and Lucille A. Carver College of Medicine and the study's principal investigator.

"Traditionally, genes that are selected for human evolution affect two things--resistance to infection and infant survival. This gene may be involved in both of these positive features."

While nearly one in 50 individuals of European extraction has the HOPA (Human Opposite Paired Element) polymorphism, only a small minority with the variant gene sequence actually have schizophrenia. About one in 30 men with HOPA has the condition. Men are more likely than women to have this form of schizophrenia because the gene is X-chromosome linked. Those with HOPA-linked schizophrenia...