OSAKA — People who suffer from chronic fatigue syndrome, an illness characterized by debilitating tiredness, have decreased levels of the neurotransmitter serotonin in their brains, according to recent findings by a joint research team.

The team of Hirohiko Kuratsune, an assistant professor at Osaka University Medical School, and researchers from Uppsala University in Sweden has paved the way with its findings to eventually determine how people develop CFS.

Their results, released at an international conference in Sweden earlier this month, also increase the chances that new drugs to treat CFS will be developed, team members said.

CFS has been identified as a disease only relatively recently, with the first wave of cases being reported in the United States in the 1980s. The cause of CFS is not clear and no remedy has been found.

The research team found irregularities in serotonin levels of patients suffering from depression, which has symptoms similar to CFS.

The substances found in serotonin were injected into six CFS patients and eight healthy people.

The team then compared how the two groups of people absorbed the serotonin.

The CFS patients produced lower levels of serotonin than the healthy group of patients, according to the team.

The researchers also tested an antidepressant drug on 39 CFS patients, 11 of whom were taken off the drug when they experienced side effects such as nausea.

The condition of 10 others improved in two months, and two of those 10 recovered completely.

The research team believes that CFS patients' ability to produce serotonin is reduced by severe stress and will look into the detailed mechanism, members said.