Both identical and fraternal female twins were examined at the University of Washington. In Phase One of a two-phase study, several interesting results were found.

Out of 51 sets of female identical twins, nearly one quarter of both twins (22%) reported having CFS. There was a much lower incidence in the fraternal twins. Of the 22 sets of fraternal twins studied, only 5% reported having CFS.

The statistical variance remained similar when comparing for fibromyalgia. Out of 74 sets of female identical twins, 34% of both twins had FM. In 23 sets of fraternal twins, only 4% of both had FM.

In addition, researchers found that the twins with CFS appeared to be more depressed and anxious than their healthy counterparts. Differences in brain scans also were examined. Twins with CFS had different patterns primarily in the frontal and temporal cortical regions in SPECT imaging.

No significant differences were found in the frequency of viral infections, and natural killer cell activity was similar in both those with and without CFS. Analysis of white blood cell subsets showed that the twins with CFS did seem to have a lower number of immunologically experienced or “memory” cells than their healthy twin. Twins with CFS were noted to have less persistent activation of the T lymphocytes.

Researchers used information from completed comprehensive Registry Booklets, psychiatric interviews and medical records to evaluate over 400 sets of twins for Phase 1 of the study. Participants were evaluated using continuous measurement and recording of physiological activity during sleep, exercise capacity testing, neuropsychological assessment, psychiatric and life events interviews, and tests of viral replication and the immune system. In addition, patients’ regional cerebral blood flow was measured with SPECT imaging.

According to Dr. Dedra Buchwald, lead researcher and University of Washington associate professor of medicine, CFS/FM and healthy twins are being used because the researchers have the unique opportunity to adjust for inherited and environmental factors such as exposures and early life experiences.

Further testing will be conducted in Phase 2 of the twins’ study to confirm Phase 1 results. In addition, researchers at the University of Washington will compare their CFS/FM-healthy twin results to results gained from testing healthy-healthy twins and try to determine how much of a role a patient’s perception plays in CFS/FM.