Sick and tired: tracking paths to chronic fatigue.

Stressful experiences and a genetic predisposition toward emotional turmoil contribute to some cases of chronic fatigue syndrome, two new studies indicate.

The investigations, published in the November Archives of General Psychiatry, add to growing evidence that several varieties of chronic fatigue syndrome (CFS) occur, each with distinct causes.

CFS affects roughly 800,000 people in the United States. It's characterized by disabling fatigue lasting 6 months or more and at least four of eight other symptoms: muscle pain, joint pain, memory or concentration loss, unusual fatigue after exercise, unrefreshing sleep, tender lymph nodes, headaches, and sore throat.

In the first of the new studies, psychologist Christine Heim of Emory University School of Medicine in Atlanta and her coworkers found that adults with CFS report a greater number of traumatic circumstances in their childhoods than other adults do.

From a representative sample of Wichita, Kan., residents, the researchers identified 43 individuals with CFS and 60 others with no fatigue problems. Two-thirds of the CFS group reported childhood experiences of emotional, physical, or sexual abuse or emotional or physical neglect. Only one-third of the nonfatigued group reported such traumas.

CFS rates were highest for individuals who cited more than one type of childhood trauma and for those who endured especially severe ordeals, Heim's team says. Depression, anxiety, and post-traumatic stress disorder also appeared frequently in participants with childhood traumas.

In some people, profound stress during childhood impairs the brain's responses to new challenges, the researchers propose. This process sets the stage for a number of ailments, including CFS, in their view.

The second new study, led by epidemiologist Nancy L. Pedersen of the Karolinska Institute in Stockholm, included 19,192 Swedish twins born between 1935 and 1958 and interviewed from 1998 to 2002. In that population of identical and fraternal twins, 447 individuals had CFS and another 1,120 reported disabling fatigue without four of the other symptoms.

Nearly one-fourth of these fatigue-troubled participants described their daily lives as "very stress filled," compared with 13 percent of the others. High stress levels contributed to CFS and persistent fatigue independently of each twin's genetic makeup, the scientists found.

The team also considered a personality tendency to experience emotional distress. Twins who scored high on this measure displayed a higher CFS rate than those with low scores did. The study revealed that genetic influences on this trait promote "chronic fatigue-like illness," the researchers speculate.

Since many adults with CFS in the new studies didn't report childhood traumas or severe daily stress, the new findings don't support the controversial notion that CFS is a by-product of depression, comments psychologist Leonard A. Jason of DePaul University in Chicago.

In a related study described in the Sept. 16 British Medical Journal, a team led by psychiatrist Ian Hickie of Sydney (Australia) University reports that 29 of 253 people who became infected with any of three viruses, including Epstein-Barr virus, developed CFS soon afterward. Preexisting stress or psychological ailments played no role in these CFS cases, the authors say.

Several genes that contribute to the body's stress-response system have also been linked to CFS.

STATS

800,000

Estimated number of people in the United States with chronic fatigue syndrome