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To estimate the prevalence of viruses associated with chronic fatigue syndrome (CFS) and to control for genetic and environmental factors, we conducted a co-twin control study of 22 monozygotic twin pairs, of which one twin met criteria for CFS and the other twin was healthy. Levels of antibodies to human herpesvirus (HHV)-8, cytomegalovirus, herpes simplex virus 1 and 2, and hepatitis C virus were measured. Polymerase chain reaction (PCR) assays for viral DNA were performed on peripheral blood mononuclear cell specimens to detect infection with HHV-6, HHV-7, HHV-8, cytomegalovirus, Epstein-Barr virus, herpes simplex virus, varicella zoster virus, JC virus, BK virus, and parvovirus B19. To detect lytic infection, plasma was tested by PCR for HHV-6, HHV8, cytomegalovirus, and Epstein-Barr virus DNA, and saliva was examined for HHV-8 DNA. For all assays, results did not differ between the group of twins with CFS and the healthy twins. [ABSTRACT FROM AUTHOR]

This study examined the effects of exhaustive exercise on cognitive functioning among 21 monozygotic twin pairs discordant for chronic fatigue syndrome (CFS). The co-twin control design adjusts for genetic and family environmental factors not generally accounted for in more traditional research designs of neuropsychological function. Participants pedaled a cycle ergometer to exhaustion; maximum oxygen output capacity (VO[sub 2max]) as well as perceived exertion were recorded. Neuropsychological tests of brief attention and concentration, speed of visual motor information processing, verbal learning and recognition memory, and word and category fluency were administered with alternate forms to participants pre- and postexercise. The preexercise neuropsychological test performance of CFS twins tended to be slightly below that of the healthy twin controls on all measures. However, twins with CFS did not demonstrate differential decrements in neuropsychological functioning after exercise relative to their healthy co-twins. Because exercise does not appear to diminish cognitive function, rehabilitative treatment approaches incorporating exercise are not contraindicated in CFS. [ABSTRACT FROM AUTHOR]

Objective: To examine the independent effects of chronic regional and widespread pain syndromes on health and functional status after accounting for comorbid chronic fatigue using a co-twin control design., Methods: We identified 95 twin pairs discordant for pain in which one twin had chronic regional or widespread pain and the other denied chronic pain. Demographic data, functional and psychological status, health behaviors, and symptoms based on the 1994 criteria for chronic fatigue syndrome (CFS) were assessed by questionnaire. Psychiatric diagnoses were based on structured interview. Random effects regression modeling estimated associations between chronic regional and widespread pain and each health measure with and without adjustment for CFS., Results: Significant differences (p