FAMILIAL PARKINSONS-DISEASE - A CASE-CONTROL STUDY OF FAMILIES

Background: Parkinson's disease (PD) patients frequently report a fami ly history of PD and this may provide etiological clues to PD. It has also been suggested that a report of a negative family history is reli able. We studied the prevalence of PD in relatives of PD patients to a ssess the reliability of family history and to evaluate possible expla nations of ''familial PD''(fPD). Methods: 81 of 650 (12.5%) PD proband s (all PD patients seen at clinic in 4 years) reported a positive fami ly history of PD. Each fPD proband was matched with non-familial PD (n fPD) proband by gender and year of birth. Screening and follow-up ques tionnaires were mailed to relatives to obtain information concerning p edigree and presence of neurodegenerative disease. Available family me mbers (regardless of disease status) were examined. Results: On examin ation, 8 persons, said to be ''normal'' by probands, relatives and the mselves, had definite or possible PD (5 fPD, 3 nfPD). The prevalence r ate of PD among first and second degree living relatives of probands v aried significantly between fPD and nfPD groups (6269/100 000 versus 1 190/100 000; p < 0.001). The weighted prevalence (taking into account the proportions of fPD and nfPD within the clinic) was 1822/100 000, a value more than 5 times higher than reported prevalence rates of PD i n the general population (p < 0.001). The prevalence rate was greater in first degree relatives than second degree. Conclusions: ''Familial parkinsonism'' cannot be explained merely by size of or advanced age w ithin families. Significant numbers of previously unrecognized PD pati ents may be identified despite a ''negative'' family history. That is, the patient's report of an absence of familial parkinsonism is freque ntly inaccurate. The prevalence rate in relatives of PD patients appea rs to be higher than the general population - regardless of the family history reported by a PD patient. We believe our study suggests that genetic influences or early life environmental exposures are likely to be of etiological importance in PD.