[Incidence and clinical profile of familial forms of Parkinson's disease. A study of 428 index-cases from a department of neurology].

Although the cause of Parkinson's disease remains to be determined, several lines of evidence favor the role of a genetic factor. We therefore studied a series of 428 index-cases of Parkinson's disease that were referred to our Department of Neurology between 1986 and 1993, with the aim to identify secondary family cases. Index-cases were divided into 2 groups. In groups A (279 cases), a retrospective analysis of patients records was performed. In group B (149 cases), a prospective study was carried out by 1992, which allowed a more complete investigation of family history. In group A, 31/279 index-cases (11.1 p. 100) had secondary familial cases of Parkinson's disease. This percentage increased up to 22.8 p. 100 among index-cases in group B (34/149 cases). In most instances, only one secondary case was detected, and very few proponents had 2, or 3 other family cases. No large family with numerous Parkinson's disease cases was disclosed. Age at onset of disease was similar in group A between sporadic and familial index-cases, whereas in group B age at onset was earlier index-cases with positive family history as compared to those without (53.9 +/- 10.4 years versus 59.7 +/- 12.1 years respectively). This may be due to the different sizes of groups A and B, whereas clinical profile analysis did not differentiate index-cases with positive family history from those without family history (sporadic cases). An anticipation of age at onset of illness of 13.9 +/- 12.2 years was found in 9 of the 15 index-cases from group B with first degree parental vertical inheritance, where clinical data were available for the second family case. These findings about age at onset may be at least partly explained by a more accurate estimation of age at onset in index-cases than that in secondary family cases. Further analysis on the possible mode of transmission of the disease among familial cases was consistent with the implication of a genetic factor in the ethiopathogenesis of the disease, with a mendelian autosomal dominant inheritence with reduced penetrance.