la senile maladies the facts, that can be ascertuined regarding heredity probably fall short of the truth to a greater extent than in the maladies of earlier life, because, as life goes on, the death of older relations lessens the opportunities of ascertaining the facts. It is often astonishing how much disease inquiry sometimes reveals in the families of those who imagine, before the inquiry is made, that they are absolutely free from all morbid heredity . . .
W. R. Gowers
(A manual of diseases of the nervous system.
London 1888, p. 5890
The relevance of genetic factors in the pathogenesis of neurologic diseases is being recognized increasingly, and enormous progress has been made in the understanding of the most common single-gene disorder of the basal ganglia, Huntington's disease.' It is less clear, however, to what extent genetic factors contribute to the pathogenesis of the most common of all basal ganglia disorders, Parkinson's disease (PD). This article reviews the literature on epidemiological and family studies, and summarizes the results of molecular genetic research in this disease. Some of our own experimental work is included in this review.
EPIDEMIOLOGICAL STUDIES
Gowers found evidence of heredity in "not more than 15%" of his personal series of patients with Parkinson's disease (PD).2 Similar figures were reported by other contemporary authors (as quoted in references 2 and 3). The first systematic genetic study of PD was carried out by Mjiines who identified a positive family history in 79