The genetic basis of many monogenic neurological diseases with parkins
onian features has been elucidated over the past few years. The clinic
al and genetic features are discussed for the diseases with prominent
parkinsonian signs. There is also accumulating evidence for a role of
genetic factors in the aetiology of idiopathic Parkinson's disease (PD
); however, the approach to polygenic diseases is quite different from
that to the simpler single-gene disorders. The role of epidemiology i
n not only establishing genetic Susceptibility, but its impact on esti
mating the size of the problem, is also discussed. A number of candida
te genes have been studied in PD but, to date, there is no conclusive
proof for any of these. It therefore seems likely that a random genome
search is required, and the technical and statistical methods are now
available. It is hoped that knowledge of the genes involved will lead
to better therapy for this incurable and common disorder.