Abstract
Twenty years ago Parkinson's disease (PD) was thought of as an environmentally determined neurodegenerative disease. It is now known that there are two autosomal dominant disease genes, alpha‐synuclein and dardarin, and three genes responsible for autosomal recessive PD, parkin, DJ‐1 and PINK‐1. Although these gene mutations are not common, their identification has led to a new understanding of the pathogenesis of PD, and to a development in the understanding of the clinical and pathological definitions of PD and Lewy body disease. Ultimately, these advances may lead to the development of new disease‐modifying therapies, but more immediately these discoveries have led to a more coherent view of the spectrum of PD and Lewy body diseases and to accurate genetic diagnosis and counselling for some families.