Environmental risk factors

In 1949, Mjones conducted the first systematic study of the genetics of Parkinson’s disease (PD) and concluded that the disease was autosomal dominant with 60% penetrance (1). Subsequent studies have found a substantially lower prevalence of familial PD, beginning an ongoing debate regarding the relative importance of genetic versus environmental factors in the pathogenesis of PD. There are several techniques that have been used to determine the genetic and environmental contributions to the etiology of PD, including family, twin, population kinship, and geographic information system (GIS) studies.