Is Parkinson's disease acquired or inherited?

A considerable proportion of patients with Parkinson's disease report having affected relatives. However, anamnestic data obtained from probands on the occurrence of secondary cases among their relatives are of limited value. In considering the possible role of heredity in Parkinson's disease it is necessary to carefully distinguish between the disease and other disorders such as essential tremor and olivopontocerebellar atrophy which may manifest parkinsonian features. Controlled family studies have shown only a very slight excess of secondary cases among index siblings as compared to spouse siblings. The concordance rate for Parkinson's disease among identical twins is extraordinarily low and does not significantly exceed that among fraternal twins or that expected from the prevalence rate among siblings found in the controlled family studies. The available evidence indicates that heredity plays no significant role in the etiology of Parkinson's disease. Consequently the disease must be considered to be acquired.