Previous twin studies report no heritability of Parkinson's disease (PD) based on cross sectional information. Here, we apply a longitudinal design and re-evaluate cross sectional data in the population-based Swedish Twin Registry (STR) using clinical as well as hospital discharge and cause of death diagnoses. In the longitudinal analyses (based on 46,436 individuals), we identified 542 twins with PD and 65 twins with Parkinsonism. Concordance rates for PD were 11% for monozygotic and 4% for same-sexed dizygotic twin pairs, with a heritability estimate of 34%. Concordance rates for PD or parkinsonism were 13% for monozygotic and 5% for same-sexed dizygotic twin pairs, with a heritability estimate of 40%. In the cross sectional analyses (based on 49,814 individuals), we identified 287 twins with PD and 79 twins with parkinsonism. Concordance rates for PD were 4% for monozygotic and same-sexed dizygotic twin pairs and 0 for opposite-sexed twin pairs. Concordance rates for PD or parkinsonism were somewhat higher but the heritability estimate was nonsignificant. Our longitudinal analyses demonstrate that PD and parkinsonism are modestly heritable.
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