Familial aggregation of Parkinson disease in Utah: A population-based analysis using death certificates

OBJECTIVE: To describe clustering of death from Parkinson disease (PD) in relatives in a large US study. METHODS: We analyzed the Utah Population Database resource, which includes genealogy data of more than 2.7 million individuals linked to 519,061 individuals with a Utah death certificate (DC). We identified individuals whose DC included PD as a cause of death using ICD coding. In those individuals whose Utah DC listed PD as a cause of death, the relative risk (RR) of death with PD was determined among close and distant relatives using sex-, birth year–, and birthplace-specific rates. RESULTS: We identified 4,031 individuals whose DC indicated PD. Among 18,127 first-degree relatives of probands with a Utah DC, the RR of death with PD was significantly increased (RR = 1.82, 95% confidence interval [CI] 1.61–2.04). The RR of death with PD was also significantly increased among 40,546 second-degree relatives with a Utah DC (RR = 1.44, 95% CI 1.29–1.60) and among 93,398 third-degree relatives with a Utah DC (RR = 1.10, 95% CI 1.03–1.18). CONCLUSIONS: Significant evidence for excess familial clustering was observed for PD deaths. The excess familial clustering and the significantly elevated RRs for PD among close and distant relatives strongly support a genetic contribution to PD mortality. These results confirm and expand the results of previous studies of PD by quantifying the risk of PD death among more distant relatives.