Table 2 Quick view for risk counseling.

First-degree relative affected

Compared to a baseline lifetime risk of 3% for the general population, this family history increases chances by about twofold or 6% (GeneReviews® Parkinson Disease Overview)

LRRK2 G2019S test result in at-risk patient of European or Ashkenazi Jewish ancestry

Compared to the baseline lifetime risk … this genetic test result increases chances to about 26%^a

GBA1 positive test result in an at-risk patient of any ancestry

Compared to the baseline lifetime risk of … risk is in the range of 10–30%^a

PRKN positive test result (homozygous) in an affected patient

Assuming the variants are on different chromosomes, the theoretical risk to each offspring for early-onset PD depends on the carrier status of the partner; risk for children to be at least a carrier is 100%, parents will be obligate carriers