Haven't read the paper, yet, but if they've really established heritability of Parkinson's risk, that is a positive result in itself. The first hit for a Parkinson's Disease twin study suggests that genetic factors play a limited role in the disease's etiology, at least in late onset:
RESULTS: Of 268 twins with suspected parkinsonism and 250 presumed
unaffected twin brothers, 193 twins with PD were identified
(concordance-adjusted prevalence, 8.67/1000). In 71 MZ and 90 DZ pairs
with complete diagnoses, pairwise concordance was similar (0.129
overall, 0.155 MZ, 0.111 DZ; relative risk, 1.39; 95% confidence
interval, 0.63-3.1). In 16 pairs with diagnosis at or before age 50
years in at least 1 twin, MZ concordance was 1.0 (4 pairs), and DZ was
0.167 (relative risk, 6.0; 95% confidence interval, 1.69-21.26).
CONCLUSIONS: The similarity in concordance overall indicates that
genetic factors do not play a major role in causing typical PD. No
genetic component is evident when the disease begins after age 50
years. However, genetic factors appear to be important when disease
begins at or before age 50 years.
http://jama.ama-assn.org/content/281/4/341.short