SNCA and Parkinson disease: Here we present the first evidence that SNCA is an important and strong predictor of faster motor symptom decline in idiopathic PD: we observed a 4-fold higher risk of PD for carriers of the SNCA-Rep1 263bp allele and, when considering both Rep1 263bp and rs356165 ‘G’ allele, we observed a strong trend for faster motor decline across categories of the combined genetic variants.