BDNF and Parkinson disease: However, in a single study on PD patients in the majority Caucasians, the allele A of the BDNF Val66Met SNP (related to decreased protein secretion) was associated with higher risk of developing levodopa‐induced dyskinesias (Foltynie et al., 2009), and futhremore the low‐activity allele A of the COMT Val158Met SNP was reported to increase the risk of levodopa‐induced dyskinesias in Dutch PD patients (de Lau et al., 2012), and to decrease the risk of wearing‐off phenomena in Chinese PD patients (Wu et al., 2014).