CHM and Parkinson disease: Supporting this concept, a clinical study on well characterized PD patients described that the low repeat REP1 allele, a complex microsatellite (259 base pairs; resulting in decreased SNCA expression) is associated with motor and cognitive dysfunctions, whereas the high-repeat REP1 allele (263 base pairs; increases SNCA expression) is associated with improving the motor and non-motor symptoms like cognition (Markopoulou et al., 2014).