SNCA and Parkinson disease: This research has yielded ambiguous results owing to the various assay techniques, the different protein forms assayed (total, oligomeric and phosphorylated) and the small populations enrolled (El-Agnaf et al. 2006; Lee et al. 2006; Li et al. 2007; Duran et al. 2010; Shi et al. 2010; Foulds et al. 2013); others also suggested gender-related differences in plasma α-synuclein expression in PD (Caranci et al. 2013).