SNCA and Parkinson disease: By quantitative proteomic analysis of frontal cortex of parkinsonism-dementia complex cases using iTRAQ labeling, alpha synuclein is identified as a candidate biomarker.[43] Lee et al. performed peptide mass finger printing to identify candidates for Alzheimer's disease associated proteins[44] and found fibrinogen gamma-A chain precursor protein to be upregulated with the progression of the disease.