However, further studies are required from pathologically (alpha-synuclein, phospho-tau, total-tau and amyloid) and cognitively characterized cohorts using medication and pathology-free, age-matched control groups to elucidate how these measures correlate with symptom severity and are influenced by Alzheimer’s disease and Parkinson’s disease pathology. This evidence concerns the gene SNCA and early-onset autosomal dominant Alzheimer disease.