SNCA and early-onset autosomal dominant Alzheimer disease: Currently, there are no specific diagnostic methods for NDDs and they are usually diagnosed based on nonspecific clinical symptoms and occasionally by biomarkers, such as β-amyloid (Aβ) for Alzheimer’s disease (AD) and a-synuclein (α-syn) for Parkinson’s disease, etc. However, it is usually too late for most treatment to startr when the aforementioned criteria become detectable.