SNCA and early-onset autosomal dominant Alzheimer disease: The relative position of each concept on the map indicates the development stage of the theme: (1) mature and essential themes are located in the upper middle region (e.g., stromal cells, in vitro studies, multiple sclerosis); (2) highly developed themes are found in the middle right region (e.g., exosomes, expression, brain); and (3) emerging themes are located in the lower right region (e.g., extracellular vesicles, Alzheimer’s disease, alpha-synuclein).