SNCA and Parkinson disease: For example, alpha-synuclein (SNCA), a Parkinson’s (PD) risk gene, shows co-expression divergence between human and mouse primarily in the substantia nigra and basal ganglia, whereas presenilin-1 (PSEN-1), an AD risk gene, which had been shown to be divergent in cortex [8] displayed significant divergence across 10 brain regions (Fig. 6f; Additional file 9: Table S8).