DHCR24 and early-onset autosomal dominant Alzheimer disease: In 2000, Greeve et al. first found that there is a significant reduction in the expression of new gene in vulnerable brain regions in Alzheimer’s disease (AD) patients, which was named selective Alzheimer’s disease indicator 1 (Seladin-1), namely 24-dehydrocholesterol reductase (DHCR24) [45, 57].