Astrocyte expressing HSD3B7 is responsible for degradation of oxysterol, the active oxidized product of cholesterol, which can be used as a marker of brain atrophy in patients holding aging neurons with AD and HD (Leoni & Caccia, 2011; Rutkowska, Preuss, Gessier, Sailer, & Dev, 2015). The gene discussed is HSD3B7; the disease is Alzheimer disease.