HMGCS2 is a mitochondrial enzyme that catalyzes the first reaction of ketogenesis and related research has mainly focused on its roles in diabetes, tumor, Alzheimer's disease, and intestinal cell differentiation (Shi et al, 2017; Wang et al, 2017, 2019b, 2020b; Wan et al, 2018; Kim et al, 2019; Tomita et al, 2020). The gene discussed is HMGCS2; the disease is early-onset autosomal dominant Alzheimer disease.