GRN and early-onset autosomal dominant Alzheimer disease: Mutations in the key metabolic microglial genes such as myeloid cells-2 gene (Trem2) and granulin gene (Grn) have been identified as risk factors for various neurodegenerative and neuroinflammatory disorders such as Alzheimer’s disease, amyotrophic lateral sclerosis and viral infections of the central nervous system [13].