TREM2 and neurodegenerative disease: Loss-of-function mutations for TREM2 such as the common rs75932628 variant (encoding R47H) have been associated with deficiencies in the innate-immune system, axonal and synaptic abnormalities, deficits in phagocytosis and progressive dementia in neurodegenerative diseases including PLOSL (Nasu-Hakola disease) as well as more recently in the sporadic forms of familial ALS and AD [6–14,49–53,85].