TREM2 mutations have also been identified as risk factors for Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), and FTD (Rayaprolu et al., 2013; Borroni et al., 2014; Cady et al., 2014; Cuyvers et al., 2014). Here, TREM2 is linked to amyotrophic lateral sclerosis.