TREM2 Variant p.R47H as a Risk Factor for Sporadic Amyotrophic Lateral Sclerosis

Importance  Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease in which microglia play a significant and active role. Recently, a rare missense variant (p.R47H) in the microglial activating gene TREM2 was found to increase the risk of several neurodegenerative diseases, including Alzheimer disease. Whether the p.R47H variant is a risk factor for ALS is not known.

Objectives  To determine whether p.R47H (rs75932628) in TREM2 is a risk factor for ALS and assess whether TREM2 expression is dysregulated in disease.

Design, Setting, and Participants  Samples of DNA from 923 individuals with sporadic ALS and 1854 healthy control individuals self-reported as non-Hispanic white were collected from ALS clinics in the United States and genotyped for the p.R47H variant in TREM2. Clinical data were obtained on ALS participants for genotype/phenotype correlations. Expression of TREM2 was measured by quantitative polymerase chain reaction and compared in spinal cord samples from 18 autopsied patients with ALS and 12 neurologically healthy controls, as well as from wild-type and transgenic SOD1G93A mice.

Main Outcomes and Measures  Minor allele frequency of rs75932628 and relative expression of TREM2.

Results  The TREM2 variant p.R47H was more common in patients with ALS than in the controls and is therefore a significant risk factor for ALS (odds ratio, 2.40; 95% CI, 1.29-4.15; P = 4.1×10−3). Furthermore, TREM2 expression was increased in spinal cord samples from ALS patients andSOD1G93A mice (P = 2.8×10−4 and P = 2.8×10−9, respectively), confirming dysregulated TREM2 in disease. Expression of TREM2 in the human spinal cord was negatively correlated with survival (P = .04) but not with other phenotypic aspects of disease.

Conclusions and Relevance  This study demonstrates that the TREM2 p.R47H variant is a potent risk factor for sporadic ALS. To our knowledge, these findings identify the first genetic influence on neuroinflammation in ALS and highlight the TREM2 signaling pathway as a therapeutic target in ALS and other neurodegenerative diseases.

JAMA Neurology 2014