TREM2 and Alzheimer disease: While some have reported decreased levels of sTREM2 and TREM2 intracellular domain (ICD) production in vitro with the R47H variant [224], the TREM2 R47H variant acted similarly to wild-type in sTREM2 production in other in vitro assays [225] and AD patients carrying the R47H variant had elevated levels of CSF sTREM2 [86].