Three prime repair exonuclease 1 is an enzyme that in humans is encoded by the TREX1 gene. This gene encodes the major 3'->5' DNA exonuclease in human cells. The protein is a non-processive exonuclease that may serve a proofreading function for a human DNA polymerase. It is also a component of the SET complex, and acts to rapidly degrade 3' ends of nicked DNA during granzyme A-mediated cell death. Mutations in this gene result in Aicardi-Goutieres syndrome, chilblain lupus, RVCL (Retinal Vasculopathy with Cerebral Leukodystrophy), and Cree encephalitis. Multiple transcript variants encoding different isoforms have been found for this gene.