Claim: There are three members of the ADAR family, ADARs 1-3, with ADAR 1 and ADAR 2 being the only enzymatically active members and never involved in editing at the Q/R site, and ADAR3 is thought to have a regulatory role in the brain and is restricted to the brain only.
Evidence: ADAR and ADARB1 are known to be catalytically active while ADARB2 is thought to be inactive.