GTPase activator for the Rho-type GTPases by converting them to an inactive GDP-bound state. Expressed predominantly in the brain. Lower expression is found in lymph nodes. Low expression is found in fetal liver. A chromosomal aberration involving ARHGAP20 may be a cause of B-cell chronic lymphocytic leukemia (B-CLL) (PubMed:15543602). Translocation t(X;11)(q21;q23) with BRWD3 does not result in fusion transcripts but disrupts both genes (PubMed:15543602). The translocation involving this gene was originally published as t(X;11)(q13;23), but BRWD3 is localized to Xq21 and not to Xq13. Extended N-terminus. Probable cloning artifact. Extended N-terminus. Extended N-terminus. Probable cloning artifact.