 Expression is at its highest level in adult neurons, Schwann cells, astrocytes, leukocytes, and oligodendrocytes.The catalytic RasGAP activity of neurofibromin is located in a central portion of the protein, that is called the GAP-related domain (GRD).The GRD is closely homologous to RasGAP and represents about 10% (229 amino acids) of the neurofibromin sequence.