 Neurofibromin is ubiquitously expressed, but expression levels vary depending on the tissue type and developmental stage of the organism.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).