These results, coupled with the numerous mutations of NF1 that cause the disease neurofibromatosis type 1, but do not appear to affect protein stability or GAP function (Abernathy et al., 1997; Fahsold et al., 2000), argue that functional domains outside the GRD may mediate important aspects of neurofibromin function in neuroblastoma tumor suppression. Here, NF1 is linked to neurofibromatosis type 1.