Schwannomas and neurofibromas, also kwown as peripheral nerve sheath tumors (PNST) are benign tumors that arise from the nerve sheath of peripheral nerves. PNST are commonly solitary tumors, but they may occur in multiple areas of the body in Neurofibromatosis. Basic research includes genotype characterization of different phenotypes of the diseases. A novel third type of recurrent NF1 microdeletion was shown to be mediated by nonallelic homologous recombination between low-copy repeats in chromosome 17q.