NF1 and neurofibromatosis type 1: Germline mutation of the NF1 gene is the cause of neurofibromatosis type I, as the gene product neurofibromin is a negative regulator of the Ras/MAPK and PI3K/mTOR signal transduction networks; its involvement in sporadic PanNETs is occasional, while about 40% of periampullary duodenal somatostatinomas associate with NF1 disease.