Glycin codon 850 (CGT) in exon 21 was changed to arginine (CGT) (p.G850R) and an FRT site flanked neomycin selection cassette was inserted into intron 20. Flp-mediated recombination removed the selection cassette. The mutation recapitulates the human c.2542G>C p.Gly848Arg variant associated with Neurofibromatosis type 1 (NF1).