Arginine codon 683 (CGA) in exon 18 was changed to a stop codon (TGA) (p.R683*) and an FRT site flanked neomycin selection cassette was inserted into intron 17. Flp-mediated recombination removed the selection cassette. The mutation recapitulates the human c.2041C>T p.Arg681* variant associated with Neurofibromatosis type 1 (NF1).