NF1 and neurofibroma: The mild phenotype without any externally visible neurofibromas observed in the current study is therefore similar to that of individuals with the NF1 p.Arg1809 missense pathogenic variants, except for the presence of brain tumors being more prevalent in the p.Met992del-positive cohort (4.8% versus 0.8%), but this difference was not statistically significant (P = 0.0640).