It is a clinical diagnosis that requires at least two of the following: a first-degree relative (parent or child) with NF1; six or more café-au-lait macules (>5 mm in pre-pubertal and >1.5 cm in post-pubertal patients); axillary and inguinal freckling; two or more hamartomatous Lisch nodules of the iris; optic pathway glioma; two or more neurofibromas of any type or one plexiform neurofibroma (PN); disease-typical bony dysplasia; or a known pathologic mutation in the NF1 gene. This evidence concerns the gene NF1 and plexiform neurofibroma.