Depending on the timing and types of progenitor cells affected externally visible features may include pigmentary features only, cutaneous or plexiform neurofibromas only, or a combination of both, and affected body regions may range from multiple body regions crossing the midline that may resemble a generalized phenotype, to a single segment of the body not crossing the midline.38 Pure gonadal mosaicism, with the somatic NF1 PVs present only in the gonads, is, however, rare.39 This evidence concerns the gene NF1 and plexiform neurofibroma.