NF1 and plexiform neurofibroma: Despite the fact, that more than 500 different mutations of the NF1 gene have been identified so far, only the in-frame deletion of Exon 17 and a whole NF1 gene deletion were associated with either solely pigmentary features of NF1 without plexiform neurofibromas or a more frequent and severe course of the disease including more cutaneous neurofibromas, frequent cognitive abnormalities, and a marfanoid habitus, respectively [10].