Exceptions include deletion of the entire NF1 gene which is associated with a severe form of the disease [15], a recurrently ascertained 3-bp in-frame deletion of exon 17 (c.2970-2972 delAAT) that is associated with the typical pigmentary NF1 features but without cutaneous or surface plexiform neurofibromas [16], and duplication of the NF1 locus which usually leads to intellectual impairment and epilepsy without the other NF1 features [17, 18]. This evidence concerns the gene NF1 and Cognitive impairment.