Such specific association is of particular relevance since isoform I is predominantly expressed in central nervous system neurons [33], and the finding that in mice, constitutional homozygous deletion of exon 23a (i.e., loss of Nf1 mRNA isoform 1 expression in all tissues) is viable, do not affect development or cause cancer predisposition but results in spatial learning and memory defects [24, 25]. This evidence concerns the gene NF1 and cancer.