Molecular analysis remains crucial in sporadic cases (to confirm the diagnosis in young children still not fulfilling the NIH criteria and to differentiate NF1 from Legius syndrome, which is caused by mutations in the SPRED1 gene), in adults requesting a prenatal/preimplantation diagnosis, or in patients presenting with spinal NF1 that may have very limited skin involvement [13], and in other atypical cases. This evidence concerns the gene NF1 and Legius syndrome.