NF1 and malignant peripheral nerve sheath tumor: In contrast, patients with a microdeletion of the NF1 region tend to have a more severe phenotype associated with large numbers and more early appearance of cutaneous neurofibromas, a higher risk for development of malignant peripheral nerve sheath tumors, more severe cognitive impairment and sometimes somatic overgrowth with large hands and feet and dysmorphic facial features (Mensink et al., 2006).