The type 1 NF1 deletion-associated phenotype includes facial dysmorphic features, severe global developmental delay, significantly lower full-scale IQ scores, higher neurofibroma burden and an increased risk of malignant peripheral nerve sheath tumours (MPNSTs) as compared to patients with intragenic NF1 mutations [5,51,52,53,54]. This evidence concerns the gene NF1 and Global developmental delay.