NF1 and Global developmental delay: Genotype–phenotype analyses suggested from very early onthat patients with NF1 microdeletions oftenexhibit a more severe clinical phenotype than patients with intragenic NF1 mutations; the former are frequently characterised bydysmorphic facial features and severe developmental delay (Kayes et al. 1992, 1994; Wu et al. 1995,1997, 1999; Riva et al. 1996, 2000; Upadhyayaet al. 1996, 1998; Leppig et al. 1997; Tonsgard et al. 1997; Valero et al. 1997; Rasmussen et al. 1998; Streubel et al. 1999; Dorschner et al. 2000; Kobayashi et al. 2012).