PMP22 and plexiform neurofibroma: There are several possible explanations: (i) Different promoters might be used during neurofibroma development; (ii) transcription and posttranscriptional modification might be involved; (iii) translation might play an important role; and (iv) it might be PMP22 protein accumulation due to increased myelin sheaths (Fig. 1D), which can stabilize PMP22 protein, in Runx1fl/fl;Runx3fl/fl;Nf1fl/fl;DhhCre.