Cephalometry in adults and children with neurofibromatosis type 1: Implications for the pathogenesis of sphenoid wing dysplasia and the "NF1 facies"

Background: Neurofibromatosis type 1 (NF1) is a common, autosomal dominant tumor-predisposition disorder that arises secondary to mutations in the tumor suppressor gene NF1. Cephalometry is an inexpensive, readily available and non-invasive technique that is under-utilized in studying the NF1 craniofacial phenotype. An analysis of NF1 cephalometry was first published by Heervëa et al. in 2011. We expand here on that first investigation with a larger cohort of adult and pediatric patients affected with NF1 and sought objective insight into the NF1 facies, said to feature hypertelorism and a broad nasal base, from cephalometric analysis. Methods: We obtained cephalograms from 101 patients with NF1 (78 adults and 23 children) from two NF1 protocols at the National Institutes of Health. Each subject had an age-, gender- and ethnicitymatched control. We used Dolphin software to make the cephalometric measurements. We assessed the normality of differences between paired samples using the ShapiroeWilk test and evaluated the significance of mean differences using paired t-tests and adjusted for multiple testing. We explored the relationship between the cephalometric measurements and height, head circumference and interpupillary distance. Results: In this dataset of American whites with NF1, we confirmed in a modestly larger sample many of the findings found by Heerva et al. in an NF1 Finnish cohort. We found a shorter maxilla, mandible, cranial base, (especially anteriorly, p = 0.0001) and diminished facial height in adults, but not children, with NF1. Only one adult exhibited hypertelorism. Conclusions: The cephalometric differences in adults arise in part from cranial base shortening and thus result in a shorter face, mid-face hypoplasia, reduced facial projection, smaller jaw, and increased braincase globularity. In addition, we suggest that NF1 sphenoid bone shortening, a common event, is consistent with an intrinsic NF1 bone cell defect, which renders the bone more vulnerable to a random "second hit" in NF1, leading to sphenoid wing dysplasia, a rare event.