A Translational Approach to Spinal Neurofibromatosis: Clinical and Molecular Insights from a Wide Italian Cohort

SIMPLE SUMMARY: At present, no systematic study of the clinical spectrum and molecular characteristics of NF1 patients with spinal neurofibromatosis (SNF), a phenotypic subclass of neurofibromatosis 1 (NF1), has been carried out. Here, we provide evidence that SNF patients are at high risk of problematic neurofibromas, presenting not only bilateral neurofibromas involving all spinal roots, but also a higher incidence of internal neurofibromas and nerve root swelling. From a histopathological view, not only neurofibromas, but also neurogangliomas are present in SNF. The analysis of 19 families with at least 1 member affected by SNF showed a high phenotypic variability within the SNF families. Furthermore, we discovered a higher prevalence of missense mutations in SNF compared to classical NF1. Both clinical features and genetic testing can help in identifying cases at risk of SNF, and that are more likely to benefit from a spinal MRI scan. ABSTRACT: Spinal neurofibromatosis (SNF), a phenotypic subclass of neurofibromatosis 1 (NF1), is characterized by bilateral neurofibromas involving all spinal roots. In order to deepen the understanding of SNF’s clinical and genetic features, we identified 81 patients with SNF, 55 from unrelated families, and 26 belonging to 19 families with at least 1 member affected by SNF, and 106 NF1 patients aged >30 years without spinal tumors. A comprehensive NF1 mutation screening was performed using NGS panels, including NF1 and several RAS pathway genes. The main features of the SNF subjects were a higher number of internal neurofibromas (p < 0.001), nerve root swelling (p < 0.001), and subcutaneous neurofibromas (p = 0.03), while hyperpigmentation signs were significantly less frequent compared with the classical NF1-affected cohorts (p = 0.012). Fifteen patients underwent neurosurgical intervention. The histological findings revealed neurofibromas in 13 patients and ganglioneuromas in 2 patients. Phenotypic variability within SNF families was observed. The proportion of missense mutations was higher in the SNF cases than in the classical NF1 group (21.40% vs. 7.5%, p = 0.007), conferring an odds ratio (OR) of 3.34 (CI = 1.33–10.78). Two unrelated familial SNF cases harbored in trans double NF1 mutations that seemed to have a subclinical worsening effect on the clinical phenotype. Our study, with the largest series of SNF patients reported to date, better defines the clinical and genetic features of SNF, which could improve the management and genetic counseling of NF1.