Systems Biology Approaches Reveal Potential Phenotype-Modifier Genes in Neurofibromatosis Type 1

Neurofibromatosis in Children: Actually and Perspectives

The three types of neurofibromatosis, namely type 1, type 2, and schwannomatosis, are generally associated with various benign tumors affecting the skin and the nervous system. On rare occasions, especially in patients with neurofibromatosis type 1 (NF1), malignant neoplasms may also be present, several of them possessing a more aggressive course than in individuals without this syndrome. As such, a clear delineation between the three variants of neurofibromatosis is crucial to establish the correct diagnosis and management, as well as predict the neoplasm-related outcomes. Neurofibromin, the principal product of the NF1 gene, is a potent inhibitor of cellular proliferation, having been linked to several key signaling pathways involved in tumor growth. Therefore, it may provide a useful therapeutic target for tumor management in these patients. In this article, we want to present the association between deficiency of neurofibromin and the consequences of the lack of this protein leading to different kinds of malignant tumors. The therapy is still uncertain and most therapeutic options are in development or clinical trials.

Recurrent NF1 gene variants and their genotype/phenotype correlations in patients with Neurofibromatosis type I

Neurofibromatosis type I, a genetic condition due to pathogenic variants in the NF1 gene, is burdened by a high rate of complications, including neoplasms, which increase morbidity and mortality for the disease. We retrospectively re-evaluated the NF1 gene variants found in the period 2000-2019 and we studied for genotype/phenotype correlations of disease complications and neoplasms 34 variants, which were shared by at least two unrelated families (range 2-11) for a total 141 of probands and 21 relatives affected by Neurofibromatosis type I. Recurrent variants could be ascribed to the most common mutational mechanisms (C to T transition, microsatellite slippage, non-homologous recombination). In genotype/phenotype correlations, the variants p.Arg440*, p.Tyr489Cys, and p.Arg1947*, together with the gross gene deletions, displayed the highest rates of complications. When considering neoplasms, carriers of variants falling in the extradomain region at the 5' end of NF1 had a lower age-related cancer frequency than the rest of the gene sequence, showing a borderline significance (p = 0.045), which was not conserved after correction with covariates. We conclude that (1) hotspots in NF1 occur via different mutational mechanisms, (2) several variants are associated with high rates of complications and cancers, and (3) there is an initial evidence toward a lower cancer risk for carriers of variants in the 5' end of the NF1 gene although not significant at the multivariate analysis.

Identification of NF1 Frameshift Variants in Two Chinese Families With Neurofibromatosis Type 1 and Early-Onset Hypertension

Background: Neurofibromatosis type 1 (NF-1) is a common autosomal dominant disorder caused by mutations in the NF1 gene. It is characterized by multiple café-au-lait macules, cutaneous neurofibromas, optic glioma, Lisch nodules, and axillary and inguinal freckling. The aim of this study was to investigate NF1 mutations in two Chinese families with NF-1 who presented with early-onset hypertension, and to determine the prevalence of hypertension associated with NF-1 to better understand this complication. Methods: Whole-exome sequencing was performed for the probands with NF-1 from two unrelated families. Possible pathogenic mutation was predicted by bioinformatic tools. Sanger sequencing was used to confirm candidate variants in all available individuals for familial co-segregation analysis. We also performed a systematic literature review of studies that reported the prevalence of hypertension in patients with NF-1. Results: In family 1, a recurrent mutation c.6789_6792delTTAC in NF1 was identified in the proband but in no other family members, indicating that this is a de novo mutation. In family 2, a novel mutation c.6934_6936delGCAinsTGCT in NF1 was detected in the proband and two other family members, which co-segregated with the disease phenotype within the family. Both mutations were predicted to be pathogenic by bioinformatic analysis. We found hypertension was a relatively common complication of NF-1, with a prevalence range of 6.1-23.4%. Ambulatory blood pressure monitoring is a stable method for detecting initial alterations of the blood pressure pattern, particularly for pre-hypertension. Conclusions: We identified one recurrent (c.6789_6792delTTAC) and one novel frame-shift mutation (c.6934_6936delGCAinsTGCT) in two unrelated families with NF-1 using whole-exome sequencing. In consideration of phenotypic heterogeneity in NF-1, genetic testing is a robust tool which helps early and accurate diagnosis. Because hypertension is not a rare complication of NF-1, routine screening for hypertension in patients with NF-1, especially children and adolescents, is important to avoid serious cardiovascular events.