Two sporadic spinal neurofibromatosis patients with malignant peripheral nerve sheath tumour

Expression analysis of NF1-mutated alleles in a rare compound heterozygous spinal NF1 patient by digital PCR

BACKGROUD

Neurofibromatosis type 1 (NF1) is a heterogeneous neurocutaneous disorder. Spinal neurofibromatosis (SNF) is a distinct clinical entity of NF1, characterized by bilateral neurofibromas involving all spinal nerve roots. Although both forms are caused by intragenic heterozygous variants of NF1, missense variants have been associated with SNF, according to a dominant inheritance model causing haploinsufficiency. Most patients carry pathogenic variants in one of the NF1 alleles; nevertheless, patients with both NF1-mutated copies have been described. Interestingly, all NF1 variants carried by the known SNF compound heterozygotes were missense/splicing variants or in-frame insertion-deletions.

AIMS

To investigate whether there is a differential expression of NF1 variant alleles in an NF1 compound heterozygous SNF patient possibly contributing to clinical phenotype.

MATERIALS & METHODS

We performed an allele-specific expression study, by chip-based digital PCR, in an SNF family carrying two NF1 missense variants. We evaluated the expression levels of the two NF1-mutated alleles both carried by the compound heterozygous SNF patient and his relatives.

RESULTS

Both alleles were expressed at comparable levels in the patient and hyper-expressed compared to the wild-type alleles of healthy controls.

DISCUSSION

Here we provide new insights into expression studies of NF1-mutated transcripts suggesting that a novel pathogenetic mechanism, caused by gain-of-function variants, could be associated with SNF.

CONCLUSIONS

Further studies should be performed in larger cohorts, opening new perspectives in the NF1 pathogenesis comprehension.

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

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.

The Arg1038Gly missense variant in the NF1 gene causes a mild phenotype without neurofibromas

Background

Neurofibromatosis type 1 (NF1) is an autosomal dominant condition caused by inactivating mutations of the NF1 gene. The wide allelic heterogeneity of this condition, with more than 3,000 pathogenic variants reported so far, is paralleled by its high clinical variability, which is observed even within the same family. The definition of genotype–phenotype correlations has been hampered by the complexity of the NF1 gene and, although a few exceptions have been recognized, the clinical course remains unpredictable in most patients.

Methods

Sequencing of NF1 in patients with cafè‐au‐lait spots identified the c.3112A>G variant. RNA analysis and a minigene assay were employed to investigate splicing.

Results

Here we report a novel genotype–phenotype correlation in NF1: the identification of the missense variant NM_000267.3:c.3112A>G p.(Arg1038Gly) in seven individuals from two unrelated families with a mild phenotype. All the patients manifest cafè‐au‐lait spots without neurofibromas or other NF1–associated complications, and Noonan syndrome features in most cases. The missense variant was not previously reported in available databases, segregates with the phenotype and involves a highly conserved residue. Both a minigene assay and patient's RNA analysis excluded an effect on splicing.

Conclusion

Our data support the correlation of the p.Arg1038Gly missense substitution with the cutaneous phenotype without neurofibromas or other complications. This finding may have relevant implications for patients and genetic counseling, but also to get insights into the function of neurofibromin.

The natural history of spinal neurofibromatosis: a critical review of clinical and genetic features

Spinal neurofibromatosis (SNF) is a related form of neurofibromatosis 1 (NF1), characterized by bilateral neurofibromas (histologically proven) of all spinal roots (and, eventually, of all the major peripheral nerve branches) with or without other manifestations of classical NF1. By rigorous application of these criteria to the 98 SNF cases published, we developed: (i) a cohort of 49 SNF patients (21 males and 28 females; aged 4-74 years]: 9 SNF families (21/49), 1 mixed SNF/NF1 family (1/49) and 27 of 49 sporadic SNF patients (including 5 unpublished patients in this report); and (ii) a group of 49 non-SNF patients including: (a) 32 patients with neurofibromas of multiple but not all spinal roots (MNFSR): 4 mixed SNF/MNFSR families (6/32); (b) 14 patients with NF1 manifestations without spinal neurofibromas, belonging to SNF (8/49) or MNFSR families (6/32); (c) 3 patients with neurofibromas in one spinal root. In addition to reduced incidence of café-au-lait spots (67% in SNF vs 56% in MNFSR), other NF1 manifestations were less frequent in either cohort. Molecular testing showed common NF1 gene abnormalities in both groups. The risk of developing SNF vs NF1 was increased for missense mutations [p = 0.0001; odds ratio (OR) = 6.16; confidence interval (CI) = 3.14-13.11], which were more frequent in SNF vs MNFSR (p = 0.0271).

Malignant schwannoma of the radial nerve with unusual presentation: a case report

Malignant schwannoma (MPNST) is a rare tumor. Many of these cases occur in patients with neurofibromatosis type I (NF-1) and they usually present as a mass lesion which rapidly increase in size with or without neurological symptoms. Here we present an unusual case of MPNST along the radial nerve in which the patient has no underlying neurofibromatosis type I.

Bilateral spinal neurofibromas in patients with neurofibromatosis 1

Neurofibromatosis 1 (NF1) is a neurocutaneous syndrome that can be inherited as autosomal dominant or may appear due to a de novo mutation. We present 8 patients (5 M and 3 F) with sporadic or non-familial spinal neurofibromatosis 1 (non-FSNF1) associated with bilateral spinal neurofibromas involving all of the paraspinal nerves. To our knowledge, this is the first series of such association described in the literature. Their ages ranged from 6 months to 20 years (average 9.8 years) at the time of radiological diagnosis. This presentation appears to be earlier than in familial spinal neurofibromas in NF1 (FSNF1). Predisposition to malignancy probably is greater in the non-FSNF1 type. MRI studies were performed routinely in all patients with NF1 and these were complemented with MRI enhanced with gadolinium and repeated at different ages in cases with paraspinal tumors. Coronal views provided the best evidence for the presence of neurofibromas in every spinal nerve. The size of the tumors and the clinical complications increased with advancing age in most patients. Giant plexiform tumors were often seen in the cervico-thoracic region. Malignant peripheral nerve sheath tumors (MPNST) were found in one patient with a sciatic tumor and another patient died suddenly at home without necropsy or pathological study. Voluminous paraspinal neurofibromas can be at risk for malignancy. More frequent neuroimaging studies may be necessary for an earlier detection. Early surgical treatment to anticipate the occurrence of MPNST during surveillance could be an option. Bilateral spinal neurofibromas are found in both patients who inherited the NF1 and in those due to de novo mutations.