Neurofibromin is a novel regulator of RAS-induced signals in primary vascular smooth muscle cells

Proteomic mapping reveals dysregulated angiogenesis in the cerebral arteries of rats with early-onset hypertension

Hypertension is associated with the presence of vascular abnormalities, including remodeling and rarefaction. These processes play an important role in cerebrovascular disease development; however, the mechanistic changes leading to these diseases are not well characterized. Using data-independent acquisition-based mass spectrometry analysis, here we determined the protein changes in cerebral arteries in pre- and early-onset hypertension from the spontaneously hypertensive rat (SHR), a model that resembles essential hypertension in humans. Our analysis identified 125 proteins with expression levels that were significantly upregulated or downregulated in 12-week-old spontaneously hypertensive rats compared to normotensive Wistar Kyoto rats. Using an angiogenesis enrichment analysis, we further identified a critical imbalance in angiogenic proteins that promoted an anti-angiogenic profile in cerebral arteries at early onset of hypertension. In a comparison to previously published data, we demonstrate that this angiogenic imbalance is not present in mesenteric and renal arteries from age-matched SHRs. Finally, we identified two proteins (Fbln5 and Cdh13), whose expression levels were critically altered in cerebral arteries compared to the other arterial beds. The observation of an angiogenic imbalance in cerebral arteries from the SHR reveals critical protein changes in the cerebrovasculature at the early onset of hypertension and provides novel insights into the early pathology of cerebrovascular disease.

Childhood-Onset Refractory Hypertension Results from Neurofibromatosis Type 1 Caused by a Splicing NF1 Mutation

INTRODUCTION

Neurofibromatosis type 1 (NF-1) is caused by mutations in the NF1 gene that encodes neurofibromin, a negative regulator of RAS proto-oncogene. Approximately one-third of the reported pathogenic mutations in NF1 are splicing mutations, but most consequences are unclear. The objective of this study was to identify the pathogenicity of splicing mutation in a Chinese family with NF-1 and determine the effects of the pre-mRNA splicing mutation by in vitro functional analysis.

METHODS

Next-generation sequencing was used to screen candidate mutations. We performed a minigene splicing assay to determine the effect of the splicing mutation on NF1 expression, and three-dimensional structure models of neurofibromin were generated using SWISS-MODEL and PROCHECK methods, respectively.

RESULTS

A pathogenic splicing mutation c.479+1G>C in NF1 was found in the proband characterized by childhood-onset refractory hypertension. In vitro analysis demonstrated that c.479+1G>C mutation caused the skipping of exon 4, leading to a glutamine-to-valine substitution at position 97 in neurofibromin and an open reading frame shift terminating at codon 108. Protein modeling showed that several major domains were missing in the truncated neurofibromin protein.

CONCLUSION

The splicing mutation c.479+1G>C identified in a Chinese patient with NF-1 and childhood-onset refractory hypertension caused the skipping of exon 4 and a truncated protein. Our findings offer new evidence for the molecular diagnosis of NF-1.

Blunted circadian variation of blood pressure in individuals with neurofibromatosis type 1

BACKGROUND

Cardiovascular events such as myocardial infarction and stroke are life-threatening complications associated with Neurofibromatosis type 1 (NF1). As previous studies observed an association between cardiovascular events and the loss of circadian variations of blood pressure, we investigated the 24 h circadian rhythm of blood pressure (BP) in 24 NF1 patients (10 males and 14 females, with a mean age of 39.5 years ± 14 years) by using ambulatory blood pressure monitoring (ABPM).

RESULTS

Only one-third of the patient were dippers, 50% were non-dippers, and 17% were risers. Reduced variability of systolic and diastolic nocturnal blood pressure was observed in NF1 patients compared with several studies of normotensive individuals (p = 0.024). In NF1 patients, the blunted systolic nocturnal decline was significantly associated with the number of neurofibromas (p = 0.049) and the presence of a plexiform neurofibroma (p = 0.020).

CONCLUSIONS

Most NF1 patients in this study showed a "non-dipper" pattern with a blunted nocturnal BP decline, which is considered an independent risk factor for cardiovascular events in normotensive and hypertensive individuals. Periodic monitoring of BP should be included in NF1 follow-up guidelines to diagnose masked hypertension or a non-dipper/riser pattern which would significantly increase the morbidity and mortality of NF1 patients to implement therapeutic strategies.

Moyamoya Vasculopathy in Neurofibromatosis Type 1 Pediatric Patients: The Role of Rare Variants of RNF213

Neurofibromatosis type 1 (NF1) is a neurocutaneous disorder caused by mutations in NF1 gene, coding for neurofibromin 1. NF1 can be associated with Moyamoya disease (MMD), and this association, typical of paediatric patients, is referred to as Moyamoya syndrome (MMS). MMD is a cerebral arteriopathy characterized by the occlusion of intracranial arteries and collateral vessel formation, which increase the risk of ischemic and hemorrhagic events. RNF213 gene mutations have been associated with MMD, so we investigated whether rare variants of RNF213 could act as genetic modifiers of MMS phenotype in a pediatric cohort of 20 MMS children, 25 children affected by isolated MMD and 47 affected only by isolated NF1. By next-generation re-sequencing (NGS) of patients' DNA and gene burden tests, we found that RNF213 seems to play a role only for MMD occurrence, while it does not appear to be involved in the increased risk of Moyamoya for MMS patients. We postulated that the loss of neurofibromin 1 can be enough for the excessive proliferation of vascular smooth muscle cells, causing Moyamoya arteriopathy associated with NF1. Further studies will be crucial to support these findings and to elucidate the possible role of other genes, enhancing our knowledge about pathogenesis and treatment of MMS.

Neurovascular complications in adults with Neurofibromatosis type 1: A national referral center experience

Neurofibromatosis type 1 (NF1) is associated with a range of vascular abnormalities. To assess the frequency, clinical and imaging spectrum of vascular complications in an adult cohort of NF1 patients, we reviewed 2068 adult NF1 patient records seen in our service between 2009 and 2019, to determine presence of vascular abnormalities, age at detection, associated symptoms and management. A literature review of the range of vascular abnormalities associated with NF1 was also undertaken. 1234 patients had magnetic resonance imaging cranial imaging. The frequency of vascular abnormalities associated with NF1 patients who had cranial imaging in this cohort was 3.5% (n = 43), the majority (n = 26, 60%) were symptomatic. Stroke and cerebral arterial stenosis were the commonest vascular complication. Eight patients (0.65%) had more than one type of vascular abnormality. One death due to a vascular complication was identified and significant morbidity resulted from other complications. We conclude that clinicians caring for patients with NF1 need to be cognizant that rapid onset of new neurological symptoms or signs may be the result of a vascular complication of NF1 and require urgent investigation and management, ideally within specialist teams who have experience of managing vascular complications of NF1.

Neurofibroma Development in Neurofibromatosis Type 1: Insights from Cellular Origin and Schwann Cell Lineage Development

BACKGROUND

Neurofibromatosis type 1 (NF1), a genetic tumor predisposition syndrome that affects about 1 in 3000 newborns, is caused by mutations in the NF1 gene and subsequent inactivation of its encoded neurofibromin. Neurofibromin is a tumor suppressor protein involved in the downregulation of Ras signaling. Despite a diverse clinical spectrum, one of several hallmarks of NF1 is a peripheral nerve sheath tumor (PNST), which comprises mixed nervous and fibrous components. The distinct spatiotemporal characteristics of plexiform and cutaneous neurofibromas have prompted hypotheses about the origin and developmental features of these tumors, involving various cellular transition processes.

METHODS

We retrieved published literature from PubMed, EMBASE, and Web of Science up to 21 June 2022 and searched references cited in the selected studies to identify other relevant papers. Original articles reporting the pathogenesis of PNSTs during development were included in this review. We highlighted the Schwann cell (SC) lineage shift to better present the evolution of its corresponding cellular origin hypothesis and its important effects on the progression and malignant transformation of neurofibromas.

CONCLUSIONS

In this review, we summarized the vast array of evidence obtained on the full range of neurofibroma development based on cellular and molecular pathogenesis. By integrating findings relating to tumor formation, growth, and malignancy, we hope to reveal the role of SC lineage shift as well as the combined impact of additional determinants in the natural history of PNSTs.

Case report: Bilateral spinal neurofibromatosis

Spinal neurofibromatosis (SNF) is a rare form of Neurofibromatosis in which neurofibromas exist bilaterally throughout all spinal roots. Despite previous attempts made to characterize and classify the disease as a separate clinical form of the disease, the low incidence rate of the disease and scarcity of previous reports calls for further studies and reports to elaborate this clinical entity. The patient in this report was a 36-year-old man presenting with lower limb weakness, unsteady gait, and paresthesia. The patient also presented with multiple cutaneous café-au-lait spots, cutaneous neurofibromas, and a large neurocutaneous neurofibroma of right facial nerve. Magnetic resonance imaging (MRI) of spine revealed bilateral spinal neurofibromas across all spinal cord roots. MRI study of head revealed no abnormalities in the brain and optic tract. The patient fulfilled both NIH criteria as well as revised criteria for NF1. Despite total spinal cord involvement, surgical intervention was withheld from the patient due to high propensity of recurrence as seen with previous attempts in removing peripheral neurofibromas, slow progression of symptoms, and lack of significant pain and impairment. SNF is often described as a form of disease with infrequent presentation of classical NF1 symptoms other than spinal tumors. The case presented here however, presented with several cutaneous neurofibromas and café-au-lait spots. Considering the positive outcome of surgical intervention in a few other reports, the decision to surgically intervene should be left to the clinical judgement of the participating surgeon, patient preference and socioeconomic background in a case-by-case manner.

Overexpression of alanine-glyoxylate aminotransferase 2 protects from asymmetric dimethylarginine-induced endothelial dysfunction and aortic remodeling

Elevated plasma concentrations of asymmetric dimethylarginine (ADMA) are associated with an increased risk of mortality and adverse cardiovascular outcomes. ADMA can be metabolized by dimethylarginine dimethylaminohydrolases (DDAHs) and by alanine-glyoxylate aminotransferase 2 (AGXT2). Deletion of DDAH1 in mice leads to elevation of ADMA in plasma and increase in blood pressure, while overexpression of human DDAH1 is associated with a lower plasma ADMA concentration and protective cardiovascular effects. The possible role of alternative metabolism of ADMA by AGXT2 remains to be elucidated. The goal of the current study was to test the hypothesis that transgenic overexpression of AGXT2 leads to lowering of plasma levels of ADMA and protection from vascular damage in the setting of DDAH1 deficiency. We generated transgenic mice (TG) with ubiquitous overexpression of AGXT2. qPCR and Western Blot confirmed the expression of the transgene. Systemic ADMA levels were decreased by 15% in TG mice. In comparison with wild type animals plasma levels of asymmetric dimethylguanidino valeric acid (ADGV), the AGXT2 associated metabolite of ADMA, were six times higher. We crossed AGXT2 TG mice with DDAH1 knockout mice and observed that upregulation of AGXT2 lowers plasma ADMA and pulse pressure and protects the mice from endothelial dysfunction and adverse aortic remodeling. Upregulation of AGXT2 led to lowering of ADMA levels and protection from ADMA-induced vascular damage in the setting of DDAH1 deficiency. This is especially important, because all the efforts to develop pharmacological ADMA-lowering interventions by means of upregulation of DDAHs have been unsuccessful.

Molecular genetic evaluation of Pediatric Renovascular hypertension due to renal artery stenosis and abdominal aortic Coarctation in Neurofibromatosis type 1

The etiology of renal artery stenosis (RAS) and abdominal aortic coarctation (AAC) causing the midaortic syndrome (MAS), often resulting in renovascular hypertension (RVH), remains ill-defined. Neurofibromatosis type 1 (NF-1) is frequently observed in children with RVH. Consecutive pediatric patients (N = 102) presenting with RVH secondary to RAS with and without concurrent AAC were prospectively enrolled in a clinical data base, and blood, saliva, and operative tissue when available, were collected. Among the 102 children were 13 having a concurrent clinical diagnosis of NF-1 (12.5%). Whole exome sequencing was performed for germline variant detection and RNASeq analysis of NF1, MAPK pathway genes, and MCP1 levels were undertaken in five NF-1 stenotic renal arteries, as well as control renal and mesenteric arteries from children with no known vasculopathy or NF-1. In 11 unrelated children with sequencing data, 11 NF1 genetic variants were identified, of which 10 had not been reported in gnomAD. Histologic analysis of NF-1 RAS specimens consistently revealed intimal thickening, disruption of the internal elastic lamina, and medial thinning. Analysis of transcript expression in arterial lesions documented an approximately 5-fold reduction in NF1 expression, confirming heterozygosity, MAPK pathway activation, and increased MCP1 expression. In summary, NF-1 related RVH in children is rare but often severe and progressive and as such, important to recognize. It is associated with histologic and molecular features consistent with an aggressive adverse vascular remodeling process. Further research is necessary to define the mechanisms underlying these findings.

An update on the central nervous system manifestations of neurofibromatosis type 1

Neurofibromatosis 1 (NF1) is an autosomal dominant genetic disorder that presents with variable phenotypes as a result of mutations in the neurofibromatosis type 1 (NF1) gene and subsequently, abnormal function of the protein product, neurofibromin. Patients with NF1 are at increased risk for central nervous system (CNS) manifestations including structural, functional, and neoplastic disease. The mechanisms underlying the varied manifestations of NF1 are incompletely understood, but the loss of functional neurofibromin, resulting in sustained activation of the oncoprotein RAS, is responsible for tumorigenesis throughout the body, including the CNS. Much of our understanding of NF1-related CNS manifestations is from a combination of data from animal models and natural history studies of people with NF1 and CNS disease. Data from animal models suggest the importance of both Nf1 mutations and somatic genetic alterations, such as Tp53 loss, for development of neoplasms, as well as the role of the timing of the acquisition of such alterations on the variability of CNS manifestations. A variety of non-neoplastic structural (macrocephaly, hydrocephalus, aqueductal stenosis, and vasculopathy) and functional (epilepsy, impaired cognition, attention deficits, and autism spectrum disorder) abnormalities occur with variable frequency in individuals with NF1. In addition, there is increasing evidence that similar appearing CNS neoplasms in people with and without the NF1 syndrome are due to distinct oncogenic pathways. Gliomas in people with NF1 show alterations in the RAS/MAPK pathway, generally in the absence of BRAF alterations (common to sporadic pilocytic astrocytomas) or IDH or histone H3 mutations (common to diffuse gliomas subsets). A subset of low-grade astrocytomas in these patients remain difficult to classify using standard criteria, and occasionally demonstrate morphologic features resembling subependymal giant cell astrocytomas that afflict patients with tuberous sclerosis complex ("SEGA-like astrocytomas"). There is also emerging evidence that NF1-associated high-grade astrocytomas have frequent co-existing alterations such as ATRX mutations and an alternative lengthening of telomeres (ALT) phenotype responsible for unique biologic properties. Ongoing efforts are seeking to improve diagnostic accuracy for CNS neoplasms in the setting of NF1 versus sporadic tumors. In addition, MEK inhibitors, which act on the RAS/MAPK pathway, continue to be studied as rational targets for the treatment of NF1-associated tumors, including CNS tumors.

The Second Life of Methylarginines as Cardiovascular Targets

Endogenous methylarginines were proposed as cardiovascular risk factors more than two decades ago, however, so far, this knowledge has not led to the development of novel therapeutic approaches. The initial studies were primarily focused on the endogenous inhibitors of nitric oxide synthases asymmetric dimethylarginine (ADMA) and monomethylarginine (MMA) and the main enzyme regulating their clearance dimethylarginine dimethylaminohydrolase 1 (DDAH1). To date, all the screens for DDAH1 activators performed with the purified recombinant DDAH1 enzyme have not yielded any promising hits, which is probably the main reason why interest towards this research field has started to fade. The relative contribution of the second DDAH isoenzyme DDAH2 towards ADMA and MMA clearance is still a matter of controversy. ADMA, MMA and symmetric dimethylarginine (SDMA) are also metabolized by alanine: glyoxylate aminotransferase 2 (AGXT2), however, in addition to methylarginines, this enzyme also has several cardiovascular protective substrates, so the net effect of possible therapeutic targeting of AGXT2 is currently unclear. Recent studies on regulation and functions of the enzymes metabolizing methylarginines have given a second life to this research direction. Our review discusses the latest discoveries and controversies in the field and proposes novel directions for targeting methylarginines in clinical settings.

A patient with neurofibromatosis type 1 presenting with bilateral frontal lobe infarctions following anterior communicating artery aneurysm rupture

Neurofibromatosis is a neurocutaneous genetic condition with dysplasia of the mesodermal and ectodermal tissues. Vascular abnormalities are well recognized in neurofibromatosis and cerebral aneurysms are rarely reported in literature. Here, we present a 20-year-old Sri Lankan female presented with headache, altered personality, disinhibited behaviour, and urinary incontinence. On imaging, she was found to have infarctions of both frontal lobes and evidence of a ruptured anterior communicating artery aneurysm with a small subarachnoid haemorrhage. Another small middle cerebral artery aneurysm was also seen in the angiogram. She was managed conservatively and gradually recovered. Because aneurysms in neurofibromatosis are usually asymptomatic and as rupture of such an aneurysm is rare, regular vascular screening is not recommended to all patients with neurofibromatosis. This is the first case report in literature in which a patient with neurofibromatosis presented with infarctions of both frontal lobes due to rupture of an anterior communicating artery aneurysm.

Cancer biomarkers in atherosclerotic plaque: Evidenced from structural and proteomic analyses

Atherosclerosis and cancer are the leading causes of mortality around the world that share common pathogenic pathways. The aim of this study is the investigation of the protein profile of atherosclerotic plaque in order to find similar biomarker between cancer and atherosclerosis. The small pieces of human coronary artery containing advanced atherosclerotic plaque is obtained from patients during bypass surgery. Structural characterization of type V plaque, including fibrous connective tissue, necrotic lipid core, cholesterol clefts and calcium deposits are performed using high resolution transmission electron microscopy (HR-TEM). The protein profile of atherosclerosis plaque is also analyzed using 2-dimensional electrophoresis and matrix-assisted laser desorption-ionization time-of-flight (MALDI-TOF). TEM analysis shows that vascular smooth muscle cells (VSMCs) exhibit different and uncommon morphologies in atherosclerotic plaque which is correlated to the proliferative state of the cells. The proteomics analysis reveals proteins related to atherosclerosis formation including Mimecan, Ras Suppressor Protein-1 (RSUP-1) and Cathepsin D which identified as biomarker of cancerous tumors. The expression of Mimecan and RSUP-1 is down-regulated in atherosclerotic plaque while the expression of Cathepsin D is up-regulated. These data support that atherosclerotic plaque presents some degree of tumorgenesis with the significant activity of VSMCs as the key player in atherogenesis.

Pulmonary hypertension associated with neurofibromatosis type 1

Neurofibromatosis type 1 (NF1), also known as von Recklinghausen disease, is a frequent autosomal dominant genetic disorder with a prevalence of 1 in 3000. Pulmonary hypertension (PH) associated with NF1 (PH-NF1) is a rare but severe complication of NF1 and is classified as Group 5 PH, defined as “PH with unclear and/or multifactorial mechanisms”. A literature review in PubMed on the association between NF1 and PH identified 18 articles describing 31 cases. PH-NF1 was characterised by a female predominance, an advanced age at diagnosis, an association with parenchymal lung disease in two out of three cases and poor long-term prognosis. NF1 is generally associated with interstitial lung disease but some cases of severe PH without parenchymal lung disease suggest that there could be a specific pulmonary vascular disease. There is no data available on the efficacy of specific pulmonary arterial hypertension treatment in PH-NF1. Therefore, these patients should be evaluated in expert PH centres and referred for lung transplantation at an early stage. As these patients have an increased risk of malignancy, careful assessment of the post-transplant malignancy risk prior to listing for transplantation is necessary. Clinical trials are needed to evaluate promising treatments targeting the RAS-downstream signalling pathways.

Pulmonary hypertension is a rare but severe complication of neurofibromatosis type 1. There are no data about the efficacy of specific PAH treatment in this disease and lung transplantation should be discussed at an early stage.http://ow.ly/JMU030lezfY

When and why is surgical revascularization indicated for the treatment of moyamoya syndrome in patients with RASopathies? A systematic review of the literature and a single institute experience

BACKGROUND

Moyamoya disease (MMD) is a cerebrovascular disorder characterized by the progressive occlusion of the supraclinoid internal carotid artery (ICA), resulting in the formation of an abnormal cerebral vascular network. When MMD occurs in association with an underlying medical condition, including some distinctive genetic disorders, it is named moyamoya syndrome (MMS). The discrimination between MMD and MMS has been validated by recent genetic researches and international reviews. Similarly to patients suffering from MMD, patients with MMS generally become symptomatic because of ischemic complications, which lead to hemiparesis, transient ischemic events, seizures, and sensory symptoms. RASopathies are a group of neurodevelopmental disorders that can be associated with MMS.

RESULTS

We retrospectively reviewed 18 RASopathy patients with MMS treated at our institution from 2000 to 2015 (16 neurofibromatosis type 1, 1 Costello syndrome, and 1 Schimmelpenning syndrome). Here, we report clinical data, performed surgical procedures, and clinic-radiological outcome of these patients. Most of them received both indirect revascularization and medical therapy.

CONCLUSIONS

At the moment, there are no univocal recommendations on which of these two treatment strategies is the treatment of choice in patients with RASopathies and MMS. We suggest that patients with a good overall prognosis (primarily depending on the distinctive underlying genetic disorder) and initial cerebrovascular disease could benefit from a prophylactic surgical revascularization, in order to prevent the cognitive impairment due to the progression of the vasculopathy.

Subarachnoid Hemorrhage Because of Distal Superior Cerebellar Artery Dissection in Neurofibromatosis Type 1

BACKGROUND

Neurofibromatosis type 1 (NF1) is a rare disease with an incidence of 1 in every 3000 births. Numerous studies have focused on the main function of NF1 as a tumor suppressor, whereas few have examined the cerebrovascular abnormalities observed in patients with NF1. It is worth noting that intracranial aneurysms are uncommon in this condition.

CASE DESCRIPTION

We report a case of NF1 with a dissection of the distal segment of the superior cerebellar artery. A 36-year-old woman presented with a distal superior cerebellar artery (SCA) dissection causing subarachnoid hemorrhage. Subsequently, because of the rich collateral blood flow distal to the dissection, N-butyl cyanoacrylate (NBCA) glue embolization was unsuccessful. Therefore, direct trapping of the artery was necessary. The patient was discharged after an uneventful postoperative period, and has remained without complications.

CONCLUSIONS

In the treatment of subarachnoid hemorrhage because of a distal SCA dissection in patients with NF1, NBCA glue embolization may be a safer option than microsurgery or coil embolization, in the acute phase, considering the possible vulnerability of the vessel wall, accessibility, morphology of the lesions, and the risk of developing unpredictable infarcts in the case of parent artery occlusion. However, regular reevaluation of the blood flow is necessary to monitor recurrence, given the rich collateral circulation.

Hypoplastic Internal Carotid Artery Co-Presenting with Neurofibromatosis and Intracranial Masses

Neurofibromatosis type 1 (NF1) is associated with systemic vascular disease, and it can also affect intracranial vasculature in a small percentage of patients. Very rarely, NF1 may co-present with hypoplasia of the internal carotid artery (ICA). Prior reports have documented NF1 with bilateral optic gliomas and a unilateral hypoplastic internal carotid artery; however, we report a case with the aforementioned findings in addition to a right-sided lentiform mass. This case report further suggests a common congenital pathway related to neurofibromin loss of function resulting in both nerve sheath tumors and cerebrovascular anomalies.

Neurofibromin is a novel regulator of Ras-induced reactive oxygen species production in mice and humans

Neurofibromatosis type 1 (NF1) predisposes individuals to early and debilitating cardiovascular disease. Loss of function mutations in the NF1 tumor suppressor gene, which encodes the protein neurofibromin, leads to accelerated p21(Ras) activity and phosphorylation of multiple downstream kinases, including Erk and Akt. Nf1 heterozygous (Nf1(+/-)) mice develop a robust neointima that mimics human disease. Monocytes/macrophages play a central role in NF1 arterial stenosis as Nf1 mutations in myeloid cells alone are sufficient to reproduce the enhanced neointima observed in Nf1(+/-) mice. Though the molecular mechanisms underlying NF1 arterial stenosis remain elusive, macrophages are important producers of reactive oxygen species (ROS) and Ras activity directly regulates ROS production. Here, we use compound mutant and lineage-restricted mice to demonstrate that Nf1(+/-) macrophages produce excessive ROS, which enhance Nf1(+/-) smooth muscle cell proliferation in vitro and in vivo. Further, use of a specific NADPH oxidase-2 inhibitor to limit ROS production prevents neointima formation in Nf1(+/-) mice. Finally, mononuclear cells from asymptomatic NF1 patients have increased oxidative DNA damage, an indicator of chronic exposure to oxidative stress. These data provide genetic and pharmacologic evidence that excessive exposure to oxidant species underlie NF1 arterial stenosis and provide a platform for designing novels therapies and interventions.

Preclinical Evidence for the Use of Sunitinib Malate in the Treatment of Plexiform Neurofibromas

PURPOSE

Plexiform neurofibromas (pNF) are pathognomonic nerve and soft tissue tumors of neurofibromatosis type I (NF1), which are highly resistant to conventional chemotherapy and associated with significant morbidity/mortality. Disruption of aberrant SCF/c-Kit signaling emanating from the pNF microenvironment induced the first ever objective therapeutic responses in a recent phase 2 trial. Sunitinib malate is a potent, highly selective RTK inhibitor with activity against c-Kit, PDGFR, and VEGFR, which have also been implicated in the pathogenesis of these lesions. Here, we evaluate the efficacy of sunitinib malate in a preclinical Krox20;Nf1(flox/-) pNF murine model.

EXPERIMENTAL DESIGN

Proliferation, β-hexosaminidase release (degranulation), and Erk1/2 phosphorylation were assessed in sunitinib treated Nf1(+/-) mast cells and fibroblasts, respectively. Krox20;Nf1(flox/-) mice with established pNF were treated sunitinib or PBS-vehicle control for a duration of 12 weeks. pNF metabolic activity was monitored by serial [(18)F]DG-PET/CT imaging.

RESULTS

Sunitinib suppressed multiple in vitro gain-in-functions of Nf1(+/-) mast cells and fibroblasts and attenuated Erk1/2 phosphorylation. Sunitinib treated Krox20;Nf1(flox/-) mice exhibited significant reductions in pNF size, tumor number, and FDG uptake compared to control mice. Histopathology revealed reduced tumor cellularity and infiltrating mast cells, markedly diminished collagen deposition, and increased cellular apoptosis in sunitinib treated pNF.

CONCLUSIONS

Collectively, these results demonstrate the efficacy of sunitinib in reducing tumor burden in Krox20;Nf1(flox/-) mice. These preclinical findings demonstrate the utility of inhibiting multiple RTKs in pNF and provide insights into the design of future clinical trials.

Nf1+/- monocytes/macrophages induce neointima formation via CCR2 activation

Persons with neurofibromatosis type 1 (NF1) have a predisposition for premature and severe arterial stenosis. Mutations in the NF1 gene result in decreased expression of neurofibromin, a negative regulator of p21(Ras), and increases Ras signaling. Heterozygous Nf1 (Nf1(+/-)) mice develop a marked arterial stenosis characterized by proliferating smooth muscle cells (SMCs) and a predominance of infiltrating macrophages, which closely resembles arterial lesions from NF1 patients. Interestingly, lineage-restricted inactivation of a single Nf1 allele in monocytes/macrophages is sufficient to recapitulate the phenotype observed in Nf1(+/-) mice and to mobilize proinflammatory CCR2+ monocytes into the peripheral blood. Therefore, we hypothesized that CCR2 receptor activation by its primary ligand monocyte chemotactic protein-1 (MCP-1) is critical for monocyte infiltration into the arterial wall and neointima formation in Nf1(+/-) mice. MCP-1 induces a dose-responsive increase in Nf1(+/-) macrophage migration and proliferation that corresponds with activation of multiple Ras kinases. In addition, Nf1(+/-) SMCs, which express CCR2, demonstrate an enhanced proliferative response to MCP-1 when compared with WT SMCs. To interrogate the role of CCR2 activation on Nf1(+/-) neointima formation, we induced neointima formation by carotid artery ligation in Nf1(+/-) and WT mice with genetic deletion of either MCP1 or CCR2. Loss of MCP-1 or CCR2 expression effectively inhibited Nf1(+/-) neointima formation and reduced macrophage content in the arterial wall. Finally, administration of a CCR2 antagonist significantly reduced Nf1(+/-) neointima formation. These studies identify MCP-1 as a potent chemokine for Nf1(+/-) monocytes/macrophages and CCR2 as a viable therapeutic target for NF1 arterial stenosis.

Neurofibromatosis 1-associated panhypopituitarism presenting as hypoglycaemic seizures and stroke-like symptoms

A 37-year-old man with a known history of neurofibromatosis 1 (NF1) presented within 2 days of diarrhoeal illness followed by encephalopathy, facial twitching, hypoglycaemia, hypotension, tachycardia and low-grade fever. Examination showed multiple café-au-lait spots and neurofibromas over the trunk, arms and legs and receptive aphasia with right homonymous hemianopia, which resolved. Workup for cardiac, inflammatory and infectious aetiologies was unrevealing. A brain MRI showed gyral swelling with increased T2 fluid-attenuated inversion recovery signal and diffusion restriction in the left cerebral cortex. Neuroendocrine findings suggested panhypopituitarism with centrally derived adrenal insufficiency. Supportive treatment, hormone supplementation, antibiotics, antivirals and levetiracetam yielded clinical improvement. A follow-up brain MRI showed focal left parieto-occipital atrophy with findings of cortical laminar necrosis. In conclusion, we describe a case of NF1-associated panhypopituitarism presenting as hypoglycaemic seizures and stroke-like findings, hitherto unreported manifestations of NF1. Prompt recognition and treatment of these associated conditions can prevent devastating complications.

Life-threatening Duodenal Ulcer Bleeding from a Ruptured Gastroduodenal Artery Aneurysm in a Patient with Neurofibromatosis Type 1

Vasculopathy is rarely reported in neurofibromatosis type 1, but when it occurs it primarily involves the aorta and its main branches. Among vasculopathies, aneurysmal dilatation is the most common form. Although several case reports concerning aneurysms or pseudoaneurysms of visceral arteries in neurofibromatosis type 1 patients have been reported, there are no reports describing gastroduodenal artery aneurysms associated with neurofibromatosis type 1. We experienced a case of life-threatening duodenal ulcer bleeding from a ruptured gastroduodenal artery aneurysm associated with neurofibromatosis type 1. We treated our patient by transarterial embolization after initial endoscopic hemostasis. To our knowledge, this is the first reported case of its type. High levels of suspicion and prompt diagnosis are required to select appropriate treatment options for patients with neurofibromatosis type 1 experiencing upper gastrointestinal bleeding. Embolization of the involved arteries should be considered an essential treatment over endoscopic hemostasis alone to achieve complete hemostasis and to prevent rebleeding.

Giant thrombosed intracavernous carotid artery aneurysm presenting as Tolosa-Hunt syndrome in a patient harboring a new pathogenic neurofibromatosis type 1 mutation: a case report and review of the literature

Neurofibromatosis type 1 (NF1) is a relatively common single-gene disorder, and is caused by heterozygous mutations in the NF1 gene that result in a loss of activity or in a nonfunctional neurofibromin protein. Despite the common association of NF1 with neurocutaneous features, its pathology can extend to numerous tissues not derived from the neural crest. Among the rare cerebrovascular abnormalities in NF1, more than 85% of cases are of purely occlusive or stenotic nature, with intracranial aneurysm being uncommon. Predominantly, the aneurysms are located in the internal carotid arteries (ICAs), being very rare bilateral aneurysms. This report describes a very unusual case of fusiform aneurysms of both ICAs in a Caucasian NF1 patient, with a new pathogenic intragenic heterozygous deletion of the NF1 gene, presenting at age 22 years with Tolosa-Hunt syndrome, because of partial thrombosis of the left giant intracavernous aneurysm. Medical treatment with anticoagulant therapy allowed a good outcome for the patient. In conclusion, early identification of cerebral arteriopathy in NF1 and close follow-up of its progression by neuroimaging may lead to early medical or surgical intervention and prevention of significant neurologic complications.

Neurofibromin-deficient myeloid cells are critical mediators of aneurysm formation in vivo

BACKGROUND

Neurofibromatosis type 1 (NF1) is a genetic disorder resulting from mutations in the NF1 tumor suppressor gene. Neurofibromin, the protein product of NF1, functions as a negative regulator of Ras activity in circulating hematopoietic and vascular wall cells, which are critical for maintaining vessel wall homeostasis. NF1 patients have evidence of chronic inflammation resulting in the development of premature cardiovascular disease, including arterial aneurysms, which may manifest as sudden death. However, the molecular pathogenesis of NF1 aneurysm formation is unknown.

METHOD AND RESULTS

With the use of an angiotensin II-induced aneurysm model, we demonstrate that heterozygous inactivation of Nf1 (Nf1(+/-)) enhanced aneurysm formation with myeloid cell infiltration and increased oxidative stress in the vessel wall. Using lineage-restricted transgenic mice, we show that loss of a single Nf1 allele in myeloid cells is sufficient to recapitulate the Nf1(+/-) aneurysm phenotype in vivo. Finally, oral administration of simvastatin or the antioxidant apocynin reduced aneurysm formation in Nf1(+/-) mice.

CONCLUSION

These data provide genetic and pharmacological evidence that Nf1(+/-) myeloid cells are the cellular triggers for aneurysm formation in a novel model of NF1 vasculopathy and provide a potential therapeutic target.

Ras-Mek-Erk signaling regulates Nf1 heterozygous neointima formation

Neurofibromatosis type 1 (NF1) results from mutations in the NF1 tumor-suppressor gene, which encodes neurofibromin, a negative regulator of diverse Ras signaling cascades. Arterial stenosis is a nonneoplastic manifestation of NF1 that predisposes some patients to debilitating morbidity and sudden death. Recent murine studies demonstrate that Nf1 heterozygosity (Nf1(+/-)) in monocytes/macrophages significantly enhances intimal proliferation after arterial injury. However, the downstream Ras effector pathway responsible for this phenotype is unknown. Based on in vitro assays demonstrating enhanced extracellular signal-related kinase (Erk) signaling in Nf1(+/-) macrophages and vascular smooth muscle cells and in vivo evidence of Erk amplification without alteration of phosphatidylinositol 3-kinase signaling in Nf1(+/-) neointimas, we tested the hypothesis that Ras-Erk signaling regulates intimal proliferation in a murine model of NF1 arterial stenosis. By using a well-established in vivo model of inflammatory cell migration and standard cell culture, neurofibromin-deficient macrophages demonstrate enhanced sensitivity to growth factor stimulation in vivo and in vitro, which is significantly diminished in the presence of PD0325901, a specific inhibitor of Ras-Erk signaling in phase 2 clinical trials for cancer. After carotid artery injury, Nf1(+/-) mice demonstrated increased intimal proliferation compared with wild-type mice. Daily administration of PD0325901 significantly reduced Nf1(+/-) neointima formation to levels of wild-type mice. These studies identify the Ras-Erk pathway in neurofibromin-deficient macrophages as the aberrant pathway responsible for enhanced neointima formation.

World Health Organization group 5 pulmonary hypertension

World Health Organization (WHO) group 5 pulmonary hypertension (PH) entails a heterogeneous group of disorders that may cause PH by unclear and/or multiple mechanisms. In particular, group 5 includes PH caused by hematologic disorders, systemic diseases, metabolic disorders, chronic renal failure, and disorders leading to pulmonary vascular occlusion or compression. This article discusses common pathogenic mechanisms leading to group 5 PH, followed by a detailed overview of epidemiology, pathogenesis, and disease-specific management of the individual group 5 conditions. Off-label use of vasomodulatory therapies, typically indicated for pulmonary arterial hypertension (WHO group 1 PH), in group 5 conditions is also discussed.

Moyamoya syndrome associated with neurofibromatosis Type 1: perioperative and long-term outcome after surgical revascularization

OBJECT

Children with neurofibromatosis Type 1 (NF1) can present with progressive arteriopathy of the branches of the internal carotid artery consistent with moyamoya syndrome. Clinical symptoms, radiographic evidence of ischemia, and the potential for disease progression may necessitate surgical revascularization to minimize the risk of stroke and progressive neurological deficits. This study aims to evaluate the presentation and surgical outcomes of these patients by reviewing clinical, radiographic, and angiographic data.

METHODS

A retrospective review was conducted of clinical and radiographic records of all children with NF1 who were diagnosed with moyamoya syndrome and underwent surgical revascularization between January 1988 and April 2012 at Boston Children's Hospital.

RESULTS

During this period, 39 patients (27 female and 12 male, ages 0.2-19.3 years) had both NF1 and moyamoya syndrome, of whom 32 underwent surgical revascularization with pial synangiosis. Of the 32 patients treated by surgical revascularization, 21 (66%) manifested ischemic symptoms and 18 (56%) had radiographic evidence of prior stroke at the time of moyamoya diagnosis. In total, 25 of 32 patients developed neurological symptoms prior to surgical intervention. Only 1 patient presented with hemorrhage. The average age at first surgery was 8.1 years (range 0.5-15.6 years). Perioperative complications in the first 7 days included stroke (n = 2), transient ischemic attack (n = 1), and infection (n = 1). Twenty-two patients had more than 6 months of follow-up, with an average clinical and radiographic postoperative follow-up period of 80.2 months (range 9.4-257.1 months). Of those patients with long-term follow-up, 21 (95%) of 22 demonstrated stable or improved neurological status despite radiographic evidence of moyamoya progression in 48% of patients.

CONCLUSIONS

Children with NF1-associated moyamoya syndrome are often diagnosed prior to development of fixed neurological deficits as a consequence of imaging studies obtained for other manifestations of NF1. The clinical, radiographic, and angiographic features in this population are comparable to primary moyamoya disease, with the exception of patients treated with cranial irradiation, who may be at greater risk for both stroke as well as perioperative complications. Despite radiographic evidence of progressive stenosis in 48% of patients, nearly all demonstrated stable or improved neurological status after surgical revascularization. Surgical revascularization for children with NF1 appears safe and is protective against further ischemic and neurological damage, with a 27-fold reduction in stroke rate.

Neurofibromatosis type 1 complicated by atypical coarctation of the thoracic aorta

Neurofibromatosis type 1 (NF1) is a relatively common autosomal dominant genetic disorder with a prevalence of 1 in 3,000 (0.03%) at birth. Clinical features are café-au-lait macules, intertriginous freckling, dermal neurofibroma, iris hamartoma (Lisch nodules), and learning disability. NF1 vasculopathy is a serious but underrecognized complication involving the cerebrovascular and cardiovascular systems. The incidence of hypertension in patients with NF1 is around 1% and is associated mainly with renal artery stenosis in children. Only a few cases of thoracic aortic coarctation in association with hypertension and neurofibromatosis have been reported. Here we describe the case of a 4-year-old girl who presented with NF1 and hypertension due to atypical coarctation of the thoracic aorta. The diagnosis of coarctation of the thoracic aorta at the Th5-to-Th6 level was made following catheterization with a pressure gradient of 40 mmHg. The patient underwent surgery comprising resection of the coarctation of the thoracic aorta and graft interposition. On the basis of our findings, annual assessment of blood pressure is advised for patients with NF1.

Development of the adult PedsQL™ neurofibromatosis type 1 module: initial feasibility, reliability and validity

BACKGROUND

Neurofibromatosis type 1 (NF1) is a common autosomal dominant genetic disorder with significant impact on health-related quality of life (HRQOL). Research in understanding the pathogenetic mechanisms of neurofibroma development has led to the use of new clinical trials for the treatment of NF1. One of the most important outcomes of a trial is improvement in quality of life, however, no condition specific HRQOL instrument for NF1 exists. The objective of this study was to develop an NF1 HRQOL instrument as a module of PedsQL™ and to test for its initial feasibility, internal consistency reliability and validity in adults with NF1.

METHODS

The NF1 specific HRQOL instrument was developed using a standard method of PedsQL™ module development - literature review, focus group/semi-structured interviews, cognitive interviews and experts' review of initial draft, pilot testing and field testing. Field testing involved 134 adults with NF1. Feasibility was measured by the percentage of missing responses, internal consistency reliability was measured with Cronbach's alpha and validity was measured by the known-groups method.

RESULTS

Feasibility, measured by the percentage of missing responses was 4.8% for all subscales on the adult version of the NF1-specific instrument. Internal consistency reliability for the Total Score (alpha =0.97) and subscale reliabilities ranging from 0.72 to 0.96 were acceptable for group comparisons. The PedsQL™ NF1 module distinguished between NF1 adults with excellent to very good, good, and fair to poor health status.

CONCLUSIONS

The results demonstrate the initial feasibility, reliability and validity of the PedsQL™ NF1 module in adult patients. The PedsQL™ NF1 Module can be used to understand the multidimensional nature of NF1 on the HRQOL patients with this disorder.

Heterozygous inactivation of the Nf1 gene in myeloid cells enhances neointima formation via a rosuvastatin-sensitive cellular pathway

Mutations in the NF1 tumor suppressor gene cause Neurofibromatosis type 1 (NF1). Neurofibromin, the protein product of NF1, functions as a negative regulator of Ras activity. Some NF1 patients develop cardiovascular disease, which represents an underrecognized disease complication and contributes to excess morbidity and mortality. Specifically, NF1 patients develop arterial occlusion resulting in tissue ischemia and sudden death. Murine studies demonstrate that heterozygous inactivation of Nf1 (Nf1(+/-)) in bone marrow cells enhances neointima formation following arterial injury. Macrophages infiltrate Nf1(+/-) neointimas, and NF1 patients have increased circulating inflammatory monocytes in their peripheral blood. Therefore, we tested the hypothesis that heterozygous inactivation of Nf1 in myeloid cells is sufficient for neointima formation. Specific ablation of a single copy of the Nf1 gene in myeloid cells alone mobilizes a discrete pro-inflammatory murine monocyte population via a cell autonomous and gene-dosage dependent mechanism. Furthermore, lineage-restricted heterozygous inactivation of Nf1 in myeloid cells is sufficient to reproduce the enhanced neointima formation observed in Nf1(+/-) mice when compared with wild-type controls, and homozygous inactivation of Nf1 in myeloid cells amplified the degree of arterial stenosis after arterial injury. Treatment of Nf1(+/-) mice with rosuvastatin, a stain with anti-inflammatory properties, significantly reduced neointima formation when compared with control. These studies identify neurofibromin-deficient myeloid cells as critical cellular effectors of Nf1(+/-) neointima formation and propose a potential therapeutic for NF1 cardiovascular disease.

Giant extracranial aneurysm of the internal carotid artery in neurofibromatosis type 1. A case report and review of the literature

Neurofibromatosis type 1 (NF-1) is an autosomal dominant disorder characterized by cutaneous pigmentations, neurofibromas, Lisch nodules and neuroectodermal tumors. Supra-aortic vessel aneurysms may affect patients with NF-1 and can be associated with rupture, ischemic complications and compression symptoms. We describe a 48-year-old woman with NF-1 and an extracranial 3×5 cm right internal carotid artery aneurysm. After balloon test occlusion the patient was treated with parent artery sacrifice which led to significant shrinkage on follow-up MR and reduction of compression symptoms. The literature concerning internal carotid artery aneurysms associated with NF-1 is reviewed evaluating the possible therapeutic options.

The plexiform neurofibroma microenvironment

Dynamic interactions between tumorigenic cells and surrounding cells, including immunomodulatory hematopoietic cells, can dictate tumor initiation, progression, and transformation. Hematopoietic-stromal interactions underpin the plexiform neurofibroma, a debilitating tumor arising in individuals afflicted with Neurofibromatosis type 1 (NF1), a common genetic disorder resulting from mutations in the NF1 tumor suppressor gene. At the tissue level, plexiform neurofibromas demonstrate a complex microenvironment composed of Schwann cells, fibroblasts, perineural cells, mast cells, secreted collagen, and blood vessels. At the cellular level, specific interactions between these cells engender tumor initiation and progression. In this microenvironment hypothesis, tumorigenic Schwann cells secrete pathological concentrations of stem cell factor, which recruit c-kit expressing mast cells. In turn, activated mast cells release inflammatory effectors stimulating the tumorigenic Schwann cells and their supporting fibroblasts and blood vessels, thus promoting tumor expansion in a feed-forward loop. Bone marrow transplantation experiments in plexiform neurofibroma mouse models have shown that tumorigenesis requires Nf1 haploinsufficiency in the hematopoietic compartment, suggesting that tumor microenvironments can depend on intricate interactions at both cellular and genetic levels. Overall, our continued understanding of critical tumor-stromal interactions will illuminate novel therapeutic targets, as shown by the first-ever successful medical treatment of a plexiform neurofibroma by targeted inhibition of the stem cell factor/c-kit axis.

Skin-derived precursor cells as an in vitro modelling tool for the study of type 1 neurofibromatosis

The most characteristic feature of neurofibromatosis type 1 (NF1) is the development of neurofibromas. It has been suggested that these tumors are caused by somatic inactivation of the wild-type NF1 allele, but the cell that originally suffers this mutation remains controversial. Several lines of evidence support the clonal origin of these tumors, and it has been recently suggested that skin-derived precursor cells (SKPs) could be the cell of origin of dermal neurofibromas. Nullizygous (NF1(-/-)) SKPs do give rise to neurofibromas when transplanted to heterozygous mice. Moreover, a nullizygous population of cells that is S100β negative is present in human neurofibromas, and NF1(+/-) multipotent progenitor cells are seemingly recruited to the tumor. This evidence supports the neurofibroma stem cell hypothesis and a putative involvement of SKPs in the aetiopathogenesis of the disease, suggesting that SKPs could become a valuable tool for the in vitro study of NF1.

Alternative splicing of the neurofibromatosis type I pre-mRNA

NF1 (neurofibromatosis type I) is a common genetic disease that affects one in 3500 individuals. The disease is completely penetrant but shows variable phenotypic expression in patients. NF1 is a large gene, and its pre-mRNA undergoes alternative splicing. The NF1 protein, neurofibromin, is involved in diverse signalling cascades. One of the best characterized functions of NF1 is its function as a Ras-GAP (GTPase-activating protein). NF1 exon 23a is an alternative exon that lies within the GAP-related domain of neurofibromin. This exon is predominantly included in most tissues, and it is skipped in CNS (central nervous system) neurons. The isoform in which exon 23a is skipped has 10 times higher Ras-GAP activity than the isoform in which exon 23a is included. Exon 23a inclusion is tightly regulated by at least three different families of RNA-binding proteins: CELF {CUG-BP (cytosine-uridine-guanine-binding protein) and ETR-3 [ELAV (embryonic lethal abnormal vision)-type RNA-binding protein]-like factor}, Hu and TIA-1 (T-cell intracellular antigen 1)/TIAR (T-cell intracellular antigen 1-related protein). The CELF and Hu proteins promote exon 23a skipping, while the TIA-1/TIAR proteins promote its inclusion. The widespread clinical variability that is observed among NF1 patients cannot be explained by NF1 mutations alone and it is believed that modifier genes may have a role in the variability. We suggest that the regulation of alternative splicing may act as a modifier to contribute to the variable expression in NF1 patients.

Pathogenesis of plexiform neurofibroma: tumor-stromal/hematopoietic interactions in tumor progression

Neurofibromatosis type 1 (NF1) is a genetic disease that results from either heritable or spontaneous autosomal dominant mutations in the NF1 gene. A second-hit mutation precedes the predominant NF1 neoplasms, which include myeloid leukemia, optic glioma, and plexiform neurofibroma. Despite this requisite NF1 loss of heterozygosity in the tumor cell of origin, nontumorigenic cells contribute to both generalized and specific disease manifestations. In mouse models of plexiform neurofibroma formation, Nf1 haploinsufficient mast cells promote inflammation, accelerating tumor formation and growth. These recruited mast cells, hematopoietic effector cells long known to permeate neurofibroma tissue, mediate key mitogenic signals that contribute to vascular ingrowth, collagen deposition, and tumor growth. Thus, the plexiform neurofibroma microenvironment involves a tumor/stromal interaction with the hematopoietic system that depends, at the molecular level, on a stem cell factor/c-kit-mediated signaling axis. These observations parallel findings in other NF1 disease manifestations and are clearly relevant to medical management of these neurofibromas.

Pulmonary hypertension in patients with neurofibromatosis type I

Neurofibromatosis type I (NF1) is a rare genetic disease caused by mutations in the NF1 gene, which codes for tumor suppressor neurofibromin. NF1 is transmitted as an autosomal dominant and fully penetrant trait with no sex predominance. Precapillary pulmonary hypertension (PH) is a severe complication of NF1, initially described in patients with advanced parenchymal lung disease, which may complicate the course of NF1. We conducted this study to describe clinical, functional, radiologic, and hemodynamic characteristics and outcome of patients with NF1-associated PH. We identified 8 new cases of NF1-associated PH in patients carrying a NF1 gene mutation. No bone morphogenic protein receptor 2 (BMPR2) point mutation or large size rearrangements were identified. Seven female patients and 1 male patient were reported, suggesting a possible female predominance. PH occurred late in the course of the disease (median age, 62 yr; range, 53-68 yr). Dyspnea and signs of right heart failure were the major symptoms leading to the diagnosis of PH. At diagnosis, patients had severe hemodynamic impairment with low cardiac index (median, 2.3 L/min per m2; range, 1.9-4.7) and elevated indexed pulmonary vascular resistance (median, 15.1 mm Hg/L/min per m2; range, 4.5-25.9). All patients were in New York Heart Association functional class III with severe exercise limitation (median 6-min walk distance, 180 m; range, 60-375 m). Most patients had associated parenchymal lung disease, but some had no or mild lung involvement with disproportionate pulmonary vascular disease. Overall, the impact of PH therapy was limited and outcomes were poor. In conclusion, PH represents a rare but severe complication of NF1, characterized by female predominance, late onset in the course of NF1, and severe functional and hemodynamic impairment. Because of poor outcome and limited impact of specific PH therapy, eligible patients require early referral for lung transplantation. Further studies are needed to better understand the pathophysiology and the role, if any, of neurofibromin in NF1-associated PH.

Moyamoya syndrome associated with neurofibromatosis type I in a pediatric patient

CONTEXT

Neurofibromatosis type 1 (NF-1) is the most prevalent autosomal dominant genetic disorder among humans. Moyamoya disease is a cerebral vasculopathy that is only rarely observed in association with NF-1, particularly in the pediatric age range. The present study reports an occurrence of this association in an infant.

CASE REPORT

An eight-month-old female presented convulsive seizures with clonic movements. The patient suffered an ischemic stroke with hemiparesis. Magnetic resonance imaging revealed radiological findings compatible with moyamoya disease. The diagnosis of NF-1 was made at the age of 20 months.

CONCLUSION

Despite the rarity of this association in childhood, children with focal neurological symptoms and a diagnosis of NF-1 deserve to be investigated for moyamoya syndrome.

Cerebrovasculopathy in NF1 associated with ocular and scalp defects

Vascular lesions are uncommon in children with neurofibromatosis 1 (NF1) but can cause serious complications. We report on a child with NF1 who presented at 18 months of age with symptomatic stenosis of the left middle cerebral artery and its branches, and associated moyamoya disease. She also had bilateral posterior embryotoxon, left corneal opacity (Peters anomaly), and cutis aplasia of the left scalp. All of these defects may have occurred as a result of disruption of the blood supply caused by NF1 vasculopathy prenatally. This constellation of vascular anomalies has not been previously reported in a patient with NF1.

The ecology of brain tumors: lessons learned from neurofibromatosis-1

Traditionally, cancer studies have primarily focused on mutations that activate growth or survival pathways in susceptible pre-neoplastic/neoplastic cells. However, recent research has revealed a critical role for non-neoplastic cells within the tumor microenvironment in the process of cancer formation and progression. In addition, the existence of regional and developmental variations in susceptible cell types and supportive microenvironments support a model of tumorigenesis in which the dynamic symbiotic relationship between neoplastic and non-neoplastic cell types dictate where and when cancers form and grow. In this review, we highlight advances in neurofibromatosis type 1 (NF1) genetically engineered mouse brain tumor (glioma) modeling to reveal how cellular and molecular heterogeneity in both the pre-neoplastic/neoplastic and non-neoplastic cellular compartments contribute to gliomagenesis and glioma growth.

Diffuse and uncontrolled vascular smooth muscle cell proliferation in rapidly progressing pediatric moyamoya disease

Moyamoya disease is a rare stroke syndrome of unknown etiology resulting from stenosis or occlusion of the supraclinoid internal carotid artery (ICA) in association with an abnormal vascular network in the basal ganglia. Although the highest incidence of moyamoya disease is in pediatric patients, pathology reports have been primarily limited to adult samples and describe occlusive fibrocellular lesions in the intimae of affected arteries. We describe the case of a young girl with primary moyamoya disease who presented at 18 months of age with right hemiparesis following an ischemic stroke. Angiography showed stenosis of the distal left ICA, left middle cerebral artery, and right ICA. An emergent left-sided dural inversion was performed. Recurrent strokes and alternating hemiplegia necessitated a right dural inversion 6 months later. Nonetheless, her aggressive disease proved uniquely refractory to surgical revascularization, and she succumbed to recurrent strokes and neurological deterioration at 2.5 years of age. Pathological specimens revealed a striking bilateral occlusion of the anterior carotid circulation resulting from intimal proliferation of smooth muscle cells (SMCs). Most strikingly, the ascending aorta and the superior mesenteric artery demonstrated similar intimal proliferation, along with SMC proliferation in the media. The systemic pathology involving multiple arteries in this extremely young child, the first case of its kind available for autopsy, suggests that globally uncontrolled SMC proliferation, in the absence of environmental risk factors and likely resulting from an underlying genetic alteration, may be a primary etiologic event leading to moyamoya disease.

Genetic variants promoting smooth muscle cell proliferation can result in diffuse and diverse vascular diseases: evidence for a hyperplastic vasculomyopathy

Genetic predisposition to early onset of occlusive vascular diseases, including coronary artery disease, ischemic stroke, and Moyamoya disease, may represent varying presentations of a common underlying dysregulation of vascular smooth muscle cell proliferation. We discuss mutations in two genes, NF1 and ACTA2, which predispose affected individuals to diffuse and diverse vascular diseases. These patients show evidence of diffuse occlusive disease in multiple arterial beds or even develop seemingly diverse arterial pathologies, ranging from occlusions to arterial aneurysms. We also present the current evidence that both NF1 and ACTA2 mutations promote increased smooth muscle cell proliferation in vitro and in vivo, which leads us to propose that these diffuse and diverse vascular diseases are the outward signs of a more fundamental disease: a hyperplastic vasculomyopathy. We suggest that the concept of a hyperplastic vasculomyopathy offers a new approach not only to identifying mutated genes that lead to vascular diseases but also to counseling and possibly treating patients harboring such mutations. In other words, this framework may offer the opportunity to therapeutically target the inappropriate smooth muscle cell behavior that predisposes to a variety of vascular diseases throughout the arterial system.

Mast cells and the neurofibroma microenvironment

Neurofibromatosis type 1 (NF1) is the most common genetic disorder with a predisposition to malignancy and affects 1 in 3500 persons worldwide. NF1 is caused by a mutation in the NF1 tumor suppressor gene that encodes the protein neurofibromin. Patients with NF1 have cutaneous, diffuse, and plexiform neurofibromas, tumors comprised primarily of Schwann cells, blood vessels, fibroblasts, and mast cells. Studies from human and murine models that closely recapitulate human plexiform neurofibroma formation indicate that tumorigenesis necessitates NF1 loss of heterozygosity in the Schwann cell. In addition, our most recent studies with bone marrow transplantation and pharmacologic experiments implicate haploinsufficiency of Nf1 (Nf1(+/-)) and c-kit signaling in the hematopoietic system as required and sufficient for tumor progression. Here, we review recent studies implicating the hematopoietic system in plexiform neurofibroma genesis, delineate the physiology of stem cell factor-dependent hematopoietic cells and their contribution to the neurofibroma microenvironment, and highlight the application of this research toward the first successful, targeted medical treatment of a patient with a nonresectable and debilitating neurofibroma. Finally, we emphasize the importance of the tumor microenvironment hypothesis, asserting that tumorigenic cells in the neurofibroma do not arise and grow in isolation.

Plexiform neurofibroma genesis: questions of Nf1 gene dose and hyperactive mast cells

PURPOSE OF REVIEW

Tumorigenic cells can co-opt normal functions of nonmalignant hematopoietic cells, promoting tumor progression. Recent mouse and human studies indicate that mast cells underpin inflammation in the plexiform neurofibroma microenvironment of neurofibromatosis type 1. In this model, Nf1 homozygous-deficient Schwann cells recruit hyperactive mast cells, promoting tumorigenesis. Here, we discuss the importance of Nf1 gene dosage, delineate hematopoietic contributions to the plexiform neurofibroma microenvironment, and highlight applications to human treatment.

RECENT FINDINGS

Previous studies found that plexiform neurofibroma formation in a mouse model requires biallelic loss of Nf1 in Schwann cells and an Nf1 heterozygous cellular background. Now, transplantation and pharmacological experiments have indicated that tumor formation specifically requires Nf1 heterozygosity of c-kit-dependent bone marrow.

SUMMARY

Neurofibromatosis type 1 results from autosomal dominant mutations of the NF1 tumor suppressor gene. Although unpredictable second-hit mutations in the remaining NF1 allele precede local manifestations such as tumor formation, human and mouse data indicate that NF1/Nf1 gene haploinsufficiency modulates cellular physiology and disease pathogeneses. In particular, Nf1 haplo insufficient mast cells demonstrate multiple gain-in-functions, and mast cells permeate neurofibroma tissue. Transplantation experiments have shown that these aberrant mast cells critically underpin the tumor microenvironment. Using these findings, clinicians have medically treated a patient with a debilitating plexiform neurofibroma.

Thoracic aortic disease in tuberous sclerosis complex: molecular pathogenesis and potential therapies in Tsc2+/- mice

Tuberous sclerosis complex (TSC) is a genetic disorder with pleiotropic manifestations caused by heterozygous mutations in either TSC1 or TSC2. One of the less investigated complications of TSC is the formation of aneurysms of the descending aorta, which are characterized on pathologic examination by smooth muscle cell (SMC) proliferation in the aortic media. SMCs were explanted from Tsc2(+/-) mice to investigate the pathogenesis of aortic aneurysms caused by TSC2 mutations. Tsc2(+/-) SMCs demonstrated increased phosphorylation of mammalian target of rapamycin (mTOR), S6 and p70S6K and increased proliferation rates compared with wild-type (WT) SMCs. Tsc2(+/-) SMCs also had reduced expression of SMC contractile proteins compared with WT SMCs. An inhibitor of mTOR signaling, rapamycin, decreased SMC proliferation and increased contractile protein expression in the Tsc2(+/-) SMCs to levels similar to WT SMCs. Exposure to alpha-elastin fragments also decreased proliferation of Tsc2(+/-) SMCs and increased levels of p27(kip1), but failed to increase expression of contractile proteins. In response to artery injury using a carotid artery ligation model, Tsc2(+/-) mice significantly increased neointima formation compared with the control mice, and the neointima formation was inhibited by treatment with rapamycin. These results demonstrate that Tsc2 haploinsufficiency in SMCs increases proliferation and decreases contractile protein expression and suggest that the increased proliferative potential of the mutant cells may be suppressed in vivo by interaction with elastin. These findings provide insights into the molecular pathogenesis of aortic disease in TSC patients and identify a potential therapeutic target for treatment of this complication of the disease.