Thorsten Rosenbaum

Single cell Ras-GTP analysis reveals altered Ras activity in a subpopulation of neurofibroma Schwann cells but not fibroblasts

Neurofibromatosis type 1 (NF1) is a common genetic disorder characterized by multiple neurofibromas, peripheral nerve tumors containing mainly Schwann cells and fibroblasts. TheNF1 gene encodes neurofibromin, a tumor suppressor postulated to function in part as a Ras GTPase-activating protein. The roles of different cell types and of elevated Ras-GTP in neurofibroma formation are unclear. To determine which neurofibroma cell type has altered Ras-GTP regulation, we developed an immunocytochemical assay for active, GTP-bound Ras. In NIH 3T3 cells, the assay detected overexpressed, constitutively activated K-, N-, and Ha-Ras and insulin-induced endogenous Ras-GTP. In dissociated neurofibroma cells from NF1 patients, Ras-GTP was elevated in Schwann cells but not fibroblasts. Twelve to 62% of tumor Schwann cells showed elevated Ras-GTP, unexpectedly revealing neurofibroma Schwann cell heterogeneity. Increased basal Ras-GTP did not correlate with increased cell proliferation. Normal human Schwann cells, however, did not demonstrate elevated basal Ras activity. Furthermore, compared with cells from wild type littermates, Ras-GTP was elevated in all mouseNf1 −/− Schwann cells but never inNf1 −/− mouse fibroblasts. Our results indicate that Ras activity is detectably increased in only some neurofibroma Schwann cells and suggest that neurofibromin is not an essential regulator of Ras activity in fibroblasts.

Mitotic recombination effects homozygosity for NF1 germline mutations in neurofibromas.

Pure populations of neurofibroma-derived Schwann cells bearing both NF1 mutated alleles (NF1−/−) have been isolated from different neurofibromas showing loss of heterozygosity of nearly the entire 17q chromosome. By comparing molecular and fluorescent in situ hybridization analysis of these cells, we demonstrate mitotic recombination is the mechanism underlying this type of loss of heterozygosity leading to reduction to homozygosity of NF1 germline mutation.

Pseudotumor cerebri as an important differential diagnosis of papilledema in children

INTRODUCTION Primary pseudotumor cerebri (PTC) in childhood is a rare but important differential diagnosis in children presenting with papilledema. It is defined as elevated cerebrospinal fluid (CSF) pressure of more than 20 cm H(2)O, normal CSF composition, and exclusion of underlying structural or systemic causes. Visual loss is a serious complication, which requires careful monitoring and management. PATIENTS AND METHODS We conducted a retrospective chart review of 12 patients with primary PTC. The mean age at presentation was 8212 years, and there was a male-to-female ratio of 7:5. The aim of this study was to investigate the clinical features of primary PTC in children, and to highlight the different treatment options in normalizing intracranial pressure in these patients. RESULTS In the majority of cases, children presented with headache. Four patients had no obvious symptoms and papilledema was found on routine eye examination. Obesity was uncommon and there was no distinct sex predilection. Acetazolamide was our drug of choice for the initial treatment. Furosemide and prednisone were used as second-line agents. Treatment was gradually decreased after resolution of the papilledema with exception of the two youngest children, who remained symptomatic. One child underwent ventricular-peritoneal shunting. DISCUSSION The treatment goals of PTC are the relief of symptoms, and preservation of visual function. Acetazolamide is an effective first-line method of lowering raised intracranial pressure. In our study group especially the young children were difficult to treat. This might indicate an age-related difference in the etiology of PTC. When medical treatment remains ineffective and visual function deteriorates, surgical treatment should be considered.

Long-term culture and characterization of human neurofibroma-derived Schwann cells.

Neurofibromas are benign tumors arising from the peripheral nerve sheath and are a typical finding in neurofibromatosis type 1 (NF1). Schwann cells are the predominant cell type in neurofibromas and thus are supposed to play a major role in the pathogenesis of these tumors. It is not known, however, if NF1 mutations in Schwann cells result in an altered phenotype that subsequently leads to tumor formation. To characterize the biological properties of neurofibroma‐derived Schwann cells we developed cell culture techniques that enabled us to isolate Schwann cells from neurofibromas and grow them in vitro for several weeks without significant fibroblast contamination. Neurofibroma‐derived Schwann cells were characterized by altered morphology, heterogeneous growth behavior, and increased expression of the P0 antigen while several other features of normal human Schwann cells were retained. We conclude that neurofibroma‐derived Schwann cells exhibit a distinct phenotype in vitro but that the observed abnormalities by themselves are insufficient to explain neurofibroma formation. Application of our improved culture conditions makes neurofibroma‐derived Schwann cells readily available for further studies to define their role in tumorigenesis in neurofibromatosis type 1. J. Neurosci. Res. 61:524–532, 2000.

Subclassification of nerve sheath tumors by gene expression profiling

Nerve sheath tumors are the most common tumors of Neurofibromatosis type 1 (NF1) patients. Dermal neurofibromas develop in nearly all NF1‐patients, whereas plexiform neurofibromas are only observed in one‐third of the patients. NF1‐patients have about a 10% lifetime risk for developing malignant pheripheral nerve sheath tumors (MPNST). The origin of these tumors is thought to be the Schwann cell lacking functional neurofibromin. However, additional genetic alterations are likely to modulate tumor biology and to contribute to individual nerve sheath tumor entities. To gain insight into the molecular events and to determine whether these tumors can be classified according to gene expression profiles, we performed expression analysis applying cDNA array technology. Nine dermal neurofibromas, 7 plexiform neurofibromas, ten MPNST and two MPNST cell cultures were examined. All tumors but 6 sporadic MPNST were obtained from NF1‐patients. We detected significant differences in gene expression patterns between neurofibromas and MPNST and between dermal neurofibromas and plexiform neurofibromas. Tumor class prediction agreed in all but one case with histological and clinical classification. NF1‐associated and sporadic MPNST could not be distinguished by their gene expression patterns. We present a panel of discriminating genes that may assist subclassification of nerve sheath tumors.

Fanconi syndrome caused by antiepileptic therapy with valproic Acid.

Summary:  Purpose: Valproic acid (VPA) is commonly used as an antiepileptic drug (AED). Regular screening for renal side effects is uncommon. Fanconi syndrome, a generalized dysfunction of renal proximal tubular cells, occurs with some inborn errors of metabolism. In addition, it can be acquired by exposure to several toxic substances. We report a case of Fanconi syndrome after long‐term therapy with VPA.

Aplasia cutis congenita of the scalp: how much therapy is necessary in large defects?

AIM To show that local antibiotic management and a regular inspection of aplasia cutis congenita of the skull can give an excellent result. METHOD This case reports a girl born with aplasia cutis congenita of the skull presenting with a large aplasia of the epidermis, dermis, subcutaneous tissue and galea, including a bone defect without any additional risk factor, e.g. early eschar formation, cerebrospinal fluid leakage or uncommon dural blood vessels. RESULTS A primarily conservative treatment with local wet and antibiotic dressings together with a systemic antibiotic treatment for the first 2 wk led to an excellent result and thus prevented untimely operative and peri-operative procedures. CONCLUSIONS Here we have shown that conservative treatment might be an option, even if the wound diameter is greater than 1 cm(2), to prevent infants from any untimely operative procedure with an elevated operative risk if any additional risk factors are excluded.

Schwann cells from human neurofibromas show increased proliferation rates under the influence of progesterone.

Neurofibromatosis type 1 (NF1) is a hereditary disease caused by mutations of the NF1 gene at 17q11.2. Loss of the NF1 gene product in Schwann cells leads to the development of benign nerve sheath tumors. These neurofibromas may occur at any time but tend to arise during periods of hormonal imbalance, suggesting that hormones influence neurofibroma growth. As steroid hormone levels rise during these times, we hypothesized that progesterone has proliferative effects on neurofibroma-derived Schwann cells. We chose specific medium conditions for selective proliferation of NF (+/−) and NF (−/−) cells from human neurofibromas. Genetic characterization was not performed, but former works have shown that under the conditions used (+/−) and (−/−) cells can be selected. Different progesterone concentrations were added at different days with BrdU-staining was performed to investigate proliferation rates and DAB-staining to identify a progesterone receptor. We could demonstrate that Schwann cells from human neurofibromas express progesterone receptors. These cells show elevated proliferation rates (highest in NF(−/−) cells) under progesterone, whereas normal human Schwann cells were not affected. These data suggest that progesterone plays an important role in the development of neurofibromas in NF1.

Connections between constitutional mismatch repair deficiency syndrome and neurofibromatosis type 1

Constitutional mismatch repair (MMR) deficiency (CMMRD) is a rare childhood cancer susceptibility syndrome resulting from biallelic germline loss‐of‐function mutations in one of the MMR genes. Individuals with CMMRD have high risk to develop a broad spectrum of malignancies and frequently display features reminiscent of neurofibromatosis type 1 (NF1). Evaluation of the clinical findings of genetically proven CMMRD patients shows that not only multiple café‐au‐lait macules but also any of the diagnostic features of NF1 may be present in a CMMRD patient. This phenotypic overlap may lead to misdiagnosis of CMMRD patients as having NF1, which impedes adequate management of the patients and their families. The spectrum of CMMRD‐associated childhood malignancies includes high‐grade glioma, acute myeloid leukaemia or rhabdomyosarcoma, also reported as associated with NF1. Reported associations between NF1 and these malignancies are to a large extent based on studies that neither proved the presence of an NF1 germline mutation nor ruled‐out CMMRD in the affected. Hence, these associations are challenged by our current knowledge of the phenotypic overlap between NF1 and CMMRD and should be re‐evaluated in future studies. Recent advances in the diagnostics of CMMRD should render it possible to definitely state or refute this diagnosis in these individuals.

Disseminated pilocytic astrocytoma involving brain stem and diencephalon: a history of atypical eating disorder and diagnostic delay.

SummaryThe association of weight loss and pediatric brain tumors that affect the diencephalon or brain stem with weight loss is a recognized, but not fully understood phenomenon. Tumors located in the hypothalamic region may induce the diencephalic syndrome (DS), which is characterized by profound emaciation with almost complete loss of subcutaneous fatty tissue. Tumors that compress or infiltrate the brain stem rarely cause both psychological disturbance and emaciation. The clinical presentation may be different, depending on the location of the lesion and age of the patient.In this report we present an unusual case of severe emaciation in a 49/12-year-old girl with a juvenile pilocytic astrocytoma of the hypothalamic region and brain stem with neuroaxis dissemination. This case illustrates the importance of considering intracranial mass-lesions in the differential diagnosis of weight loss, psychological disturbance and atypical eating disorder. We discuss the importance of tumor multifocality and the role of patient age in the clinical presentation with reference to the literature.