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PubMed2001

Electro-oculogram in patients with neurofibromatosis type 1.

PURPOSE: The electro-oculogram (EOG) is a powerful test to evaluate the functional status of the retinal pigment epithelium (RPE). Clinically detectable changes of the RPE desribed in neurofibromatosis type 1 (NF-1) patients include combined hamartoma of the retina/RPE and congenital hypertrophy of the RPE. The goal of this study was to determine whether the function of RPE as measured by EOG is also changed in individuals with NF-1. PATIENTS: Studies were undertaken in 20 patients with clinically diagnosed NF-1 and compared to 16 normal healthy controls. METHODS: Standard EOG and flash ERG recordings were performed in accordance with International Society for Clinical Electrophysiology of Vision (ISCEV) standards. RESULTS: In NF-1 patients the Arden indexes of the EOG test were significantly higher primarily due to the lower values of dark troughs. Supernormal EOGs were present in 60% of NF-1 patients in comparison to the control group mean +2 SD. No one patient showed so high abnormalities during flash ERG examination. CONCLUSIONS: Dysfunction of the RPE may be characteristic feature of individuals with NF- 1.

Adult↗
PubMed2002

Visual evoked potentials in children with neurofibromatosis type 1.

The purposes of this investigation were to determine: (a) if visual evoked potential (VEP) abnormalities could be identified in children with neurofibromatosis type 1 (NF1) with no evidence of optic pathway or brain neoplasias on MRI; and (b) if VEP abnormalities could be explained by the presence of hyperintense T2-weighted foci on MRI testing, known as unidentified bright objects (UBOs). To answer these questions, VEPs were recorded from 16 children with NF1 and compared to 13 normal subjects in the same age range tested with the same protocol. Pattern-reversal VEPs were recorded at four stimulus sizes both monocularly and binocularly, the latter to hemi-field stimuli. Flash VEPs were recorded in dark- and light-adapted conditions. VEP measurements and MRI readings for UBOs were conducted in a masked fashion. Ten of the 16 children with NF1 had abnormal VEPs to at least one of the four types of stimuli. Abnormalities included delayed responses (n=6), absent flash VEP P2 component (n=3), or both (n= 1). Abnormalities of the P2 component of the dark-adapted flash VEP were the most common finding (n=7), although no single testing strategy was able to identify all children with abnormal VEPs. UBOs were present in all children, demonstrating that their presence does not fully account for VEP abnormalities in children with NF1. This study also demonstrates that VEP abnormalities are present also in the absence of neoplasias of the optic pathways or of the brain. Our results are suggestive of a primary abnormality of visual processing in children with NF1.

Adolescent↗
PubMed2001

Combined hamartoma of the retina and retinal pigment epithelium associated with neurofibromatosis type-1.

BACKGROUND: Retinal tumors are occasionally seen in patients with neurofibromatosis type-1 (NF-1). These are usually astrocytic hamartomas or angiomas. Combined hamartoma of the retina and retinal pigment epithelium are tumors also described in NF-1, but this association has not been definitively established yet. METHOD: We report on a child with NF-1, who presented a combined hamartoma of the retina and retinal pigment epithelium in both eyes. RESULTS: The diagnosis of bilateral combined hamartoma of the retina and retinal pigment epithelium in our patient was performed on the basis of the ophthalmoscopic appearance of the lesions. NF-1 was diagnosed following the current international clinical criterion, supplemented by neuroimaging findings. CONCLUSION: Despite the extreme rarity of this association, we believe that it is not coincidental, as the presence of a hamartomatous retinal lesion in a patient with a systemic hamartomatous neuroectodermic disease would be, at least, rational. Thus, NF-1 must be excluded in patients with combined hamartoma of the retina and retinal pigment epithelium.

Child↗
PubMed2000

Insights into the pathogenesis of neurofibromatosis 1 vasculopathy.

Intrinsic lesions of arterial walls are an important manifestation of neurofibromatosis 1 (NF1). Neurofibromin is expressed in blood vessel endothelial and smooth muscle cells, and NF1 vasculopathy may result from an alteration of neurofibromin function in these cells. Elucidation of the role of neurofibromin in the maintenance and repair of blood vessels may lead to novel approaches to the treatment of NF1 vasculopathy and vascular disease in general.

Endothelium, Vascular↗
PubMed2000

Diffuse but unilateral gingival enlargement associated with von Recklinghausen neurofibromatosis: a case report.

BACKGROUND: An 8-year old girl was referred for diagnosis and treatment to the Department of Periodontology Oral Surgery of the University Hospital of Liège with an unusual clinical situation: a major, non-inflammatory, diffuse but unilateral enlargement of the interproximal, marginal and attached gingiva around all teeth of the right side of both the upper maxilla and mandible, whereas the alveolar process of the left side of upper and lower arches appeared strictly normal. METHOD: The clinical examination showed delayed eruption of some permanent teeth in the 1st and 4th quadrants. Except for its asymmetric occurrence, this gingival enlargement strongly resembled phenytoin-induced enlargement or gingival fibromatosis. This unilateral expression was evocative of a vascular or neurologic pathology. Several large "café-au-lait" spots were found disseminated on the body. Several selective surgical removals of thick gingival caps impairing the eruption of some permanent teeth were performed, and the removed tissues were histologically analyzed. RESULTS: Because of the presence of the large "café-au-lait" spots, a clinical diagnosis of Von Recklinghausen's disease was given and later confirmed several times by the histological analysis of the gingival biopsies. Now, 6 years later, this gingival enlargement due to the development of intra-gingival neurofibromas is stable and all permanent teeth have had a normal eruption, but alveolar bone growth has been partly impaired by the presence of the tumor. CONCLUSIONS: The present case of unilateral diffuse hyperplasia is a unique clinical expression of neurofibromatosis type I, a slowly evolving neurodermic dysplasia.

Cafe-au-Lait Spots↗
PubMed1990

Paternal origin of new mutations in von Recklinghausen neurofibromatosis.

Von Recklinghausen neurofibromatosis (NF-1) is a common autosomal dominant disorder. The estimated new mutation rate (1 x 10(-4] is one of the highest for a human disorder. Here we report that in 12 of 14 families we have analysed, the new mutation is of paternal origin. This result is similar to that recently obtained for retinoblastoma. In other genetic disorders that show a bias towards paternal origin of new mutations, there is a marked increase in the incidence of mutations with paternal age, consistent with the mutations arising from replication errors in mitosis of spermatogonial stem cells. In retinoblastoma and NF-1, however, such paternal age effects are slight or absent. The mechanism or timing of germline mutation could therefore be different in the two cases.

Adult↗
PubMed1990

Sequence homology shared by neurofibromatosis type-1 gene and IRA-1 and IRA-2 negative regulators of the RAS cyclic AMP pathway.

Neurofibromatosis type-1 (NF-1) is one of the most frequently inherited genetic disorders affecting humans. NF-1 primarily affects cells of neural crest origin and is characterized by patches of skin pigmentation (café-au-lait spots) and neurofibromas. Cloning of the human NF-1 gene shows that it encodes an 11-13 kilobase transcript that is frequently disrupted in NF-1 patients. The frequent disruption of the NF-1 gene in NF-1 patients combined with the autosomal dominant mode of inheritance of NF-1 strongly suggest that the NF-1 gene is a tumour-suppressor gene. We have now sequenced a portion of the murine NF-1 gene and show that the predicted amino-acid sequence is nearly the same as the corresponding region of the human NF-1 gene product. Northern blotting identified mouse NF-1 transcripts that are equivalent in size and complexity to those in human tissues, and Southern blotting shows that this region of the NF-1 gene is evolutionarily well conserved. Finally, computer searches identified homology between the mouse NF-1 gene and IRA-1 and IRA-2, two genes identified in Saccharomyces cerevisiae that negatively regulate the RAS-cyclic AMP pathway. These findings provide important new insights into the possible function of the NF-1 gene.

Adenylyl Cyclases↗
PubMed1991

Differential regulation of rasGAP and neurofibromatosis gene product activities.

The ras-encoded p21ras proteins bind GTP very tightly, but catalyse hydrolysis to GDP very slowly. In humans, two genes encode proteins that stimulate this GTPase activity (GAP, or GTPase-activating proteins), one of relative molecular mass 120,000, referred to as p120-GAP, and another NF1-GAP, which is encoded by the neurofibromatosis type-1 gene. Both GAPs are widely expressed in mammalian tissues. Here we show that although they will both bind oncogenic mutants of p21ras, neither will stimulate their GTPase activity. NF1-GAP binds to the p21ras proteins up to 300 times more efficiently than p120-GAP. The two GAPs are inhibited to different extents by certain lipids: micromolar concentrations of arachidonate, phosphatidate and phosphatidylinositol-4,5-bisphosphate affect only NF1-GAP. This inhibition does not compete with p21ras, and lipid-inactivated NF1-GAP can still bind p21ras. We used the detergent dodecyl maltoside, which inhibits only NF1-GAP, to distinguish between the two activities in cell extracts and found both types present together in several mammalian cell lines. In contrast, GAP activity in extracts of Xenopus oocytes was not affected by dodecyl maltoside. By these criteria, the mammalian cells contain both GAP activities and the oocytes have only p120-like GAP activity. These results indicate that more than one GAP regulates p21ras in the same cell.

Animals↗
PubMed1994

Neurofibromatosis and childhood leukaemia/lymphoma: a population-based UKCCSG study.

There is a well-known raised risk of leukaemia in children with neurofibromatosis type 1 (NF-1). We carried out the first detailed population-based study of leukaemia and non-Hodgkin lymphoma (NHL) associated with NF-1 in order to estimate the risk and elucidate the relationship between these conditions. Over the 17 year study period there were five cases of chronic myelomonocytic leukaemia (CMML) in patients with NF-1 (relative risk 221; 95% CI 71-514), 12 cases of acute lymphoblastic leukaemia (ALL) (relative risk 5.4; 95% CI 2.8-9.4) and five cases of NHL (relative risk 10.0; 95% CI 3.3-23.4). Marrow cytogenetics could be reviewed for seven patients. Specific abnormalities found were monosomy 21 in a child with CMML and 7p+, 17p- in a child with ALL. No abnormalities were reported of 17q, which includes the NF1 gene. CMML occurred predominantly in boys, who also had a family history of NF-1. ALL and NHL were more often found in children with no previous family history.

Adolescent↗
PubMed1997

The ocular presentation of neurofibromatosis 2.

Neurofibromatosis 2 (NF2) is an inherited disorder characterised primarily by bilateral vestibular schwannomas and other central nervous system tumours. Individuals with NF2 also have early onset cortical and posterior subcapsular or capsular cataract and other ocular abnormalities, such as retinal hamartomas. Although their diagnostic significance is rarely appreciated, the ocular manifestations are often the first sign of disease. We describe 5 cases that illustrate the diverse ocular manifestations of NF2.

Adolescent↗
PubMed2001

Ampullary adenocarcinoma in neurofibromatosis type 1. Case report and literature review.

Periampullary tumors in patients affected by Neurofibromatosis Type 1 (NF-1) are usually carcinoids or stromal tumors and, rarely, adenocarcinomas. We report a case of an adenocarcinoma of the ampulla of Vater in a 54-year-old woman with NF-1 admitted to the hospital with jaundice and undergoing pancreato-duodenectomy. Histologically, the resected specimen showed an adenocarcinoma of the ampulla as being a part of a complex atypical epithelial proliferation extended from the papilla to the mucosa of the duodenum and distal choledochus, islet-cell adenomatosis of the pancreas and multiple gastric, duodenal, jejunal stromal tumors. The ampullary and periampullary adenocarcinomas in NF-1 patients have peculiar features, suggesting a widespread predisposition to cancer development in periampullary tissues and requiring widely demolitive surgery. Moreover, they occur at a younger age than those occurring in non-NF-1 patients, may be associated with additional periampullary epithelial tumors, are often operable and may present long survival.

Adenocarcinoma↗
PubMed2002

Mechanism for the learning deficits in a mouse model of neurofibromatosis type 1.

Neurofibromatosis type I (NF1) is one of the most common single-gene disorders that causes learning deficits in humans. Mice carrying a heterozygous null mutation of the Nfl gene (Nfl(+/-) show important features of the learning deficits associated with NF1 (ref. 2). Although neurofibromin has several known properties and functions, including Ras GTPase-activating protein activity, adenylyl cyclase modulation and microtubule binding, it is unclear which of these are essential for learning in mice and humans. Here we show that the learning deficits of Nf1(+/-) mice can be rescued by genetic and pharmacological manipulations that decrease Ras function. We also show that the Nf1(+/-) mice have increased GABA (gamma-amino butyric acid)-mediated inhibition and specific deficits in long-term potentiation, both of which can be reversed by decreasing Ras function. Our results indicate that the learning deficits associated with NF1 may be caused by excessive Ras activity, which leads to impairments in long-term potentiation caused by increased GABA-mediated inhibition. Our findings have implications for the development of treatments for learning deficits associated with NF1.

Animals↗
PubMed1993

Neurofibromatosis type 1 gene mutations in neuroblastoma.

The introduction of human chromosome 17 suppresses the tumourigenicity of a neuroblastoma cell line in the absence of any effects on in vitro growth and the neurofibromatosis type 1 (NF1) gene may be responsible. Here we report that 4 out of 10 human neuroblastoma lines express little or no neurofibromin and that two of these lines show evidence of NF1 mutations, providing further proof that NF1 mutations occur in tumours that are not commonly found in NF1 patients. We also show that NF1 deficient neuroblastomas show only moderately elevated ras-GTP levels, in contrast to NF1 tumour cells, indicating that neurofibromin contributes differently to the negative regulation of ras in different cell types.

3T3 Cells↗
PubMed1993

Mutations in the neurofibromatosis 1 gene in sporadic malignant melanoma cell lines.

Neurofibromatosis type 1 (NF1) is a common autosomal dominant disorder characterized by progressive and variable involvement of tissues predominantly derived from the neural crest and a predisposition toward malignancies. The NF1 gene encodes neurofibromin, a GTPase-activating protein containing a GAP-related domain (NF1-GRD) that is capable of down-regulating ras by stimulating its intrinsic GTPase activity. We report a homozygous deletion of most of NF1 in one of eight malignant melanoma cell lines leading to loss of detectable mRNA and protein, as well as the apparent absence of protein and mRNA in another melanoma. This data suggests that NF1 can function as a tumour suppressor gene in the development or progression of malignant melanoma.

Chromosome Mapping↗
PubMed1994

Mutations in transcript isoforms of the neurofibromatosis 2 gene in multiple human tumour types.

The neurofibromatosis 2 gene (NF2) has recently been isolated and predicted to encode a novel protein related to the moesin-ezrin-radixin family of cytoskeleton-associated proteins. Here we describe a novel isoform of the NF2 transcript that shows differential tissue expression and encodes a modified C terminus of the predicted protein. Mutations affecting both isoforms of the NF2 transcript were detected in multiple tumour types including melanoma and breast carcinoma. These findings provide evidence that alterations in the NF2 transcript occur not only in the hereditary brain neoplasms typically associated with NF2, but also as somatic mutations in their sporadic counterparts and in seemingly unrelated tumour types. The NF2 gene may thus constitute a tumour suppressor gene of more general importance in tumorigenesis.

Alternative Splicing↗
PubMed1997

A mouse model for the learning and memory deficits associated with neurofibromatosis type I.

Neurofibromatosis type I (NF1) is one of the most commonly inherited neurological disorders in humans, affecting approximately one in 4,000 individuals. NF1 results in a complex cluster of developmental and tumour syndromes that include benign neurofibromas, hyperpigmentation of melanocytes and hamartomas of the iris. Some NF1 patients may also show neurologic lesions, such as optic pathway gliomas, dural ectasia and aqueduct stenosis. Importantly, learning disabilities occur in 30% to 45% of patients with NF1, even in the absence of any apparent neural pathology. The learning disabilities may include a depression in mean IQ scores, visuoperceptual problems and impairments in spatial cognitive abilities. Spatial learning has been assessed with a variety of cognitive tasks and the most consistent spatial learning deficits have been observed with the Judgement of Line Orientation test. It is important to note that some of these deficits could be secondary to developmental abnormalities and other neurological problems, such as poor motor coordination and attentional deficits. Previous studies have suggested a role for neurofibromin in brain function. First, the expression of the Nf1 gene is largely restricted to neuronal tissues in the adult. Second, this GTPase activating protein may act as a negative regulator of neurotrophin-mediated signalling. Third, immunohistochemical studies suggest that activation of astrocytes may be common in the brain of NF1 patients. Here, we show that the Nf1+/- mutation also affects learning and memory in mice. As in humans, the learning and memory deficits of the Nf1+/- mice are restricted to specific types of learning, they are not fully penetrant, they can be compensated for with extended training, and they do not involve deficits in simple associative learning.

Acoustic Stimulation↗
PubMed2006

A prospective study of neurofibromatosis type 1 cancer incidence in the UK.

Neurofibromatosis type 1 (NF1) is an autosomal dominant condition affecting around one in 3000 live births. The manifestations of this condition are extremely variable, even within families, and genetic counselling is consequently difficult with regard to prognosis. Individuals with NF1 are acknowledged to be at increased risk of malignancy. Several studies have previously attempted to quantify this risk, but have involved relatively small study populations. We present prospective data from 448 individuals with NF1 with a total of 5705 years of patient follow-up. These data have been collected via the UK NF1 association for patients. Demographic information on the affected individuals was cross-referenced with UK cancer registry data by the UK Office of National Statistics. The overall risk of cancer was 2.7 times higher in this cohort of NF1 patients than in the general population (95% confidence interval (CI) 1.9-3.7). The cumulative risk of a malignancy by age 50 years was 20% (95% CI 14-29%); beyond this age, the risk of cancer was not significantly elevated (P=0.27). The most frequent types of cancer were connective tissue (14% risk by age 70, 95% CI 7.8-24%) and brain tumours (7.9, 95% CI 3.9-16%). There was no statistically significant excess of cancers at other sites (P=0.22).

Adolescent↗
PubMed2006

Neurofibromatosis type 1 protein and amyloid precursor protein interact in normal human melanocytes and colocalize with melanosomes.

The neurofibromatosis type 1 (NF1) gene product, neurofibromin, is known to interact with Ras, thereby negatively regulating its growth-promoting function. Although this is a well-established interaction, the discovery of other neurofibromin interacting partners could reveal new functional properties of this large protein. Using yeast two-hybrid analysis against a brain cDNA library, we identified a novel interaction between the amyloid precursor protein and the GTPase activating protein-related domain of neurofibromin. This interaction was further analyzed in human melanocytes and confirmed by immunoprecipitation and colocalization studies. In addition, we observed a colocalization of amyloid precursor protein and neurofibromin with melanosomes. Amyloid precursor protein has been proposed to function as a vesicle cargo receptor for the motor protein kinesin-1 in neurons. This colocalization of amyloid precursor protein and neurofibromin with melanosomes was lost in melanocytes obtained from normal skin of a NF1 patient. We suggest that a complex between amyloid precursor protein, neurofibromin, and melanosomes might be important in melanosome transport, which could shed a new light on the etiopathogenesis of pigment-cell-related manifestations in NF1.

Cafe-au-Lait Spots↗