Neurofibromatosis 2 (NF2) is a dominantly inherited disorder characterized by the occurrence of bilateral vestibular schwannomas and other central nervous system tumors including multiple meningiomas. Genetic linkage studies and investigations of both sporadic and familial tumors suggest that NF2 is caused by inactivation of a tumor suppressor gene in chromosome 22q12. We have identified a candidate gene for the NF2 tumor suppressor that has suffered nonoverlapping deletions in DNA from two independent NF2 families and alterations in meningiomas from two unrelated NF2 patients. The candidate gene encodes a 587 amino acid protein with striking similarity to several members of a family of proteins proposed to link cytoskeletal components with proteins in the cell membrane. The NF2 gene may therefore constitute a novel class of tumor suppressor gene.

Oncogene-induced senescence functions to limit tumor development. However, a complete understanding of the signals that trigger this type of senescence is currently lacking. We found that mutations affecting NF1, Raf, and Ras induce a global negative feedback response that potently suppresses Ras and/or its effectors. Moreover, these signals promote senescence by inhibiting the Ras/PI3K pathway, which can impact the senescence machinery through HDM2 and FOXO. This negative feedback program is regulated in part by RasGEFs, Sprouty proteins, RasGAPs, and MKPs. Moreover, these signals function in vivo in benign human tumors. Thus, the ultimate response to the aberrant activation of the Ras pathway is a multifaceted negative feedback signaling network that terminates the oncogenic signal and participates in the senescence response.

The neurofibromatoses are a diverse group of genetic conditions that share a predisposition to the development of tumors of the nerve sheath. Schwannomatosis is a recently recognized third major form of neurofibromatosis (NF) that causes multiple schwannomas without vestibular tumors diagnostic of NF2. Patients with schwannomatosis represent 2.4 to 5% of all patients requiring schwannoma resection and approximately one third of patients with schwannomatosis have anatomically localized disease with tumors limited to a single limb or segment of spine. Epidemiologic studies suggest that schwannomatosis is as common as NF2, but that familial occurrence is inexplicably rare. Patients with schwannomatosis overwhelmingly present with pain, and pain remains the primary clinical problem and indication for surgery. Diagnostic criteria for schwannomatosis are needed for both clinicians and researchers, but final diagnostic certainly will await the identification of the schwannomatosis locus itself.

An approach to global restriction mapping is described that is applicable to any complex source DNA. By analyzing a single restriction digest for each member of a redundant set of A clones, a data base is constructed that contains fragment-size lists for all the clones. The clones are then grouped into subsets, each member of which is related to at least one other member by a significant overlap. Finally, a tree-searching algorithm seeks restriction maps that are consistent with the fragment-size lists for all the clones in each subset. The feasibility of the approach has been demonstrated by collecting data on 5000 A clones containing random 15-kilobase inserts of yeast DNA. It is shown that these data can be analyzed to produce regional maps of the yeast genome, extending in some cases for over 100 kilobases. In combination with hybridization probes to previously cloned genes, these local maps are already useful for defining the physical arrangement of closely linked genes. They may in the future serve as building blocks for the construction of a continuous global map.Fifteen years after the discovery of site-specific restriction endonucleases, the restriction map has become the standard medium for displaying the functional organization of short segments of DNA. For regions spanning up to 50 kilobases (kb), restriction maps are routinely constructed and have become indispensable tools both for organizing existing data and for planning experiments. In a few favorable cases, maps as long as 600 kb have been constructed at a resolution of a few kb (1-3), but it has proven difficult to extend existing mapping methods beyond this range. Given that the average human chromosome contains 105 kb of DNA, there is a gross disparity between the present limits of restriction-mapping techniques and the sequence complexity of cellular genomes.In this paper, we describe a project that is aimed at constructing a restriction map of total nuclear DNA from the yeast Saccharomyces, whose haploid genome size has been estimated to be 1.5 x 104 kb (4). The data collection has involved picking X clones at random and measuring the sizes of the restriction fragments generated by a single digest of each clone. Because enough clones have been analyzed to provide redundant sampling of most regions of the genome, it is possible to extract mapping information from the unordered fragment-size lists by an algorithm that systematically imposes the requirement that the set of restriction fragments generated from a single clone must be contiguous.At the present stage of the yeast project, we have analyzed 5000 X clones with average insert sizes of 15 kb, thereby achieving a sampling redundancy on the order of five. Using the data, it is now possible to construct maps of from 20 to >100 kb around most arbitrary starting points in the yeast genome. These local maps have already defined the physical arrangement of clusters of genes that previously had only been linked genetically, and they point the way toward the development of a global phy...

Purpose By incorporating major developments in genetics, ophthalmology, dermatology, and neuroimaging, to revise the diagnostic criteria for neurofibromatosis type 1 (NF1) and to establish diagnostic criteria for Legius syndrome (LGSS). Methods We used a multistep process, beginning with a Delphi method involving global experts and subsequently involving non-NF experts, patients, and foundations/patient advocacy groups. Results We reached consensus on the minimal clinical and genetic criteria for diagnosing and differentiating NF1 and LGSS, which have phenotypic overlap in young patients with pigmentary findings. Criteria for the mosaic forms of these conditions are also recommended. Conclusion The revised criteria for NF1 incorporate new clinical features and genetic testing, whereas the criteria for LGSS were created to differentiate the two conditions. It is likely that continued refinement of these new criteria will be necessary as investigators (1) study the diagnostic properties of the revised criteria, (2) reconsider criteria not included in this process, and (3) identify new clinical and other features of these conditions. For this reason, we propose an initiative to update periodically the diagnostic criteria for NF1 and LGSS.

Tuberous sclerosis complex (TSC), an autosomal dominant disease caused by mutations in either TSC1 or TSC2, is characterized by the development of hamartomas in a variety of organs. Concordant with the tumor-suppressor model, loss of heterozygosity (LOH) is known to occur in these hamartomas at loci of both TSC1 and TSC2. LOH has been documented in renal angiomyolipomas (AMLs), but loss of the wild-type allele in cortical tubers appears to be very uncommon. Analysis of second, somatic events in tumors for which the status of both TSC1 and TSC2 is known is essential for exploration of the pathogenesis of TSC-lesion development. We analyzed 24 hamartomas from 10 patients for second-hit mutations, by several methods, including LOH, scanning of all exons of both TSC1 and TSC2, promoter methylation of TSC2, and clonality analysis. Our results document loss of the wild-type allele in six of seven AMLs, without evidence of the inactivation of the second allele in many of the other lesions, including tumors that appear to be clonally derived. Laser-capture microdissection further demonstrated loss of the second allele in all three cellular components of an AML. This study thus provides evidence that, in both TSC1 and TSC2, somatic mutations resulting in the loss of wild-type alleles may not be necessary in some tumor types-and that other mechanisms may contribute to tumorigenesis in this setting.

Schwannomas are benign nerve sheath tumors that most commonly occur singularly in otherwise normal individuals. Multiple schwannomas in a single patient are most often seen in neurofibromatosis 2 (NF2), but several recent reports suggest that schwannomatosis may also be a distinct clinical entity. We studied the clinical, radiographic, and pathologic features of 14 patients with multiple schwannomas who did not have vestibular schwannoma diagnostic of NF2. Most patients had peripheral nerve tumors that presented with pain. Many also had spinal nerve root and cranial nerve tumors. Three had multiple tumors limited to a single limb. We found that these 14 individuals did not exhibit phenotypic overlap with the neurofibromatoses. Only 1 of 14 patients had a positive family history. We conclude that patients with multiple schwannomas, who do not have vestibular schwannoma, comprise a distinct clinical problem, but further molecular genetic analysis is needed to define the pathophysiology of this disorder.

Patients with multiple schwannomas without vestibular schwannomas have been postulated to compose a distinct subclass of neurofibromatosis (NF), termed "schwannomatosis." To compare the molecular-genetic basis of schwannomatosis with NF2, we examined the NF2 locus in 20 unrelated schwannomatosis patients and their affected relatives. Tumors from these patients frequently harbored typical truncating mutations of the NF2 gene and loss of heterozygosity of the surrounding region of chromosome 22. Surprisingly, unlike patients with NF2, no heterozygous NF2-gene changes were seen in normal tissues. Examination of multiple tumors from the same patient revealed that some schwannomatosis patients are somatic mosaics for NF2-gene changes. By contrast, other individuals, particularly those with a positive family history, appear to have an inherited predisposition to formation of tumors that carry somatic alterations of the NF2 gene. Further work is needed to define the pathogenetics of this unusual disease mechanism.