Short CommunicationFluorescence in situ hybridization analysis of allelic losses involving the long arm of chromosome 17 in NF1-associated neurofibromas
Introduction
Neurofibromatosis type 1 (NF1) is a common autosomal dominant condition characterized by multiple benign neurofibromas, cafe-au-lait spots, Lisch nodules, and increased risk of malignancy [1]. Skin neurofibromas (cutaneous or subcutaneous, which usually develop during adolescence and adulthood) are primarily of cosmetic significance. These small tumors, rich in extracellular matrix and sparsely populated by Schwann and mesenchymal cells, involve terminal nerves and have virtually no risk of malignant transformation. In contrast, plexiform neurofibromas typically involve deep nerves, can become very large, and usually cause serious functional impairment. Since plexiform tumors often occur on critical nerves and are not discrete masses, surgical removal is rarely successful, and patients suffer compromised function and may ultimately succumb to their disease. Plexiform tumors develop in 10%–20% of NF1 patients, and these highly cellular masses are believed to progress to highly transformed malignant peripheral nerve sheath tumors (MPNST) in approximately 6% of cases [2]. NF1 is associated with germline NF1 gene mutations (chromosome band 17q11.2), resulting in absent or abnormal neurofibromin [2]. NF1 tumor pathogenesis, however, remains poorly understood. Neurofibromas are composed primarily of Schwann cells, fibroblasts, and, in a much lower proportion, other cell types such as perineurial cells, endothelial cells, pericytes, mast cells, and neural cells [3]. Despite their multicellular composition, a clonal origin has been demonstrated for both cutaneous and plexiform neurofibromas [4]. Several cellular and molecular data have suggested that Schwann cells are the neurofibromin-deficient cells in benign neurofibromas [5], [6]. Approximately 25% of NF1 tumors show loss of heterozygosity (LOH), supporting the tumor suppressor hypothesis for the NF1 gene [7], [8]. Other studies, however, have almost not detected LOH by using a large series of patients, neurofibromas, and markers [9], or have detected LOH at a lower percentage [10]. In this study, 11 plexiform, 4 cutaneous, and 6 subcutaneous neurofibromas were examined using an interphase dual-color fluorescence in situ hybridization (FISH) technique [11], [12] to detect and quantitate NF1 loss of alleles.
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Patients and samples
The tumor samples investigated were selected randomly from a file of neurofibromas examined between 1988 and 2001 at the Department of Dermatology and Plastic Surgery at the University “La Sapienza” in Rome. Twenty-one paraffin-embedded neurofibromas from 19 patients (12 women, 7 men) were analyzed. The tumors comprised 4 cutaneous, 6 subcutaneous, and 11 plexiform neurofibromas. Table 1 summarizes the clinical data of the individual patients.
FISH
All specimens were fixed in 10% formalin and
Results and discussion
The FISH results are summarized in Table 1. All skin (cutaneous and subcutaneous) neurofibromas examined were disomic for chromosome 17 because 70% or more of the cells showed two α-satellite probe control signals. Ten plexiform neurofibromas presented two CEP 17 probe signals in more than 70% of analyzed nuclei, whereas one (sample 2654-97) was monosomic for chromosome 17 because in 89% of examined nuclei only one α-satellite probe signal was detected, supporting loss of one chromosome 17 (
Acknowledgements
The authors thank Prof. M. Rocchi (Resources for Molecular Cytogenetics, Bari, Italy) for providing the NF1 locus-specific BAC probe. The financial support of the Italian Ministry of Health (RC0304MD38) and of the Italian Ministry of Instruction, University, and Research (RBNE01JJ45) is gratefully acknowledged.
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