Multiple endocrine neoplasia 1 gene alterations in MEN1-associated and sporadic lipomas.

Multiple endocrine neoplasia 1 (MEN1) syndrome is characterized by the development of parathyroid adeno-mas, pituitary adenomas, and duodenal and/or pancreatic neuroendocrine tumors. The vast majority, and possibly all, of these tumors are characterized by two genetic hits—germline mutation of the MEN1 tumor suppressor gene combined with allelic deletion of the corresponding wild-type allele (1). Alterations of the MEN1 gene are not only found in MEN1-associated tumors but also, with decreasing frequency, in sporadic neuroendocrine tumors of the fore-gut (2,3), parathyroid tumors (4), and pituitary adenomas (5). Lipomatous tumors are known to occur in a relatively high proportion of patients with MEN1 disease. In this study, we attempted to determine the role of the MEN1 gene in the development of MEN1-associated and sporadic lipomas. For genetic tissue analysis of MEN1-associated lipomas, we obtained preparations by touching tumor tissue to a glass slide to transfer a limited number of cells; we then performed fluorescence in situ hybridization (FISH) on such touch preparations to detect deletions of the MEN1 wild-type allele in two tumors that were excised from two patients with known MEN1 gene germline mutations (case 1—a 61-year-old male with an abdominal wall lipoma, mutation status L22R; case 2—a 69-year-old male with a lipoma of the right thigh, mutation status W436R). FISH was performed using as a probe cosmid clone c10B11 (size, 40 kilobases), which contains the MEN1 gene (6). For analysis of sporadic lipomas, we performed poly-merase chain reaction (PCR)-based single-strand conformation polymor-phism and sequence analysis using for-malin-fixed, paraffin-embedded tissue. FISH analysis of the two lipomas, which were excised from patients with known MEN1 disease, revealed loss of one MEN1 allele in 53% of the cells examined from case 1 (Fig. 1, left panel) and in 63% of the cells examined from case 2. It appears from this finding that the lipoma cells are affected by genetic deletion, whereas both MEN1 gene copies were visualized in normal cellular constituents. Furthermore, in both cases, two copies of the chromosome 11 alpha satellite, located in the centromere, were present in all of the cells, as shown by a control probe. In conjunction with a recent PCR-based deletion analysis of three lipomas (7), our results confirm the hypothesis that mutation of the MEN1 gene and subsequent loss of the wild-type allele are associated with or causative for the development of lipo-matous tumors in patients with MEN1 disease. To investigate the role of the MEN1 …