Neurofibromatosis 1 (NF1) is one of the most common autosomal dominant diseases. Although there is a considerable variability in clinical expression, NF1 is almost fully penetrant in adult patients and may be associated with a variety of skeletal anomalies. Spinal deformities are the most common skeletal manifestation, with an incidence estimated from 10-25% in various studies. Some NF1 patients have a dystrophic form of scoliosis, which is characterized by early age at onset and rapid progression. Complications have been reported during spinal instrumentation of dystrophic curves due to soft, non-resistant vertebral bony tissue, suggesting that an alteration of bone quality may occur in NF1 patients. Recent studies have suggested that decreased bone mineral density (BMD) may occur among patients with NF1. We performed a cross-sectional study on 104 adults with NF1, using quantitative ultrasonometry (QUS) to investigate whether decreased BMD is a general phenomenon in NF1 patients. The data reveal that BMD, as measured by age- and gender- adjusted Z-scores, is significantly lower in NF1 patients than in the normal reference population. The decrease in BMD appears to be even more marked among NF1 patients with scoliosis that requires surgical treatment. The findings indicate that NF1 produces a generalized alteration of bone in addition to the focal osseous dysplasias of the vertebrae, tibia, and sphenoid wing that characterize this condition. The pathological mechanism underlying these bony changes remains to be elucidated.
Colorectal tumorigenesis has been associated with the progressive acquisition of a variety of genetic alterations. These include mutations of the Ki-ras proto-oncogene in codons 12 and 13, which account for 85% of genetic changes in colorectal cancer. In murine in vitro models of oncogenic transformation, an association between ras-mediated transformation and downregulation of different components of the MHC class I antigen processing machinery (APM) has been described. In order to investigate whether this association also exists in human tumors, 10 cases of high-grade intraepithelial neoplasia (HIN), as well as primary tumors and autologous lymph node metastases from 42 patients with colorectal carcinoma, were monitored by allele-specific restriction analysis for Ki-ras mutations. In parallel, APM component expression and tumor cell proliferation were analyzed by immunohistochemistry. In comparison to autologous colorectal mucosa, TAP1, LMP2 and tapasin loss was found in 68%, 67% and 80% of HIN, respectively. In contrast, impaired TAP1, LMP2 and tapasin expression was found in 42%, 42% and 63% of primary adenocarcinomas of stage III disease and in 63%, 47% and 79% of the matched lymph node metastases, respectively. More than 60% of colorectal tumor lesions with TAP1, LMP2 and/or tapasin defects displayed Ki-ras mutations. The frequency of TAP1, LMP2 and tapasin loss varied between 33% of primary adenocarcinomas, 40% of HIN to approximately 67% of metastases. These data suggest that i) APM component deficiencies occur more frequently in Ki-ras-mutated colorectal carcinoma lesions and ii) APM abnormalities in conjunction with Ki-ras mutations appear to be associated with disease stage. These findings support the hypothesis that Ki-ras mutations may contribute to immune escape mechanisms of tumors by downregulating the MHC class I APM component expression. © 2003 Wiley-Liss, Inc. Key words: ras; MHC; colorectal cancer; antigen processingImmune responses against tumors are mainly based on the activation of cytotoxic CD8 ϩ T lymphocytes (CTL), which recognize endogenously generated and processed antigenic peptides in the context of MHC class I molecules. The classical MHC class I antigen processing and presentation pathway involves protein degradation mediated by the multimeric proteasome complex, particularly the interferon (IFN)-␥ inducible subunits LMP2, LMP7 and LMP10. 1,2 The yielded peptides are then translocated across the endoplasmic reticulum (ER) membrane via the ATPdependent heterodimeric transporters associated with antigen processing subunits TAP1 and TAP2. [3][4][5] In the ER, the assembly of newly synthesized MHC class I heavy chain (HC) molecules with  2 -microglobulin ( 2 -m) and peptide is assisted by transient interactions with a number of ER-resident chaperones. These include calnexin, calreticulin, protein disulfide isomerase, the thioloxidoreductase ER60 and tapasin. 6 During peptide loading, a multimeric TAP complex is formed that consists of both TAP subunits, the MHC class I antigens, calr...
HLA class I APM component abnormalities appear to represent an immune escape mechanism of RCC. This finding emphasizes the need to evaluate the integrity and expression of these molecules in patients with RCC, especially in those selected for treatment with T-cell based immunotherapy.
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