Apparent preferential loss of heterozygosity at TSC2 over TSC1 chromosomal region in tuberous sclerosis hamartomas

To investigate the molecular mechanisms of tuberous sclerosis (TSC) histopathologic lesions, we have tested for loss of heterozygosity the two TSC loci (TSC1 and TSC2) and seven tumor suppressor gene-containing regions (TP53, NF1, NF2, BRCA1, APC, VHL, and MLM) in 20 hamartomas from 18 TSC patients. Overall, eight angiomyolipomas, eight giant cell astrocytomas, one cortical tuber, and three rhabdomyomas were analyzed. Loss of heterozygosity at either TSC locus was found in a large fraction of the informative patients, both sporadic (7/14) and familial (1/4). Interestingly, a statistically significant preponderance of loss of heterozygosity at TSC2 was observed in the sporadic group (P < 0.01). Among the possible explanations considered, the bias in the selection for TSC patients with the most severe organ impairment seems particularly appealing. According to this view, a TSC2 defect might confer a greater risk for early kidney failure or, possibly, a more rapid growth of a giant cell astrocytoma. None of the seven antioncogenes tested showed loss of heterozygosity, indicating that the loss of either TSC gene product may be sufficient to promote hamartomatous cell growth. Finally, the observation of loss of heterozygosity at different markers in an astrocytoma and in an angiomyolipoma from the same patient might suggest the multifocal origin of the second-hit mutation. Genes Chromosom Cancer 15:18–25 (1996). © 1996 Wiley-Liss, Inc.     

Multifocal renal cell carcinoma in sibs from a chromosome 9 linked (TSC1) tuberous sclerosis family.

Multifocal renal cell carcinomas (RCCs), together with angiomyolipomas (AMLs) and renal cysts, were identified in early adult life in two sisters with tuberous sclerosis (TSC). They were members of a multigenerational tuberous sclerosis family showing strong evidence for a mutant TSC causing gene on chromosome 9 (TSC1). Previous reports of multifocal RCC in young patients with TSC suggest that constitutional mutations at the TSC loci may predispose to RCC. In the rat a germline mutation affecting the TSC2 gene is associated with transmission of multifocal RCC as an autosomal dominant trait. However, the cases reported here are the first to suggest a similar role for the TSC1 gene in renal cell carcinogenesis.     

中国人结肠癌染色体12p12-13杂合性丢失的研究

目的通过对中国人结肠癌染色体12p12-13杂合性丢失（loss of heterozygosity,LDH）分析，了解KRAS2基因与结肠癌发生发展的关系。方法从10例结肠癌手术切除标本中，提取肿瘤、癌旁及相应正常组织的DNA，用PCR．变性聚丙烯酰胺凝胶电泳．免疫荧光标记多重微卫星PCR法，对染色体12p12-13杂合性丢失进行分析。结果10例癌旁组织中有3例（30％）在12p12-13处至少有一个位点出现杂合性丢失，其中D12S1034出现频率最高，为28．57％（2／7）；10例原发性结肠癌标本中6例（60％）在12p12-13处至少有一个位点出现有杂合性丢失，D12S1034和D12S1591是高频率丢失集中的区域，均占42．86％（3／7）；癌旁组织、癌组织均发生LDH的标本有3例，占30％（3／10）；仅在癌组织中发生LDH的标本有3例，占30％（3／10）；仅在癌旁组织中发生LDH，癌组织无信号的标本1例；杂合性丢失的频率与肿瘤患者的年龄、性别、肿瘤大小、肿瘤部位及淋巴结转移均无关。结论SRAS2基因所在的12p12-13区域在结肠癌发生发展过程中出现基因组不稳定，该区域的高频杂合性丢失可能直接影响野生型KRAS2基因的转录与翻译。     

Identification of markers flanking the tuberous sclerosis locus on chromosome 9 (TSC1).

Analysis of a large tuberous sclerosis pedigree confirmed linkage to a locus on the long arm of chromosome 9, with recombination events placing the disease gene distal to gelsolin and proximal to dopamine beta-hydroxylase.     

Novel TSC2 mutation in a patient with pulmonary tuberous sclerosis: lack of loss of heterozygosity in a lung cyst

A Japanese patient with tuberous sclerosis (TSC), who manifested with multiple lung cysts and pneumothorax, is described. All exons of two TSC genes, TSC1 and TSC2, in peripheral blood leukocytes from the patient were analyzed by polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP). A novel T-to-G transition was found in exon 19 of TSC2 at nucleotide position 2168. This mutation caused an amino acid change, L717R. There was no such mutation in any other family members or in 100 normal Japanese. An automated sequencer-assisted quantitative analysis of normal and mutated SSCP-bands revealed no loss of heterozygosity (LOH) in the lung cyst tissue of the patient.     

Loss of heterozygosity is detected at chromosomes 1p35-36 (NB), 3p25 (VHL), 16p13 (TSC2/PKD1), and 17p13 (TP53) in microdissected apocrine carcinomas of the breast.

INTRODUCTION: Apocrine carcinomas of the breast are an unusual special category of predominantly AR+, ER-, and PR- breast cancer, characterized by cells with abundant, eosinophilic cytoplasm and nuclei with often prominent nucleoli. To further investigate these lesions, loss of heterozygosity (LOH) was evaluated at multiple chromosomal loci, including loci frequently mutated in breast cancer. MATERIALS AND METHODS: Twenty-five intraductal apocrine carcinomas, 11 invasive apocrine carcinomas, and six apocrine hyperplasias were retrieved from the files of the Armed Forces Institute of Pathology (Washington, DC) and Fairfax Hospital (Fairfax, VA). Cells from lesional as well as normal tissues were microdissected. LOH was performed at a number of chromosomal loci, including loci commonly altered in breast cancer: 1p35-36 (NB), 3p25.5 (VHL), 8p12 (D8S136), 9p21 (p16), 11p13 (D11S904), 11q13 (INT-2 and PYGM), 16p13.3 (TSC2/PKD1 gene region), 17p13 (TP53), 17q13 (NM23), and 22q12 (D22S683). RESULTS: Among informative in situ and invasive apocrine carcinomas, LOH was present in 33% of 15 cases for 17p13 (TP53), as well as 36% of 14 cases for 3p25 (VHL), 30% of 10 cases for 1p35-36 (NB), and 27% of 11 cases for 16p13.3 (TSC2/PKD1). A higher frequency of LOH was noted among invasive apocrine carcinomas (30 to 50%) compared with in situ apocrine carcinomas (23 to 33%) at these loci. LOH was present simultaneously for TP53 and either VHL or NB in five cases. Infrequent (< or =12%) or absent LOH was detected at the remaining loci, including several loci commonly mutated in breast cancer (i.e., INT2, PYGM, and NM23). LOH was not detected in any of the six apocrine hyperplasias. CONCLUSION: An intermediate frequency of allelic loss was detected at multiple tumor suppressor gene loci, including 17p13 (TP53), as well as 1p35-336 (NB), 3p25 (VHL), and 16p13 (PKD1/ TSC2), in apocrine carcinomas of the breast, with a higher overall frequency of LOH noted among invasive tumors compared with in situ tumors. Aside from LOH at p53, LOH was infrequent or absent at several other loci commonly mutated in breast cancer. This preliminary molecular evidence supports immunohistochemical data that apocrine carcinomas of the breast may possess unique mechanisms of carcinogenesis, compared with ordinary ductal carcinomas. However, further study is needed to support this assertion and to determine if the LOH detected is truly etiologic or if it is the result of genetic progression.     

Detailed mapping and loss of heterozygosity analysis suggests a suppressor locus involved in sporadic breast cancer within a distal region of chromosome band 17p13.3

The chromosome region 17p13.3 is thought to encode a tumoursuppressor gene involved in sporadic breast cancer and othermalignancies. Physical ordering of markers has been carriedout by a series of multicolour fluorescent in situ hybridisation(FISH) experiments, using isolated yeast artificial chromosomes(YACs) and cosmids. Eight polymorphic markers ordered withinthis new physical map and one external marker were used to investigatethe pattern of loss of heterozygosity in a panel of 40 sporadicbreast tumour patients. The data revealed a region of high loss(60%) within distal 17p13.3, defined by markers D17S926, D17S695and D17S849 which mapped close together. A contig of YACs wasconstructed physically linking these three markers.     

Mutational analysis of the tuberous sclerosis gene TSC2 in patients with pulmonary lymphangioleiomyomatosis

Pulmonary lymphangioleiomyomatosis (LAM) is a rare disorder limited almost exclusively to women of reproductive age. LAM affects about 5% of women with tuberous sclerosis complex (TSC). LAM also occurs in women who do not have TSC (sporadic LAM). TSC is a tumour suppressor gene syndrome characterised by seizures, mental retardation, and tumours in the brain, heart, and kidney. Angiomyolipomas, which are benign tumours with smooth muscle, fat, and dysplastic vascular components, are the most common renal tumour in TSC. Renal angiomyolipomas also occur in 63% of sporadic LAM patients. We recently found that 54% of these angiomyolipomas have TSC2 loss of heterozygosity, leading to the hypothesis that sporadic LAM is genetically related to TSC. In this study, we screened DNA from 21 women with sporadic LAM for mutations in all 41 exons of TSC2. Twelve of the patients had known renal angiomyolipomas. No TSC2 mutations were detected. We did find three silent TSC2 polymorphisms. We conclude that patients with sporadic LAM, including those with renal angiomyolipomas, do not have a high frequency of germline mutations in the coding region of TSC2.     

Loss of heterozygosity on chromosome 17p13 in breast carcinomas identifies tumors with high proliferation index.

The capacity of breast tumor cells to proliferate is considered a potential prognostic factor together with other histopathologic parameters. The authors determined the proliferation index on a large panel of human primary breast tumors by measuring the levels of incorporation of bromodeoxyuridine (BrdU) by fresh tumor specimens in culture. Previous analysis showed that the percentage of cells entering the S-phase of the cell cycle strongly correlates with tumor grade, tumor size, and estrogen and progesterone receptor status. The capacity of tumor cells to proliferate might be associated with specific genetic mutations in primary tumors. To test this hypothesis, a panel of 96 human breast carcinomas, for which the BrdU labeling index (LI) was known, were tested for loss of heterozygosity (LOH) or increased copy number (ICN) at chromosomes 1q, 3p, 13q, 17p, and 18q. On chromosome 17p, LOH and ICN were observed in 27% and 12%, respectively, of the informative breast tumors. The LOH on chromosome 17p was significantly associated with tumors having an elevated BrdU proliferation index (P = 0.022). No association (P = 0.45) was observed between BrdU LI and tumor size (T2 + T3 compared with T1), tumor grade, and lymph node status. Increased copy number on chromosome 17p, LOH or ICN on 1q, and LOH on 13q14, 18q, and 3p also showed no significant correlation with cell kinetic parameters. These data are consistent with the presence of a gene or genes on chromosome 17p13 near the YNZ22.1 locus whose normal functioning is necessary for controlling breast tumor cells proliferation in vivo.     

Analysis of 65 tuberous sclerosis complex (TSC) patients by TSC2 DGGE, TSC1/TSC2 MLPA, and TSC1 long-range PCR sequencing, and report of 28 novel mutations

Tuberous sclerosis complex (TSC) is a severe autosomal-dominant disorder characterized by the development of benign tumors (hamartomas) in many organs. It can lead to intellectual handicap, epilepsy, autism, and renal or heart failure. An inactivating mutation in either of two tumor-suppressor genes-TSC1 and TSC2-is the cause of this syndrome, with TSC2 mutations accounting for 80-90% of all mutations. Molecular diagnosis of TSC is challenging, since TSC1 and TSC2 consist of 21 and 41 coding exons, respectively, and the mutation spectrum is very heterogeneous. Here we report a new approach for detecting mutations in TSC: a denaturing gradient gel electrophoresis (DGGE) analysis for small TSC2 mutations, a multiplex ligation-dependent probe amplification (MLPA) analysis for large deletions and duplications in TSC1 or TSC2, and a long-range PCR/sequencing-based analysis for small TSC1 mutations. When applied in this order, the three methods provide a new sensitive and time- and cost-efficient strategy for the molecular diagnosis of TSC. We analyzed 65 Danish patients who had been clinically diagnosed with TSC, and identified pathogenic mutations in 51 patients (78%). These included 36 small TSC2 mutations, four large deletions involving TSC2, and 11 small TSC1 mutations. Twenty-eight of the small mutations are novel. For the missense mutations, we established a functional assay to demonstrate that the mutations impair TSC2 protein function. In conclusion, the strategy presented may greatly help small- and medium-sized laboratories in the pre- and postnatal molecular diagnosis of TSC.     

Novel intragenic polymorphisms in the tuberous sclerosis 2 (TSC2) gene. Mutations in brief no. 184. Online

Twenty-three unrelated patients with tuberous sclerosis have been screened for the presence of mutations in six regions of the TSC2 gene. Eight novel intragenic polymorphisms have been found, one in intron 36 and seven in intron 4, with the use of SSCP analysis. Four of these polymorphisms alter the recognition sequence of specific restriction enzymes and can be detected as RFLPs. Study in a random sample of unrelated individuals from Northern Greece, showed that these polymorphisms have mean observed and expected heterozygosity values of 0.2996 and 0.3349, respectively and could be useful for linkage analysis. It is most likely that the wild type alleles from two pairs of these polymorphisms are strongly associated. A 667 bp segment of intron 4 (954 bp) and an additional 75 bp of intron 36 (352bp) were sequenced, thus completing the sequence of both introns.     

Loss of heterozygosity on chromosome 10, 13q(Rb), 17p,and p53 gene mutations in human brain gliomas.

Using the methods of restriction fragment length polymorphism (RFLP) and single strand conformation polymorphism (SSCP) analyses, we have examined 33 cases of human gliomas with various malignant grades to detect the deletions of putative tumor suppressor gene loci, chromosome 10, 13q(retinoblastoma gene, Rb), 17p, and p53 mutation. We observed loss of heterozygosity (LOH) at loci on chromosome 10 (36%), 13q(Rb) (54%), and 17p(50%) in malignant gliomas. There, however was no allelic loss on chromosome 10 and 17p in low-grade gliomas. Rb gene deletions were seen in low-grade gliomas, including oligodendroglioma and ependymoma. This finding suggests that Rb inactivation may be an early genetic event in the development and progression of gliomas. We correlated the results of LOH on chromosome 17p and p53 mutation. Among the 8 cases which showed LOH on chromosome 17p, only three cases (38%) revealed p53 mutations. Low incidence of p53 mutations in cases with chromosome 17p deletions suggests that some other tumor suppressor genes may be located on chromosome 17p.     

9q34 loss of heterozygosity in a tuberous sclerosis astrocytoma suggests a growth suppressor-like activity also for the TSC1 gene

Tuberous sclerosis is an autosomal dominant disease whose characteristicfeature is the development of multiple hamartomas in a varietyof organs and tissues. Two major loci have been identified sofar: TSC1 on chromosome 9q34 and TSC2 on chromosome 16p13.3.Loss of heterozygosity at 16p13.3-associated markers has beenrecently observed in hamartomatous lesions of some tuberoussclerosis patients. Here we report the first evidence of lossof heterozygosity at the TSC1 critical region in a giant cellastrocytoma of a familial tuberous sclerosis case. Segregationanalysis showed that the 9q34 haplotype lost carried the putativenormal TSC1 gene. These data support the hypothesis of botha germline and somatic loss-of-function mutation for the developmentof tuberous sclerosis hamartomas and suggest a tumor-suppressor-likeactivity also for the TSC1 gene product. Finally, the possiblesignificance of a second small region of loss of heterozygosityat 9p21, found in the same astrocytoma, is discussed.     

具有家族史鼻咽癌4p15.1-4q12区等位基因杂合性丢失分析

目的确定有家族史鼻咽癌患者4p15．1-4q12区域等位基因杂合性丢失（loss of heterozygosity，LOH）的分布和频率，为进一步缩小该区域内易感基因的范围提供新的线索和依据。方法收集具有家族史的鼻咽癌患者石蜡包埋的活检组织标本，采用显微切割的方法在肿瘤组织石蜡切片上分离肿瘤细胞和正常淋巴细胞，选定7个定位于4p15．1-4q12区域内的高密度微卫星位点，多重PCR扩增和丙烯酰胺凝胶电泳后，Genescan软件对各位点LOH进行分析。结果25例具家族史鼻咽癌患者中，23例在4p15．1-4q12区至少存在一个微卫星位点的LOH（92％）。其中D4S2382位点LOH的频率最高，达到56％；D4S350和D4S1547位点LOH频率均约为50％。最小共同缺失区位于位点D4S350和D4S1547之间。结论鼻咽癌4p15．1—4q12区域内的易感基因可能位于微卫星位点D4S350和D4S1547附近。     

Loss of tuberin in both subependymal giant cell astrocytomas and angiomyolipomas supports a two-hit model for the pathogenesis of tuberous sclerosis tumors.

Tuberous sclerosis complex (TSC) is an autosomal dominant disorder characterized by seizures, mental retardation, and tumors of skin, brain, heart, and kidney. In this study, we focused on two of the most frequent tumors in TSC patients, renal angiomyolipomas and subependymal giant cell astrocytomas (SEGAs). Two questions were addressed. First, is loss of tuberin, the product of the TSC2 gene, seen in both renal and central nervous system tumors from TSC patients? Second, when loss of tuberin occurs, does it affect each of the cell types seen in these tumors? We used a loss of heterozygosity approach to identify tumors from TSC2 patients. We found loss of tuberin immunostaining in the spindle and epithelioid cells but not in the giant cells of six TSC2 SEGAs. We also found loss of tuberin immunostaining in all three cell types (smooth muscle, fat, and vessels) of six TSC2 angiomyolipomas. Chromosome 16p13 loss of heterozygosity occurred in both spindle and epithelioid cells of a SEGA and in smooth muscle and fat but not the vessels of two angiomyolipomas. These results support a two-hit tumor suppressor model for the pathogenesis of SEGAs and angiomyolipomas. The vascular elements of angiomyolipomas and the giant cells of SEGAs may be reactive rather than neoplastic.     

Exon scanning of the entire TSC2 gene for germline mutations in 40 unrelated patients with tuberous sclerosis

Tuberous sclerosis complex (TSC) is a dominantly inherited multisystem disorder resulting in the development of hamartomatous growths in many organs. Genetic heterogeneity has been demonstrated linking the familial cases to either TSC1 at 9q34.3, or TSC2 at 16p13.3. About two-thirds of the TSC cases are sporadic and appear to represent new mutations. While both genes are thought to account for all familial cases, with each representing approximately 50% of the mutations, the proportion of sporadic cases with mutations in TSC1 and TSC2 is yet to be determined. We have examined the entire coding sequence of the TSC2 gene in 20 familial and 20 sporadic cases and identified a total of twenty-one mutations representing 50% and 55% of familial and sporadic cases respectively. Our rate of mutation detection is significantly higher than other published reports. Twenty out of 21 mutations are novel and include 6 missense, 6 nonsense, 5 frameshifts, 2 splice alterations, a 34 bp deletion resulting in abnormal splicing, and an 18 bp deletion which maintains the reading frame. The mutations are distributed throughout the coding sequence with no specific hot spots. There is no apparent correlation between mutation type and clinical severity of the disease. Our results document that at least 50% of sporadic cases arise from mutations in the TSC2 gene. The location of the mutations described here, particularly the missense events, should be valuable for further functional analysis of this tumor suppressor protein. Hum Mutat 12:408–416, 1998. © 1998 Wiley-Liss, Inc.     

Loss of heterozygosity at chromosome regions 22q11–12 and 11p15.5 in renal rhabdoid tumors

Rhabdoid tumors of the kidney are highly malignant neoplasms that occur primarily within the first 3 years of life. Although they are regarded as distinct from Wilms' tumors, their pathogenesis remains unclear. Whereas most cytogenetic studies of these tumors have revealed normal karyotypes, a few reports have indicated abnormalities at chromosome regions 22q and 11p15.5. We analyzed 30 primary renal rhabdoid tumors for loss of heterozygosity (LOH) at both regions and found that 24 of 30 tumors (80%) had LOH at chromosome arm 22q and that 5 of 30 (17%) had LOH at chromosome band 11p15.5. All of the five tumors with LOH at chromosome arm 11p also had LOH at chromosome arm 22q. The data suggest that there is a gene in chromosome 22, probably a tumor suppressor, inactivation of which may be involved in the genesis of renal rhabdoid tumors. A second gene in chromosome segment 11p15.5, in the region of the putative WT2 gene, may also be involved, in at least a subset of rhabdoid tumors. In addition, five tumors were characterized by microsatellite instability at three or more of 21 loci examined, suggesting a possible role for a replicative error in tumorigenesis or progression in some cases of renal rhabdoid tumors. Genes Chromosom Cancer 15:10–17 (1996). © 1996 Wiley-Liss, Inc.