Desmoplastic cerebral astrocytomas of infancy: a histopathologic, immunohistochemical, ultrastructural, and molecular genetic study

The desmoplastic cerebral astrocytoma of infancy (DCAI) is a rare tumor that presents as a large hemispheric mass in infants. Despite an ominous histologic picture that may resemble a sarcoma, the tumor is astrocytic and has a good prognosis. We present two cases of DCAI, with histopathologic, immunohistochemical, ultrastructural, and molecular genetic data, and draw the following conclusions: (1) the diagnosis of DCAI requires a high index of suspicion and immunohistochemical or ultrastructural proof of astrocytic differentiation; (2) the data argue against nosologically equating these tumors with the desmoplastic infantile ganglioglioma, pleomorphic xanthoastrocytoma, or gliofibroma; (3) the components of the extensive tumor basal lamina may be elaborated by the tumor cells themselves and may contribute in an autocrine fashion to the slow growth of these lesions; and (4) if the lack of allelic loss on chromosomes 17p (including the p53 tumor suppressor gene locus) and 10 seen in our cases is found in other cases of DCAI, this may further distinguish the DCAI from other astrocytomas.

A (CA)n dinucleotide repeat assay for evaluating loss of allelic heterozygosity in small and archival human brain tumor specimens

Southern blotting is a widely used method of determining loss of chromosomal alleles in tumors, but cannot be used to analyze small biopsies and most fixed, embedded tissues. These problems preclude analysis of many surgical neuropathology specimens. We have employed a polymerase chain reaction assay for loss of heterozygosity (LOH) based on the (CA)n dinucleotide repeat polymorphisms found in abundance throughout the human genome. We compared this method to conventional Southern blotting in detecting LOH on chromosome 10 in gliomas. From tissue sections of 14 paraffin-embedded, formalin-fixed gliomas, we amplified the (CA)n repeat D10S89 locus and compared (CA)n repeat patterns between tumor DNA and constitutional DNA. Loss of one chromosome 10 (CA)n repeat allele was seen in informative glioblastomas that showed allelic loss by Southern blotting, but not in gliomas that had maintained both alleles. The (CA)n repeat method can be applied to small and fixed, embedded specimens, is rapid and simple to perform, and uses highly polymorphic probes. We suggest that (CA)n repeats are a less exclusive and more rapid means of studying LOH in brain tumors than Southern blotting, and will provide further mapping data for the identification of tumor suppressor genes integral to glial tumorigenesis.

Cytogenetic and molecular studies of a familial renal cell carcinoma

In a previously studied family with inherited renal cell carcinoma (RCC), RCC was shown to segregate with a constitutional balanced t(3;8)(p14.2;q24.1). In addition, we recently showed that in a RCC tumor from this family the constitutional translocation became unbalanced, suggesting a genetic mechanism that may be associated with the primary genetic events of tumorigenesis. We now report that the RCC tumor cells from this case showed additional cytogenetic alterations, possibly related to tumor progression, which include an additional tumor-specific translocation involving band 14 of chromosome 13. Because this band contains the retinoblastoma (RB) gene, we examined the tumor for aberrations in the RB gene using DNA sequence polymorphism analysis and pulsed-field gel electrophoresis (PFGE), but did not detect alterations in the RB gene.

Anti-oncogenes and the development of tumors in the human nervous system

Two distinct mechanisms of tumorigenesis have been identified in humans. One mechanism is associated with the activation of growth-promoting factors such as proto-oncogenes, growth factors, and growth factor receptors. However, there is overwhelming evidence for the existence of an alternative tumor mechanism that is related to the loss or inactivation of genes that normally suppress cell growth. These genes have been called "anti-oncogenes" or "tumor-suppressor" genes. They appear to be involved fundamentally in the development of many human cancers. This article reviews the potential importance of tumor-suppressor genes in tumor development and growth control in the human nervous system.

Repression of the basal c-fos promoter by wild-type p53

Mutations in the p53 gene are the most common genetic alterations observed in many inherited and sporadic forms of human cancer. Recent studies indicate that wild-type p53 may be involved in the regulation of gene expression. In the present report we examined the effect of p53 on the human c-fos promoter. Using a transient co-transfection assay we show that wild-type human p53, but not a transforming mutant of p53, negatively regulates the activity of the c-fos promoter in a dose-dependent manner. Promoter deletion analysis maps a sequence conferring p53 repression to the basal promoter region between nucleotides -53 and +42 relative to the cap site. In contrast, p53 strongly stimulates transcription when a sequence previously reported to bind p53 (TGCCT repeat) was inserted in front of the HSV-TK promoter driving CAT. These findings raise the question as to whether p53 may mediate its inhibitory effect on c-fos gene expression by interfering, directly or indirectly, with components of the basal transcriptional machinery.

Evidence for a tumor suppressor gene on chromosome 19q associated with human astrocytomas, oligodendrogliomas, and mixed gliomas

Previous studies have shown frequent allelic losses of chromosomes 9p, 10, 17p, and 22q in glial tumors. Other researchers have briefly reported that glial tumors may also show allelic losses of chromosome 19, suggesting a putative tumor suppressor gene locus on this chromosome (D. T. Ransom et al., Proc. Am. Assoc. Cancer Res., 32:302, 1991). To evaluate whether loss of chromosome 19 alleles is common in glial tumors of different types and grades, we performed Southern blot restriction fragment length polymorphism analysis for multiple chromosome 19 loci in 122 gliomas from 116 patients. Twenty-nine tumors had loss of constitutional heterozygosity of 19q, and four tumors had partial deletions of 19q. Allelic losses on 19q were restricted to grade III anaplastic astrocytomas (4/9) and grade IV glioblastomas (11/46), grade II oligodendrogliomas (2/5) and grade III anaplastic oligodendrogliomas (2/2), and grade II (5/8) and grade III (5/7) mixed oligoastrocytomas. These data demonstrate genetic similarities between astrocytomas, oligodendrogliomas, and mixed glial tumors and indicate the presence of a glial tumor suppressor gene on chromosome 19q.

p53 mutations are associated with 17p allelic loss in grade II and grade III astrocytoma

Loss of genetic material on the short arm of chromosome 17 is observed in approximately 40% of human astrocytomas (WHO grades II and III) and in approximately 30% of cases of glioblastoma multiforme (WHO grade IV). Previous studies of glioblastoma multiforme have shown that the p53 gene, located on the short arm of chromosome 17, is frequently mutated in these glioblastomas. To explore whether lower-grade astrocytomas are also associated with corresponding mutations of the p53 gene, we have investigated a series of 22 human astrocytomas of WHO grades II and III both for loss of heterozygosity on chromosome 17p and for p53 mutations. Mutations in the conserved regions of the p53 gene were identified by single strand conformation polymorphism analysis of exons 5, 6, 7, and 8 and were verified by direct DNA sequencing of the polymerase chain reaction products. p53 mutations were observed in 3 of 8 grade II astrocytomas and 4 of 14 grade II astrocytomas. In all 22 tumors, allelic loss of the short arm of chromosome 17 was investigated by restriction fragment length polymorphism analysis. One-half of the grade II astrocytomas (4 of 8) and grade III astrocytomas (7 of 14) exhibited allelic loss on chromosome 17p. Mutations in the p53 gene were exclusively observed in tumors with allelic loss on 17p. Our results show that p53 mutations are not restricted to glioblastoma multiforme and may be important in the tumorigenesis of lower-grade astrocytomas and that p53 mutations in lower-grade astrocytomas are associated with loss of chromosome 17p. These findings are consistent with a recessive mechanism of action of p53 in WHO grade II and III astrocytoma tumorigenesis.

Genes associated with tumor suppression and growth control in the human nervous system

Cancer, the uncontrolled proliferation of a population of somatic cells, is fundamentally a genetic disorder. Although the specific array of genetic changes causing individual tumor types remains largely obscure, the past two decades have witnessed a tremendous increase in our understanding of the specific genes regulating cell differentiation, proliferation, and senescence. There appear to be two distinct fundamental genetic mechanisms of tumorigenesis. One mechanism is associated with the activation of growth-promoting factors such as proto-oncogenes. Alternatively, tumor formation may be induced as the result of the loss or inactivation of genes which normally regulate or suppress cell growth. These genes have been termed 'tumor suppressor' genes or 'anti-oncogenes'. This review focuses on the role of 'tumor suppressor' genes in tumor formation and growth control of the human nervous system.

Parental origin of chromosome 22 loss in sporadic and NF2 neuromas

It has recently been proposed that the maternally derived chromosome might be preferentially lost in nonfamilial cases of embryonal or early onset malignant tumors. This observation pointed to a potential role of the parental imprinting of the genome during gametogenesis which would be at least partly maintained in the somatic cells. Neuromas are benign tumors that develop from Schwann cells. They occur either sporadically or in individuals that have a genetic predisposition due to neurofibromatosis type 2 (NF2) and usually are multiple. Regardless of the context of occurrence, in approximately 40% of the investigated cases a loss of a chromosome 22 has been documented either by karyotype analysis or by monitoring somatic loss of heterozygosity. We have now examined the parental origin of the chromosome 22 lost in 19 cases of neuromas of patients with unaffected parents among which 11 were non-NF2 patients (sporadic and unique neuroma) and 8 were NF2 patients (bilateral acoustic or multiple neuromas). In both sets of tumors, the lost chromosome 22 can be of either parental origin. A close to threefold preference for the loss of the maternally derived chromosome was observed and should be either confirmed or disproved by studying a larger number of patients.

Molecular genetics of neurofibromatosis 2 and related tumors (acoustic neuroma and meningioma)

Meningioma and acoustic neuroma are among the most frequent primary tumors of the central nervous system. They usually arise as sporadic and solitary tumors. They also develop as multiple tumors in the autosomal dominant genetic disorder neurofibromatosis 2 (NF2). Molecular analysis of meningioma and acoustic neuroma revealed that loss of chromosome 22 alleles was the most frequent genetic alteration found in either sporadic or inherited cases. Subsequent studies showed that a marker in the middle of the long arm of chromosome 22 was linked to the disease in NF2 pedigrees. In this paper, the most recent findings concerning the genetics of NF2 and related tumors are reviewed, and strategy to isolate and characterize the NF2 gene is presented.

Genetic flanking markers refine diagnostic criteria and provide insights into the genetics of Von Hippel Lindau disease

Von Hippel Lindau disease (VHL) is a hereditary syndrome, associated with tumors and cysts in multiple organ systems, whose expression and age of onset are highly variable. The availability of a genetic test for the early and reliable detection of individuals carrying the defective gene would be beneficial for VHL patients and their relatives, since many of the manifestations of VHL can be successfully treated if detected in their early stages, while the complications of undetected disease can be devastating. We have previously shown that the VHL gene maps to chromosome 3p. To provide genetic markers for the development of a reliable diagnostic test, and to further narrow and eventually clone the VHL defect, we have generated DNA markers for chromosome 3p. With these markers, we have performed a multipoint genetic linkage analysis in 28 VHL pedigrees, comprising 470 individuals, 164 of whom were affected with VHL. Here we report the identification of tightly linked markers, including flanking markers that bracket the VHL gene to a small region on chromosome 3p25-p26. This finding has several major implications. While visceral cysts of the kidney, pancreas, and epididymis are commonly found in VHL and are considered diagnostic criteria for this disorder, they also occur in the general population. The presence of cysts, unaccompanied by other more typical lesions such as retinal and cerebellar hemangioblastoma, may therefore represent a major diagnostic problem, leading to errors in the assessment of disease status. The application of flanking markers for the VHL gene for presymptomatic diagnostic testing confirms that epididymal cysts are indeed not suitable as a diagnostic criterion in this disorder. Pheochromocytomas occur nonuniformly in VHL families and may also be associated with other hereditary tumor syndromes; our genetic studies imply that the phenotype in VHL families with and without pheochromocytomas is caused by defects within the same gene. The absence or presence of this tumor type is therefore due to the pleiotropic expression of a single gene rather than to the existence of several different genes for VHL. The region on chromosome 3p13-p14 known to contain several chromosomal translocation breakpoints in families with "pure familial renal cell carcinoma" is quite proximal to the VHL locus in 3p25-p26 we have identified. Chromosome 3p may therefore contain two loci for renal cell carcinoma: one gene (or genes) in 3p13-p14 and the VHL gene in 3p25-p26, whose aberration is also associated with other typical manifestations of VHL. Since renal cell carcinoma, pheochromocytoma, and visceral cysts can occur sporadically even in young people and may also be associated with other tumor syndromes, the availability of flanking markers for the VHL gene will be useful in identifying VHL gene carriers, particularly among those individuals at risk in whom these are the only manifestations of disease. The isolation and characterization of the VHL gene, based on the identification of flanking markers, will have important implications for diagnosis and treatment of patients with VHL, as well as for a much larger number of individuals having the sporadic counterparts of VHL-associated tumor types.

Toward the isolation of the primary genetic defect in von Hippel-Lindau disease

Von Hippel-Lindau disease (VHL) is a devastating hereditary tumor syndrome associated with various forms of cancer in multiple organ systems, including endothelial-derived tumors in the central nervous system, pheochromocytomas, and, a particularly frequent cause of death in VHL, renal cell carcinomas. Using DNA linkage analysis in a number of families displaying VHL, we recently showed that the primary defect in VHL maps to the short arm of chromosome 3. On the basis of the approximate knowledge of its chromosomal location, we have meanwhile bracketed this putative "tumor suppressor" gene to a small region of approximately 10 cM in chromosome 3p25-p26. The identification of closely linked flanking markers, together with the apparent genetic homogeneity of VHL, should allow for the development of a reliable diagnostic genetic test and provides the starting point for directed chromosomal "walking" and "jumping" toward the isolation of the defective gene itself. The characterization of the VHL gene should ultimately have important implications not only for patients with VHL, but also for a much larger number of cancer patients in the general population, afflicted with the sporadic counterparts of VHL-associated tumor types, such as renal cell carcinoma.

Central nervous system involvement in Von Hippel-Lindau disease

Fifty individuals with Von Hippel-Lindau disease (VHL) were studied with gadolinium-enhanced magnetic resonance imaging (MRI) to determine the frequency and distribution of CNS lesions. The associated clinical features were also reviewed. Thirty-six (72%) of the 50 had 1 or more CNS tumors. The most frequently affected sites in the CNS excluding the retina were the cerebellum (52%), spinal cord (44%), and brainstem (18%). New regional predilections for the craniocervical junction and conus medullaris were demonstrated by this study. Forty-one percent of all VHL patients with CNS tumors were neurologically asymptomatic: cerebellar tumors (50%), spinal cord tumors (50%), and brainstem tumors (44%) were often without clinical signs or symptoms. Multiple lesions were common. The mean age of all VHL patients (34.5 years) was similar to the mean age of all CNS VHL patients (34.4 years), suggesting a lack of age association. CNS lesions commonly occurred in the 2nd decade of life. All patients at risk for VHL should be evaluated using gadolinium-enhanced MRI after 10 years of age, although ophthalmic examination should be initiated within the 1st 2 years of life. Enhanced MRI is particularly useful in the detection of CNS tumors in patients with the VHL gene.

Clonal origin of pituitary adenomas

Benign pituitary adenomas are among the most common neurosurgical tumors and account for a diversity of clinical syndromes due to their hormone content and release. To determine whether these tumors arise from a single cell or multiple cells, the authors studied X chromosome inactivation in deoxyribonucleic acid (DNA) isolated from pituitary adenomas in women. Tumors of three different hormonal subtypes were examined. One tumor contained cells immunoreactive for prolactin and human growth hormone; one tumor contained foci immunoreactive for the beta-subunits of luteinizing hormone and follicle-stimulating hormone; and the third tumor had no immunoreactive prolactin, human growth hormone, beta-subunits of thyroid-stimulating hormone, luteinizing hormone, or follicle-stimulating hormone, or the alpha-subunit. Analysis of the DNA revealed that, in each of the three pituitary tumors, one X chromosome was active in all cells and one X chromosome was inactive, indicating that each of these tumors was monoclonal in origin. It is concluded that clinically evident pituitary tumors arise from a genetic mutation in a single cell.

Progress toward the isolation and characterization of the genes causing neurofibromatosis

Neurofibromatosis 1 and neurofibromatosis 2 are clinically distinct autosomal dominant disorders that affect an estimated 1.5 million individuals throughout the world. The genetic defect in each disorder has been mapped to different chromosomes, NF1 to chromosome 17 and NF2 to chromosome 22. Progress towards the cloning of the NF1 gene has proceeded rapidly. The NF1 locus was bracketed using genetic linkage analysis on NF1 affected pedigrees. Physical mapping methods were then used to precisely map the translocation breakpoints in each of two NF1 affected individuals who harbored constitutional chromosomal translocations in the putative NF1 region of chromosome 17. The region of DNA located between the two translocations has been cloned in cosmids and yeast artificial chromosomes and a number of RNA coding sequences have been identified. The identification of the NF1 gene will depend on finding mutations in the DNA of affected individuals. In the case of NF2, progress seems to have been less rapid, in part due to the lower availability of NF2 affected pedigrees. The genetic defect has been mapped to the long arm of chromosome 22 by studies of chromosomal loss in the tumours associated with this disease. Subsequent genetic mapping has confirmed this location. Flanking DNA markers for the NF2 locus have been identified. The region of DNA between these markers is in the order of 5-10 Mb. The identification of chromosomal aberrations in patients with NF2 that involve chromosome 22 will play an important role in the identification of the NF2 gene in much the same way as they have in NF1.

Loss of the Y chromosome in meningiomas. A molecular genetic approach

Loss of the Y chromosome in meningiomas from 17 male patients was examined by cytogenetic analysis and by Southern blot hybridization with a series of Y-specific DNA probes. Cytogenetic analysis revealed loss of the Y chromosome in seven of 17 (41%) of the tumors whereas Southern blot hybridization showed loss of Y-associated sequences in only three of 17 (18%). Although the incidence of Y-chromosome loss was less by Southern blot hybridization than by cytogenetic analysis, the finding that loss of Y is present in the original uncultured tumor specimen suggests that a gene or genes on the Y chromosome may play a role in growth control of meningioma cells, and loss of this gene may be associated with tumor progression. The difference in the incidence of Y loss between the two methods indicates that both methods should be used when examining chromosome losses.

von Hippel-Lindau disease: radiologic screening for visceral manifestations

The visceral manifestations of von Hippel-Lindau (VHL) disease can cause significant morbidity and mortality. The authors prospectively screened 37 persons from a single kindred. Twenty-five subjects underwent abdominal ultrasound (US), contrast material-enhanced abdominal computed tomography (CT), and nonenhanced abdominal magnetic resonance (MR) imaging. Eight subjects younger than 16 years of age underwent abdominal US and MR imaging only. Scrotal US was employed in 25 male patients. Eleven subjects had renal cysts or tumors. Contrast-enhanced CT depicted renal abnormalities in 10 of these subjects, US in seven, and MR imaging in nine. Among 12 subjects with pancreatic cysts or tumors, CT showed pancreatic abnormalities in all 12, US in nine, and MR imaging in nine. Three subjects (mean age, 34.5 years) had renal tumors, and three had pancreatic masses. Scrotal US revealed epididymal cystadenomas in seven subjects; two of these tumors were surgically verified. A combination of contrast-enhanced CT and scrotal US in male patients appears to be the best way to screen for visceral manifestations of VHL disease.

Flanking markers bracket the neurofibromatosis type 2 (NF2) gene on chromosome 22

Neurofibromatosis 2 or bilateral acoustic neurofibromatosis (NF2) is a severe autosomal dominant disorder characterized by the development of multiple tumors of the nervous system, including meningiomas, gliomas, neurofibromas, ependymomas, and particularly acoustic neuromas. Polymorphic DNA markers have revealed frequent loss of one copy of chromosome 22 in the tumor types associated with NF2. Family studies have demonstrated that the primary defect in NF2 is linked to DNA markers on chromosome 22, suggesting that it involves inactivation of a tumor suppressor gene. We have employed a combination of multipoint linkage analysis and examination of deletions in primary tumor specimens to precisely map the NF2 locus between flanking polymorphic DNA markers on chromosome 22. The 13-cM region bracketed by these markers corresponds to 13% of the genetic length of the long arm of chromosome 22 and is expected to contain less than 5 x 10(6) bp of DNA. The delineation of flanking markers for NF2 should permit accurate presymptomatic and prenatal diagnosis for the disorder and greatly facilitate efforts to isolate the defective gene on the basis of its location.

Characterization of a translocation within the von Recklinghausen neurofibromatosis region of chromosome 17

The genetic defect causing von Recklinghausen neurofibromatosis (NF1) has been mapped to the proximal long arm of chromosome 17 by linkage analysis. Flanking markers have been identified, bracketing NF1 in 17q11.2 and laying the foundation for isolating the disease gene. Recently, a family in which a mother and her two children show both the symptoms of NF1 and the presence of a balanced translocation, t(1;17)(p34.3;q11.2), has been identified. We have examined the possibility that the translocation has occurred in or near the NF1 gene by constructing a somatic cell hybrid line containing the derivative chromosome 1 (1qter-p34.3::17q11-qter). On chromosome 1, the breakpoint occurred between SRC2 and D1S57, which are separated by 14 cM. The translocation breakpoint was localized on chromosome 17 between D17S33 and D17S57, markers that also flank NF1 within a region of 4 cM. These data are consistent with the possibility that the translocation event is the cause of NF1 in this pedigree. Consequently, the isolation of the translocation breakpoint, by approach from either the chromosome 1 or the chromosome 17 side, may facilitate the identification of the NF1 gene.