17q Markers Research Articles

Malignant Pheochromocytoma in a 16-Year-Old Patient with Neurofibromatosis Type 1

Patients with neurofibromatosis type I (NF1) feature a high risk of developing benign and malignant tumors, mainly those with a neuroectodermal origin, the risk being about 4 times higher than in the general population. Pheochromocytoma (PHEO) is a sporadic tumor (1∶100,000) arising from the adrenal medulla. Pheochromocytoma is a rare condition when occurring in conjunction with NF1 and occurs in about 1% of patients, rarely in those of pediatric age. In this study we present a 16-year-old patient with NF1 and malignant PHEO. Loss of heterozygosity analysis in PHEOs shows a reduction to homozygosity, observed for both 17p and 17q markers. This case confirms the importance of surveillance for malignant neoplasias in NF1 patients during childhood and adolescence. On the other hand, since 30% of PHEOs had germline mutations and, more rarely, somatic mutations, patients with PHEO should be investigated for associated genetic syndromes.

Mechanisms of Loss of Heterozygosity in Neurofibromatosis Type 1-Associated Plexiform Neurofibromas

Plexiform neurofibromas constitute a serious burden for patients with neurofibromatosis type 1 (NF1), a common autosomal dominant disorder characterized by pigmentary changes and tumorous skin lesions (neurofibromas). Despite the prominence of these benign tumors in NF1 patients, the mechanisms underlying the tumor-associated loss of heterozygosity (LOH) in plexiform neurofibromas have not been extensively studied. We performed LOH analysis on 43 plexiform neurofibromas from 31 NF1 patients, the largest study of its kind to date. A total of 13 (30%) plexiform neurofibromas exhibited LOH involving 17q markers. In three tumors, LOH was found to be confined to the NF1 gene region. However, in none of the tumors was a somatic NF1 microdeletion, mediated by non-allelic homologous recombination between either NF1-REPs or SUZ12 genes, detected. Thus, NF1 microdeletions do not appear to be frequent somatic events in plexiform neurofibromas. Determination of NF1 gene copy number by multiplex ligation-dependent probe amplification indicated that although tumors with smaller regions of LOH were characterized by 17q deletions, no NF1 gene copy number changes were detected in six plexiform neurofibromas with more extensive LOH. To our knowledge, mitotic recombination has not previously been reported to be a frequent cause of LOH in plexiform neurofibromas.

Prohibitin mutations are uncommon in prostate cancer families linked to chromosome 17q

Linkage studies have provided evidence for a prostate cancer susceptibility locus on chromosome 17q. The mitochondrial protein prohibitin (PHB) is a plausible candidate gene based on its chromosomal location (17q21) and known function. All coding regions and intron/exon junctions of the PHB gene were sequenced in 32 men from families participating in the University of Michigan Prostate Cancer Genetics Project that demonstrated evidence of linkage to 17q markers. Although a number of nucleotide variants were identified, no coding region substitutions were identified in any of the 32 men with prostate cancer from 32 unrelated multiplex prostate cancer families. PHB mutations do not appear to account for the linkage signal on 17q21-22 detected in PCGP families. Fine mapping of this region is in progress to refine the candidate region and highlight additional candidate prostate cancer susceptibility genes for sequence analysis.

Truncating BRCA1 Mutations Are Uncommon in a Cohort of Hereditary Prostate Cancer Families with Evidence of Linkage to 17q Markers

A genome-wide scan of 175 hereditary prostate cancer families from the University of Michigan Prostate Cancer Genetics Project provided evidence of prostate cancer linkage to 17q markers near the BRCA1 gene. To examine the possibility that germ-line BRCA1 mutations were associated with hereditary prostate cancer, individuals from 93 families with evidence of linkage to chromosome 17q were screened for germ-line BRCA1 mutations. One individual from each of the 93 families, the majority with three or more cases of prostate cancer, were screened for BRCA1 mutations with denaturing high-performance liquid chromatography (HPLC). Fragments exhibiting denaturing HPLC variant patterns were additionally analyzed by direct sequencing. Sixty-five of the individuals selected for sequencing from 65 unrelated families were determined to have wild-type BRCA1 sequence by denaturing HPLC. One individual from a family with both prostate and ovarian cancer was found to have a truncating BRCA1 mutation (3829delT). An additional 27 germ-line variants were identified, including 15 missense variants. These sequencing results suggest that BRCA1 truncating mutations do not account for the linkage evidence on chromosome 17 observed in University of Michigan Prostate Cancer Genetics Project families. A recently completed combined genome scan has also detected linkage to 17q22, and studies are ongoing to identify the relevant prostate cancer susceptibility gene in this region.

Distal chromosome 17q loss in Barrett's esophageal and gastric cardia adenocarcinomas: implications for tumorigenesis.

The molecular genetic mechanisms underlying esophageal cancer are poorly understood. However, a novel gene that may be involved in esophageal carcinogenesis was recently localized by others to distal 17q by linkage analysis of kindreds with palmoplantar keratoderma and squamous cell carcinoma of the esophagus. To help determine whether a distal 17q gene may also be involved in the pathogenesis of primary Barrett's esophageal and gastric cardia adenocarcinomas, we performed loss of heterozygosity (LOH) analysis of 21 Barrett's and 18 gastric cardia adenocarcinomas at loci spanning 17q: cen-BRCA1-SSTR2-D17S2058-D17S929-D17S722-+ ++D17S937-D17S802-tel. Over 50% of the Barrett's and cardia adenocarcinomas demonstrated loss of an allele at one or more informative distal 17q markers. One common overlapping region of loss involved loci mapped to distal 17q24-proximal 17q25, which tentatively defines a potential chromosomal region distal to BRCA1 involved in the pathogenesis or progression of both types of adenocarcinomas. LOH analysis of DNA from matched microdissected sections of Barrett's metaplasia suggested that loss of D17S2058 in this region may be an early event in the malignant transformation of Barrett's metaplasia. No statistically significant correlations between 17q LOH and tumor stage or patient survival were noted. In summary, LOH mapping of 17q in Barrett's and cardia adenocarcinomas suggests the existence of at least one putative distal 17q tumor suppressor gene involved in the pathogenesis of these tumors.

Strong indication for a breast cancer susceptibility gene on chromosome 8p12-p22: linkage analysis in German breast cancer families.

Chromosomal losses involving the short arm of chromosome 8 are frequent in a variety of tumor types, including breast cancer, suggesting the presence of one or more tumor suppressor genes in this region. Previous linkage analysis and studies of loss of heterozygosity (LOH) have suggested the presence of a putative third breast cancer susceptibility gene around D8S505 at 8p12-p22. We have performed linkage analysis in two German breast cancer families, showing negative lod scores with 17q and 13q markers, using seven adjacent microsatellite markers from 8p12-p22. Incorporating LOH data from tumors of the affected family members a maximum cumulative three-point lod score of 3.30 at theta = 0.00 was obtained with D8S137 and D8S131. Our findings considerably strengthen the evidence for a third breast cancer susceptibility locus (BRCA3) mapping to the short arm of human chromosome 8.

SUBLOCALIZATION OF SMALLEST COMMON REGIONS OF DELETION ON CHROMOSOME 17Q12-Q23 IN SPORADIC PRIMARY BREAST-TUMORS

Frequent loss of heterozygosity (LOH) on the long arm of chromosome 17 has been described in breast tumor DNAs by a number of groups, and recent fine genetic mapping and cloning of an inherited breast-ovarian cancer susceptibility locus (BRCA1) to a small region of 17q12-q21 has focused interest on this area. The absence of sporadic mutations in the BRCA1 gene in breast tumors studied so far suggests that there may be other tumor suppressor genes in the region involved in sporadic breast cancer. We studied 28 sporadic breast cancers with 14 highly polymorphic markers on chromosome 17 (2 on 17p and 12 on 17q). Most of the 17q markers are located within the 17q12-q23 region. We confirmed that 50% of tumors have deletions of at least one locus on chromosome arm 17q, and that half the deleted cases probably correspond to monosomies 17 or 17q. The other half correspond to a partial deletion on 17q and were used to identify 2 smallest common deleted regions (SCDR1 and SCDR2) on 17q12-q23. SCDR1 comprised the THRA1 gene, but not the 2 flanking loci tested (D17S250 and D17S800); while SCDR2 was defined by loci GIP and GH. BRCA1 was deleted in half the cases but it is outside the SCDR1. Moreover, breast tumors in young women frequently showed chromosome 17 alterations.

A common missense mutation in the adhalin gene in three unrelated Brazilian families with a relatively mild form of autosomal recessive limb-girdle muscular dystrophy.

Autosomal recessive limb-girdle muscular dystrophies (AR LGMD) represent a heterogeneous group of diseases with a wide spectrum of clinical variability, classified phenotypically into two main groups, the most severe forms (Duchenne-like muscular dystrophy, DLMD, or severe childhood autosomal recessive muscular dystrophy, SCARMD) and the milder forms. Four genes causing AR LGMD have been mapped: the 15q (LGMD2a), the 2p (LGMD2b), the 13q locus (LGMD2c) and the adhalin gene on chromosome 17q (LGMD2d). In the present report we have performed linkage analysis with 17q markers in three mild AR LGMD and in four DLMD families with adhalin deficiency and unlinked to 2p, 15q or 13q genes. Linkage was observed only among the mild cases. Patients from these three 17q-linked families showed near or total deficiency of adhalin in muscle biopsies. An identical missense mutation was identified in all three 17q-linked unrelated families. These results indicate that AR LGMD with a mild phenotype is caused by mutations in the adhalin gene. In addition, they demonstrate that there is at least one other locus for DLMD associated with adhalin deficiency.

Analysis of familial breast cancer in genetic analysis workshop 9: summary of findings.

As part of the 9th Genetic Analysis Workshop held in Val Morin, Quebec, October 16-18, 1994, four workshop participants analyzed a large breast cancer data set. This data set consisted of phenotype and genetic marker data on 3884 individuals in 214 families with at least four cases of breast cancer contributed by members of an international breast cancer consortium. Two of the four papers [Barrett and Rigby; Commenges; this issue] utilized variants of affected pair methods to assess linkage of breast/ovarian cancer to the 17q markers in the data set. The third paper by Bansal et al. used a Monte-Carlo approach to examine the question of intrafamilial clustering of breast and ovarian cancer. The last paper in the series [Leal and Ott] described a method of computing support intervals for risk estimates when there are uncertainties associated with the parameter estimates used to compute these risks.

Loss of neurofibromin in adrenal gland tumors from patients with neurofibromatosis type I.

The neurofibromatosis type I gene encodes a protein, neurofibromin, which may function as a tumor suppressor gene product. Recent studies have demonstrated loss of neurofibromin in tumors from NF1 and non-NF1 patients, including neurofibrosarcomas, neuroblastomas and malignant melanomas. Since neurofibromin is expressed in the adrenal gland, six pheochromocytomas and one adrenal cortical tumor were examined for neurofibromin expression. In all seven tumors, no neurofibromin could be detected. Furthermore, loss of heterozygosity (LOH) analysis demonstrated that in one of the pheochromocytomas, reduction to homozygosity was observed for both 17p and 17q markers while the adrenal cortical tumor demonstrated LOH for only 17q markers. The frequent LOH surrounding the NF1 locus and lack of neurofibromin expression in these tumors suggest that NF1 gene mutations may contribute to the development of adrenal gland neoplasms in patients with NF1.

DNA Screening for Breast/Ovarian Cancer Susceptibility Based on Linked Markers

Linkage to chromosome 17q has been identified in hereditary breast cancer and hereditary breast/ovarian cancer syndrome. A hereditary breast/ovarian cancer syndrome kindred was identified that yielded a highly significant lod score (4.20) when 17q markers were studied, enabling us to identify those who probably carried the cancer-associated gene among the high-risk members of the family. High-risk members of the hereditary breast/ovarian cancer syndrome kindred were offered counselling on the basis of 17q markers. Family members responding positively received one-to-one genetic counseling in a structured setting. Subjects were educated before disclosure, and the immediate impact of this information was assessed after disclosure. We provided genetic counseling on the basis of linkage findings to 32 relatives (four men and 28 women). Women who were told they were linkage positive expressed an increased motivation for surveillance and prophylactic surgery. Most women who were told they were linkage negative indicated that they would not proceed with prophylactic surgery but would continue careful surveillance. To date, there has been no evidence of serious emotional disturbances resulting from this disclosure. We believe that this experience can be used by cancer geneticists and physicians in developing protocols for genetic counseling in cancer-associated hereditary disorders. Physicians must understand current developments in cancer genetics and linkage so that they can be applied to genetic counseling and treatment of high-risk patients.

Genetic alterations of the tumour suppressor gene regions 3p, 11p, 13q, 17p, and 17q in human breast carcinomas.

Fifty-nine primary breast carcinomas and 11 metastases were examined to identify genetic alterations in the tumour suppressor gene regions 3p, 11p, 13q, 17p, and 17q. Loss of heterozygosity (LOH) was frequently observed on chromosome arms 17p (p144D6 lost in 75%, pYNZ22.1 in 55%, and TP53 in 48% of the primary tumours), 13q (RBI lost in 40% of the primary tumours), and 17q (pRMU3 lost in 35%, pTHH59 in 29%, and NM23HI in 26% of the primary tumours). Loss of all the markers except p144D6 was observed even more frequently in the metastases. Pairwise comparisons for concordance of allele losses on 17p indicated that there might be two genes on 17p implicated in breast cancer development; the TP53 gene and a gene located close to the p144D6 and pYNZ22.1 markers. LOH of the RBI gene was associated with LOH of pYNZ22.1 and p144D6, but not with LOH of TP53. LOH of RBI and TP53 was associated with occurrence of ductal carcinomas, RBI and p144D6 losses with tumour size, and p144D6 losses with positive node status as well. LOH of TP53 and the three 17q markers NM23HI, pTHH59, and pRMU3 was most frequently observed in tumours from postmenopausal women. p144D6 losses occurred most frequently in progesterone receptor-negative tumours, whereas pTHH59 losses occurred most frequently in oestrogen receptor-negative tumours. LOH of the investigated loci was not associated with ERBB2 protooncogene amplification, with positive family history of breast cancer, or with survival.

Dissociation of cytotoxicity and DNA cleavage activity induced by topoisomerase II-reactive intercalating agents in hamster-human somatic cell hybrids.

Previous studies using the mutant Chinese hamster ovary cell line VpmR-5 indicate that its resistance to epipodophyllotoxins and intercalating agents is likely to be mediated through a qualitative change in type II topoisomerase that confers resistance to drug-stimulated DNA cleavage activity. In a further investigation of the genetic basis of drug resistance in VpmR-5 cells, we fused a hypoxanthine-guanine phosphoribosyl transferase-deficient subline of VpmR-5 (Vtgm-6) with normal human lymphocytes and analyzed the resultant hybrid lines (HL) for altered drug sensitivity. In all, 3 of 16 hybrid clones exhibited partial reconstitution of sensitivity to etoposide, mitoxantrone, doxorubicin, and 5-iminodaunorubicin while retaining complete resistance to m-AMSA. However, enhanced sensitivity to drug-induced DNA cleavage activity was observed only for etoposide. Biochemical and molecular-marker analysis of the hybrids failed to identify human chromosome 17 (the provisional location of TOP2) or any other human chromosome that is consistently and uniquely associated with drug sensitivity. We therefore sought to verify the chromosomal assignment of TOP2 by Southern blot hybridization of TOP2 cDNA on a human hybrid mapping panel and confirmed its location on chromosome 17. However, no hybridizing sequence to the TOP2 cDNA was found in any of the 16 Vtgm-6 hybrid lines. Efforts to select more directly for human chromosome 17 VpmR-5 hybrids using microcell fusion of mouse A9 cells carrying human 17 linked to pSV2neo were unsuccessful. None of the five hybrid clones thus obtained had 17q markers, including the gene for TOP2. Although the mechanism underlying partial reversion to a drug-sensitive phenotype in the original Vtgm-6 hybrid lines has yet to be defined, the data obtained in these lines indicate that anthracycline- and anthracenedione-induced cytotoxic effects can be dissociated from DNA cleavage activity. This suggests that pathways distal to cleavable-complex formation or, alternatively, independent of interactions with topoisomerase II that involve other intracellular targets are important in mediating the cytotoxicity produced by these drugs.

A moderately frequent HindIII polymorphism at the human NGFR locus (17q12 – 17q22)

The clone Lambda6 contains human NGFR sequences cloned in the vector CH28. HindIII (AAGCTT) reveals allelic bands of 13 kb and 8.3+4.7 kb with a constant band of 8.8 kb. The NGFR locus has been assigned to 17q12->17q22 with somatic cell hybrid analysis and in situ hybridization. The HindIII site polymorphism shows tight genetic linkage to HOX2 and other 17q markers. No significant deviation from Hardy-Weinberg equilibrium has been observed. No departure from Mendelian expectations in 39 offspring of segregating matings was found.

Dicentric chromosome 17 in patients with leukemia

A putative isochromosome of the long arm of chromosome #17 was identified in bone marrow cells from each of six patients with leukemia. Adequate sample was available for detailed study in four patients, and in each of these four cases examination with multiple staining techniques implied that the rearrangement is a dicentric chromosome, dic(17)(p11.2). An asymmetry of constriction at the two centromeric regions suggested that one centromere was inactive. The data presented here suggest that many of the presumed i(17q) markers observed in leukemia may actually represent dicentric rearrangements.