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.     

Subject index for volume 1

The mutant gene causing von Recklinghausen neurofibromatosis (NF1) was recently shown to map to chromosome 17. We have used additional markers for chromosome 17 to narrow further the location of the gene defect. A preliminary multipoint linkage analysis suggests that the NF1 gene is located on the long arm of chroomsome 17, flanked by D17Z1 and NGFR. Linkage analysis with the human oncogene homolog erbA1, which maps to this region, suggests that this cancer-related gene is not the primary cause of NF1.     

Unequal meiotic crossover: a frequent cause of NF1 microdeletions

Neurofibromatosis type 1 is a common autosomal dominant disorder caused by mutations of the NF1 gene on chromosome 17. In only 5%-10% of cases, a microdeletion including the NF1 gene is found. We analyzed a set of polymorphic dinucleotide-repeat markers flanking the microdeletion on chromosome 17 in a group of seven unrelated families with a de novo NF1 microdeletion. Six of seven microdeletions were of maternal origin. The breakpoints of the microdeletions of maternal origin were localized in flanking paralogous sequences, called "NF1-REPs." The single deletion of paternal origin was shorter, and no crossover occurred on the paternal chromosome 17 during transmission. Five of the six cases of maternal origin were informative, and all five showed a crossover, between the flanking markers, after maternal transmission. The observed crossovers flanking the NF1 region suggest that these NF1 microdeletions result from an unequal crossover in maternal meiosis I, mediated by a misalignment of the flanking NF1-REPs.     

Neurofibromatosis type 2 appears to be a genetically homogeneous disease

Neurofibromatosis type 2 (NF2) is an autosomal dominant syndrome characterized by the development of vestibular schwannomas and other tumors of the nervous system, including cranial and spinal meningiomas, schwannomas, and ependymomas. The presence of bilateral vestibular schwannomas is sufficient for the diagnosis. Skin manifestations are less common than in neurofibromatosis type 1 (NF1; von Recklinghausen disease). The apparent clinical distinction between NF1 and NF2 has been confirmed at the level of the gene locus by linkage studies; the gene for NF1 maps to chromosome 17, whereas the gene for NF2 has been assigned (in a single family) to chromosome 22. To increase the precision of the genetic mapping of NF2 and to determine whether additional susceptibility loci exist, we have performed linkage analysis on 12 families with NF2 by using four polymorphic markers from chromosome 22 and a marker at the NF1 locus on chromosome 17. Our results confirm the assignment of the gene for NF2 to chromosome 22 and do not support the hypothesis of genetic heterogeneity. We believe that chromosome 22 markers can now be used for presymptomatic diagnosis in selected families. The NF2 gene is tightly linked to the D22S32 locus (maximum lod score 4.12; recombination fraction 0). A CA-repeat polymorphism at the CRYB2 locus was the most informative marker in our families (lod score 5.99), but because the observed recombination fraction between NF2 and CRYB2 was 10 cM, predictions using this marker will need to be interpreted with caution.     

Linkage analysis of neurofibromatosis type I, using chromosome 17 DNA markers.

The gene for von Recklinghausen neurofibromatosis type 1 (NF1) has recently been mapped to the pericentromeric region of human chromosome 17. To further localize the NF1 gene, linkage analysis using chromosome 17 DNA markers was performed on 11 multigeneration families with 175 individuals, 57 of whom were affected. The markers used were D17Z1 (p17H8), D17S58 (EW301), D17S54 (EW203), D17S57 (EW206), D17S73 (EW207), CRI-L946, HOX-2, and growth hormone. Tight linkage was found between NF1 and D17Z1, D17S58, and D17S57 with a recombination fraction of zero. One recombinant was detected between NF1 and D17S73, showing linkage with a 10% recombination fraction. No linkage was detected between NF1 and CRI-L946 or between HOX-2 and growth hormone. Our data are consistent with the proposed gene order pter D17S58-D17Z1-NF1-D17S57-D17S73 qter.     

A refined genetic map of the region of chromosome 17 surrounding the von recklinghausen neurofibromatosis (NF1) gene

The von Recklinghausen neurofibromatosis (NF1) gene has been mapped to the pericentromeric region of chromosome 17. We conducted linkage analyses of NF1 by using 10 polymorphic DNA markers from this chromosomal region. We ascertained 20 American Caucasian NF1 families (163 individuals, 98 NF1 affected) in Michigan and Ohio and also studied a large family ascertained primarily in North Carolina. The following markers were used in this study: HHH202, TH17.19, D17Z1, ERBA1, EW203, EW206, EW207, EW301, CRI-L581, and CRI-L946. NF1 did not recombine with either TH17.19 or HHH202 in any of the informative meioses surveyed (maximum lod scores of 17.04 and 7.21, respectively, at a recombination fraction of .00), indicating that these markers map very close to the NF1 gene. We also report evidence of three instances of recombination between NF1 and the centromeric marker D17Z1 (maximum lod score of 13.43 at a recombination fraction of .04), as well as two crossovers between pairs of marker loci. We find no evidence of locus heterogeneity, and our results support the localization of the NF1 gene to proximal chromosome 17q.     

Refined physical and genetic mapping of the NF1 region on chromosome 17.

A total of 15 polymorphic markers were used to construct a genetic map that encompasses the NF1 locus on chromosome 17. The markers were a subset of a large collection of chromosome 17-specific probes and were selected for marker typing in NF1 families after physical localization to the pericentric region of the chromosome. Multilocus data for a total of 17 informative NF1 families and 39 other families were included in genetic analyses. No recombination was observed between NF1 and four markers, one or more of which was informative in 86% of parents. More-refined physical mapping studies demonstrated that all four of the markers are proximal to the chromosome 17 translocation breakpoints from two NF1 patients bearing balanced translocations. The region flanking the disease locus spans a distance of 1 centimorgan (cM) in males and 9 cM in females. Close flanking markers were informative in 76% of meioses. Sex differences in recombination rates in the pericentric region were highly significant statistically.     

Tightly linked markers for the neurofibromatosis type 1 gene

Relationships among genetic markers in the region of the neurofibromatosis type 1 (NF1) gene on chromosome 17 were investigated by linkage studies in a large sample set of affected families and in a panel of 58 normal families. A new marker, pHHH202 (D17S33), was included along with two markers known to be closely linked to NF. The maximum likelihood estimate of the recombination rate between the pHHH202 and NF1 loci was found to be O. Multilocus analysis suggested the following marker order: pA10-41-(p3-6, pHHH202); the NF1 gene fell with equal likelihood between either pA10-41-p3-6 or p3-6-pHHH202. The odds against NF1 being outside this cluster of tightly linked markers were greater than 15:1.     

The order of loci in the pericentric region of chromosome 17, based on evidence from physical and genetic breakpoints.

Previous genetic analyses of chromosome 17 markers and NF1 (Fain et al. 1987) were extended in an attempt to order marker loci that map physically to 17cen----17q12. Three additional markers (HHH202, CRI-L581, and CRI-L946) were included in the analyses. Recombinants within the cluster of seven unordered marker loci were identified by pairwise analyses for each family and by examining the within-sibship segregation patterns for different markers. Changes in the segregation pattern for different loci define genetic breakpoints. Given that interference is complete in the region, markers with the same segregation pattern lie on one side of the breakpoint, while markers with different segregation patterns lie on opposite sides of the breakpoint. If the order of boundary markers is known, markers on each side of a breakpoint can be oriented in relation to the centromere. The order cen-(HHH202/NF1)-(EW207)-(EW203/CRI-L581)- (CRI-L946)-(HOX-2/NGFR)-qter was inferred by combining information from physical breakpoints in a panel of mouse/human hybrids and information from genetic breakpoints found in 16 NF1 families.     

Precise localization of NF1 to 17q11.2 by balanced translocation.

A female patient is described with von Recklinghausen neurofibromatosis (NF1) in association with a balanced translocation between chromosome 17 and 22 [46,XX,t(17;22)(q11.2;q11.2)]. The breakpoint in chromosome 17 is cytogenetically identical to a previously reported case of NF1 associated with a 1;17 balanced translocation and suggests that the translocation events disrupt the NF1 gene. This precisely maps the NF1 gene to 17q11.2 and provides a physical reference point for strategies to clone the breakpoint and therefore the NF1 gene. A human-mouse somatic cell hybrid was constructed from patient lymphoblasts which retained the derivative chromosome 22 (22pter----22q11.2::17q11.2----17qter) but not the derivative 17q or normal 17. Southern blot analysis with genes and anonymous probes known to be in proximal 17q showed ErbA1, ErbB2, and granulocyte colony-stimulating factor (CSF3) to be present in the hybrid and therefore distal to the breakpoint, while pHHH202 (D17S33) and beta crystallin (CRYB1) were absent in the hybrid and therefore proximal to the breakpoint. The gene cluster including ErbA1 is known to be flanked by the constitutional 15;17 translocation breakpoint in hybrid SP3 and by the acute promyelocytic leukemia (APL) breakpoint, which provides the following gene and breakpoint order: cen-SP3-(D17S33,CRYB1)-NF1-(CSF3,ERBA1, ERBB2)-APL-tel. The flanking breakpoints of SP3 and API are therefore useful for rapidly localizing new markers to the neurofibromatosis critical region, while the breakpoints of the two translocation patients provide unique opportunities for reverse genetic strategies to clone the NF1 gene.     

Genetic linkage studies of chromosome 17 RFLPs in von Recklinghausen neurofibromatosis (NF1)

Recent localization of the gene for von Recklinghausen neurofibromatosis (NF1) to chromosome 17 has led to studies to identify additional tightly linked probes that can be used in defining the primary genetic defect in NF1. We have examined and obtained blood for DNA linkage studies on over 250 individuals from 10 multigeneration neurofibromatosis families. We have analyzed 130 members in 7 families with the available chromosome 17 NF1 linked probes, pE51, D17S71, and D17Z1, as well as two probes generated from our own chromosome 17/19 enriched library (LDR92, LDR152A). Tight linkage was found between NF1 and the centromeric probe D17Z1 (theta = 0.04) and between NF1 and D17S71 (theta = 0.08). A definite recombinant was seen for the D17Z1 marker, which previously had not exhibited crossingover. Chromosome 17 DNA markers pE51, LDR92, and LDR152A gave slightly positive scores, which were not statistically significant.     

Linkage analysis of chromosome 17 markers in British and South African families with neurofibromatosis type 1

Nine markers from the pericentromeric region of chromosome 17 were typed in 16 British and five South African families with neurofibromatosis type 1 (NF1). The markers--p17H8, pHHH202, and EW204--were linked to NF1 at recombination fractions less than 1%. No evidence of locus heterogeneity was detected. Inspection of recombinant events in families informative for several markers suggests that the NF1 gene is located between the markers EW301 (cen-p11.2) and EW206 (cen-q12) and possibly distal to pHHH202 (q11.2-q12).     

Molecular organization and haplotype analysis of centromeric DNA from human chromosome 17: Implications for linkage in neurofibromatosis

The alpha satellite DNA subset located at the centromere of human chromosome 17 has been shown to be tightly linked genetically to the gene for von Recklinghausen neurofibromatosis (NF1). The centromeric DNA polymorphisms used for linkage analyses in NF1 are complex and involve a "locus" (D17Z1) that spans over one million base pairs of satellite DNA. To understand more completely the basis for these polymorphisms and how they might be best scored and used in the analysis of NF1, we have examined the molecular composition of the alpha satellite array on individual copies of chromosome 17 by two complementary approaches. First, we have analyzed segregation of chromosome 17 alpha satellite haplotypes in large, three-generation families that provide information on the different types of alpha satellite segregating in a block fashion. Second, we have analyzed directly the extent of variation in different D17Z1 arrays by genomic blotting analysis of haploid copies of chromosome 17 isolated in rodent/human somatic cell hybrids. The data indicate the existence of a wide range of different alpha satellite variants on individual copies of chromosome 17, each haplotype differing in the size, restriction map, and relative proportion of particular polymorphic repeat forms. Despite this complexity, the D17Z1 markers provide a potentially useful and genetically close starting point for the molecular and clinical analysis of NF1.     

The gene for von Recklinghausen neurofibromatosis (NF1) maps to the pericentromeric region of chromosome 17 in Chinese families

Linkage analysis of six Chinese families with neurofibromatosis type 1 (NF1) confirms the location of the NF1 gene to the region of the proximal long arm of chromosome 17, as in Caucasian populations. The diagnosis of NF1 was made according to internationally accepted criteria. The markers used were D17S71, D17S58, D17S33, and EVI2A. The overall odds in favor of NF1 lying within this linkage group in the families studied are over 150,000:1, with a maximum location score of 5.112 for the interval D17S58-EVI2A.     

Linkage analysis of von Recklinghausen neurofibromatosis to DNA markers on chromosome 17

Several recent studies indicate that the von Recklinghausen neurofibromatosis (NF1) gene is located near the centromere of chromosome 17 in some families. However, variable expressivity and a very high mutation rate suggest that defects at several different loci could result in phenotypes categorized as NF1. In order to assess this possibility and to map the NF1 gene more precisely, we have used two polymorphic DNA markers from chromosome 17 to screen several pedigrees for linkage to NF1. We ascertained a large Caucasian pedigree (33 individuals sampled, 17 NF1 affected) as well as eight smaller pedigrees and nuclear families (50 individuals sampled, 30 NF1 affected). Here, we report strong evidence of linkage of NF1 to the centromeric marker D17Z1 (maximum lod = 4.42) and a weaker suggestion of linkage to the ERBA1 oncogene (maximum lod = 0.57), both at a recombination fraction of zero. Since obligate cross-overs with NF1 were not observed for either marker in any of the informative families tested, the possibility of NF1 locus heterogeneity is not supported.     

Genetic linkage mapping of chromosome 17 markers and neurofibromatosis type 1

The von Recklinghausen neurofibromatosis (NF1) gene has been localized to the pericentromeric region of chromosome 17. We have screened six multigenerational families with multiple, tightly linked markers to aid in mapping this region of the chromosome. More than 150 members in six families were typed with probes including HHH202, D17Z1, EW203, EW206, EW207, EW301, pA10-41, D17S37, and D17S36. Two-point lod scores for NF1 versus all markers were calculated. HHH202 demonstrated the tightest linkage to NF1 with theta = .0, z = 3.86 (95% confidence limits [CL] of theta = .0-.13), suggesting that HHH202 be considered as a potential candidate marker for use in carrier detection and prenatal diagnosis. Pairwise marker-to-marker lod scores were used in examining the most likely order of subsets of the markers. Of those tested, the most likely order was (pter)-pA10-41-EW301-D17Z1-HHH202-NF1-E W206-EW207-EW203-(qter). In addition, we have ascertained an NF1 x NF1 half-cousin mating in which there are four affected family members who are potentially homozygous for the disease gene. Two of these four individuals have been sampled and typed for marker loci. When their D17Z1 genotypes are considered, the probability that both these individuals are heterozygous is 85%.     

The neurofibroma in von Recklinghausen neurofibromatosis has a unicellular origin.

von Recklinghausen neurofibromatosis (NF1) is the most common hereditary syndrome predisposing to neoplasia. NF1 is an autosomal dominant disease caused by a single gene which maps to chromosome 17q11.2. The most common symptomatic manifestation of NF1 is the benign neurofibroma. Our previous studies of tumors in NF1, studies which detected a loss of heterozygosity for DNA markers from the NF1 region of chromosome 17 in malignant tumors, did not detect a loss in neurofibromas. We report here that a more extensive study, including the analysis of neurofibromas from 19 unrelated NF1 patients by using seven probes, failed to detect a single instance of loss of heterozygosity. This finding suggests that neurofibromas are either polyclonal or monoclonal in origin but arise by a mechanism different from that of NF1 malignancies. In order to investigate the first possibility, we analyzed neurofibromas from female NF1 patients by using an X chromosome-specific probe, from the phosphoglycerokinase (PGK) gene, which detects an RFLP. The detected alleles carry additional recognition sites for the methylation-sensitive enzyme HpaII, so that the allele derived from the active X chromosome is digested by HpaII while the one from the hypermethylated, inactive X chromosome is not. We analyzed neurofibromas from 30 unrelated females with NF1. Eight patients were heterozygous for the PGK RFLP. By this assay, neurofibromas from all eight appeared monoclonal in origin. These results suggest that benign neurofibromas in NF1 arise by a mechanism that is different from that of malignant tumors.(ABSTRACT TRUNCATED AT 250 WORDS)     

Chromosome 17 markers and von Recklinghausen neurofibromatosis: A genetic linkage study in a British population

A genetic linkage study of the RFLPs identified by nine DNA probes localized to the pericentromeric region and long arm of chromosome 17 has been undertaken in 16 families with von Recklinghausen neurofibromatosis (NF1). Close linkage has been shown with the markers CRI-L946 (D17S36), CRI-L581 (D17S37), p17H8 (D17Z1), and pA10-41 (D17S71). The ERBA1 and COL1A1 loci may also be closely linked, but the data are limited. The results for HOX2 and NGFR suggest only loose linkage with the NF1 gene, while no linkage was found between NF1 and the growth hormone locus. No suggestion of nonallelic heterogeneity of NF1 was found in this study.     

The achondroplasia gene is not linked to the locus for neurofibromatosis 1 on chromosome 17

Summary We have investigated genetic linkage of von Recklinghausen neurofibromatosis (NF1) and achondroplasia (ACH) using chromosome-17 markers that are known to be linked to NF1. Physical proximity of the two loci was suggested by the report of a patient with mental retardation and the de novo occurrence of both NF1 and ACH. Since the chance of de novo occurrence of these two disorders in one individual is 1 in 600 million, this suggested a chromosomal deletion as a single unifying molecular event and also that the ACH and NF1 loci might be physically close. To test this, we performed linkage analysis on a three-generation family with ACH. We used seven DNA probes that are tightly linked to the NF1 locus, including DNA sequences that are known to flank the NF1 locus on the centromeric and telomeric side. We detected two recombinants between the ACH trait and markers flanking the NF1 locus. In one recombinant, the flanking markers themselves were nonrecombinant. Multi-point linkage analysis excluded the ACH locus from a region surrounding the NF1 locus that spans more than 15cM (lod score < -2). Therefore, analysis of this ACH pedigree suggests that the ACH locus is not linked to the NF1 locus on chromosome 17.     

Formation of a minichromosome by excision of the proximal region of 17q in a patient with von Recklinghausen neurofibromatosis

An interstitial deletion, 17cen----q11.2 (or q12), and a small extra chromosome was found in a sporadic case of von Recklinghausen neurofibromatosis (NF1). In situ hybridization with a chromosome 17-specific alpha-satellite probe showed that the small chromosome was derived from the deleted region, most likely by an excision/ring formation. This chromosome rearrangement is in agreement with the localization of the von Recklinghausen neurofibromatosis (NF1) locus to the proximal region of 17q, but with a more distal breakpoint than observed in two previously described reciprocal translocations associated with NF1. If the NF1 gene has been truncated by the present rearrangement, it may suggest that the NF1 gene is a very large gene at the genomic level. Alternatively, NF1 in this patient may be caused by the gradual loss in somatic cells of the small chromosome carrying an intact NF1 gene, thereby suggesting a recessive mechanism at the gene level. Finally, an intact NF1 gene may have been placed in close proximity with alpha-satellite sequences, which might cause inactivation of the gene. The small supernumerary chromosome may not only facilitate the cloning of the NF1 gene itself, but also offers explanations of the mechanism underlying development of the disease.