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.     

Flanking markers for the gene causing von Recklinghausen neurofibromatosis (NF1)

The defective gene causing von Recklinghausen neurofibromatosis (NF1), one of the most common inherited disorders affecting the human nervous system, was recently mapped to chromosome 17. We have used additional DNA markers to further narrow and bracket the NF1 defect. A multipoint linkage analysis suggests that the NF1 gene is flanked by D17Z1 on the centromeric side and by EW 207 on the telomeric side of the long arm of chromosome 17. The identification of closely linked flanking markers should allow us to develop a reliable prenatal and presymptomatic diagnostic test for this serious neurological disorder and provides the basis for applying chromosome-specific cloning techniques for the isolation and characterization of the mutant gene.     

Physical mapping of the von Recklinghausen neurofibromatosis region on chromosome 17

The von Recklinghausen neurofibromatosis (NF1) locus has been linked to chromosome 17, and recent linkage analyses place the gene on the proximal long arm. NF1 probably resides in 17q11.2, since two unrelated NF1 patients have been identified who possess constitutional reciprocal translocations involving 17q11.2 with chromosomes 1 and 22. We have used a somatic-cell hybrid from the t(17;22) individual, along with other hybrid cell lines, to order probes around the NF1 locus. An additional probe, 17L1, has been isolated from a NotI linking library made from flow-sorted chromosome 17 material and has been mapped to a region immediately proximal to the translocation breakpoint. While neither NF1 translocation breakpoint has yet been identified by pulse-field gel analysis, an overlap between two probes, EW206 and EW207, has been detected. Furthermore, we have identified the breakpoint in a non-NF1 translocation, SP-3, on the proximal side of the NF1 locus. This breakpoint has been helpful in creating a 1,000-kb pulsed-field map, which includes the closely linked NF1 probes HHH202 and TH17.19. The combined somatic-cell hybrid and pulsed-field gel analysis we report here favors the probe order D17Z1-HHH202-TH17.19-CRYB1-17L1-NF1- (EW206, EW207, EW203, L581, L946)-(ERBB2, ERBA1). The agreement in probe ordering between linkage analysis and physical mapping is excellent, and the availability of translocation breakpoints in NF1 should now greatly assist the cloning of this locus.     

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.     

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.     

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.     

Linkage disequilibrium in the neurofibromatosis 1 (NF1) region: implications for gene mapping.

To test the usefulness of linkage disequilibrium for gene mapping, we compared physical distances and linkage disequilibrium among eight RFLPs in the neurofibromatosis 1 (NF1) region. Seven of the polymorphisms span most of the NF1 gene, while the remaining polymorphism lies approximately 70 kb 3' to a stop codon in exon 49. By using Centre d'Etude du Polymorphisme Humain (CEPH) kindreds, 91-110 unrelated parents were genotyped. A high degree of disequilibrium is maintained among the seven intragenic polymorphisms (r > .82, P < 10(-7)), even though they are separated by as much as 340 kb. The 3' polymorphism is only 68 kb distal to the next polymorphism, but disequilibrium between the 3' polymorphism and all others is comparatively low (magnitude of 4 < .33, P values .27-.001). This result was replicated in three sets of unrelated kindreds: the Utah CEPH families, the non-Utah CEPH families, and an independent set of NF1 families. Trigenic, quadrigenic, three-locus, and four-locus disequilibrium measures were also estimated. There was little evidence of higher-order linkage disequilibrium. As expected for a disease with multiple mutations, no disequilibrium was observed between the disease gene and any of the RFLPs. The observed pattern of high disequilibrium within the gene and a loss of disequilibrium 3' to the stop codon could have implications for gene mapping studies. These are discussed, and guidelines for linkage disequilibrium studies are suggested.     

A gene for distal arthrogryposis type I maps to the pericentromeric region of chromosome 9.

Club foot is one of the most common human congenital malformations. Distal arthrogryposis type I (DA-1) is a frequent cause of dominantly inherited club foot. Performing a genomewide search using short tandem repeat (STR) polymorphisms, we have mapped a DA-1 gene to the pericentromeric region of chromosome 9 in a large kindred. Linkage analysis has generated a positive lod score of 5.90 at theta = 0, with the marker GS-4. Multiple recombinants bracketing the region have been identified. Analysis of an additional family demonstrated no linkage to the same locus, indicating likely locus heterogeneity. Of the autosomal congenital contracture disorders causing positional foot deformities, this is the first to be mapped.     

Progress towards identifying the neurofibromatosis (NF1) gene

Von Recklinghausen neurofibromatosis (NF1) is a common autosomal dominant disorder of humans. Linkage analysis has recently mapped the NF1 gene to the proximal long arm of chromosome 17. The identification of two NF1 patients with balanced translocations has now allowed the location of the gene to be narrowed to a few hundred kilobases of chromosome band 17q11.2, using a combination of somatic cell hybrid technology, linking clones and pulsed field gel electrophoresis.     

A human SHC-related sequence maps to chromosome 17, the SHC gene maps to chromosome 1

The SHC gene encodes a protein that is thought to act as an adapter in many signal transduction pathways; the SHC protein probably facilitates the activation of RAS proteins in response to a variety of factors. We have mapped the human SHC gene and have identified a new SHC-related sequence. We have sequenced the region corresponding to the SHC 3 UTR from both loci and have mapped cosmids by fluorescence in situ hybridization. The human SHC gene maps to the proximal long arm of chromosome 1 and the SHC-related sequence maps to the proximal long arm of chromosome 17. A number of cancers have been positioned in the proximal long arm of chromosome 1; this is of interest given the oncogenic potential of the SHC protein.     

Dominant hereditary inclusion-body myopathy gene (IBM3) maps to chromosome region 17p13.1

We recently described an autosomal dominant inclusion-body myopathy characterized by congenital joint contractures, external ophthalmoplegia, and predominantly proximal muscle weakness. A whole-genome scan, performed with 161 polymorphic markers and with DNA from 40 members of one family, indicated strong linkage for markers on chromosome 17p. After analyses with additional markers in the region and with DNA from eight additional family members, a maximum LOD score (Zmax) was detected for marker D17S1303 (Zmax=7.38; recombination fraction (theta)=0). Haplotype analyses showed that the locus (Genome Database locus name: IBM3) is flanked distally by marker D17S945 and proximally by marker D17S969. The positions of cytogenetically localized flanking markers suggest that the location of the IBM3 gene is in chromosome region 17p13.1. Radiation hybrid mapping showed that IBM3 is located in a 2-Mb chromosomal region and that the myosin heavy-chain (MHC) gene cluster, consisting of at least six genes, co-localizes to the same region. This localization raises the possibility that one of the MHC genes clustered in this region may be involved in this disorder.     

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.     

A conserved alternative splice in the von Recklinghausen neurofibromatosis (NF1) gene produces two neurofibromin isoforms, both of which have GTPase-activating protein activity.

Sequence analysis has shown significant homology between the catalytic regions of the mammalian ras GTPase-activating protein (GAP), yeast Ira1p and Ira2p (inhibitory regulators of the RAS-cyclic AMP pathway), and neurofibromin, the protein encoded by the NF1 gene. Yeast expression experiments have confirmed that a 381-amino-acid segment of neurofibromin, dubbed the GAP-related domain (GRD), can function as a GAP. Using the RNA polymerase chain reaction with primers flanking the NF1-GRD, we have identified evidence for alternative splicing in this region of the NF1 gene. In addition to the already published sequence (type I), an alternative RNA carrying a 63-nucleotide insertion (type II) is present in all tissues examined, although the relative amounts of types I and II vary. The insertion is conserved across species but is not present in GAP, IRA1, or IRA2. GenBank searches have failed to identify significant similarity between the inserted sequence and known DNA or protein sequences, although the basic amino acid composition of the insertion shares features with nuclear targeting sequences. Expression studies in yeasts show that despite the partial disruption of the neurofibromin-IRA-GAP homology by this insertion, both forms of the NF1-GRD can complement loss of IRA function. In vivo assays designed to compare the GAP activity of the two alternatively spliced forms of the NF1-GRD show that both can increase the conversion of GTP-bound ras to its GDP-bound form, although the insertion of the 21 amino acids weakens this effect. The strong conservation of this alternative splicing suggests that both type I and II isoforms mediate important biological functions of neurofibromin.     

Phenotypic and genetic characterization of novel variant in the NF1 gene underlying neurofibromatosis type 1 in five Chinese families

Science China Life Sciences -     

Linkage studies with chromosome 17 DNA markers in 45 neurofibromatosis 1 families

A locus for von Recklinghausen neurofibromatosis (NF1) has recently been mapped near the chromosome 17 centromere. We have extended these linkage studies by genotyping 45 NF1 families with three DNA probes known to be linked to the chromosome 17 centromeric region. Of 34 families informative for NF1 and at least one of the three probes, 28 families show no recombinants with the disease gene. These data provide additional support for genetic homogeneity of NF1 and for a primary NF1 locus linked to the chromosome 17 centromere. Among the informative families were 7 families with apparent new NF1 mutations. Our data suggest that these mutations are probably at the chromosome 17 NF1 locus.     

Eye disorders in neurofibromatosis (NF1)

Neurofibromatosis type 1 (NF 1) is an autosomal dominant disorder with high index of spontaneous mutations and extremely varied and impredictible clinical manifestations. The aim of this work was to give an account of eye disorders in NF1. 132 patients of age 0-16 years with NF1 were followed up for 15 years. They were checked repeatedly for ophthalmologic disorders. Frequent eye disorders were: Lisch nodules (Iris hamartomas, IH) 78%, hyperthelorism 19.7%, bulbomotoric disorders 15.9%, disorders of the optic disc 16.7% and optic gliomas (18.9%). The highest incidence of eye disorders by NF1 patients showed Lisch nodules (IH). Its ease of clinical recognition and if present with other diagnostic signs (for instance café au lait patches) could be deemed as reliable diagnostic criterion of NF1 in childhood.     

Mutational and functional analysis of the neurofibromatosis type 1 (NF1) gene

Neurofibromatosis type 1 (NF1) is one of the most common autosomal dominant disorders. It is caused by mutations in the NF1 gene which comprises 60 exons and is located on chromosome 17q. The NF1 gene product, neurofibromin, displays partial homology to GTPase-activating protein (GAP). The GAP-related domain (GRD), encoded by exons 20–27a, is the only region of neurofibromin to which a biological function has been ascribed. A total of 320 unrelated NF1 patients were screened for mutations in the GRD-encoding region of the NF1 gene. Sixteen different lesions in the NF1 GRD region were identified in a total of 20 patients. Of these lesions, 14 are novel and together comprise three missense, two nonsense and three splice site mutations plus six deletions of between 1 and 4 bp. The effect of one of the missense mutations (R1391S) was studied by in vitro expression of a site-directed mutant and GAP activity assay. The mutant protein, R1391S, was found to be some 300-fold less active than wild-type NF1 GRD. The mutations reported in this study therefore provide further material for the functional analysis of neurofibromin as well as an insight into the mutational spectrum of the NF1 GRD. Received: 13 July 1996 / Revised: 6 August 1996