A genetic map of human chromosome 17p

Molecular mapping of four ovule lethal mutants in soybean

We report genetic mapping of four soybean ovule lethal mutants, PS-1, PS-2, PS-3, and PS-4, which had been identified as female partial-sterile mutants from a gene-tagging study. The four mutants had been classified into two mutation classes: (1) PS-1-sporophytic mutation affects sporophytically expressed genes; and (2) PS-2, PS-3, and PS-4 mutants-female gametophyte-specific mutations affect gametophytically expressed genes and are transmitted through the male, but not the female gametes. Molecular mapping demonstrated that these four mutant genes and previously reported female-partial sterile gene, Fsp1, are located independently on soybean molecular linkage groups (MLG-) using SSR markers. PS-1, designated as Fsp2 and Genetic Type Collection number T364, is located between SSR markers Satt170 and Satt363 on MLG-C2 and linked by 13.9 cM and 12.1 cM, respectively. PS-2, designated as Fsp3 and Genetic Type Collection number T365H, is located between SSR markers Satt538 and Satt429 on MLG-A2 and linked by 13.3 cM and 25.4 cM, respectively. PS-3, designated as Fsp4 and Genetic Type Collection number T366H, is located on the terminus of MLG-F and linked to Sat 152 by 13.1 cM. PS-4, designated as Fsp5 and Genetic Type Collection number T367H, is located between SSR markers Satt324 and Satt138 on MLG-G and linked by 19.6 cM and 7.5 cM, respectively. SSR markers adjacent to Fsp3, Fsp4, and Fsp5 were distorted from a 1:2:1 ratio and fit a 1:1 ratio. The segregation distortions of SSR markers adjacent to Fsp3, Fsp4, and Fsp5 are in support of male, but not female transmission of the Fsp3, Fsp4, and Fsp5 gametes.

Inherited neuropathies: from gene to disease

Inherited disorders of peripheral nerves represent a common group of neurologic diseases. Charcot-Marie-Tooth neuropathy type 1 (CMT1) is a genetically heterogeneous group of chronic demyelinating polyneuropathies with loci mapping to chromosome 17 (CMT1A), chromosome 1 (CMT1B) and to another unknown autosome (CMT1C). CMT1A is most often associated with a tandem 1.5-megabase (Mb) duplication in chromosome 17p11.2-12, or in rare patients may result from a point mutation in the peripheral myelin protein-22 (PMP22) gene. CMT1B is associated with point mutations in the myelin protein zero (P0 or MPZ) gene. The molecular defect in CMT1C is unknown. X-linked Charcot-Marie-Tooth neuropathy (CMTX), which has clinical features similar to CMT1, is associated with mutations in the connexin32 gene. Charcot-Marie-Tooth neuropathy type 2 (CMT2) is an axonal neuropathy, also of undetermined cause. One form of CMT2 maps to chromosome 1p36 (CMT2A), another to chromosome 3p (CMT2B) and another to 7p (CMT2D). Dejerine-Sottas disease (DSD), also called hereditary motor and sensory neuropathy type III (HMSNIII), is a severe, infantile-onset demyelinating polyneuropathy syndrome that may be associated with point mutations in either the PMP22 gene or the P0 gene and shares considerable clinical and pathological features with CMT1. Hereditary neuropathy with liability to pressure palsies (HNPP) is an autosomal dominant disorder that results in a recurrent, episodic demyelinating neuropathy. HNPP is associated with a 1.5-Mb deletion in chromosome 17p11.2-12 and results from reduced expression of the PMP22 gene. CMT1A and HNPP are reciprocal duplication/deletion syndromes originating from unequal crossover during germ cell meiosis. Other rare forms of demyelinating peripheral neuropathies map to chromosome 8q, 10q and 11q. Hereditary neuralgic amyotrophy (familial brachial plexus neuropathy) is an autosomal dominant disorder causing painful, recurrent brachial plexopathies and maps to chromosome 17q25.

Fine mapping of de novo CMT1A and HNPP rearrangements within CMT1A-REPs evidences two distinct sex-dependent mechanisms and candidate sequences involved in recombination

The molecular mechanism resulting in the duplication or deletion of a 1.5 Mb region of 17p11.2-p12, associated, respectively, with Charcot-Marie-Tooth type 1A (CMT1A) and hereditary neuropathy with liability to pressure palsies (HNPP), has been proposed to be an unequal crossing-over during meiosis between the two chromosome 17 homologues generated by misalignment of the proximal and distal CMT1A-REP repeats, two homologous sequences flanking the 1.5 Mb CMT1A/HNPP monomer unit. In a recent study of a large series of de novo cases of CMT1A and HNPP, two distinct sex-dependent mechanisms were identified. Rearrangements of paternal origin, essentially duplications, were indeed generated by unequal meiotic crossing-over between the two chromosome 17 homologues, but duplications and deletions of maternal origin resulted from an intrachromosomal process, either unequal sister chromatid exchange or, in the case of deletion, excision of an intrachromatidal loop. In order to determine how these recombinations occur, 24 de novo crossover breakpoints were localized within the 1.7 kb rearrangement hot spot by comparing the sequences of the parental CMT1A-REPs with the chimeric copy in affected offspring. Nineteen out of 21 paternal crossovers were found in a 741 bp hot spot. All the breakpoints of maternal origin (n = 3), however, were located outside this interval, but in closely flanking sequences, supporting the hypothesis that two distinct sex-dependent mechanisms are involved. Several putative recombination promoting sequences in the hot spot, which are rare or absent in the surrounding 7.8 kb, were identified.

Deletion mapping on chromosome 17p in medulloblastoma

Medulloblastoma is the most frequent paediatric brain tumour. Because of the uniform histology, a common genetic mechanism has been postulated. Loss of heterozygosity (LOH) studies support evidence that a candidate gene, which functions as a tumour-suppressor gene, is located in 17p13. Eighteen tumours were examined for loss of heterozygosity at 15 different loci at chromosome 17p. Nine of 18 (50%) tumours had allelic loss in 17p 13.3-13.2. The smallest region of overlap, which harbours the disease gene, includes markers from UT222 (D17S675) to UT49 (D17S731) and spans a region of less than 6 cM. Candidate genes within this region are HIC-1, a potential tumour-suppressor gene, and DPH2L, a gene that has been cloned from the ovarian critical region. The putative region excludes the p53 gene and the ABR gene, which have been favoured by others. LOH of chromosome 17p may be used as a new prognostic biological marker. Children with an allelic loss had a poorer prognosis than those patients without loss of heterozygosity (P<0.05).

Two patients with duplication of 17p11.2: the reciprocal of the Smith-Magenis syndrome deletion?

J.M. and H.G. are two unrelated male patients with developmental delay. Cytogenetic analysis detected a duplication of 17p11.2 in both patients. The extent of the duplicated region was determined using single copy DNA probes: cen-D17S58-D17S29-D17S258-D17S71-D17S445-+ ++D17S122-tel. Four of the six markers, D17S29, D17S258, D17S71, and D17S445, were duplicated by dosage analysis. Fluorescent in situ hybridization (FISH) analysis of H.G., using cosmids for locus D17S29, confirmed the duplication in 17p11.2. Because the deletion that causes the Smith-Magnesis syndrome involves the same region of 17p11.2 as the duplication in these patients, the mechanism may be similar to that proposed for the reciprocal deletion/duplication event observed in Hereditary Neuropathy with Liability to Pressure Palsies (HNPP) and Charcot-Marie-Tooth Type 1A disease (CMT1A).

Vincristine treatment triggering the expression of asymptomatic Charcot-Marie-Tooth disease

A 16-year-old male suffering from Ewing's sarcoma of the pelvis was treated with vincristine as part of his chemotherapeutic protocol. The boy was never known to suffer from any neurological problems. His father had a mild limp, attributed to prolonged "taxi driving," that was never investigated medically. The first course of treatment, which included 2 mg of vincristine, resulted in clinical improvement. However, at the same time the patient developed severe weakness of both upper and lower limbs, areflexia, and gradually a pes cavus deformity. Nerve conduction studies were suggestive of severe peripheral sensorimotor neuropathy, axonal and demyelinative. A definite diagnosis of Charcot-Marie-Tooth was confirmed by molecular analysis showing the typical duplication of 1.5 megabases at 17 p11.2. This unique manifestation of vincristine neurotoxicity is reported and discussed.

Developmental profile in a patient with monosomy 10q and dup(17p) associated with a peripheral neuropathy

We report on a patient with dup(17p) and monosomy (10q) resulting from a familial translocation. Manifestations typical of both syndromes were present. The overall development of this patient was better by comparison with similar reported cases of either anomaly. Our evaluation detected severe gross motor delay and signs of a demyelinating peripheral neuropathy. This patient is trisomic for the region of 17p which includes the peripheral myelin protein-22 (PMP-22) gene, known to be duplicated in Charcot-Marie-Tooth neuropathy type 1A (CMT1A). Our analysis in this patient suggests that trisomy for the PMP-22 gene led to the demyelinating neuropathy and contributed to his severe motor developmental delay.

Molecular genetic analysis of the 17p11.2 region in patients with hereditary neuropathy with liability to pressure palsies (HNPP)

Hereditary neuropathy with liability to pressure palsies (HNPP) is in most cases associated with an interstitial deletion of the same 1.5-Mb region at 17p11.2 that is duplicated in Charcot-Marie-Tooth type 1A (CMT1A) patients. Unequal crossing-over following misalignment at flanking repeat sequences (CMT1A-REP), either leads to tandem duplication in CMT1A patients or deletion in HNPP patients. With the use of polymorphic DNA markers located within the CMT1A/HNPP duplication/deletion region we detected the HNPP deletion in 16 unrelated HNPP patients, 11 of Belgian and 5 of French origin. In all cases, the 1.5-Mb size of the HNPP deletion was confirmed by EcoRI dosage analysis using a CMT1A-REP probe. In the 16 HNPP patients, the same 370/320-kb EagI deletion-junction fragments were detected with pulsed field gel electrophoresis (PFGE), while in CMT1A patients, a 150-kb EagI duplication-junction fragment was seen. Thus, PFGE analysis of EagI-digested DNA with a CMT1A-REP probe allows direct detection of the HNPP deletion or the CMT1A duplication for DNA diagnostic purposes.

A de novo duplication in 17p11.2 and a novel mutation in the Po gene in two Déjérine-Sottas syndrome patients

Déjérine-Sottas syndrome (DSS), or hereditary motor and sensory neuropathy (HMSN) type III, is a severe hypertrophic demyelinating neuropathy with infantile onset. The clinical symptoms are similar to those found in Charcot-Marie-Tooth disease type 1 (CMT1) or HMSN type I patients, but they are more severe. DSS is genetically heterogeneous. Dominant mutations in two major peripheral myelin protein genes, PMP22 and Po, are associated with a DSS phenotype. Mutations in the same genes are also responsible for the CMT1 phenotype. A 1.5-Mb duplication in 17p11.2 is the major mutation found in familial and sporadic CMT1 patients. We studied two genetically sporadic DSS patients. The presence of a de novo duplication in one patient was revealed by Southern blot analysis, using polymorphic markers located in the duplicated area. The 17p11.2 allele segregation in this patient and in her parents suggests that the duplication is of maternal origin. In the other patient, single-strand conformation polymorphism (SSCP) analysis of the 6 exons of the Po gene revealed two additional bands in exon 3. Sequencing of this exon identified a novel dominant mutation replacing a sequence of 8 bp by a mutated sequence of 5 bp. The mutation apparently leads to the replacement of 4 amino acids at positions 86-89 by three different amino acids, in an area that is part of a predicted beta-strand. Our findings support the suggestion that DSS and CMT1 disease should not be considered as two different clinical entities.

DNA analysis as a tool to confirm the diagnosis of asymptomatic hereditary neuropathy with liability to pressure palsies (HNPP) with further evidence for the occurrence of de novo mutations

We performed DNA analysis in four families with hereditary neuropathy with liability to pressure palsy (HNPP). An interstitial deletion of the 17 p11.2 region was found in typically affected patients as well as in as yet asymptomatic patients. The opportunity for an individual genotyping permitted to ascertain a de novo deletion in one clinically affected case with no relevant familial history. DNA analysis thus becomes the most sensitive tool in diagnosing HNPP, since potentially affected patients may lack either informative familial history, or clinical symptoms or even suggestive EMG or histopathological data (tomaculas).

Prenatal diagnosis of Charcot-Marie-Tooth disease type 1A (CMT1A) using molecular genetic techniques

Charcot-Marie-Tooth disease type 1A (CMT1A) is a frequent hereditary motor and sensory neuropathy of the peripheral nerves. In most cases, the disease is associated with a 1.5 Mb tandem duplication at 17p11.2. A 42-year-old pregnant women requested prenatal diagnosis because of her age and since both her husband and two children were severely affected with CMT1. The CMT1A duplication was demonstrated in the father's, the two children's, and the fetus's DNA using different molecular genetic methods. Although cytogenetical analysis showed a normal female karyotype in the fetus, the parents decided to terminate the pregnancy because of the genetic risk associated with the CMT1A duplication.

Charcot-Marie-Tooth disease: molecular characterization of patients from central and southern Italy

The syndrome of peroneal muscular atrophy, or Charcot-Marie-Tooth (CMT), disease represents the most common inherited peripheral neuropathy, with a prevalence of about 1 per 2500. The disease is usually transmitted in an autosomal dominant fashion, although it can display all the mendelian patterns of inheritance. The chromosome 17-linked form (CMT1a) appears to be the most common form of the disease in all the ethnic groups studied so far, Italians included, and is due to a tandem duplication in 17p11.2. In order to study the distribution of CMT types and to establish a genotype-phenotype correlation in patients from Central and Southern Italy, we collected 19 CMT pedigrees diagnosed in the years 1992-1993. Simple tandem repeats (STR) polymorphism analysis with the marker RM11-GT and Southern blotting with the probes pVAW409R3 and pVAW412 were performed, demonstrating a high prevalence (about 60%) of 17p duplication in the families studied. No clinical or electrophysiological differences were noted between CMT1 patients with or without 17p duplication, respectively. Two families affected by CMT2 showed no evidence of rearrangement at the D17S122 locus. These data are consistent with the hypothesis of a different molecular basis for CMT2.

Non-radioactive detection of 17p11.2 duplication in CMT1A: a study of 78 patients

Charcot-Marie-Tooth disease type 1 (CMT1) is a peripheral neuropathy characterised by progressive distal muscular atrophy and sensory loss with markedly decreased nerve conduction velocity, mostly inherited as an autosomal dominant trait. The most common form, type 1A, is associated with a 1.5Mb DNA duplication in region p11.2-p12 of chromosome 17 in many patients. In this study a non-radioactive test for detection of the CMT1A duplication based on an RM11-GT microsatellite polymorphism is presented. Although different methods have been devised for this purpose, the present method has the advantage of being rapid, informative, economical, easily interpretable, and, therefore, it represents a very useful tool for diagnosis of CMT1A, especially before clear manifestation of clinical symptoms. Seventy-eight patients diagnosed clinically as having CMT and evaluated by electrophysiological methods were tested with an RM11-GT microsatellite and with probe pVAW409R3. The CMT1A duplication was found in 76% of the 56 unrelated patients. RM11-GT was the most informative marker with a heterozygosity of 89%.

Linkage and mutation analysis in an extended family with Charcot-Marie-Tooth disease type 1B

Charcot-Marie-Tooth disease type 1 (CMT1) or hereditary motor and sensory neuropathy type I (HMSNI) is an autosomal dominant peripheral neuropathy. In most families the disease segregates with a 1.5 Mb duplication on chromosome 17p11.2 (CMT1A). A few patients have been found with point mutations in the PMP-22 gene. In some families linkage has been found with markers located on chromosome 1q21-q25 (CMT1B) and more recently mutations have been identified in the P0 gene. We analysed an extended CMT1 pedigree (CMT-B) without the CMT1A duplication. Significant positive linkage with chromosome 1 indicated that this family is of the CMT1B subtype. Sequencing of the candidate gene P0 located in chromosome band 1q21-q23 showed a C to A point mutation at position 446 in exon 3 resulting in an Asp134Glu substitution. Since the P0 mutation cosegregated with CMT1 disease we suggest that this mutation is the primary genetic cause of CMT1B in family CMT-B.

Partitioned pulsed-field gel electrophoresis-PCR (PPF-PCR): a new method for pulsed-field mapping for STS and microsatellites

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Hereditary motor and sensory neuropathy with diaphragm and vocal cord paresis

We describe two kindreds with an autosomal dominant inherited disorder characterized by a variable degree of muscle weakness of limbs, vocal cords, and intercostal muscles and by asymptomatic sensory loss, beginning in infancy or childhood in severely affected persons. Life expectancy in severely affected patients is shortened because of respiratory failure. Because nerve conduction velocities are normal and it is an inherited axonal neuropathy, we classify the disorder as a variety of hereditary motor and sensory neuropathy type II (HMSN II) (HMSN IIc). The present report provides further evidence for heterogeneity among the hereditary motor and sensory neuropathy type II disorders. In one large pedigree with the type IIc disorder, no linkage to DNA markers known to map near the HMSN IA locus on chromosome 17p or the HMSN IB locus on chromosome 1q was demonstrated.

Detailed analysis of loss of heterozygosity on chromosome band 17p13 in breast carcinoma on the basis of a high-resolution physical map with 29 markers

We have constructed a physical map of chromosome band 17p13, using 29 markers that had been localized to 17p13 by means of fluorescence in situ hybridization (FISH) and analysis by pulsed-field gel electrophoresis (PFGE). The map spans nearly 8 Mb of genomic DNA, and the estimated average distance between each marker is roughly 290 kb. The p13 band of chromosome 17 is thought to contain a putative tumor suppressor gene in addition and distal to TP53. Deletion mapping in a large number of breast carcinomas indicated that the tumor suppressor gene lies between the loci defined by cC117-708 (D17S878) and p144D6 (D17S34), which are an estimated 7 Mb apart. Our results should contribute to construction of a contig map of chromosome band 17p13 with cosmid and/or YAC (yeast artificial chromosome) clones, and to isolation of the putative tumor suppressor gene.

Amplification of the anonymous marker D17S67 in malignant astrocytomas

Loss of heterozygosity (LOH) for chromosome arms 9p, 10p, 10q, and 17p and amplification of the epidermal growth factor receptor (EGFR) gene have been identified as frequent genetic changes in malignant astrocytomas. We have found amplification of the anonymous marker D17S67 on chromosome arm 17p in 10% (3 of 30 cases) of astrocytomas of the highest malignancy grade. The tumors with D17S67 amplification displayed other genetic changes on chromosome 17, including additional amplifications and deletions. All three patients with D17S67 amplification developed severe brain edema and died within 1 month after operation.

Screening of dominantly inherited Charcot-Marie-Tooth neuropathies

Sixty-three families with dominantly inherited Charcot-Marie-Tooth (CMT) neuropathies including 730 subjects (total) from which 356 affected were studied clinically, electrophysiologically (MNCVs and EMGs), by genetic linkage, and screened for DNA duplication. Thirty-eight families (60.3%) were type 1A (demyelinating CMT mapped on chromosome 17). DNA duplication was present in 36 families (94.8% of CMT1A families). One CMT1A family (2.6%) showed no duplication but suggested genetic linkage with markers of chromosome 17. One CMT1A family (2.6%) revealed nonduplication in some affected members and duplication in other affected members. The disease in that family segregated with the same chromosome 17 markers regardless of duplication status. The other CMT families with dominant inheritance but without duplication included one family with CMT1B (demyelinating CMT mapped on chromosome 1) (1.6%), 14 families with CMT2 axonal neuropathy (22.2%), and 10 families with X-linked dominant CMT (15.9%).

Clinical, cytogenetic, and molecular evidence for an infant with Smith-Magenis syndrome born from a mother having a mosaic 17p11.2p12 deletion

We describe an infant with del(17) (p11.2p12) whose deleted chromosome was inherited from a mosaic mother. The child had manifestations consistent with Smith-Magenis syndrome. The mother appeared to be of normal intelligence and she had minimal findings of Smith-Magenis syndrome. Separation of chromosome 17 homologues in somatic cell hybrids and molecular studies confirmed the cytogenetic diagnoses and the fact that the mother was mosaic. Furthermore, molecular analysis demonstrated novel breakpoints in this family, with the deletion extending into and completely encompassing the markers duplicated in Charcot-Marie-Tooth (CMT) disease. Although this Smith-Magenis syndrome patient is completely deleted for the CMT region, her electrophysiological findings are different from those found in CMT. This is the only reported case of Smith-Magenis syndrome with transmission from a partially affected mosaic mother. Transmission of interstitial deletions from mosaic parents may be more common than thought; therefore, parental chromosomes should be examined when interstitial deletions are identified.

Charcot-Marie-Tooth disease type 1A: mutational mechanisms and candidate gene

Charcot-Marie-Tooth disease type 1A, the most common inherited peripheral neuropathy, is associated with a submicroscopic DNA duplication of 1.5 Mb that can arise de novo, and which is flanked by a > 17 kb mosaic repeat. The PMP22 gene, encoding a peripheral myelin protein, maps within the duplication. In a subset of Charcot-Marie-Tooth patients, point mutations can occur within the gene. Thus, the alternative mechanisms of overexpression of PMP22 and structural alterations in the protein encoded can cause the disease phenotype.

DNA deletion associated with hereditary neuropathy with liability to pressure palsies

Hereditary neuropathy with liability to pressure palsies (HNPP) is an autosomal dominant disorder that causes episodes of focal demyelinating neuropathy following minor trauma to peripheral nerves. We assign the HNPP locus to chromosome 17p11.2 and demonstrate the presence of a large interstitial deletion associated with this disorder in three unrelated pedigrees. De novo deletion is documented in one pedigree. The deleted region appears uniform in all pedigrees and includes the gene for peripheral myelin protein 22 (PMP-22), suggesting that underexpression of PMP-22 may cause HNPP. The deletion in HNPP spans approximately 1.5 Mb and includes all markers that are known to map within the Charcot-Marie-Tooth neuropathy type 1A (CMT1A) duplication. Furthermore, the breakpoints in HNPP and CMT1A map to the same intervals in 17p11.2, suggesting that these genetic disorders may be the result of reciprocal products of unequal crossover.

Stable inheritance of the CMT1A DNA duplication in two patients with CMT1 and NF1

Charcot-Marie-Tooth disease type 1A (CMT1A) was recently demonstrated to be associated with a large DNA duplication in 17p11.2p12. The gene for neurofibromatosis type 1 (NF1) or von Recklinghausen disease maps to 17q11.2. We have identified 2 unrelated patients who were diagnosed with both CMT1 and NF1. Molecular analysis of these patients demonstrated the presence of the CMT1A duplication and inheritance of this DNA rearrangement from a parent affected with CMT. Analysis of genomic DNA isolated from the neurofibroma removed from one of these patients showed the same 500 kb SacII junction fragment associated with the CMT1A duplication that was found in genomic DNA isolated from the blood. These results lend further support to the hypothesis that the CMT1A duplication is a stable DNA rearrangement. In addition, the molecular analysis of these 2 patients suggests that 2 common autosomal dominant conditions (CMT1 and NF1) can occur in the same individual, not because of an underlying single molecular defect, but rather, secondary to a chance phenomenon.

Charcot-Marie-Tooth type 1A duplication appears to arise from recombination at repeat sequences flanking the 1.5 Mb monomer unit

We have constructed a 3.1 megabase (Mb) physical map of chromosome 17p11.2-p12, which contains a submicroscopic duplication in patients with Charcot-Marie-Tooth disease type 1A (CMT1A). We find that the CMT1A duplication is a tandem repeat of 1.5 Mb of DNA. A YAC contig encompassing the CMT1A duplication and spanning the endpoints was also developed. Several low copy repeats in 17p11.2-p12 were identified including the large (> 17 kb) CMT1A-REP unit which may be part of a mosaic repeat. CMT1A-REP flanks the 1.5 Mb CMT1A monomer unit on normal chromosome 17 and is present in an additional copy on the CMT1A duplicated chromosome. We propose that the de novo CMT1A duplication arises from unequal crossing over due to misalignment at these CMT1A-REP repeat sequences during meiosis.

Duplication within chromosome 17p11.2 in 12 families of French ancestry with Charcot-Marie-Tooth disease type 1a. The French CMT Research Group

Hereditary motor and sensory neuropathy type I (HMSN I), also designated Charcot-Marie-Tooth disease type 1 (CMT1), is a peripheral neuropathy frequently inherited as an autosomal dominant trait, characterised by progressive distal muscular atrophy and sensory loss with markedly decreased nerve conduction velocity. A duplication within chromosome 17p11.2, cosegregating with the disease, has recently been reported in several CMT1a families. In order to estimate the frequency of this anomaly and determine the location of a duplication in this region, 12 CMT1 families were analysed with polymorphic DNA markers located within 17p11.2-12. Duplications were found in all families including loci D17S61 (EW401), D17S122 (VAW409R3a and RM11-GT), and D17S125 (VAW412R3). The duplications were completely linked and associated with the disease (lod score of 20.77 at zero recombination). Screening for the RM11-GT microsatellite showed that most of the duplicated haplotypes were heterozygous, supporting the hypothesis that the duplication resulted from an unequal crossing over. There was no significant haplotype association within the duplicated region suggesting that the duplication resulted de novo as an independent event in each family. In one family, recombination within the duplicated region was observed, indicating that genetic instability in 17p11.2 might be related to a high recombination rate. Since most cases of CMT1a seem to result from this segmental trisomy, it can be used as a basis for DNA diagnosis of the disease.

Molecular genetics and neuropathology of Charcot-Marie-Tooth disease type 1A

Charcot-Marie-Tooth (CMT) syndrome describes a genetically and clinically heterogeneous group of polyneuropathies. Electrophysiologically, at least two types of CMT can be distinguished; CMT1 which has decreased nerve conduction velocities (NCV) and CMT2 which has normal or near normal NCV with decreased amplitudes. For CMT1, three gene loci (on chromosomes 1, 17 and the X chromosome) have been mapped. The locus on chromosome 17, CMT type 1A (CMT1A), is responsible for the most common form of CMT which has recently been shown to be associated with a large DNA duplication. Recent data demonstrates that the CMT1A phenotype results from an inherited DNA rearrangement and a gene dosage effect. The trembler (Tr) and allelic tremblerJ (TrJ) mice have been proposed as animal models for CMT. Tr has similar electrophysiological and neuropathological features to CMT1 patients and maps to mouse chromosome 11 in a region of conserved synteny with human chromosome 17p. Tr and TrJ have recently been shown to have different point mutations in regions encoding putative transmembrane domains of the myelin specific protein PMP-22. The human peripheral nerve-specific PMP-22 gene maps within the CMT1A duplication. PMP-22 is thus a candidate gene for CMT1A. This paper describes the molecular genetics of CMT1A and sural nerve pathology in CMT1A patients with the CMT1A duplication.

Somatic cell hybrids, sequence-tagged sites, simple repeat polymorphisms, and yeast artificial chromosomes for physical and genetic mapping of proximal 17p

Somatic cell hybrids retaining the deleted chromosome 17 from 15 unrelated Smith-Magenis syndrome (SMS) [del(17)(p11.2p11.2)] patients were obtained by fusion of patient lymphoblasts with thymidine kinase-deficient rodent cell lines. Seventeen sequence-tagged sites (STSs) were developed from anonymous markers and cloned genes mapping to the short arm of chromosome 17. The STSs were used to determine the deletion status of these loci in these and four previously described human chromosome 17-retaining hybrids. Ten STSs were used to identify 28 yeast artificial chromosomes (YACs) from the St. Louis human genomic YAC library. Four of the 17 STSs identified simple repeat polymorphisms. The order and location of deletion breakpoints were confirmed and refined, and the regional assignment of several probes and cloned genes were determined. The cytogenetic band locations and relative order of six markers on 17p were established by fluorescence in situ hybridization mapping to metaphase chromosomes. The latter data confirmed and supplemented the somatic cell hybrid results. Most of the hybrids derived from [del(17)(p11.2p11.2)] patients demonstrated a similar pattern of deletion for the marker loci and were deleted for D17S446, D17S258, D17S29, D17S71, and D17S445. However, one of them demonstrated a unique pattern of deletion. This patient is deleted for several markers known to recognize a large DNA duplication associated with Charcot-Marie-Tooth (CMT) disease type 1A. These data suggest that the proximal junction of the CMT1A duplication is close to the distal breakpoint in [del(17)(p-11.2p11.2)] patients.

CEPH maps

There are CEPH genetic maps on each homologous human chromosome pair. Genotypes for these maps have been generated in 88 laboratories that receive DNA from a reference panel of large nuclear pedigrees/families supplied by the Centre d'Etude du Polymorphisme Humain. These maps serve as useful tools for the localization of both disease genes and other genes of interest.

A genetic linkage map of 96 loci on the short arm of human chromosome 3

We constructed a genetic map of 96 loci on the short arm of human chromosome 3 (3p) in 59 families provided by the Centre d'Etude du Polymorphisme Humaine (CEPH). Twenty-nine continuously linked loci were placed on the map with likelihood support of at least 1000:1; one locus, D3S213, was placed on the map with likelihood support of 871:1; D3Z1, an alpha satellite centromeric repeat probe, was placed on the map with likelihood support of 159:1; 65 loci were assigned regional locations. The average heterozygosity of the uniquely ordered markers was 49%. The map extends from 3p26, the terminal band of 3p, to the centromere (from D3S211 to D3Z1). Multipoint linkage analysis indicated that the male, female, and sex-averaged maps extend for 102, 147, and 116 cM, respectively. The mean genetic distance between uniquely ordered loci on the sex-averaged map was 4.0 cM. Probe density was greatest for the region of 3p between D3F15S2e and the telomere. The sex-averaged map contained two intervals greater than 10 cM. Seventeen probes were localized by fluorescence in situ hybridization. The loci described in this report will be useful in building an integrated genetic and physical map of this chromosome.

The gene for the peripheral myelin protein PMP-22 is a candidate for Charcot-Marie-Tooth disease type 1A

Charcot-Marie-Tooth disease type 1A (CMT1A) is an autosomal dominant peripheral neuropathy associated with a large DNA duplication on the short arm of human chromosome 17. The trembler (Tr) mouse serves as a model for CMT1A because of phenotypic similarities and because the Tr locus maps to mouse chromosome 11 in a region of conserved synteny with human chromosome 17. Recently, the peripheral myelin gene Pmp-22 was found to carry a point mutation in Tr mice. We have isolated cDNA and genomic clones for human PMP-22. The gene maps to human chromosome 17p11.2-17p12, is expressed at high levels in peripheral nervous tissue and is duplicated, but not disrupted, in CMT1A patients. Thus, we suggest that a gene dosage effect involving PMP-22 is at least partially responsible for the demyelinating neuropathy seen in CMT1A.

Linkage analysis of distal hereditary motor neuropathy type II (distal HMN II) in a single pedigree

We describe a six generation family affected with the autosomal dominant form of distal hereditary motor neuropathy type II (distal HMN II). The distal HMN shows similarities with the hereditary motor and sensory neuropathies type I and II (HMSN I and HMSN II) or Charcot-Marie-Tooth disease type 1 and 2 (CMT 1 and CMT 2) and with some proximal HMN or spinal muscular atrophies (SMA). Gene loci have been assigned to chromosomes 1q, 17p, and 19q for CMT 1 and to chromosome 5q for recessive SMA. In this study we excluded all four regions for the presence of distal HMN II, indicating that this neuropathy is genetically different from CMT 1 and recessive SMA.

Gene dosage is a mechanism for Charcot-Marie-Tooth disease type 1A

Charcot-Marie-Tooth disease type 1A (CMT1A) is the most common inherited peripheral neuropathy in humans, characterized electrophysiologically by decreased nerve conduction velocities (NCVs). CMT1A is associated with a large submicroscopic DNA duplication in proximal 17p. In this report we demonstrate that a patient with a cytogenetically visible duplication, dup(17)(p11.2p12), has decreased NCV. Molecular analysis demonstrated this patient was duplicated for all the DNA markers duplicated in CMT1A as well as markers both proximal and distal to the CMT1A duplication. These data support the hypothesis that the CMT1A phenotype can result from a gene dosage effect.

Framework multipoint map of the long arm of human Chromosome 4 and telomeric localization of the gene for FSHD

Mapping the long arm of Chromosome (Chr) 4 has assumed medical relevance with the establishment of linkage of facioscapulohumeral muscular dystrophy (FSHD) to distal 4q markers. We have constructed a multipoint linkage map using DNA markers that map to the long arm of Chr 4. Segregation data were collected for 17 DNA markers on the multigenerational CEPH mapping families, and data for one marker were taken from the published CEPH database. Genotypic information for six of these markers was also collected from a set of 24 families that exhibited inheritance of FSHD. Multipoint analyses allowed us to construct a map of 12 loci, connecting two previously separate linkage groups. Significant sex-specific differences in recombination were found for some genetic intervals. Four loci from the distal region of this map showed linkage with FSHD. A map using these terminal markers gave the strongest support for FSHD in the most distal position over all other possible positions.

Estimation of the size of the chromosome 17p11.2 duplication in Charcot-Marie-Tooth neuropathy type 1a (CMT1a). HMSN Collaborative Research Group

We have previously shown a duplication in 17p11.2 with probe pVAW409R3 (D17S122) in 12 families with hereditary motor and sensory neuropathy type I (HMSN I) or Charcot-Marie-Tooth disease type 1 (CMT1). In this study we aimed to estimate the size of the duplication using additional polymorphic DNA markers located in 17p11.2-p12. Two other 17p11.2 markers, pVAW412R3 (D17S125) and pEW401 (D17S61), were found to be duplicated in all HMSN I patients tested. Furthermore, all HMSN I patients showed the same duplication junction fragment with probe pVAW409R3. On the genetic map the duplicated markers span a minimal distance of 10 cM while on the physical map they are present in the same NotI restriction fragment of 1150 kb. The discrepancy between the genetic and physical map distances suggests that the 17p11.2 region is extremely prone to recombinational events. The high recombination rate may be a contributing factor to the genetic instability of this chromosomal region.

Charcot-Marie-Tooth disease type 1a (CMT1a): evidence for trisomy of the region p11.2 of chromosome 17 in south Wales families

The gene for Charcot-Marie-Tooth disease type 1a (CMT1a) has been localised to chromosome 17p11.2. Locus D17S122 is recognised by the DNA probe pVAW409R3 which detects an MspI polymorphism with three alleles in the normal population. Subjects with CMT1a show evidence of trisomy for this region of chromosome 17 by displaying either all three alleles or a dosage effect when only two alleles are present. This phenomenon was seen in 10 out of 11 families with type I hereditary motor and sensory neuropathy (HMSN) where affected subjects were heterozygous for the MspI polymorphisms. This mutation is likely to have arisen from a non-reciprocal recombination event between non-sister chromatids of homologous chromosomes at meiosis I. The detection of this partial trisomy offers a rapid method for the diagnosis of CMT1a in families not suitable for linkage analysis.

Clinical and genetic heterogeneity of Charcot-Marie-Tooth disease

The autosomal dominant forms of hereditary motor and sensory neuropathies include the hypertrophic form (CMT1) and the neuronal form of Charcot-Marie-Tooth disease (CMT2). While at least two distinct loci have been shown to be linked to the CMT1 phenotype (CMT1A and CMT1B, on chromosomes 17 and 1, respectively), whether the CMT2 phenotype results from mutations allelic to either of the CMT1 genes remains unknown. Studying one CMT1 and two CMT2 pedigrees, we were able to exclude the CMT2 disease locus from the region of chromosome 17 (Z = -2.80 at theta = 0.05 for D17S58) where the CMT1A gene maps (Z = +3.67 at theta = 0.00). Similarly, negative lod score values were obtained in CMT2 for the region of chromosome 1 where the CMT1B gene has been located (Z = -3.09 at theta = 0.05 for D1S61). The present study therefore provides evidence for genetic heterogeneity between the hypertrophic and the neuronal forms of Charcot-Marie-Tooth disease and demonstrates that the CMT2 gene is not allelic to either of the CMT1 genes mapped to date.

PCR amplification of chromosome-specific alpha satellite DNA: definition of centromeric STS markers and polymorphic analysis

Alpha satellite DNA is a tandemly repetitive DNA family found at the centromere of every human chromosome. Chromosome-specific subsets have been isolated for over half the chromosomes and have prove useful as markers for both genetic and physical mapping. We have developed specific oligonucleotide primer sets for polymerase chain reaction (PCR) amplification of alpha satellite DNA from chromosomes 3, 7, 13/21, 17, X, and Y. For each set of primers, PCR products amplified from human genomic DNA are specific for the centromere of the target chromosome(s), as shown by somatic cell hybrid mapping and by fluorescence in situ hybridization. These six subsets represent several evolutionarily related alpha satellite subfamilies, suggesting that specific primer pairs can be designed for most or all chromosomal subsets in the genome. The PCR products from chromosome 17 directly reveal the polymorphic nature of this subset, and a new DraI polymorphism is described. The PCR products from chromosome 13 are also polymorphic, allowing in informative cases genetic analysis of this centromeric subset distinguished from the highly homologous chromosome 21 subset. These primer sets should allow placement of individual centromeres on the proposed STS map of the human genome and may be useful for somatic cell hybrid characterization and for making in situ probes. In addition, the ability to amplify chromosome-specific repetitive DNA families directly will contribute to the structural and functional analysis of these abundant classes of DNA.

DNA duplication associated with Charcot-Marie-Tooth disease type 1A

Charcot-Marie-tooth disease type 1A (CMT1A) was localized by genetic mapping to a 3 cM interval on human chromosome 17p. DNA markers within this interval revealed a duplication that is completely linked and associated with CMT1A. The duplication was demonstrated in affected individuals by the presence of three alleles at a highly polymorphic locus, by dosage differences at RFLP alleles, and by two-color fluorescence in situ hybridization. Pulsed-field gel electrophoresis of genomic DNA from patients of different ethnic origins showed a novel SacII fragment of 500 kb associated with CMT1A. A severely affected CMT1A offspring from a mating between two affected individuals was demonstrated to have this duplication present on each chromosome 17. We have demonstrated that failure to recognize the molecular duplication can lead to misinterpretation of marker genotypes for affected individuals, identification of false recombinants, and incorrect localization of the disease locus.

A genetic linkage map of human chromosome 5 with 60 RFLP loci

A genetic map of human chromosome 5 that contains 60 restriction fragment length polymorphism (RFLP) loci in one linkage group has been constructed. Segregation data using these markers and 40 large multigenerational families supplied by the Centre d'Etude du Polymorphisme Humain have been collected. Linkage analyses were performed with the program package CRI-MAP; using odds greater than 1000:1, 30 RFLP loci could be placed on the map. This genetic map spans 289 cM sex-equal, 353 cM in females, and 244 cM in males. While the relative rate of recombination for female meioses is nearly twice that of males over much of the chromosome, several instances of statistically significant excess male recombination were observed. The order of probes on the genetic map has been confirmed by their physical order as determined by somatic cell hybrid lines containing deletions of normal chromosome 5. There is concordance between the physical positions of markers and their genetic positions. Our most distal probes on the genetic map are cytologically localized to the most distal portions of the chromosome. This suggests that our genetic map spans most of chromosome 5.

Localization of Charcot-Marie-Tooth disease type 1a (CMT1A) to chromosome 17p11.2

Charcot-Marie-Tooth (CMT) disease type 1a has been previously localized to chromosome 17 using the markers D17S58 and D17S71. In that report we were unable to provide unequivocal localization of the CMT1A gene on either the proximal p or the q arm. Therefore, data from one additional CMT1A family and typing of other probes spanning the pericentromeric region of chromosome 17 (D17S73, D17S58, D17S122, D17S125, D17S124) were analyzed. Multipoint analysis demonstrates convincing evidence (log likelihood difference greater than 5) that the CMT1A gene lies within 17p11.2 and most likely between the flanking markers D17S122 and D17S124.

A centromere-based genetic map of the short arm of human chromosome 6

A genetic map of the short arm of chromosomes 6 (6p) has been constructed with 20 genetic markers that define 16 loci, including a locus at the centromere. The 40 CEPH families and, for 4 loci, 13 additional Utah families were genotyped. All 16 loci form a single linkage group extending from near the telomeric region to the centromere, covering 159 cM (Haldane) on the female map and 94 cM on the male map. Sex differences in recombination frequencies are noted for the 6p map, with an excess occurring in males at the distal end. The genetic order of loci is consistent with their physical localization on 6p. Proximal to the three most distal loci on the map, markers are especially dense, providing an extended region on 6p useful for localizing genes of interest.

Duplication in chromosome 17p11.2 in Charcot-Marie-Tooth neuropathy type 1a (CMT 1a). The HMSN Collaborative Research Group

Hereditary motor and sensory neuropathy type I (HMSN I) or Charcot-Marie-Tooth disease type 1 (CMT 1) is an autosomal dominant disorder of the peripheral nervous system characterized by progressive weakness and atrophy of distal limb muscles. In the majority of HMSN I families, linkage studies localized the gene (CMT 1a) to the pericentromeric region of chromosome 17. We have detected with probe pVAW409R3 (D17S122) localized in 17p11.2 a duplication, co-segregating with the disease in 12 HMSN I families. In these families the duplication was present in all 128 patients but absent in the 84 unaffected and 44 married-in individuals (lod score of 58.44 at zero recombination). Further, on one HMSN I family the disease newly appeared simultaneously with a de novo duplication originating from an unequal crossing-over event at meiosis. Since different allelic combinations were found segregating with the duplication in different families linkage disequilibrium was not a significant factor. These findings led us to propose that the duplication in 17p11.2 itself is the disease causing mutation in all the HMSN I families analyzed.

Inheritance of proliferative breast disease in breast cancer kindreds

Previous studies have emphasized that genetic susceptibility to breast cancer is rare and is expressed primarily as premenopausal breast cancer, bilateral breast cancer, or both. Proliferative breast disease (PBD) is a significant risk factor for the development of breast cancer and appears to be a precursor lesion. PBD and breast cancer were studied in 103 women from 20 kindreds that were selected for the presence of two first degree relatives with breast cancer and in 31 control women. Physical examination, screening mammography, and four-quadrant fine-needle breast aspirates were performed. Cytologic analysis of breast aspirates revealed PBD in 35% of clinically normal female first degree relatives of breast cancer cases and in 13% of controls. Genetic analysis suggests that genetic susceptibility causes both PBD and breast cancer in these kindreds. This study supports the hypothesis that this susceptibility is responsible for a considerable portion of breast cancer, including unilateral and postmenopausal breast cancer.

Mapping the human genome: current status

The human genome has already been the subject of extensive research activity even though the Human Genome Project is only just officially starting. This review and the accompanying wall chart attempt to provide an integrated, quantitative, and detailed summary of the status of knowledge on the human genome in mid-1990. The analysis has highlighted the rudimentary nature of many of the information links needed for the task. While this overview could not be fully comprehensive and required simplifying assumptions, the results have provided estimates of relative progress on a region-by-region basis throughout the genome.