Translocation breakpoint in two unrelated Tourette syndrome cases,within a region previously linked to the disorder

Tourette syndrome (TS) is a complex neuropsychiatric disorder characterized by both motor and vocal tics. The etiology of TS is poorly understood; however, evidence of genetic transmission arises from family and twin studies. A complex mode of inheritance has been suggested, likely involving contributions of several genes with different effect size. We describe here two unrelated families wherein balanced t(6;8) chromosomal translocations occur in individuals diagnosed with TS. In one of these families, the transmission of the translocation is associated with learning and behavioral difficulties; in the other family, one parent is unaffected and the other cannot be traced, thus transmission cannot be demonstrated and it is possible that the translocation may have occurred de novo. The breakpoint on chromosome 8 occurs within the q13 band in both families, suggesting that a gene or genes in this region might contribute to the TS phenotype. Existing linkage and cytogenetic data, suggesting involvement of chromosome 8 in TS families and individuals, further support this hypothesis. We have identified two YAC clones mapping distal and proximal to the chromosome 8 translocation site, as determined by fluorescent in situ hybridization (FISH). PCR amplification of genetic markers in this region, using isolated chromosomes from one of the patients, followed by BAC screening with the closest flanking genetic markers, has identified a 200-kb BAC, which, by FISH, we have demonstrated encompasses the chromosome 8 breakpoint in both families. The fact that the chromosomal breaks in the TS cases from both families occur within such a small region of chromosome 8 further supports the hypothesis that disruption of a gene or genes in this part of chromosome 8 contributes to the clinical phenotype.     

CNTNAP2 is disrupted in a family with Gilles de la Tourette syndrome and obsessive compulsive disorder

Gilles de la Tourette syndrome (GTS) is a sporadic or inherited complex neuropsychiatric disorder characterized by involuntary motor and vocal tics. There is comorbidity with disorders like obsessive compulsive disorder and attention deficit hyperactivity disorder. Until now linkage analysis has pointed to a number of chromosomal locations, but has failed to identify a clear candidate gene(s). We have investigated a GTS family with a complex chromosomal insertion/translocation involving chromosomes 2 and 7. The affected father [46,XY,inv(2) (p23q22),ins(7;2) (q35-q36;p21p23)] and two affected children [46,XX,der(7)ins(7;2)(q35-q36;p21p23) and 46,XY,der(7)ins(7;2)(q35-q36;p213p23)] share a chromosome 2p21-p23 insertion on chromosome 7q35-q36, thereby interrupting the contactin-associated protein 2 gene (CNTNAP2). This gene encodes a membrane protein located in a specific compartment at the nodes of Ranvier of axons. We hypothesize that disruption or decreased expression of CNTNAP2 could lead to a disturbed distribution of the K(+) channels in the nervous system, thereby influencing conduction and/or repolarization of action potentials, causing unwanted actions or movements in GTS.     

Evidence That the Saethre-Chotzen Syndrome Locus Lies between D7S664 and D7S507, by Genetic Analysis and Detection of a Microdeletion in a Patient

The locus for Saethre-Chotzen syndrome, a common autosomal dominant disorder of craniosynostosis and digital anomalies, was previously mapped to chromosome 7p between D7S513 and D7S516. We used linkage and haplotype analyses to narrow the disease locus to an 8-cM region between D7S664 and D7S507. The tightest linkage was to locus D7S664 ( = 7.16, θ = .00). Chromosomes from a Saethre-Chotzen syndrome patient with t(2;7) (p23;p22) were used for in situ hybridization with YAC clones containing D7S664 and D7S507. The D7S664 locus was found to lie distal to the 7p22 breakpoint, and the D7S507 locus was deleted from the translocation chromosomes. These genetic and physical mapping data independently show that the disease locus resides in this interval.     

Closing in on the Rieger syndrome gene on 4q25: mapping translocation breakpoints within a 50-kb region.

Rieger syndrome (RGS) is an autosomal dominant disorder of morphogenesis affecting mainly the formation of the anterior eye chamber and of the teeth. RGS has been localized to human chromosome 4q25 by linkage to epidermal growth factor (EGF). We have constructed a detailed physical map and a YAC contig of the genomic region encompassing the EGF locus. Using FISH, several YACs could be shown to cross the breakpoint in two independent RGS patients with balanced 4q translocations. Alu- and LINE-fragmentation of a 2.4-Mb YAC generated a panel of shorter YACs ranging in size from 2.4 Mb to 75 kb. Several fragmentation YACs were subcloned in cosmids, which were mapped to specific subregions of the original YAC by hybridization to the fragmentation panel to further refine the localization of the translocation breakpoints, allowing mapping of the breakpoints to within the most-telomeric 200 kb of the original 2.4-Mb YAC. FiberFISH of cosmids located in this 200-kb region mapped the two translocation breakpoints within a 50-kb region approximately 100-150 kb centromeric to D4S193, significantly narrowing down the candidate region for RGS. The mapping data and resources reported here should facilitate the identification of a gene implicated in Rieger syndrome.     

Ts65Dn -- localization of the translocation breakpoint and trisomic gene content in a mouse model for Down syndrome

Fluorescent in situ hybridization (FISH) -- using mouse chromosome paints, probes for the mouse major centromeric satellite DNA, and probes for genes on chromosomes (Chr) 16 and 17 -- was employed to locate the breakpoint in a translocation used to produce a mouse model for Down syndrome. The Ts65Dn trisomy is derived from the reciprocal translocation T(16;17)65Dn. The Ts65Dn mouse carries a marker chromosome containing the distal segment of Chr 16, a region that shows linkage conservation with human Chr 21, and the proximal end of Chr 17. This chromosome confers trisomy for most of the genes in the Chr 16 segment and Ts65Dn mice show many of the phenotypic features characteristic of Down syndrome. We used FISH on metaphase chromosomes from translocation T65Dn/+ heterozygotes and Ts65Dn mice to show that the Chr 17 breakpoint is distal to the heterochromatin of Chr 17, that the Ts65Dn marker chromosome contains a small portion of Chr 17 euchromatin, that the Chr 16 breakpoint lies between the Ncam2 and Gabpa/App genes, and that the Ts65Dn chromosome contains >80% of the human Chr 21 homologs. The significance of this finding is discussed in terms of the utility of this mouse model.     

Localization of the translocation breakpoint in a female with Menkes syndrome to Xq13.2-q13.3 proximal to PGK-1.

Menkes syndrome is a rare X-linked recessive disorder characterized by an inability to metabolize copper. A female patient with both this disease and an X; autosome translocation with karyotype 46,X,t(X;2)(q13;q32.2) has previously been described. The translocation breakpoint in Xq13 coincides with a previous assignment of the Menkes gene at Xq13 by linkage data in humans and by analogy to the mottled mutations which are models for Menkes disease in the mouse. Therefore, this translocation probably interrupts the gene for Menkes syndrome in band Xq13. We describe here experiments to precisely map the translocation breakpoint within this chromosomal band. We have established a lymphoblastoid cell line from this patient and have used it to isolate the der(2) translocation chromosome (2pter----2q32::Xq13----Xqter) in human/hamster somatic cell hybrids. Southern blot analyses using a number of probes specific for chromosomes X and 2 have been studied to define precisely the location of the translocation breakpoint. Our results show that the breakpoint in this patient--and, therefore, likely the Menkes gene--maps to a small subregion of band Xq13.2-q13.3 proximal to the PGK1 locus and distal to all other Xq13 loci tested.     

Characterization of a complex philadelphia translocation (1p-;9q+;22q-) by gene mapping

Summary Human-Chinese hamster somatic cell hybrids were obtained using circulating leucocytes from a chronic myeloid leukaemia (CML) patient carrying a complex Philadelphia (Ph¹) translocation (1p-; 9q+; 22q-). Hybrid clones which showed segregation of the translocation chromosomes were studied. The chromosome 22 markers ACO2, ARSA, and NAGA segregated with the 1p- derivative; and the chromosome 1 markers UMPK, PGD, and ENO1 segregated with the 9q+ derivative. Hence, molecular evidence has been obtained for the translocation of the distal part of 22q to chromosome 1 and for the translocation of the distal part of 1p to chromosome 9. No conclusions could be drawn either about translocation of chromosome 9 material or about a possible difference in breakpoint in chromosome 22 when compared with six cases of 9;22 translocations similarly studied and previously reported. In addition, a more precise mapping of PGM1 was obtained, the gene being proximal to UMPK and the breakpoint in 1p32.     

Cloning and characterization of the breakpoint regions of a chromosome 11;18 translocation in a patient with hamartoma of the retinal pigment epithelium

Mutations of various tumor suppressor genes, e.g., PTEN, TSC1, and TSC2, are known to be responsible for different inherited diseases presenting with multiple hamartomas, a benign tumor resembling neoplasia that results from faulty organ development. Combined hamartoma of the retinal pigment epithelium (RPE) and retina is a rare, congenital, focal malformation of the fundus. So far, no disease gene has been associated with this disorder. By molecular analysis of an apparently balanced and reciprocal translocation between the short arms of chromosomes 11 and 18, t(11;18)(p13;p11.31), in a patient with hamartoma of the RPE and retina, we selected PAC clones crossing the breakpoints on both derivative chromosomes 11 and 18. For the overlapping chromosome 11 clone, two EST clusters were identified, suggesting the existence of at least two genes in the breakpoint region. We constructed a PAC contig and showed that at least three exons of a novel gene map to the breakpoint region on chromosome 18. Based on the results of FISH analysis with the PAC clones of this contig, we suggest the occurrence of a complex rearrangement.     

Der(22) syndrome and velo-cardio-facial syndrome/DiGeorge syndrome share a 1.5-Mb region of overlap on chromosome 22q11

Derivative 22 (der[22]) syndrome is a rare disorder associated with multiple congenital anomalies, including profound mental retardation, preauricular skin tags or pits, and conotruncal heart defects. It can occur in offspring of carriers of the constitutional t(11;22)(q23;q11) translocation, owing to a 3:1 meiotic malsegregation event resulting in partial trisomy of chromosomes 11 and 22. The trisomic region on chromosome 22 overlaps the region hemizygously deleted in another congenital anomaly disorder, velo-cardio-facial syndrome/DiGeorge syndrome (VCFS/DGS). Most patients with VCFS/DGS have a similar 3-Mb deletion, whereas some have a nested distal deletion endpoint resulting in a 1.5-Mb deletion, and a few rare patients have unique deletions. To define the interval on 22q11 containing the t(11;22) breakpoint, haplotype analysis and FISH mapping were performed for five patients with der(22) syndrome. Analysis of all the patients was consistent with 3:1 meiotic malsegregation in the t(11;22) carrier parent. FISH-mapping studies showed that the t(11;22) breakpoint occurred in the same interval as the 1.5-Mb distal deletion breakpoint for VCFS. The deletion breakpoint of one VCFS patient with an unbalanced t(18;22) translocation also occurred in the same region. Hamster-human somatic hybrid cell lines from a patient with der(22) syndrome and a patient with VCFS showed that the breakpoints occurred in an interval containing low-copy repeats, distal to RANBP1 and proximal to ZNF74. The presence of low-copy repetitive sequences may confer susceptibility to chromosome rearrangements. A 1.5-Mb region of overlap on 22q11 in both syndromes suggests the presence of dosage-dependent genes in this interval.     

Molecular characterisation of the t(1;15)(p22;q22) translocation in the prostate cancer cell line LNCaP

Although chromosome translocations are well-documented recurrent events in hematological malignancies and soft tissue sarcomas, their significance in carcinomas is less clear. We report here the molecular characterization of the reciprocal translocation t(1;15)(p22;q22) in the prostate carcinoma cell line, LNCaP. The chromosome 1 breakpoint was localized to a single BAC clone, RP11-290M5, by sequential FISH analysis of clones selected from the NCBI chromosome 1 map. This was further refined to a 580-bp region by Southern blot analysis. A 2.85-kb fragment spanning the der(1) breakpoint was amplified by long-range inverse PCR. The breakpoint on chromosome 1 was shown to lie between the CYR61 and the DDAH1 genes with the der(1) junctional sequence linking the CYR61 gene to the TSPAN3 (TM4SF8) gene on chromosome 15. Confirmatory PCR and FISH mapping of the der(15) showed loss of chromosome material proximal to the breakpoint on chromosome 15, containing the PSTPIP1 and RCN2 genes. On the available evidence we conclude that this translocation does not result in an in-frame gene fusion. Comparative expressed sequence hybridization (CESH) and comparative genomic hybridization (CGH) analysis, showed relative down-regulation of gene expression surrounding the breakpoint, but no gross change in genomic copy number. Real-time quantitative RT-PCR for genes around the breakpoint supported the CESH data. Therefore, here we may have revealed a gene down-regulation mechanism associated with a chromosome translocation, either through small deletion at the breakpoint or through another means of chromosome domain related gene regulation.     

Fine mapping and cloning of the breakpoint associated with Menkes syndrome in a female patient.

The gene responsible for Menkes syndrome has been assigned to Xq13 by a combination of comparative mapping and linkage analysis. A previous report has mapped the translocation breakpoint associated with the disease in a female patient to an interval delimited by PGK1 and a group of six more proximal Xq13 markers, including DXS56. We have characterized a number of PGK1- or DXS56-positive YACs, from which we have generated six new markers. One of them identifies a small overlap region between a PGK1-positive YAC and three DXS56-positive YACs, distal to the Menkes breakpoint. A 560-kb region covered by a DXS56-positive YAC has been restriction-mapped and subcloned, disclosing a 187-kb MluI fragment astride the breakpoint. A probe mapping distal to the rearrangement in the same interval reveals altered PGFE fragments in a hybrid constructed from the translocation patient's DNA. We describe the development of a cosmid contig extending 150 kb from a nearby CpG island across the breakpoint. This contig includes four adjacent clones displaying cross-specific hybridization.     

Tourettesyndrome免疫病因学研究进展

多发性抽动症（Tourette syndrome）是一种慢性神经精神性疾病,好发于儿童和青少年,主要表现为一个或多个部位肌肉运动性或发声性抽动,发作期持续超过一年,间歇期不超过3个月。TS的病因和发病机制至今仍未明确,目前认为其发病与免疫因素,环境心理因素,遗传因素,生物化学因素等多种因素有关,目前,A族B溶血性链球菌与Ts的发生跟发展的关系已有所报道,较多研究是关于链球茵感染的,一些免疫相关研究发现与链球菌感染有关的小儿自身免疫性神经精神疾病会引发或加重抽动症状。另外,过敏性变态反应性疾病与Ts患儿的自身免疫应答活跃的关系也有所报道。神经．内分泌一免疫网络学说认为,外周免疫系统跟中枢神经系统之间,可通过直接接触或通过产生并释放出来的生物活性因子进行信息交流。细胞因子正是两大系统间相互作用的信使,不仅可以调节免疫,而且还可以调控神经元和神经胶质细胞的功能。细胞因子与神经介质、内分泌激素共同组成机体细胞间的信号分子,参与免疫系统并激活神经递质及激素间的信息传递,与精神障碍和心理机体反应密切相关。因此,有关免疫病因学异常可能是部分易感患儿发病的机制,文章从感染免疫学,过敏性变态反应性疾病,以及细胞因子调节网络等与免疫相关的几个方面加以综述。     

A Contiguous Clone Map over 3 Mb on the Long Arm of Chromosome 11 across a Balanced Translocation Associated with Schizophrenia

Forty-nine clones derived by microdissection of a schizophrenia-associated t(1;11)(q42.1;q14.3) breakpoint region have been assigned by somatic cell hybrid mapping to seven discrete intervals on the long arm of human chromosome 11. Eleven of the clones were shown to map to a small region immediately distal to the translocation breakpoint on 11q.A 3-Mb contiguous clone map of this region was established by isolation of corresponding YAC recombinants. The contig was oriented and shown to traverse the translocation breakpoint by FISH and microsatellite marker analysis. This contig will facilitate the isolation of candidate sequences whose expression may be affected by the translocation.     

Regional and physical mapping studies characterizing the Greig polysyndactyly 3;7 chromosome translocation, t(3;7)(p21.1;p13)

The Greig polysyndactyly-craniofacial anomalies syndrome is an autosomal dominant disorder involving a gene(s) located in band 7p13. We have isolated and characterized a reciprocal 3;7 chromosome translocation that resulted in the syndrome. We have identified two closely linked (0 cM) conserved DNA sequences (P137/p944B) that flank the translocation breakpoint. A pulsed-filed analysis combined with available genetic linkage information demonstrates that the disorder is linked (2 cM) to the T-gamma receptor locus, lending considerable support to the hypothesis that the mouse mutant extra-toes is the counterpart of the Greig syndrome. We have found no evidence that physically links the EGF receptor to the P137/p944B region, again compatible with mouse linkage relationships. The isolation of the der(3) chromosome from the 3;7 translocation has allowed us to regionally localize probes within the 3p21.1 band. For three probes commonly used in heterozygosity experiments with human cancers involving chromosome 3, we have determined that the order from centromere to telomere is D3S3, D3S2, and DNF15S2. Our pulsed-field studies also demonstrate the utility of band density differences combined with partial digests in evaluating linkage relationships. The P137/p944B probes should be useful in examining other hereditary disorders with phenotypic similarities to the Greig syndrome.     

Sequence analysis of the breakpoint regions of an X;5 translocation in a female with Duchenne muscular dystrophy.

X;autosome translocations in females with Duchenne muscular dystrophy (DMD) provide an opportunity to study the mechanisms responsible for chromosomal rearrangements that occur in the germ line. We describe here a detailed molecular analysis of the translocation breakpoints of an X;autosome reciprocal translocation, t(X;5)(p21;q31.1), in a female with DMD. Cosmid clones that contained the X-chromosome breakpoint region were identified, and subclones that hybridized to the translocation junction fragment in restriction digests of the patient's DNA were isolated and sequenced. Primers designed from the X-chromosomal sequence were used to obtain the junction fragments on the der(X) and the der(5) by inverse PCR. The resultant clones were also cloned and sequenced, and this information used to isolate the chromosome 5 breakpoint region. Comparison of the DNA sequences of the junction fragments with those of the breakpoint regions on chromosomes X and 5 revealed that the translocation arose by nonhomologous recombination with an imprecise reciprocal exchange. Four and six base pairs of unknown origin are inserted at the exchange points of the der(X) and der(5), respectively, and three nucleotides are deleted from the X-chromosome sequence. Two features were found that may have played a role in the generation of the translocation. These were (1) a repeat motif with an internal homopyrimidine stretch 10 bp upstream from the X-chromosome breakpoint and (2) a 9-bp sequence of 78% homology located near the breakpoints on chromosomes 5 and X.     

Refinement of a Translocation Breakpoint Associated with Blepharophimosis–Ptosis–Epicanthus Inversus Syndrome to a 280-kb Interval at Chromosome 3q23

Blepharophimosis syndrome (BPES) is an autosomal dominant disorder of craniofacial development, the features of which include blepharophimosis, ptosis, and epicanthus inversus. Although it has been suggested that BPES is genetically heterogeneous, a major locus for this condition resides at chromosome 3q23. We have previously mapped a translocation breakpoint associated with BPES to the D3S1316–D3S1615 interval. The markers in this region have subsequently been shown to lie in a different order, with the BPES locus mapping to the 1-cM D3S1576 and D3S1316 interval. In the current investigation, a physical map, consisting of 60 yeast artificial chromosome (YAC) clones and 1 bacterial artificial chromosome, that spans this region has been constructed. Ten expressed sequence tags and the cellular retinol-binding protein I locus have been mapped to the contig. YAC end isolation has led to the creation of novel STSs that have been used to reduce the size of the BPES critical region to a 280-kb interval, which has been cloned in two nonchimeric YACs.     

Fine structure DNA mapping studies of the chromosomal region harboring the genetic defect in neurofibromatosis type 1

To better map the location of the von Recklinghausen neurofibromatosis (NF1) gene, we have characterized a somatic cell hybrid designated 7AE-11. This microcell-mediated, chromosome-transfer construct harbors a centromeric segment and a neo-marked segment from the distal long arm of human chromosome 17. We have identified 269 cosmid clones with human sequences from a 7AE-11 library and, using a panel of somatic cell hybrids with a total of six chromosome 17q breakpoints, have mapped 240 of these clones on chromosome 17q. The panel included a hybrid (NF13) carrying a der(22) chromosome that was isolated from an NF1 patient with a balanced translocation, t(17;22) (q11.2;q11.2). Fifty-three of the cosmids map into a region spanning the NF13 breakpoint, as defined by the two closest flanking breakpoints (17q11.2 and 17q11.2-q12). RFLP clones from a subset of these cosmids have been mapped by linkage analysis in normal reference families, to localize the NF1 gene more precisely and to enhance the potential for genetic diagnosis of this disorder. The cosmids in the NF1 region will be an important resource for testing DNA blots of large-fragment restriction-enzyme digests from NF1 patient cell lines, to detect rearrangements in patients' DNA and to identify the 17;22 NF1 translocation breakpoint.     

Common sequence motifs at the rearrangement sites of a constitutional X/autosome translocation and associated deletion.

Reciprocal chromosome translocations are common de novo rearrangements that occur randomly throughout the human genome. To learn about causative mechanisms, we have cloned and sequenced the breakpoints of a cytologically balanced constitutional reciprocal translocation, t(X;4)(p21.2;q31.22), present in a girl with Duchenne muscular dystrophy (DMD). Physical mapping of the derivative chromosomes, after their separation in somatic cell hybrids, reveals that the translocation disrupts the DMD gene in Xp21 within the 18-kb intron 16. Restriction mapping and sequencing of clones that span both translocation breakpoints as well as the corresponding normal regions indicate the loss of approximately 5 kb in the formation of the derivative X chromosome, with 4-6 bp deleted from chromosome 4. RFLP and Southern analyses indicate that the de novo translocation is a paternal origin and that the father's X chromosome contains the DNA that is deleted in the derivative X. Most likely, deletion and translation arose simultaneously from a complex rearrangement event that involves three chromosomal breakpoints. Short regions of sequence homology were present at the three sites. A 5-bp sequence, GGAAT, found exactly at the translocation breakpoints on both normal chromosomes X and 4, has been preserved only on the der(4) chromosome. It is likely that the X-derived sequence GGAATCA has been lost in the formation of the der(X) chromosome, as it matches an inverted GAATCA sequence present on the opposite strand exactly at the other end of the deleted 5-kb fragment. These findings suggest a possible mechanism which may have juxtaposed the three sites and mediated sequence-specific breakage and recombination between nonhomologous chromosomes in male meiosis.