Preferential involvement of the short arm in chromosome 8-derived supernumerary markers and ring as identified by chromosome arm painting

We report on the use of fluorescence in situ hybridization (FISH) with specific chromosome 8 arm painting to characterize further small supernumerary chromosome 8-derived markers/rings (SMC/SRC) identified in three patients. Two patients (patients 1 and 2) who carried the marker (SMC) were evaluated because of mental retardation and minor facial anomalies. The patient (patient 3) who carried the ring (SRC) had ventriculomegaly. Parental blood chromosomes of patients 2 and 3 were normal and unavailable on patient 1. The identification of the SMC/SRC was first characterized by FISH specific alpha-repeat centromeric probes, second by FISH whole chromosome painting (WCP), and finally by FISH chromosome arm painting (CAP). The latter showed involvement of only the short arm of chromosome 8 in all three SMC/SRC cases, suggesting a U-type exchange mechanism.     

Tetrasomy 15q25→qter: Cytogenetic and molecular characterization of an analphoid supernumerary marker chromosome

Tetrasomy for the distal long arm of chromosome 15 is a rare finding. It has been previously described in seven patients, all of whom had a supernumerary marker chromosome (SMC) derived from distal 15q. These SMC contained no apparent centromeres (C‐band/α‐satellite negative), and belong to a novel class of SMC with neocentromeres. We present the oldest surviving patient with tetrasomy for distal 15q. The proposita was a 10‐year‐old girl with moderate to severe mental retardation, absent speech, hypotonia, minor facial anomalies, unusual digits, and pigmentation anomalies. Mosaicism for a symmetrical SMC was identified in metaphases from lymphocytes and fibroblasts. Parental karyotypes were normal, indicating a de novo origin for the SMC. FISH with a whole chromosome paint for chromosome 15 showed that the SMC was derived entirely from chromosome 15. However, C‐banding and FISH with chromosome 15 probes D15Z1, D15S11, SNRPN, and PML were all negative. FISH with the FES probe at 15q26 showed hybridization to both ends of the SMC. The marker was interpreted as an analphoid inverted duplication of 15q25→qter containing a presumed neocentromere. Previous molecular studies suggested either a mitotic or paternal meiotic origin for these distal 15q SMC. However, molecular analysis with chromosome 15 polymorphic markers showed that the analphoid SMC(15) in the proposita originated from a maternal meiotic error. The origins and mechanisms involved in formation of these distal 15q SMC appear to be more diverse than for the proximal pseudodicentic SMC(15). Am. J. Med. Genet. 94:393–398, 2000. © 2000 Wiley‐Liss, Inc.     

联合应用多种细胞及分子细胞遗传学技术确诊额外标记染色体

目的应用比较基因组杂交技术（comparative genomic hybridization，CGH）、荧光原位杂交（fluorescence in situ hybridization，FISH）和传统细胞遗传学技术分析1例额外标记染色体（supernumerary marker chromosome，SMC），探讨这些技术的联合使用在识别新发生的标记染色体方面的临床应用。方法1例智力低下患儿，通过常规G显带技术分析其染色体核型。针对发现的SMC，通过CGH分析其起源，通过FISH技术证实。同时应用N带和C带技术分析SMC的随体组成和着丝粒组成。结合已有的文献报道，分析该SMC的表型效应。结果染色体G带分析显示患者为携带SMC的嵌合体，核型描述为mos．47，XX，＋may[31]／48，XX，＋2mar[29]。CGH分析显示患儿基因组中有15q11→q14片段重复，以15q探针与患者中期分裂相进行FISH检测证实SMC来源于15号染色体。应用检测缺失型Prader-wiUi综合征／Angelman综合征的UBE3A探针与患者中期分裂相检测显示SMC有两个UBE3A杂交信号，对照的PML位点没有信号。N带显示SMC携带双随体，c带分析SMC为双着丝粒。综合上述结果，患者核型为：mos．47，xx，＋der（15）（pter＋q14：：q14→pter）[31]／48，XX，＋2der（15）（pter→q14：：q14→pter）[29]．ish der（15）（WCPl5＋，UBE3A＋＋，PML-）。结论CGH对于检测出不平衡染色体结构重排具有提示作用，结合FISH和传统的细胞遗传学技术，为确定SMC的结构组成提供了可信的技术平台，为分析这类异常核型个体的表型、预后和复发风险提供了依据。     

Duplication of chromosome region 8p23.1 → p23.3: A benign variant?

Chromosome analysis was performed in a 34‐year‐old man who was phenotypically normal except for oligoasthenozoospermia. In this patient, analysis of GTG‐banded chromosomes showed in one chromosome 8 additional chromosomal material of unknown origin. To characterize the aberrant chromosome more precisely, a paint specific for chromosome region 8pter → 8p23.1 was generated by microdissection and degenerated oligonucleotide primed‐polymerase chain reaction (DOP‐PCR) and used as fluorescence in situ hybridization (FISH) paint. After reverse painting, hybridization signals were only found on the short arm of the two chromosomes 8, with an enlarged signal on the derivative chromosome 8. The duplication was characterized further with band‐specific FISH probes. We concluded that (part of) chromosome region 8p23.1 → p23.3 was duplicated. Chromosome analysis of the parents showed that the dup(8) was of maternal origin and that the fertile brother of the index patient also was a carrier of the chromosome aberration. There was no history of miscarriages. We suggest that duplication of region 8p23.1 → p23.3 can be regarded as euchromatic variant or duplication with no phenotypic effect. Am. J. Med Genet. 91:18–21, 2000. © 2000 Wiley‐Liss, Inc.     

Supernumerary marker chromosomes (SMCs) in Turner syndrome are mostly derived from the Y chromosome

DNA and FISH (fluorescence in situ hybridization) analysis were carried out in 12 patients with stigmata of Turner syndrome to determine whether the Supernumerary M arker C hromosome (SMC) found cytogenetically in each of these patients was derived from the Y chromosome. The presence of a Y chromosome in these patients may predispose them to develop gonadoblastoma. PCR-Southern blot analysis, followed by FISH, was used to detect the presence of Y chromosome material. The S ex determining R egion Y (SRY), T estis S pecific P rotein Y -encoded (TSPY) and Y -chromosome R NA R ecognition M otif (YRRM) genes, which map at Yp11.31, Yp11.1–11.2 and Yp11.2/Yq11.21–11.23, respectively, were selected as markers, because they span the whole Y chromosome, and more importantly, they are considered to be involved in the development of gonadoblastoma. It was shown that in 12 patients, all of whom had an SMC, the SMC of 11 was derived from the Y chromosome. Furthermore, the presence of the SRY, TSPY and YRRM gene sequences was determined and FISH analysis confirmed the Y origin of the SMCs. The methodology described in this report is a rapid, reliable and sensitive approach which may be easily applied to determine the Y origin of an SMC carried in Turner syndrome. The identification of an SMC is important for the clinical management and prognostic counseling of these patients with Turner syndrome.     

Minute supernumerary marker chromosomes identified in two patients with a related,larger pseudodicentric chromosome*

We describe two cases in which a minute supernumerary marker chromosome (SMC) was identified in addition to a larger pseudodicentric chromosome. Case 1, a phenotypically normal male, had mosaicism for a psu dic(15;15)(q11.2;q11.2) chromosome and a minute SMC. Fluorescence in situ hybridization (FISH) showed that the minute SMC was D15Z1 positive, indicating a chromosome 15 origin. Case 2 was a 22‐week fetus with mosaicism for a normal and two abnormal cell lines: one had a psu dic (22;22)(q11.2;q11.2) chromosome containing euchromatin, usually associated with cat eye syndrome; the other a minute SMC. The minute SMC was positive with the D14Z1/D22Z1 α‐satellite probe, indicating a chromosome 14 or chromosome 22 origin. Deletion of centromeric material was proposed as one mechanism of centromere inactivation in dicentric chromosomes. The origin of these two minute SMC suggests that they were derived from one of the centromeres of the larger pseudodicentric chromosome. These stable minute SMC may be the by‐product of a deletion event inactivating one centromere of a dicentric chromosome to generate a pseudodicentric chromosome. Alternatively, the minute SMC may originate from further rearrangement of the larger pseudodicentric chromosome. These cases suggest possible mechanisms for the origin of minute SMC. © 2001 Wiley‐Liss, Inc.     

Segregation of a supernumerary del(15) marker chromosome in sperm

Supernumerary marker chromosomes (SMC) can be associated with both normal and abnormal phenotypes. In addition, SMC are found at higher frequency in males with infertility. We identified a SMC, characterized as a del(15)(q11.2) chromosome, in a phenotypically normal male. Using fluorescence in situ hybridization (FISH), we examined the segregation of the del(15) chromosome in sperm from this patient. Only 6.23% of sperm nuclei showed disomy using a chromosome 15 alpha-satellite FISH probe, instead of the expected 50%. In addition, FISH analysis showed no increase for non-disjunction of chromosome 18, excluding an interchromosomal effect for this chromosome. The significant decrease in sperm bearing the del(15) may be due to tissue-specific mosaicism or a result of some form of selection against the del(15) during spermatogenesis. This finding provides a basis for the observation that SMC(15) are less likely to be inherited from a paternal carrier.     

Mosaic inv dup(8p) marker chromosome with stable neocentromere suggests neocentromerization is a post‐zygotic event

Marker chromosomes containing active human neocentromeres have been described in individuals where the chromosomes are non‐mosaic, suggesting that they are mitotically stable, but also in individuals where there is mosaicism, raising the possibility of neocentromere instability. We report two independently ascertained individuals who are mosaic for a supernumerary marker chromosome, shown by reverse chromosome painting to have an 8p origin, resulting in mosaicism for tetrasomy 8p23.1→pter in the patient. The markers have a primary constriction but show no detectable centromeric α‐satellite DNA. The marker in Patient 1 demonstrated no centromere protein CENP‐B binding, but associated with nine different functionally critical centromere proteins. Investigation of peripheral blood lymphocytes from this patient on five separate occasions over a 13‐year period showed 23–46% mosaicism for the marker chromosome with no decrease in incidence. In vitro investigation of primary and secondary sub‐clones of a lymphoblast cell line derived from the patient demonstrated 100% stability of the marker chromosome indicating that neocentromere instability is unlikely to be responsible for the mosaicism in the patient. This and other available data support a general model of neocentromerization as a post‐zygotic event, irrespective of whether the supernumerary chromosome fragment has arisen during meiosis or post‐fertilization at mitosis. © 2001 Wiley‐Liss, Inc.     

Protelomeric sequences are deleted in cases of short arm inverted duplication of chromosome 8

We present a patient with a de novo inverted duplication of the short arm of chromosome 8. Molecular analysis confirmed the cytogenetic suspicion of a simultaneous deletion of the tip of the short arm and indicated the maternal origin of the abnormality. This deletion made no detectable contribution to the phenotype of the patient which was comparable to that of previous cases of 8p duplication. Similar investigations of inverted duplications involving other chromosomes may reveal unexpected deletions with significant phenotypic consequences. © 1994 Wiley-Liss, Inc.     

A supernumerary marker chromosome originating from two different regions of chromosome 18

By random amplification of a microdissected chromosome using the degenerate oligonucleotide primed polymerase chain reaction (DOP-PCR) and forward painting (microFISH), we characterised an extra structurally abnormal chromosome (ESAC) or supernumerary marker chromosome in a mentally retarded girl with a pattern of dysmorphic features. It could be clearly shown that the small marker chromosome originates from two different regions of chromosome 18, 18p11.1-->18q11.1 and 18q12.3-->18q21.1 respectively. Maternal origin of the de novo ESAC and biparental origin of the normal homologues of chromosome 18 were shown by PCR of several highly polymorphic microsatellites. In this case, application of microFISH was a prerequisite for rapid and precise characterisation of an ESAC. A definite identification of this discontinuous supernumerary marker chromosome would not have been possible using FISH with centromere specific probes or multicolour FISH approaches.     

Lung hypoplasia in a patient with del(2)(q33‐q35) demonstrated by chromosome microdissection

We report on a 17‐month‐old girl with multiple malformations, including lung hypoplasia, multiple ventricular septal defects, craniofacial anomalies, and malrotation of the intestine. Moreover, the patient showed Robin sequence, developmental delay, as well as pre‐ and postnatal growth retardation. Postnatal cytogenetic analysis revealed an interstitial deletion on the long arm of chromosome 2. Microdissection and reverse chromosome painting of the aberrant chromosome 2 as well as FISH with a panel of chromosome 2q band‐specific YACs mapped the deletion to 2q33‐q35. Lung hypoplasia has not been described so far in patients with del(2)(q33‐q35). A review of previously reported patients showed variable phenotypes apparently due to different deleted chromosomal segments. Am. J. Med. Genet. 94:184–188, 2000. © 2000 Wiley‐Liss, Inc.     

Partial trisomy and monosomy 8p due to inversion duplication

Fluorescent in situ hybridization with probes specific for a chromosomal subregion and chromosome-specific libraries (chromosome painting) are important new methods for assessing chromosome rearrangements. In this paper we present four patients with additional chromosomal material on chromosome 8p who have been studied using G-banding techniques, chromosome painting and FISH with cosmid probes specific for the region 8p23.1 → 8pter. In all cases we found a partial inversion duplication of 8p along with a deletion of the region 8p23.1 → 8pter.     

Origins of accessory small ring marker chromosomes derived from chromosome 1

Three patients with accessory small ring chromosomes derived from chromosome 1 are presented together with additional clinical details and cytogenetic analyses of a previously reported patient. Cytogenetic analysis was undertaken by FISH using a reverse painting probe generated from one of the patients by microdissection of the r(1) chromosome and with a BAC923C6 which maps to 1p12. Results indicated that patients with r(1) chromosomes consisting of 1q12 heterochromatin and short arm pericentric euchromatin which extends to at least the BAC923C6 were associated with a normal or mild phenotype. Patients with abnormal phenotypes possessed two types of rings. One patient had evidence for contiguous pericentric short arm euchromatin which extended from the centromere to beyond the BAC923C6. Two patients showed molecular cytogenetic results which were compatible with non-contiguous chromosome 1 euchromatin. The diversity of origin of r(1)s will hamper attempts to define phenotype/genotype relationships.     

Small familial supernumerary ring chromosome 2: FISH characterization and genotype‐phenotype correlation

A child and his mother were found to be mosaic for a small supernumerary marker chromosome (SMC) that was identified and characterized by means of fluorescent in situ hybridization. The marker chromosome was derived from the pericentromeric region of chromosome 2; the involvement of proximal 2q was determined by YAC probes. The proband was referred because of psychotic illness and mild mental retardation, whereas his mother presented only minor dysmorphisms. There are only a few published reports concerning SMC(2) or proximal 2q trisomy. We reviewed the previously reported cases in an attempt to establish genotype‐phenotype correlations, which are particularly important when SMCs are identified in prenatal diagnosis. © 2002 Wiley‐Liss, Inc.     

Marker chromosome identification by micro-FISH

Micro-FISH was used to elucidate the chromosomal origin of marker chromosomes in three patients. Ten copies of marker chromosomes were collected with microneedles from GTG banded metaphases, transferred to a collecting drop and amplified by means of DOP-PCR. The PCR products were labeled with biotin-14-dATP and used as FISH probes for hybridization to normal metaphase chromosomes and to metaphase chromosomes of the patients (reverse painting). With the generation of chromosome region-specific painting probes by PCR amplification of microdissected DNA and subsequent FISH it was possible to identify the marker chromosomes in all patients. One marker appeared to be derived from the centromere region of the X-chromosome and the proximal third of the long arm, one from the centromere region of chromosome 17 and one marker chromosome was identified as an isochromosome 18p.     

Identification of supernumerary ring chromosome 1 mosaicism using fluorescence in situ hybridization

We report on a 15-year-old black boy with severe mental retardation, multiple congenital anomalies, and a supernumerary ring chromosome mosaicism. Fluorescence in situ hybridization with a chromosome 1 painting probe (pBS1) identified the ring as derived from chromosome 1. The karyotype was 46,XY/47,XY,+r(1)(p13q23). A review showed 8 reports of ring chromosome 1. In 5 cases, the patients had a non-supernumerary ring chromosome 1 resulting in partial monosomies of the short and/or long arm of chromosome 1. In 3 cases, the presence of a supernumerary ring resulted in partial trisomy of different segments of chromosome 1. In one of these cases the supernumerary ring was composed primarily of the centromere and the heterochromatic region of chromosome 1, resulting in normal phenotype. Our patient represents the third report of a supernumerary ring chromosome 1 resulting in abnormal phenotype. © 1995 Wiley-Liss, Inc.     

Diagnosis of four chromosome abnormalities of unknown origin by chromosome microdissection and subsequent reverse and forward painting

A molecular cytogenetic method consisting of chromosome microdissection and subsequent reverse/forward chromosome painting is a powerful tool to identify chromosome abnormalities of unknown origin. We present 4 cases of chromosome structural abnormalities whose origins were ascertained by this method. In one MCA/MR patient with an add(5q)chromosome, fluorescence in situ hybridization (FISH), using probes generated from a microdissected additional segment of the add(5q) chromosome and then from a distal region of normal chromosome 5, confirmed that the patient had a tandem duplication for a 5q35-qter segment. Similarly, we ascertained that an additional segment of an add(3p) chromosome in another MCA/MR patient had been derived from a 7q32-qter segment. In a woman with a history of successive spontaneous abortions and with a minute marker chromosome, painting using microdissected probes from the whole marker chromosome revealed that it was i(15)(p10) or psu dic(15;15)(q11;q11). Likewise, a marker observed in a fetus was a ring chromosome derived from the paracentromeric region of chromosome 19. We emphasize the value of the microdissection-based chromosome painting method in the identification of unknown chromosomes, especially for marker chromosomes. The method may contribute to a collection of data among patients with similar or identical chromosome abnormalities, which may lead to a better clinical syndrome delineation. © 1996 Wiley-Liss, Inc.     

Characterization of an analphoid supernumerary marker chromosome derived from 15q25-->qter using high-resolution CGH and multiplex FISH analyses

Supernumerary marker chromosomes (SMCs) without detectable alphoid DNA are predicted to have a neocentromere and have been referred to as mitotically stable neocentromere marker chromosomes (NMCs). We report the molecular cytogenetic characterization of a new case with analphoid NMC derived from 15q25-->qter using high-resolution comparative genomic hybridization (HR-CGH) and multiplex fluorescence in situ hybridization analyses with various alpha-satellite DNA probes, all-human-centromere probe (AHC), whole chromosome painting probes, and a subtelomere probe. The propositus is a dysmorphic infant who, at age 3 months, showed accelerated growth, partial deafness, and a phenotype similar to that of the eight previously reported cases of distal 15q tetrasomy. Chromosome studies showed that he had a de novo extra SMC in 80% of cells examined. HR-CGH revealed rev ish enh(15)(q25qter). Molecular cytogenetic analysis and molecular DNA polymorphism study demonstrated that this extra SMC is an NMC containing an inverted duplication of the distal long arm of chromosome 15 (tetrasomy 15q25-->qter) which originated paternally, i.e. ish der(15)(qte-->q25::q25[neocen]-->qter)(AHC-, CEP15-, WCP15+, PCP15q++). This case further elucidates the phenotype related to tetrasomy of this specific chromosome segment and represents a new report of a neocentromere on distal chromosome 15q suggesting that this region appears to be susceptible to the formation of neocentromeres.     

Detailed characterization of 12 supernumerary ring chromosomes using micro‐FISH and search for uniparental disomy

Twelve patients with varying degrees of mosaicism for a supernumerary ring chromosome were studied. The ring chromosomes were characterized using microdissection in combination with degenerate nucleotide‐primed polymerase chain reaction (PCR) and reverse painting (micro‐FISH). This method made it possible to determine the chromosomal origin of the ring chromosomes in detail, and thus to compare the phenotypes of similar cases. Eleven of the marker chromosomes were derived from the most proximal part of 1p, 3p, 3q, 5p, 7q, 8p, 8q, 9p, 10p and 20p. One marker chromosome had a complex origin, including the proximal and the most distal part of 20q. Eight of the families were also investigated for uniparental disomy (UPD) using microsatellite analysis. One case with maternal UPD 9 was found in a child with a ring chromosome derived from chromosome 9, r(9)(p10p12). © 2001 Wiley‐Liss. Inc.     

Direct duplication of 8p21.3→p23.1: A cytogenetic anomaly associated with developmental delay without consistent clinical features

We report six cases in two families and a sporadic case with a direct duplication of region 8p21.3→23.1. In one family, the duplication started in the mother and was transmitted to one son and one daughter. In the second family, the father was mosaic for the anomaly that was transmitted to his two daughters. The cytogenetic anomaly was initially described as an 8p+ with banding analysis and then delineated with fluorescence in situ hybridization (FISH) using whole‐chromosome 8 painting, 8p specific painting, and 8p or 8p/8q subtelomeric probes. Deletion was not detected in the subtelomeric region of the abnormal chromosome 8 examined in one family and in the sporadic case. The phenotypic picture varies from normal to moderate mental retardation in the affected individuals. No consistent minor anomalies or congenital defects were observed among these cases. After comparing the chromosome region involved in our cases with those in others having direct or inverted duplications of 8p, it is thought that the segment 8p21.1→21.3 might be the critical region for an 8p duplication syndrome. The parental origin of the duplication does not seem to impact its clinical significance. © 2001 Wiley‐Liss, Inc.