Down syndrome: characterisation of a case with partial trisomy of chromosome 21 owing to a paternal balanced translocation (15;21) (q26;q22.1) by FISH.

A patient with a typical Down syndrome (DS) phenotype and a normal karyotype was studied by FISH. Using painting probes, we found that the patient had partial trisomy of chromosome 21 owing to an unbalanced translocation t(15;21) (q26; q22.1) of paternal origin. To correlate genotype with phenotype as accurately as possible, we localised the breakpoint using a contig of YACs from the long arm of chromosome 21 as probes and performed FISH. We ended up with two YACs, the most telomeric giving signal on the der (15) in addition to signal on the normal chromosome 21 and the most centromeric giving signal only on both normal chromosomes 21. From these results we could conclude that the breakpoint must be located within the region encompassing YACs 280B1 and 814C1, most likely near one end of either YAC or between them, since neither YAC814C1 nor 280B1 crossed the breakpoint (most likely between marker D21S304 and marker D21S302) onband 21q22.1. The same study was performed on the chromosomes of the father and of a sister and a brother of the patient; all three carried a balanced translocation between chromosomes 15 and 21 and had a normal phenotype. We also performed a prenatal study using FISH for the sister. The fetus was also a carrier of the balanced translocation.     

Recombination in a male carrier of two reciprocal translocations involving chromosomes 14, 14', 15, and 21 leading to balanced and unbalanced rearrangements in offspring

We report an unusual case of a familial complex chromosome rearrangement (CCR), ascertained through prenatal diagnosis. The fetus carried an apparently balanced CCR with a recombinant 3-segment chromosome derived from two paternal reciprocal translocations involving both homologs of chromosome 14 and chromosomes 15 and 21, respectively. A probably normal phenotype was predicted and confirmed after birth. His older sister carried an unbalanced karyotype with partial trisomy 14 and partial monosomy 21, and displayed an apparently normal, paternally derived chromosome 14 that resulted from recombination between two derivative chromosomes. Fluorescent in situ hybridization (FISH) and molecular studies were essential for the characterization of the rearrangement. The "rebuilding," through recombination, of a chromosome involved in two different translocations in a progenitor, was demonstrated for the first time by molecular analysis. Our family is another good example of how balanced familial complex translocations are in a state of flux and can change from one generation to the next.     

Tetrasomy 21 pter→q21.3 due to an extra +dic(21;21)mat in a severely psychomotor-retarded female patient without Down syndrome phenotype

Complete or partial tetrasomy 21 has been reported only in rare cases. We report a Japanese female patient with tetrasomy 21 due to an extra chromosome derived from chromosome 21 (Chr21). The patient had severe psychomotor retardation without Down syndrome (DS) phenotype; she showed short stature, microcephaly, round face, cleft lip and palate, and other dysmorphic features. The chromosome analyses for the patient detected an extra dicentric Chr21 consisting of two partial Chr21 copies fused together within their long arms. Her karyotype was revealed to be 47,XX,+dic(21;21). Allelic ratios of heterozygous SNPs observed in the patient indicated the maternal origin of the extra Chr21. Copy number and structural variant analyses using whole genome sequencing data indicated that the distal breakpoint of the dicentric Chr21 was located within 21q21.3 and that the extra Chr21 did not simply consist of inverted duplications of the pter→q21.3 region, but likely contained multiple partial deletions, duplications, and inversions within it. Fluorescence in situ hybridization results were consistent with the karyotype and genomic analyses. The patient's lack of DS phenotype turned out to be due to the normal copy number of the DS critical region (21q22.13–22.3). A possible molecular mechanism leading to the complex genomic rearrangements in the tetrasomic region consists mainly of breakage-fusion-bridge cycles with an unequal crossing-over event.     

Recurrent trisomy 21: four cases in three generations

Recurrent trisomy 21: four cases in three generations.While gonadal mosaicism can lead to recurrence of trisomy 21 (T21) for a single couple, the recurrence of free T21 in multiple members of a single pedigree has rarely been reported. We present an unusual pedigree with four cases of Down syndrome (DS) with free T21 were born to four separate women related through three generations of one family. The mothers were aged 18, 21, 29, and approximately 30 years at the time of the births. Using microsatellite markers, we excluded most of chromosome 21, excepting two small regions within 21q11.1 and 21q22.3, as being shared among the mothers of the DS children. However, two members of the pedigree, including one DS mother with a normal G-banded karyotype, carried supernumerary alleles at markers 2503J9TG, D21S369, and D21S215, which span the region from 21pter to 21q11.1. Fluorescence in situ hybridization using a centromeric probe hybridizing to chromosomes 13 and 21 did not reveal a novel location, ruling out a cryptic centromeric translocation between chromosome 21 and any chromosome other than chromosome 13. The level of meiotic recombination on chromosome 21 was unusually high in this family as well. We hypothesize that a cryptic rearrangement within the highly repetitive region of 21q11.1 is present in this family, disrupting pairing and leading to an increased risk of non-disjunction of chromosome 21 in this family.     

Preimplantation genetic diagnosis of chromosome balance in embryos from a patient with a balanced reciprocal translocation

Duplications or deletions are present in a high percentage of the gametes produced by individuals carrying balanced translocations. Preimplantation genetic diagnosis was used to examine chromosome balance in embryos from a patient having a reciprocal translocation within the short arms of chromosomes 5 and 8 (46,XX,t(5;8)(p13;p23)). This woman has two sisters with the translocation unbalanced, resulting in a partial trisomy for chromosome 5 and partial monosomy for chromosome 8 (46,XX,-8, +der(8)t(5;8)(p13;p23)) with associated mental retardation and physical abnormalities. The patient and her husband desired to have children without the abnormal chromosome balance and wished to reduce the likelihood of spontaneous abortion or need for therapeutic abortion. Fluorescence in-situ hybridization (FISH) probes for the alpha-satellite region of chromosome 8 and for a region on the short arm of chromosome 5 (5p15.2) were tested initially on lymphocytes from the patient and her sisters. The hybridization signal for chromosome 5 was detected in the expected two copies for the patient and three copies for the sisters in 87% of the cells. Two hybridization signals for chromosome 8 were detected in 96% of the cells from all individuals. Additional probe testing was done using blastomeres from polyspermic embryos. The couple then proceeded with a stimulated in- vitro fertilization (IVF) cycle and biopsies were done on 13 embryos at the 7-10-cell stage using a method of zona drilling and fluid displacement. Diagnosis was possible on at least one blastomere for nine embryos. Three embryos had nuclei with three hybridization signals for chromosome 5, three had fewer than two signals for one or both chromosomes, one was mosaic, and two had two signals for each chromosome. The latter were transferred to the patient, but pregnancy was not achieved. The results demonstrate that preimplantation genetic diagnosis for patients with reciprocal translocations can be used to identify embryos having normal chromosome balance. The potential advantages and limitations of this approach are discussed.      

Two cases of partial trisomy 21 (pter-q22.1) without the major features of Down syndrome

We report two cases of partial trisomy 21 with clinical features distinct from Down syndrome (DS). These patients presented with moderate mental retardation and short stature, but the typical facial appearance of DS was not observed. Each patient had a similarly sized extra chromosome 21. We performed FISH analysis to examine whether deletions of reported approximately 5 Mb DS critical region (DSCR) might be associated with unusual clinical features in these cases. The results showed that each of their extra chromosomes 21 contained a distal part of chromosome 3p or 14q at the telomeric region of chromosome 21q. The translocation breakpoint of 21q for each patient was located on the centromeric side of DSCR (DSCR was deleted) and the sizes of partial trisomy 21 in respective patients are approximately 34.5 (21pter-q22.12) and approximately 33.0 Mb (21pter-q22.11). In one patient, the additional region of the short arm of chromosome 3 was 3pter-p26.1 from maternal origin, measuring approximately 9 Mb in size. The second patient had an extra 14q32.1-qter of maternal origin, measuring approximately 14 Mb in size. These are one of the shortest partial distal trisomy among reported cases. Taken together, two patients with partial trisomy 21 lack all of DSCR on 21q22, and their distinct clinical features are likely caused by the genes located at 21pter-q22.1 and the distal part of chromosome 3p or 14q.     

Tertiary trisomy due to a reciprocal translocation of chromosomes 5 and 21 in a four-generation family

Tertiary trisomy, or double trisomy, is a rare occurrence. We present two individuals with a previously unreported tertiary trisomy for chromosomes 5p and 21q in an eight-generation pedigree. Their phenotypes are compared with other partial trisomies of either 5p or 21q from the literature. The propositus was diagnosed with trisomy 21 at 2 years of age after a karyotype study for short stature and developmental delay. His phenotype was described as atypical for Down syndrome. He presented at 9 years of age because of pervasive behavioral problems and obesity. He was brachycephalic with a flattened nasal bridge, but he lacked other characteristics of trisomy 21. Because of lack of phenotypic evidence of Down syndrome, a repeat karyotype was obtained and showed 47,XY, +der(21)t(5;21)(p15.1; q22.1), incorporating partial trisomies of both chromosomes 5 and 21. Mother had a balanced translocation, 46, XX,t(5;21)(p15.1; q22.1); 8 other relatives were examined. The translocation originated from the maternal great-grandmother, but only the propositus and his mentally retarded aunt had a similar phenotye and the derivative chromosome. Fluorescence in situ hybridization showed absence of band 21q22.2 in the derivative chromosome of the propositus and his aunt, indicating that neither had trisomy for the Down syndrome critical region. These cases represent a unique double partial trisomy of chromosome arms 5p and 21q that occurred because of 3:1 malsegregation of a reciprocal translocation. These cases further demonstrate that phenotypic discordance with cytogenetic results dictate further investigation using advanced cytogenetic hybridization.     

Down综合征与正常核型的孪生姐妹细胞遗传学及DNA多态性分析

目的报告1对异卵孪生姊妹,分别为21三体综合症患者和表型核型正常的个体,并讨论患者额外21号染色体的来源.方法对孪生姊妹进行外周血淋巴细胞染色体核型分析和15个DNA微卫星位点多态性分析.结果孪生姐姐核型为47,XX, 21,孪生妹妹核型为46,XX.孪生姊妹15个STR位点与其父母比较,5个位点上显示有来自母亲的不同标志物,6个位点上显示有来自父亲的不同标志物.21三体综合征患者在D21S11位点上显示有3个不同的标志物,其中2个源自母亲.结论孪生姐妹为异卵孪生,孪生姐姐额外的21号染色体来自于母亲第1次减数分裂不分离.     

Microarray detection of a de novo der(X)t(X;11)(q28;p13) in a girl with premature ovarian failure and features of Beckwith–Wiedemann syndrome

We report an 18-year-old girl with premature ovarian failure (POF), tall stature, and urinary incontinence. Chromosome studies including array comparative genomic hybridization showed that she was the carrier of an unbalanced de novo translocation between the X chromosome and chromosome 11, resulting in partial monosomy Xq and partial trisomy 11p. Microsatellite analysis demonstrated that the patient had paternal duplication of 11p13p15.5, which contributed to some of her features consistent with Beckwith-Wiedemann syndrome (BWS). The combined phenotype of BWS and POF suggests that the translocated portion of 11p remains active.     

Analysis of a familial three way translocation involving chromosomes 3q, 6q, and 15q by high resolution banding and fluorescent in situ hybridisation (FISH) shows two different unbalanced karyotypes in sibs.

We report on a familial three way translocation involving chromosomes 3, 6, and 15 identified by prometaphase banding and fluorescence in situ hybridisation (FISH). Two mentally retarded sibs with different phenotypic abnormalities, their phenotypically normal sister and mother, and two fetuses of the phenotypically normal sister were analysed. The terminal regions of chromosomes 3q, 6q, and 15q were involved in a reciprocal translocation, in addition to a paracentric inversion of the derivative chromosome 15. Conventional cytogenetic studies with high resolution GTG banding did not resolve this rearrangement. FISH using whole chromosome paints (WCPs) identified the chromosomal regions involved, except the aberrant region of 3q, which was undetectable with these probes. Investigation of this region with the subtelomeric FISH probe D3S1445/D3S1446 showed a balanced karyotype, 46,XX,t(3;15;6) (q29;q26.1;q26), inv der(15) (q15.1q26.1) in two adult females and one fetus. It was unbalanced in two sibs, showing two different types of unbalanced translocation resulting in partial trisomy 3q in combination with partial monosomy 6q in one patient and partial trisomy 15q with partial monosomy 6q in the other patient and one fetus. These represent apparently new chromosomal phenotypes.     

Tertiary trisomy due to a reciprocal translocation of chromosomes 5 and 21 in a four‐generation family

Tertiary trisomy, or double trisomy, is a rare occurrence. We present two individuals with a previously unreported tertiary trisomy for chromosomes 5p and 21q in an eight‐generation pedigree. Their phenotypes are compared with other partial trisomies of either 5p or 21q from the literature. The propositus was diagnosed with trisomy 21 at 2 years of age after a karyotype study for short stature and developmental delay. His phenotype was described as atypical for Down syndrome. He presented at 9 years of age because of pervasive behavioral problems and obesity. He was brachycephalic with a flattened nasal bridge, but he lacked other characteristics of trisomy 21. Because of lack of phenotypic evidence of Down syndrome, a repeat karyotype was obtained and showed 47,XY,+der(21)t(5;21)(p15.1; q22.1), incorporating partial trisomies of both chromosomes 5 and 21. Mother had a balanced translocation, 46,XX,t(5;21)(p15.1; q22.1); 8 other relatives were examined. The translocation originated from the maternal great‐grandmother, but only the propositus and his mentally retarded aunt had a similar phenotye and the derivative chromosome. Fluorescence in situ hybridization showed absence of band 21q22.2 in the derivative chromosome of the propositus and his aunt, indicating that neither had trisomy for the Down syndrome critical region. These cases represent a unique double partial trisomy of chromosome arms 5p and 21q that occurred because of 3:1 malsegregation of a reciprocal translocation. These cases further demonstrate that phenotypic discordance with cytogenetic results dictate further investigation using advanced cytogenetic hybridization. Am. J. Med. Genet. 92:311–317, 2000. © 2000 Wiley‐Liss, Inc.     

Familial robertsonian translocation 15;21 and rare paracentric inv(21): unexpected re-inversion in a child with translocation trisomy 21

We present a family with a Robertsonian translocation (RT) 15;21 and an inv(21)(q21.1q22.1) which was ascertained after the birth of a child with Down syndrome. Karyotyping revealed a translocation trisomy 21 in the patient. The mother was a carrier of a paternally inherited RT 15;21. Additionally, she and her mother showed a rare paracentric inversion of chromosome 21 which could not be observed in the Down syndrome patient. Thus, we concluded that the two free chromosomes 21 in the patient were of paternal origin. Remarkably, short tandem repeat (STR) typing revealed that the proband showed one paternal allele but two maternal alleles, indicating a maternal origin of the supernumerary chromosome 21. Due to the fact that chromosome analysis showed structurally normal chromosomes 21, a re-inversion of the free maternally inherited chromosome 21 must have occurred. Re-inversion and meiotic segregation error may have been co-incidental but unrelated events. Alternatively, the inversion or RT could have predisposed to maternal non-disjunction.     

Familial transmission of a deletion of chromosome 21 derived from a translocation between chromosome 21 and an inverted chromosome 22

Chromosome analysis of a newborn boy with Down syndrome resulted in the identification of a family with an unusual derivative chromosome 22. The child has 46 chromosomes, including two chromosomes 21, one normal chromosome 22, and a derivative chromosome 22. Giemsa banding and fluorescent in situ hybridization (FISH) studies show that the derivative chromosome is chromosome 22 with evidence of both paracentric and pericentric inversions, joined to the long arm of chromosome 21 from 21q21.2 to qter. The rearrangement results in partial trisomy 21 extending from 21q21.2 to 21q terminus in the patient. The child's mother, brother, maternal aunt, and maternal grandmother are all carriers of the derivative chromosome. All have 45 chromosomes, with one normal chromosome 21, one normal chromosome 22, and the derivative chromosome 22. The rearrangement results in the absence of the short arm, the centromere, and the proximal long arm of chromosome 21 (del 21pter21q21.2) in carriers. Carriers of the derivative chromosome in this family have normal physical appearance, mild learning disabilities and poor social adjustment. Am. J. Med. Genet. 70:399–403, 1997. © 1997 Wiley-Liss, Inc.     

Identification of the origin of centromeres in whole-arm translocations using fluorescent in situ hybridization with alpha-satellite DNA probes

We detected 2 patients with whole-arm translocations resulting in a derivative chromosome consisting of 18q and 21q. Because the breakpoints were near the centromere, classical cytogenetic techniques could not determine the centromeric origin of the derivative chromosomes. Using nonradioactive in situ hybridization with a chromosome 18 alpha-satellite DNA probe (D18Z1), the centromeres in the abnormal chromosomes were determined to be from chromosome 18. The abnormality in one patient resulted in monosomy 18p with a karyotype 45,XX, -18, -21, + der(18)t(18;21) (p11;q11)mat complement. The second patient with a 46,XX, -21, + der(18)t(18;21)(p11;q11) de novo karyotype had complete trisomy of 18q. In both cases the appropriate phenotype was observed.     

Tetrasomy 21 pter→q22.1 and Down syndrome: Molecular definition of the region

Down syndrome is usually caused by complete trisomy 21. Rarely, it is due to partial trisomy of the segment 21q22. We report on a 33-month-old girl with tetrasomy 21 pter → q22.1 resulting from an extra chromosome idic(21)(q22.1). She has craniofacial traits typical of Down syndrome, including brachycephaly, third fontanel, upward slanting palpebral fissures, round face, and protruding tongue. Speech development is quite delayed whereas motor development is only mildly retarded. The molecular content of the extra isodicentric chromosome was defined by molecular genetic investigations using 13 single copy probes unique to chromosome 21, and SOD1 expression studies. The child was found to have 4 copies of the region defined by D21S16 (21cen) through D21S93 on 21q22.1 and two copies of the remaining region defined by SOD1 → D21S55 → D21S123. In view of the recent assignment of Down syndrome facial characters to the 21q22 region, defined in part by D21S55, it is significant that this child shows a subset of Down syndrome facial manifestations, without duplication of this region. These results suggest that genes contributing to the facial and some of the hand manifestations of Down syndrome also exist in the chromosomal region proximal to D21S55 in band 21q22.1. © 1994 Wiley-Liss, Inc.     

Partial duplication of 13q31.3-q34 and deletion of 13q34 associated with diaphragmatic hernia as a sole malformation in a fetus

Partial duplications and deletions of chromosome 13 are rare and the phenotypic expressions of both aneuploidies are highly variable. Here we report on a fetus diagnosed prenatally with partial trisomy of 13q and a diaphragmatic hernia as a sole malformation. The parents had decided to terminate the pregnancy after the finding of diaphragmatic hernia by ultrasound scan, which was also confirmed by autopsy of the fetus. Subsequently chromosome analysis, fluorescence in situ hybridization (FISH), and array comparative genomic hybridization (array CGH) was carried out on fetal tissue. The chromosome analysis revealed additional material on chromosome 13, which was shown to be from the same chromosome, by FISH analysis. Array CGH demonstrated a partial duplication and a small deletion at the distal long arm of chromosome 13. The parents had normal karyotypes. This is the first case of a de novo pure partial duplication of 13q31.3-q34 and distal deletion of 13q34 with a phenotype apparently only involving a diaphragmatic hernia and three lung lobes on both sides. Microarray analysis was useful in refining the chromosomal imbalance and suggesting a candidate region for diaphragmatic hernia. ? 2012 Wiley Periodicals, Inc.     

Mosaic Down syndrome in a patient with low-level mosaicism detected by microarray

Down syndrome (DS) is the most common aneuploidy in liveborns with an estimated frequency of 1 in 650-1,000 births. Approximately 1-2% of all live-born DS individuals have mosaicism. The correlation between the percentage of mosaicism and the severity of the phenotype in mosaic trisomy 21 has been determined in previous studies. Patients with low percent of trisomy 21 have less phenotypic manifestations, higher IQs, and better overall survival. We report on a 1-day-old baby girl with subtle features of DS and low-level trisomy 21 mosaicism (8-13% in lymphocytes, 31% in buccal cells) with normal high resolution chromosome analysis. The aneuploidy was detected by 6.0 SNP microarray and confirmed by fluorescent in situ hybridization (FISH). Further studies to detect mosaicism are recommended from blood (using interphase FISH) or other tissues in the evaluation of a child with features of DS and a normal blood metaphase karyotype. SNP microarray technology appears to be a useful adjunct, being able to detect low-level mosaicism in these cases.     

Chromosome painting using FISH (fluorescence in situ hybridization) with chromosome-6-specific library demonstrates the origin of a de novo 6q+ marker chromosome

Brøndum-Nielsen K, Bajalica S, Wulff K, Mikkelsen M. Chromosome painting using FISH (fluorescence in situ hybridization) with chromosome-6-specific library demonstrates the origin of a de novo 6q+ marker chromosome.
Clin Genet 1993: 43: 235–239. © Munksgaard, 1993
We report the application of chromosome painting using FISH (fluorescence in situ hybridization) to demonstrate the origin of a de novo 6q + marker chromosome. A girl with a mental retardation/multiple malformation syndrome was shown to have the karyotype 46,XX, 6q+. Banding analysis could not determine the origin of the extra chromosomal material. Using FISH with a chromosome-6-specific library we showed that the marker chromosome was completely painted, indicating an origin from chromosome 6. The child's phenotype was compared with previously reported cases with partial chromosome 6 trisomy. A clinically recognized syndrome emerged, although she apparently also demonstrated novel features.     

Meiotic origin of two ring chromosomes 18 in a girl with developmental delay

We report on the cytogenetic, fluorescence in situ hybridization (FISH), and molecular results obtained for a patient with a mild and nonspecific pattern of minor anomalies and developmental delay. In the proband's karyotype one chromosome 18 was replaced by a ring chromosome 18 in all metaphases, with deletion of the terminal regions. Furthermore, 56% of the metaphases contained a supernumerary small ring chromosome. Microdissection followed by FISH analysis demonstrated that the small ring chromosome consisted of material from the pericentromeric region of chromosome 18. The karyotype was defined as 46,XX,r(18)(p11.3q23)[88]/47,XX,r(18)(p11.3q23)+r(18)(p11.22q12.2)[112]. Thus, the patient has a deletion at 18pter and at 18qter, and a mosaic partial trisomy of the pericentromeric region of chromosome 18. We undertook molecular analysis using DNA samples of the patient and her parents in order to clarify the origin and possible mode of formation of the chromosome abnormalities. Our results show a paternal origin of the structurally normal chromosome 18 and a maternal origin for both ring chromosomes 18. Interestingly, the smaller ring chromosome did not arise postzygotically from the larger ring, since the two ring chromosomes contain genetic material derived from the two different maternal chromosomes 18. The abnormalities appear to have arisen during a meiotic division, and it could be speculated that both ring chromosomes 18 arose simultaneously due to complex pairing and recombination events. After fertilization, the small ring chromosome was lost in a subset of cells, thus leading to mosaicism.     

A novel maternally-derived insertional translocation resulting in partial trisomy 4q13.2-q22.1 with complex translocation t(8;20) in a family with intellectual disability

We characterized the chromosomal aberration in family with intellectual disability, including two affected children and their affected mother. Initial standard karyotypes of the three individuals showed an apparently balanced translocation of chromosomes 8 and 20. Using molecular cytogenetic techniques, we observed complex structural chromosomal aberration comprising of reciprocal translocation between chromosomes 8 and 20 with pericentric inversion (8p11.12q22.3) and insertion of chromosome 4 segments into both der(8) and der(20). In particular, the insertion of chromosome 4 was complex. Two segments (4q13.2-q13.3 and 4q21.21-q22.1) were inserted into the der(8)t(8;20) breakpoint and one segment (4q13.3-q21.21) into the der(20)t(8;20) breakpoint. Both children inherited two normal chromosomes 4 from their parents and the der(8) and der(20) from the mother, resulting in partial trisomy of 4q13.2-q22.1. Interestingly, the mother, in addition to the same complex insertions and inversion, was founded to have a deletion of 4q13.2-q22.1 in one of her chromosomes 4, yielding no genetic imbalance but with potential disruption of intellectual dysfunction-related gene(s) at the breakpoints as the cause of her intellectual impairment. This family is the third case report of an insertional translocation mechanism causing partial trisomy 4q syndrome. Our study demonstrates that an insertion of an extra chromosomal segment, not primarily involving in translocation breakpoints, which results in partial trisomy, can be an unapparent cause of the abnormal phenotypes.