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Haapaniemi Kouru K, Malmgren H, White I, Rodriguez Sanchez A, Syk Lundberg E. Meiotic segregation analyses of reciprocal translocations in spermatozoa and embryos: no support for predictive value regarding PGD outcome. Reprod Biomed Online 2017; 34:645-652. [PMID: 28336162 DOI: 10.1016/j.rbmo.2017.02.013] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2016] [Revised: 02/24/2017] [Accepted: 02/28/2017] [Indexed: 11/28/2022]
Abstract
Translocation heterozygotes have an increased risk of producing gametes with unbalanced chromosome content. This often leads to reproductive problems such as infertility, repeated miscarriages or birth of an affected child. To increase the chances of having a healthy live-born child, translocation heterozygotes often opt for preimplantation genetic diagnosis (PGD). The aim of this study was to investigate whether there is a correlation between chromosome segregation in spermatozoa from translocation heterozygotes and the number of balanced embryos produced during PGD that may be used to predict the PGD outcome. Ten male reciprocal translocation heterozygotes that went through PGD at a Stockholm PGD centre were included. We analysed 1000 spermatozoa from each patient and between 3 and 29 embryos from the total of PGD cycles that the couples went through. Fluorescence in-situ hybridization (FISH) analysis of spermatozoa and embryos was performed with the same DNA probes. We found that the proportion of balanced spermatozoa was much higher than the proportion of balanced embryos during PGD. Our results indicate that a sperm FISH analysis prior to PGD is not a reliable predictor of the PGD outcome. PGD is a valuable reproductive alternative for translocation heterozygotes with reproductive problems and should be offered to these couples.
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Affiliation(s)
- Katarina Haapaniemi Kouru
- Department of Molecular Medicine and Surgery, Clinical Genetics Unit, Karolinska Institutet, Stockholm SE 17176, Sweden; Fertility Centre Stockholm, Storangsvagen 10, Stockholm SE 11541, Sweden.
| | - Helena Malmgren
- Department of Molecular Medicine and Surgery, Clinical Genetics Unit, Karolinska Institutet, Stockholm SE 17176, Sweden
| | - Irene White
- Department of Molecular Medicine and Surgery, Clinical Genetics Unit, Karolinska Institutet, Stockholm SE 17176, Sweden
| | - Ana Rodriguez Sanchez
- Department of Molecular Medicine and Surgery, Clinical Genetics Unit, Karolinska Institutet, Stockholm SE 17176, Sweden
| | - Elisabeth Syk Lundberg
- Department of Molecular Medicine and Surgery, Clinical Genetics Unit, Karolinska Institutet, Stockholm SE 17176, Sweden
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Olszewska M, Fraczek M, Huleyuk N, Czernikiewicz A, Wiland E, Boksa M, Zastavna D, Panasiuk B, Midro AT, Kurpisz M. Chromatin structure analysis of spermatozoa from reciprocal chromosome translocation (RCT) carriers with known meiotic segregation patterns. Reprod Biol 2013; 13:209-20. [DOI: 10.1016/j.repbio.2013.06.002] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2012] [Revised: 05/21/2013] [Accepted: 06/21/2013] [Indexed: 10/26/2022]
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Godo A, Blanco J, Vidal F, Anton E. Accumulation of numerical and structural chromosome imbalances in spermatozoa from reciprocal translocation carriers. Hum Reprod 2012; 28:840-9. [PMID: 23250926 DOI: 10.1093/humrep/des431] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
STUDY QUESTION Is there a relationship between the occurrence of specific segregation modes and the production of additional numerical abnormalities in spermatozoa from reciprocal translocation carriers? STUDY ANSWER The production of aneuploid and diploid spermatozoa tends to be associated with an unbalanced segregation outcome of the rearranged chromosomes. WHAT IS KNOWN ALREADY Carriers of reciprocal translocations have an increased genetic reproductive risk as a consequence of producing higher numbers of unbalanced spermatozoa. These imbalances can originate during the segregation of the rearranged chromosomes and also from the occurrence of interchromosomal effects (ICEs). Usually, the outcome of both events is studied independently by means of sperm fluorescent in situ hybridization (FISH). STUDY DESIGN, SIZE, DURATION We designed a sequential FISH protocol based on two successive hybridization rounds to study the segregation outcome of the rearranged chromosomes and the presence of additional numerical abnormalities in the same sperm nuclei. The study was performed between February 2010 and February 2012. MATERIALS, SETTING, METHODS Sperm samples from eight reciprocal translocation carriers were processed for FISH analysis. Numerical abnormalities for chromosomes X, Y, 13, 18 and 21 were evaluated in the first hybridization round. The aneuploid and diploid nuclei were relocated and analysed for the segregation outcome of the rearranged chromosomes in the second hybridization round. In every carrier, another population of non-selected spermatozoa was also analysed with the aim of defining the general segregation outcome of each reorganization event. MAIN RESULTS AND THE ROLE OF CHANCE Overall, the selected population of aneuploid and diploid spermatozoa showed significant increased frequencies of unbalanced segregation modes of the rearranged chromosomes (3:1, 4:0 and 'other') when compared with the non-selected population of spermatozoa. A P-value of <0.05 was chosen to determine if differences observed were statistically significant. LIMITATIONS, REASONS FOR CAUTION FISH only allows the analysis of a limited number of chromosomes. Information about the content of additional chromosomes would have been useful in order to broaden the number of aneuploid spermatozoa population, and to infer a more accurate possible mechanism for generating chromosomal imbalances. WIDER IMPLICATIONS OF THE FINDINGS There was no previous data about a relationship between chromosomal numerical abnormalities and segregation of rearranged chromosomes. Our findings are consistent with a possible gathering of chromosomal abnormalities in a given nucleus. This information can be used towards a better understanding of the meiotic mechanisms involved in non-disjunction events in gametes from reciprocal translocation carriers. Also, it would help to provide a better reproductive genetic risk assessment in these patients. STUDY FUNDING/COMPETING INTERESTS This work was supported by funding of projects SAF2010-2241 (Ministerio de Ciencia e Innovación, Spain), SGR2009-282 (Generalitat de Catalunya, Spain) and UAB CF-180034 (Universitat Autònoma de Barcelona, Spain). The authors declare the lack of competing interests in this study.
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Affiliation(s)
- A Godo
- Unitat de Biologia Cel·lular (Facultat de Biociències), Universitat Autònoma de Barcelona, Bellaterra 08193, Spain
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Cassuto NG, Le Foll N, Chantot-Bastaraud S, Balet R, Bouret D, Rouen A, Bhouri R, Hyon C, Siffroi JP. Sperm fluorescence in situ hybridization study in nine men carrying a Robertsonian or a reciprocal translocation: relationship between segregation modes and high-magnification sperm morphology examination. Fertil Steril 2011; 96:826-32. [DOI: 10.1016/j.fertnstert.2011.07.1143] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2011] [Revised: 07/11/2011] [Accepted: 07/26/2011] [Indexed: 11/30/2022]
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Hultén MA. On the origin of crossover interference: A chromosome oscillatory movement (COM) model. Mol Cytogenet 2011; 4:10. [PMID: 21477316 PMCID: PMC3103480 DOI: 10.1186/1755-8166-4-10] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2011] [Accepted: 04/08/2011] [Indexed: 12/28/2022] Open
Abstract
BACKGROUND It is now nearly a century since it was first discovered that crossovers between homologous parental chromosomes, originating at the Prophase stage of Meiosis I, are not randomly placed. In fact, the number and distribution of crossovers are strictly regulated with crossovers/chiasmata formed in optimal positions along the length of individual chromosomes, facilitating regular chromosome segregation at the first meiotic division. In spite of much research addressing this question, the underlying mechanism(s) for the phenomenon called crossover/chiasma interference is/are still unknown; and this constitutes an outstanding biological enigma. RESULTS The Chromosome Oscillatory Movement (COM) model for crossover/chiasma interference implies that, during Prophase of Meiosis I, oscillatory movements of the telomeres (attached to the nuclear membrane) and the kinetochores (within the centromeres) create waves along the length of chromosome pairs (bivalents) so that crossing-over and chiasma formation is facilitated by the proximity of parental homologs induced at the nodal regions of the waves thus created. This model adequately explains the salient features of crossover/chiasma interference, where (1) there is normally at least one crossover/chiasma per bivalent, (2) the number is correlated to bivalent length, (3) the positions are dependent on the number per bivalent, (4) interference distances are on average longer over the centromere than along chromosome arms, and (5) there are significant changes in carriers of structural chromosome rearrangements. CONCLUSIONS The crossover/chiasma frequency distribution in humans and mice with normal karyotypes as well as in carriers of structural chromosome rearrangements are those expected on the COM model. Further studies are underway to analyze mechanical/mathematical aspects of this model for the origin of crossover/chiasma interference, using string replicas of the homologous chromosomes at the Prophase stage of Meiosis I. The parameters to vary in this type of experiment will include: (1) the mitotic karyotype, i.e. ranked length and centromere index of the chromosomes involved, (2) the specific bivalent/multivalent length and flexibility, dependent on the way this structure is positioned within the nucleus and the size of the respective meiocyte nuclei, (3) the frequency characteristics of the oscillatory movements at respectively the telomeres and the kinetochores.
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Affiliation(s)
- Maj A Hultén
- Department of Molecular Medicine and Surgery and Center for Molecular Medicine, CMM L8:02, Karolinska Institutet, Karolinska University Hospital, Solna, S-17 1 76 Stockholm, Sweden.
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Benet J, Oliver-Bonet M, Cifuentes P, Templado C, Navarro J. Segregation of chromosomes in sperm of reciprocal translocation carriers: a review. Cytogenet Genome Res 2006; 111:281-90. [PMID: 16192706 DOI: 10.1159/000086901] [Citation(s) in RCA: 85] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2004] [Accepted: 01/12/2005] [Indexed: 11/19/2022] Open
Abstract
Reciprocal translocations, the most frequent structural aberration in humans, are mainly transmitted by one of the parents. In order to analyze the chromosomal content of the spermatozoa from carriers of chromosomal reorganizations, two methods have been used, karyotyping of sperm chromosomes by the human-hamster system and fluorescence in situ hybridization (FISH) in decondensed sperm nuclei. In this work, we review 92 sperm chromosome segregation studies from 85 different reciprocal translocation carriers, including a triple translocation carrier. Using the human-hamster method, a total of 5,818 spermatozoa from 44 reciprocal translocation carriers have been analyzed, 43 of them carrying a single reciprocal translocation and one was a carrier of a double reciprocal translocation. A segregation analysis in a carrier of a t(2;22;11) has been also reported. Carrying out FISH in sperm nuclei, a total of 237,042 spermatozoa from 46 reciprocal translocation carriers have been analyzed. Six of these were also analyzed by the human-hamster system. Taking into account both methods, a total of 76 different reciprocal translocations have been studied. In 74 of these 76 translocations, the reorganization occurs between autosomes, and in the other two, the Y chromosome is involved. Although along general lines, there are similarities between the results obtained by the two methods of analysis, variations are observed when the distribution of the different types of segregations that produce imbalances is compared. As a general rule reciprocal translocation carriers produce more unbalanced sperm than normal or balanced sperm. The results reported also corroborate that the proportion of unbalanced forms depends on the characteristics of the reorganization and that it varies widely. Thus the importance of performing a detailed meiotic behavior analysis for each particular translocation in order to obtain enough information to give adequate genetic counseling is stressed. Aspects as to the possible overestimation of 3:1 segregations or the presence of interchromosomal effects still need to be elucidated.
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Affiliation(s)
- J Benet
- Departament de Biologia Cellular, Fisiologia i Immunologia, Facultat Medicina, Universitat Autònoma de Barcelona, Bellaterra, Spain.
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Lorda-Sánchez I, Diego-Alvarez D, Ayuso C, de Alba MR, Trujillo MJ, Ramos C. Trisomy 2 due to a 3:1 segregation in an abortion studied by QF-PCR and CGH. Prenat Diagn 2005; 25:934-8. [PMID: 16088866 DOI: 10.1002/pd.1239] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Balanced reciprocal translocation is one of the known causes of recurrent spontaneous abortions. Cytogenetic studies of unbalanced miscarriages are difficult due to the growth failure of early loss and usually macerated abortions. We present a molecular study of an abortion in which the father carries a balanced reciprocal translocation t(2;17)(q32.1;q24.3) using QF-PCR and CGH techniques. DNA analysis showed the presence of a trisomy 2 due to a 3:1 interchange segregation. Recombinant events could also be investigated by comparing DNA samples from the family. We propose QF-PCR in addition to CGH as an efficient diagnostic method to improve our knowledge of unbalanced offspring in balanced translocation carriers.
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Oliver-Bonet M, Navarro J, Codina-Pascual M, Abad C, Guitart M, Egozcue J, Benet J. From spermatocytes to sperm: meiotic behaviour of human male reciprocal translocations. Hum Reprod 2004; 19:2515-22. [PMID: 15333594 DOI: 10.1093/humrep/deh492] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
BACKGROUND Human male translocation carriers may present alterations in the meiotic process due to the presence of the translocated chromosomes. The aim of this work was to study the mechanisms that affect meiotic segregation in translocation carriers by analysing different stages of the meiotic process. METHODS Meiotic studies using fluorescence in-situ hybridization on both spermatocytes and sperm nuclei were performed in two translocation carriers, t(11;17)(q13.1;p11.2) and t(10;14)(q24;q32). RESULTS A ring configuration was the main type of quadrivalent found in metaphase I. Overall chiasma frequency was significantly decreased in the t(11;17) carrier. In the t(10;14) carrier, chiasma frequency within the interstitial region of chromosomes 10 and 14 was increased and the recombination pattern was modified. As expected from the frequencies of interstitial chiasmata found in metaphase I in the two subjects, the incidence of asymmetric dyads was sporadic in t(11;17) and very high in t(10;14). In both carriers, segregation frequencies observed at metaphase II were not different from the segregation data obtained in decondensed sperm nuclei. CONCLUSIONS The concordance observed among results obtained in different spermatogenic stages indicates an absence of cellular selection based on chromosomal imbalances. Results obtained in the aneuploidy assay have not provided any evidence for an interchromosomal effect.
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Affiliation(s)
- M Oliver-Bonet
- Unitat de Biologia, Facultat de Medicina, Departament de Biologia Cel.lular, Fisiologia i d'Immunologia, Universitat Autònoma de Barcelona, Bellaterra and Consorci Hospitalari Parc Taulí, Sabadell, Spain.
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Morel F, Douet-Guilbert N, Le Bris MJ, Herry A, Amice V, Amice J, De Braekeleer M. Meiotic segregation of translocations during male gametogenesis. ACTA ACUST UNITED AC 2004; 27:200-12. [PMID: 15271199 DOI: 10.1111/j.1365-2605.2004.00490.x] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Balanced reciprocal and Robertsonian translocations are the most common structural chromosomal abnormalities in humans. Generally, they are without consequence for the carrier, but for various degrees of oligoasthenoteratozoospermia in men. As these carriers can produce a significant percentage of gametes with an unbalanced combination of the parental rearrangement, there is a more or less significant risk, according to cases, of chromosomal imbalances for their offspring. Therefore, techniques were developed to study the meiotic segregation of these translocations in males. Direct investigation of human sperm chromosomes became possible by karyotyping spermatozoa after penetration of zona-free hamster oocytes and, more recently, using fluorescent in situ hybridization (FISH). This paper reviews the results obtained using these techniques in Robertsonian and reciprocal translocations. The studies on spermatozoa from translocation carriers help the comprehension of the mechanisms of the meiotic segregation. They should be integrated in the genetic exploration of the infertile men, in order to give them a personalized risk assessment of unbalanced spermatozoa, specially as a correlation was found recently between the percentage of abnormal spermatozoa and that of abnormal embryos.
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Affiliation(s)
- Frédéric Morel
- Laboratoire d'Histologie, Embryologie et Cytogénétique, Faculté de Médecine et des Sciences de la Santé, Université de Bretagne Occidentale, CHU Morvan, Brest, France
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Rives N, Jarnot M, Mousset-Siméon N, Joly G, Macé B. Fluorescence in situ hybridisation (FISH) analysis of chromosome segregation and interchromosomal effect in spermatozoa of a reciprocal translocation t(9,10)(q11;p11.1) carrier. J Hum Genet 2003; 48:535-540. [PMID: 14523620 DOI: 10.1007/s10038-003-0072-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2003] [Accepted: 08/10/2003] [Indexed: 10/26/2022]
Abstract
A couple was referred for exploration of repetitive abortions. The man was found to be a carrier of a balanced reciprocal translocation t(9;10)(q11;p11.1). The meiotic segregation of chromosomes 9 and 10 was analysed in 5,157 spermatozoa from this translocation carrier and in 15,255 spermatozoa from three control donors using three-colour fluorescence in situ hybridisation (FISH). The theoretical viability of the different segregation patterns was performed using the computer system HC Forum developed by the Department of Cytogenetics at the Grenoble University Medical School, La Tronche, France. A normal or balanced constitution was found in 56.25% of the analysed spermatozoa. The tertiary 3:1 segregation mode was the most frequently observed (14.37%). The frequencies of adjacent-1, adjacent-2 and 3:1 interchange modes were 12.85, 9.38 and 7.14% respectively. The cumulative frequency of non-viable imbalance was estimated at 20.91% according to the theorical viability of the different segregation patterns. Spermatozoa aneuploidy frequency was also evaluated for chromosomes X, Y and 18, and there was no evidence of interchromosomal effect in spermatozoa from the translocation carrier. FISH analysis of spermatozoa in combination with the viability theorical estimation of the different segregation patterns could be considered a useful tool for genetic counselling in carriers of reciprocal translocation.
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Affiliation(s)
- Nathalie Rives
- Reproductive Biology Laboratory, Rouen University Hospital, 1 rue de Germont, 76031, Rouen cedex, France.
| | - Marion Jarnot
- Reproductive Biology Laboratory, Rouen University Hospital, 1 rue de Germont, 76031, Rouen cedex, France
| | - Nathalie Mousset-Siméon
- Reproductive Biology Laboratory, Rouen University Hospital, 1 rue de Germont, 76031, Rouen cedex, France
| | - Géraldine Joly
- Reproductive Biology Laboratory, Rouen University Hospital, 1 rue de Germont, 76031, Rouen cedex, France
| | - Bertrand Macé
- Reproductive Biology Laboratory, Rouen University Hospital, 1 rue de Germont, 76031, Rouen cedex, France
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Mackie Ogilvie C, Scriven PN. Meiotic outcomes in reciprocal translocation carriers ascertained in 3-day human embryos. Eur J Hum Genet 2002; 10:801-6. [PMID: 12461686 DOI: 10.1038/sj.ejhg.5200895] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2002] [Revised: 07/30/2002] [Accepted: 08/26/2002] [Indexed: 11/08/2022] Open
Abstract
Chromosomes involved in reciprocal translocations form quadrivalents at meiosis. These quadrivalents segregate, with or without recombination, to give 32 different meiotic outcomes, only two of which are normal or balanced. This paper presents data collected from 25 cycles of preimplantation genetic diagnosis for 18 couples carrying 15 different reciprocal translocations. Embryos were tested using fluorescence in situ hybridisation with probes for the translocated and centric segments. Overall, 47.7% (71 out of 149) of embryos tested showed signal patterns consistent with alternate segregation, 24.8% adjacent-1 segregation, 10.1% adjacent-2 segregation, 15.4% 3 : 1 segregation and 2% 4 : 0 segregation. For most translocations, alternate segregation was apparently the most frequent mode. Alternate and adjacent-1 frequencies were similar in male and female carriers; however, 5.7% of embryos from female translocation carriers showed adjacent-2 segregation and 20.0% showed 3 : 1 segregation, whilst the corresponding figures for male carriers were 20.5 and 4.5%. Overall, 2.8% of embryos were mosaic and 2.3% of embryos showed chaotic constitutions for the chromosomes tested. The pregnancy success rate for these 25 cycles was 38.8% per embryo transfer and also 38.8% per couple.
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Affiliation(s)
- Caroline Mackie Ogilvie
- Guy's and St Thomas' Centre for Preimplantation Genetic Diagnosis, Cytogenetics Department, Guy's, King's and St Thomas' School of Medicine, London and Guy's and St Thomas' Hospital NHS Trust, London, UK.
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Armstrong SJ, Goldman AS, Speed RM, Hultén MA. Meiotic studies of a human male carrier of the common translocation, t(11;22), suggests postzygotic selection rather than preferential 3:1 MI segregation as the cause of liveborn offspring with an unbalanced translocation. Am J Hum Genet 2000; 67:601-9. [PMID: 10936106 PMCID: PMC1287520 DOI: 10.1086/303052] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2000] [Accepted: 07/20/2000] [Indexed: 11/03/2022] Open
Abstract
The t(11;22)(q23;q11) translocation is the only non-Robertsonian rearrangement for which there are a large number of unrelated families, apparently with the same breakpoints. These families most often have been ascertained through an abnormal child with the karyotype 47,XX or XY, +der(22) t(11;22)(q23;q11). To explain the high incidence of 3:1 segregants, rarely seen in offspring of carriers of other reciprocal translocations, a number of theoretical models have been suggested. We have used both electron microscope analysis of the synaptonemal complex (SC) and dual-color FISH to investigate the meiotic chromosome behavior in a male carrier of the translocation who has the karyotype 46,XY, t(11;22)(q23;q11). Chromosome synapsis, first-meiotic chiasma configuration, and segregation behavior of this translocation have been analyzed directly. Examination of SCs by electron microscopy showed pachytene-cross formation in 49/50 nuclei. Approximately 50% (26/50) revealed a classical fully synapsed quadrivalent. A proportion of these (10/26), however, showed some central asymmetry, suggesting heterologous synapsis. The remaining cells appeared to have incomplete synapsis. FISH analysis showed only quadrivalents in all 100 metaphase I nuclei. The chiasma frequency was increased within the interstitial segments, in comparison with the same region in normal bivalents. All types of segregation category were found in metaphase II nuclei. There was no indication of preferential 3:1 anaphase I segregation. We conclude that the +der(22) constitution in offspring of carriers of t(11;22)(q23;q11) is not likely to be due to meiotic 3:1 segregation being especially common. Rather, the +der(22) constitution is more likely to be the result of postzygotic selection against other unbalanced karyotypes.
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Affiliation(s)
- S J Armstrong
- LFS Research Unit, Regional Genetic Services, Heartlands Hospital, and School of Biosciences, The University of Birmingham, Birmingham, United Kingdom.
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