Frequency of Chromosome Disorders In Patients with Sperm Number Anomaly
PDF
Cite
Share
Request
Original Investigation
VOLUME: 36 ISSUE: 1
P: 74 - 79
January 2025

Frequency of Chromosome Disorders In Patients with Sperm Number Anomaly

Gazi Med J 2025;36(1):74-79
1. Department of Medical Genetics Başkent University Faculty of Medicine, Ankara, Türkiye
No information available.
No information available
Received Date: 20.03.2024
Accepted Date: 15.05.2024
Online Date: 09.01.2025
Publish Date: 09.01.2025
PDF
Cite
Share
Request

ABSTRACT

Objective

Chromosome abnormalities play an important role in male infertility. The rate of chromosome disorders in infertile men is higher as 5.8% when compared to the normal population (0.5%).

Methods

This study aimed to determine the frequency of cytogenetic abnormalities in infertile men with abnormal sperm counts and to show that rare chromosomal rearrangements can be detected by karyotyping.

Results

In our clinical practice, we detected nearly all chromosome numerical and structural anomalies involved in infertility. It includes inversions, translocations, deletions, insertions, complex rearrangements, isochromosomes, Klinefelter syndrome, mosaicism, and 47, XYY.    

Conclusion

Our results emphasize the importance of conventional cytogenetic analysis for infertile males. The detection of rare or known chromosome abnormalities will prevent unnecessary investigations and enable us the application of precision in medicine.

Keywords:
Abnormal sperm counts, chromosome abnormalities, genetic counselling

INTRODUCTION

Infertility is increasing in various global communities and is defined as the inability to achieve pregnancy after continuous, unprotected sexual intercourse for at least a year or more. Around 15% of couples are affected by this condition. 40-50% due to male factors (1, 2). Mechanical issues, unexplained cases, and identifiable genetic defects are the predominant factors contributing to male infertility. Genetic defects include four groups: (1) Y chromosome deletions, (2) single gene disorders, (3) multifactorial causes, and (4) structural and numerical chromosome abnormalities (3). Male infertility generally lies in abnormal semen analysis. Abnormal semen analysis does not always indicate infertility; it only lowers the probability of pregnancy. Patients with nonobstructive abnormal sperm counts have an increased risk of chromosomal abnormalities. Infertile men exhibit a higher chromosome anomaly rate (5.8%) in contrast to the lower rate observed in the general population (0.5%) (4). This means a fold increase. Chromosomal anomalies are documented at rates of 10.00-23.62% in cases of nonobstructive azoospermia and 1.10-13.33% in cases of severe oligozoospermia (5). Complex chromosomal rearrangements (CCR) refer to structural abnormalities that entail a minimum of three chromosomes, each with three or more breakpoints (6). CCRs are rare occurrences and can manifest as balanced, unbalanced, familial, or spontaneous occurrence. The majority of individuals carrying CCR are female, with a minority being male (7). The identification of most male carriers with CCRs has been through infertility assessment, whereas a minority has been identified through abnormalities in children or recurrent abortions (8, 9, 10). The risk of conceiving offspring with diverse anomalies and experiencing reproductive failure is heightened among CCR carriers because of segregation of the derivative chromosome or meiotic failure (11, 12, 13). Female CCR carriers are typically identified following the occurrence of babies with congenital abnormalities or experiencing recurrent abortions. Nevertheless, male CCR carriers do not always exhibit infertility or subfertility; in several cases, infertility issues arise as a result of hypospermatogenesis or spermatogenic failure. Several documented cases highlight the occurrence of CCRs in males diagnosed with oligozoospermia or azoospermia (14). In this study, we aimed to determine the types and frequency of chromosome abnormalities in patients with abnormal sperm counts.

MATERIALS AND METHODS

Karyotype results of patients with abnormal sperm counts who applied to the cytogenetic laboratory of Başkent University Genetic Diseases Diagnosis Center between January 2007 and December 2019 were retrospectively evaluated. Numerical and structural chromosomal anomaly distribution was determined according to sperm counts. 968 males were divided according to the sperm count of semen analysis into azoospermia (group 1), oligozoospermia (group 2), and oligoastenozoospermia (group 3). This study was approved by Başkent University Institutional Review Board (approval number: KA 24/108, date: 06.03.2024) and supported by Başkent University Research Fund.

Statistical Analysis

Standard cytogenetic investigations were conducted using established methods for phytohemagglutinin-stimulated cultures of peripheral blood lymphocytes. Chromosome spreads underwent processing for the analysis of GTG bands. Chromosomes were subjected to GTG banding following the standard karyotyping protocol, with an examination of 30 metaphases and interpretation carried out at resolution levels of 450 and 650 bands. Fluorescence in situ hybridization (FISH) was conducted on metaphases from transformed lymphoblast cell lines using human probes, following standard protocols and manufacturer's manuals (15).

RESULTS

All detected anomalies in our cases fall into the first group. The number of patients with sex chromosome abnormalities was higher than that of patients with autosomal chromosome anomalies (17.56 and 0.72 %, respectively (Table 1). Although the numerical anomaly rate was 15.9%, the structural anomaly rate was lower (2.37%) (Table 2). A total of 154 numerical anomalies were detected. Klinefelter syndrome (KS) was the most common finding 15.56% (151 patients), from which mosaic karyotypes were identified as 47, XXY/ 46, XY in 12 patients. There is also another mosaic patient with 47, XXY/ 48, XXXY karyotype. 47, XYY karyotype was detected in one patient. A total of 21 structural anomalies were detected. We had 9 patients with 46, XX karyotype in whom was detected translocation between chromosome X p arm with chromosome Y p arm. The SRY gene is shown on the derivative X-chromosome's p arm by FISH. In total, 16 reciprocal translocations were performed. Deletions were detected in 2 patients. The other structural abnormalities included one complex abnormality, one insertion, and one isochromosome.

Complex Chromosomal Rearrangement

The proband (Figure 1, III-4) is a 38-year-old man with primer infertility. He has been married for 2 years and has no consanguinity with his wife. They have not tried assisted reproductive treatment (ART). He had a normal phenotype and hormone profile, azoospermia, and no sperm in TESE. He has no Y-chromosome microdeletion. Karyotype analysis (Figure 2a) is 46,XY,t(2;12) (p24:q21), ins(4;2) (q21;p13p24) and the result is confirmed by metephase FISH (Figure 2b). Proband has 2 brothers and 1 sister, all of whom have normal offspring. A family study for segregation analysis was offered, but it could not be done because the couple did not accept.

DISCUSSION

We retrospectively evaluated the karyotype results of 968 patients with abnormal sperm counts and detected chromosomal disorders only in patients with azoospermia. In our cohort of patients with azoospermia, the rate of chromosomal abnormalities was 18.28 %, which was close to that reported by Pylyp et al. (1) in Ukrainian patients (17%), Kleiman et al. (12) in Israel (16.6 %), and higher than previously reported by Kumtepe et al. (16) in Türkiye (12 %), Wang et al. (17) in China (8.5 %), Lakshmi Rao et al. (18) in India (7.9 %), and Gekas et al. (19) in France (6.9 %) (1, 12, 16, 17, 18, 19). Being the most prevalent X-chromosome abnormality, KS is the most prevalent X-chromosome abnormality and is the most frequent genetic factor contributing to male infertility. Individuals diagnosed with pure KS (47, XXY), mosaic, or variant KS often experience significant impairment in spermatogenesis, resulting in severe oligozoospermia or azoospermia. Among infertile men, the prevalence of KS is notably higher, escalating from approximately 3% in unselected cases to approximately 13% in patients diagnosed with azoospermia. Hence, KS is the most common genetic cause of azoospermia (20, 21). Males with KS commonly display phenotypic traits associated with hypergonadotropic hypogonadism and testosterone deficiency, only a subset (approximately 25% to 40%) of cases receive an accurate diagnosis (22, 23). Lakshmi Rao et al. (18) and Kleiman et al. (12) reported the rates of KS in their cohort as (4.41%) and (5.5%) respectively (12, 17). We identified 139 (14.36 %) pure KSs and 12 (1.2 %) mosaic types. This was not close to the rate reported by Pylyp et al. (1) among Ukrainian patients (64%) and (18%) respectively. Although oligozoospermia and normozoospermia patients were evaluated in the study mentioned above, all of our patients had only azoospermia. This may explain why the detected patient rates were different from ours. In the majority of cases, men with the 47, XYY karyotype are fertile, but they are observed more frequently within infertile populations, accounting for nearly 0.1%. In our study, we have one 47, XYY infertile man, which means 0.1%. Rearrangements among acrocentric chromosomes, including chromosomes 13, 14, 15, 21, and 22, result in Robertsonian translocations. This results in the loss of genetic material, resulting in a chromosomal complement of 45 chromosomes. This condition is observed in approximately 0.9% of men diagnosed with severe male factor infertility (24). Although it affects sperm production, we did not detect this in our patient group. The reciprocal translocation mechanism involves the exchange of genetic material between two or more chromosomes. The prevalence of balanced chromosomal translocations is tenfold higher in infertile men, constituting a notable factor in male infertility (25). In this study, we have 16 reciprocal translocations in total. The most common (9 cases) was 46, X, t(X; Y), (p22;q11). 46 XX DSD (differences in sex development) were observed in phenotypically normal males. Various etiological theories have been proposed. SRY-positive individuals are expected to undergo crossover events between the pseudoautosomal regions of sex chromosomes during paternal meiosis (26). The existence of the SRY gene was demonstrated using FISH in all patients who were identified as XX males. Our findings support this theory. The isochromosome of Yp, i(Yp), is the least frequently observed structural rearrangement involving the Y chromosome (27). Individuals exhibiting delayed puberty, along with symptoms like gynecomastia, reduced growth rate, and infertility, and requiring testosterone treatment to induce the development of secondary sex characteristics may present with the potential effects associated with 45,X/46,X,i(Yp). We have one isochromosome 46,X,i(Yp) from 968 infertile males (0.1%). Complex chromosomal abnormalities (CCRs) are rare occurrences in the population, with approximately 255 documented cases to date (6). CCRs typically arise from either two concurrent classical translocations or jumping translocations, where a donor chromosomal segment is translocated to multiple recipient chromosome sites (28, 29, 30). In general, males with CCR exhibit issues related to infertility stemming from either hypospermatogenesis or spermatogenic failure (31). In this cohort, type 2 CCR was detected, and the rate of complex anomaly was 0.1%. In phenotypically normal individuals, a balanced CCR is typically observed. Such cases often have a familial component, which is primarily transmitted through female carriers. These cases are often referred for advanced maternal age, recurrent spontaneous abortion, or the birth of a malformed child (32-36). Transmission through males is a rare event (37, 38). A significant portion of CCR, approximately 70-75%, arises as de novo chromosomal rearrangements, predominantly of paternal origin (32). These are equally distributed among individuals with a normal phenotype (49%), and those displaying phenotypic abnormalities (51%). This distribution can be attributed to submicroscopic imbalances or other genetic defects (39-41). De novo balanced CCRs are often identified due to issues related to infertility, although a limited number of cases involving fertile carriers have also been documented (24, 42-45). Using multicolor FISH technologies of sperm sorting studies, accurate procedures for on-site analysis of CCRs have been established to facilitate the offer of preimplantation genetic diagnosis (PGD) to couples easily. There are six cases of PGD in CCR carriers in whom spontaneous abortion did not occur (46, 47). The detection of chromosomal disorders is important for predicting and preventing the risk of new pregnancies because they lead to unbalanced gametes. With karyotyping, in men with sperm number and structure anomalies, in addition to explaining the cause of their condition, future infertility treatment and options for having a healthy baby can also be determined. If any chromosomal abnormality is detected, PGD ought to be proposed to the patients as a solution to prevent such genotypic defects, which are the cause of different phenotypic abnormalities with undesired effects on health and the quality of life afterward in offspring (48). Pregnancy rates after transfer of an euploid/balanced embryo are 60%-70%, which is equivalent to the rate for euploid embryos in normal patients (49, 50).

CONCLUSION

In conclusion, by chromosomal aberrations infertility in men can be caused (32). Each detected chromosomal disorder has its own hereditary and phenotypic risks. Therefore, determining the chromosomal aberration and explaining the risks specific to the detected condition to the family through genetic counseling are important for them to decide on pregnancy options and inform other family members at risk. For example, in patients with Yq del, the risk of transmission to male children and the resulting infertility should be explained. The family should decide on ART treatments after knowing these risks. Thus, the cause of men's infertility requires detailed comprehensive genetic counseling, especially to prevent recurrence in off spring. While PGD offers promise, it comes with challenges and ethical considerations. The accuracy of diagnosis, potential mosaicism, and the emotional impact on parents are critical aspects to navigate. Striking a balance between the benefits and ethical concerns is imperative to ensure the responsible and equitable application of PGD in the context of chromosomal rearrangements. Our results emphasize the importance of conventional cytogenetic analysis in infertile males. The detection of rare or known chromosome abnormalities will prevent unnecessary investigations and enable us the application of precision in medicine.

Ethics

Ethics Committee Approval: This study was approved by Başkent University Institutional Review Board (approval number: KA 24/108, date: 06.03.2024).
Informed Consent: Retrospective study
Footnotes

Authorship Contributions

Concept: M.N., E.A., Z.Y.Ç., Design: Z.Y.Ç., Supervision: Z.Y.Ç., Resources: M.N., E.A., Z.Y.Ç., Material: M.N., E.A., Data Collection or Processing: M.N., E.A., Z.Y.Ç., Analysis or Interpretation: M.N., E.A., Z.Y.Ç., Literature Search: M.N., E.A., Z.Y.Ç., Writing: M.N., E.A., Z.Y.Ç., Critical Review: M.N., E.A., Z.Y.Ç.
Conflict of Interest:
Financial Disclosure: This study was approved by Baskent University Institutional Review Board (project no: KA 24/108) and supported by Baskent University Research Fund.

References

1
Pylyp LY, Spinenko LO, Verhoglyad NV, Zukin VD. Chromosomal abnormalities in patients with oligozoospermia and non-obstructive azoospermia. J Assist Reprod Genet. 2013; 30: 729-32.
2
Kumar N, Singh AK. Trends of male factor infertility, an important cause of infertility: A review of literature. J Hum Reprod Sci. 2015; 8: 191-6.
3
Demirhan O. Chromosome Abnormalities Related to Male Infertility. Clin Med. 2023; 5: 1052.
4
Shah K, Sivapalan G, Gibbons N, Tempest H, Griffin DK. The genetic basis of infertility. Reproduction. 2003; 126: 13-25.
5
Zhang ZB, Jiang YT, Yun X, Yang X, Wang RX, Dai RL, et al. Male infertility in Northeast China: a cytogenetic study of 135 patients with non-obstructive azoospermia and severe oligozoospermia. J Assist Reprod Genet. 2012; 29: 83-7.
6
Pellestor F, Anahory T, Lefort G, Puechberty J, Liehr T, Hédon B, et al. Complex chromosomal rearrangements: origin and meiotic behavior. Hum Reprod Update. 2011; 17: 476-94.
7
Yang Y, Hao W. Identification of a familial complex chromosomal rearrangement by optical genome mapping. Mol Cytogenet. 2022; 15: 41.
8
Chandley AC, Edmond P, Christie S, Gowans L, Fletcher J, Frackiewicz A, et al. Cytogenetics and infertility in man. I. Karyotype and seminal analysis: results of a five-year survey of men attending a subfertility clinic. Ann Hum Genet. 1975; 39: 231-54.
9
Joseph A, Thomas IM. A complex rearrangement involving three autosomes in a phenotypically normal male presenting with sterility. J Med Genet. 1982; 19: 375-7.
10
Siffroi JP, Benzacken B, Straub B, Le Bourhis C, North MO, Curotti G, et al. Assisted reproductive technology and complex chromosomal rearrangements: the limits of ICSI. Mol Hum Reprod. 1997; 3: 847-51.
11
Priya PK, Mishra VV, Liehr T, Ziegler M, Tiwari S, Patel A, et al. Characterization of a complex chromosomal rearrangement involving chromosomes 1, 3, and 4 in a slightly affected male with bad obstetrics history. J Assist Reprod Genet. 2018; 35: 721-5.
12
Pai GS, Thomas GH, Mahoney W, Migeon BR. Complex chromosome rearrangements. Report of a new case and literature review. Clin Genet. 1980; 18: 436-44.
13
Kim JW, Chang EM, Song SH, Park SH, Yoon TK, Shim SH. Complex chromosomal rearrangements in infertile males: complexity of rearrangement affects spermatogenesis. Fertil Steril. 2011; 95: 349-52.
14
Cai T, Yu P, Tagle DA, Lu D, Chen Y, Xia J. A de novo complex chromosomal rearrangement with a translocation 7:9 and 8q insertion in a male carrier with no infertility. Hum Reprod. 2001; 16: 59-62.
15
Liehr T, Kreskowski K, Ziegler M, Piaszinski K, Rittscher K. The standard FISH procedure. Fluorescence In Situ Hybridization (FISH) Application Guide. 2017:109-18. doi:10.1007/978-3-662-52959-1_9. Avaliable from: https://link.springer.com/protocol/10.1007/978-3-662-52959-1_9#citeas
16
Kumtepe Y, Beyazyurek C, Cinar C, Ozbey I, Ozkan S, Cetinkaya K, et al. A genetic survey of 1935 Turkish men with severe male factor infertility. Reprod Biomed Online. 2009; 18: 465-74.
17
Wang RX, Fu C, Yang YP, Han RR, Dong Y, Dai RL, et al. Male infertility in China: laboratory finding for AZF microdeletions and chromosomal abnormalities in infertile men from Northeastern China. J Assist Reprod Genet. 2010; 27: 391-6.
18
K Lakshmi Rao, K Arvind Babu, MK Kanakavalli, VV Padmalatha, Mamata Deenadayal, Lalji Singh. Prevalence of chromosome defects in azoospermic and oligoastheno-teratozoospermic South Indian infertile men attending an infertility clinic. Reprod Biomed Online. 2005; 10: 467-72.
19
Gekas J, Thépot F, Turleau C, Siffroi JP, Dadoune JP, Briault S, et al. Chromosomal factors of infertility in candidate couples for ICSI: an equal risk of constitutional aberrations in women and men. Hum Reprod. 2001; 16: 82-90.
20
Van Assche E, Bonduelle M, Tournaye H, Joris H, Verheyen G, Devroey P, et al. Cytogenetics of infertile men. Hum Reprod. 1996; 11: 1-24
21
Vincent MC, Daudin M, De Mas P, Massat G, Mieusset R, Pontonnier F, et al. Cytogenetic investigations of infertile men with low sperm counts: a 25-year experience. J Androl. 2002; 23: 18-22
22
Groth KA, Skakkebæk A, Høst C, Gravholt CH, Bojesen A. Clinical review: Klinefelter syndrome--a clinical update. J Clin Endocrinol Metab. 2013; 98: 20-30.
23
Bojesen A, Juul S, Gravholt CH. Prenatal and postnatal prevalence of Klinefelter syndrome: a national registry study. J Clin Endocrinol Metab. 2003; 88: 622-6.
24
Poot M, Hochstenbach R. Prevalence and Phenotypic Impact of Robertsonian Translocations. Mol Syndromol. 2021; 12: 1-11.
25
Van Assche E, Bonduelle M, Tournaye H, Joris H, Verheyen G, Devroey P, et al. Cytogenetics of infertile men. Hum Reprod. 1996; 11: 1-24.
26
Dauwerse JG, Hansson KB, Brouwers AA, Peters DJ, Breuning MH. An XX male with the sex-determining region Y gene inserted in the long arm of chromosome 16. Fertil Steril. 2006; 86: 463.
27
Rossella Gaudino, Evelina Maines, Fabiana Guizzardi, Valeria Vezzoli, Csilla Krausz, Paolo Cavarzere, et al. 45, X/46, X, i(Yp): Importance of Assessment and Support during Puberty and Adolescence. Sex Dev. 2019; 13: 118-24.
28
Gribble SM, Prigmore E, Burford DC, Porter KM, Ng BL, Douglas EJ, et al. The complex nature of constitutional de novo apparently balanced translocations in patients presenting with abnormal phenotypes. J Med Genet. 2005; 42: 8-16.
29
Seller MJ, Bint S, Kavalier F, Brown RN, Ogilvie CM. Multicolor banding detects a complex three chromosome, seven breakpoint unbalanced rearrangement in an ICSI-derived fetus with multiple abnormalities. Am J Med Genet A. 2006; 140: 1102-7.
30
Reddy KS. The conundrum of a jumping translocation (JT) in CVS from twins and review of JTs. Am J Med Genet A. 2010; 152: 2924-36.
31
Bartels I, Starke H, Argyriou L, Sauter SM, Zoll B, Liehr T. An exceptional complex chromosomal rearrangement (CCR) with eight breakpoints involving four chromosomes (1;3;9;14) in an azoospermic male with normal phenotype. Eur J Med Genet. 2007; 50: 133-8.
32
Batista DA, Pai GS, Stetten G. Molecular analysis of a complex chromosomal rearrangement and a review of familial cases. Am J Med Genet. 1994; 53: 255-63.
33
Timár L, Béres J, Kosztolányi G, Németh I. De novo complex chromosomal rearrangement in a woman with recurrent spontaneous abortion and one healthy daughter. Hum Genet. 1991; 86: 421.
34
Kotzot D, Holland H, Köhler M, Froster UG. A complex chromosome rearrangement involving chromosome 8, 11, and 12 analyzed by conventional cytogenetic investigations, fluorescence in situ hybridisation, and spectral karyotyping. Ann Genet. 2001; 44: 135-8.
35
Gardner RJM, Sutherland GR., Chromosome Abnormalities and Genetic Counselling, 20043rd New York: Oxford University Press Inc, New York. Available from: https://books.google.com.tr/books?id=4R38MQJh-UAC&lpg=PP1&hl=tr&pg=PP1#v=onepage&q&f=false
36
Karmous-Benailly H, Giuliano F, Massol C, Bloch C, De Ricaud D, Lambert JC, et al. Unbalanced inherited complex chromosome rearrangement involving chromosome 8, 10, 11 and 16 in a patient with congenital malformations and delayed development. Eur J Med Genet. 2006; 49: 431-8.
37
Röthlisberger B, Kotzot D, Brecevic L, Koehler M, Balmer D, Binkert F, et al. Recombinant balanced and unbalanced translocations as a consequence of a balanced complex chromosomal rearrangement involving eight breakpoints in four chromosomes. Eur J Hum Genet. 1999; 7: 873-83.
38
Gruchy N, Barreau M, Kessler K, Gourdier D, Leporrier N. A paternally transmitted complex chromosomal rearrangement (CCR) involving chromosomes 2, 6, and 18 includes eight breakpoints and five insertional translocations (ITs) through three generations. Am J Med Genet A. 2010; 152: 185-90.
39
Madan K, Nieuwint AW, van Bever Y. Recombination in a balanced complex translocation of a mother leading to a balanced reciprocal translocation in the child. Review of 60 cases of balanced complex translocations. Hum Genet. 1997; 99: 806-15.
40
Patsalis PC. Complex chromosomal rearrangements. Genet Couns. 2007; 18: 57-69
41
Kumar A, Becker LA, Depinet TW, Haren JM, Kurtz CL, Robin NH, et al. Molecular characterization and delineation of subtle deletions in de novo "balanced" chromosomal rearrangements. Hum Genet. 1998; 103: 173-8.
42
Sills ES, Kim JJ, Witt MA, Palermo GD. Non-obstructive azoospermia and maturation arrest with complex translocation 46,XY t(9;13;14)(p22;q21.2;p13) is consistent with the Luciani-Guo hypothesis of latent aberrant autosomal regions and infertility. Cell Chromosome. 2005; 4: 2.
43
Bartels I, Starke H, Argyriou L, Sauter SM, Zoll B, Liehr T. An exceptional complex chromosomal rearrangement (CCR) with eight breakpoints involving four chromosomes (1;3;9;14) in an azoospermic male with normal phenotype. Eur J Med Genet. 2007; 50: 133-8.
44
Karadeniz N, Mrasek K, Weise A. Further delineation of complex chromosomal rearrangements in fertile male using multicolor banding. Mol Cytogenet. 2008; 1: 17.
45
Walker S, Howard PJ, Hunter D. Familial complex autosomal translocations involving chromosomes 7, 8, and 9 exhibiting male and female transmission with segregation and recombination. J Med Genet. 1985; 22: 484-91.
46
Escudero T, Estop A, Fischer J, Munne S. Preimplantation genetic diagnosis for complex chromosome rearrangements. Am J Med Genet A. 2008; 146: 1662-9.
47
Lim CK, Cho JW, Kim JY, Kang IS, Shim SH, Jun JH. A healthy live birth after successful preimplantation genetic diagnosis for carriers of complex chromosome rearrangements. Fertil Steril. 2008; 90: 1680-4.
48
Tharapel AT, Tharapel SA, Bannerman RM. Recurrent pregnancy losses and parental chromosome abnormalities: a review. Br J Obstet Gynaecol. 1985; 92: 899-914.
49
Velilla E, Escudero T, Munné S. Blastomere fixation techniques and risk of misdiagnosis for preimplantation genetic diagnosis of aneuploidy. Reprod BioMed Online. 2002; 4: 210-7.
50
Wilton L, Thornhill A, Traeger-Synodinos J, Sermon KD, Harper JC. The causes of misdiagnosis and adverse outcomes in PGD. Hum Reprod. 2009; 24: 1221-8.