REVIEW ARTICLE
Sperm aneuploidy in infertile male patients: a systematic review of the literature A. Chatziparasidou1,2, N. Christoforidis1,2, G. Samolada1 & M. Nijs1,2 1 Embryolab SA, IVF Unit, Kalamaria, Thessaloniki, Greece; 2 Embryolab Academy, Kalamaria, Thessaloniki, Greece
Keywords Chromosomal abnormalities—male infertility—sperm aneuploidy Correspondence Alexia Chatziparasidou, Embryolab Academy, Ethnikis Antistaseos. 173-175, Kalamaria, Thessaloniki, Greece. Tel.: +0030 2310 475 717 Fax: +0030 2310 475 718 E-mail: [email protected] Accepted: August 18, 2014 doi: 10.1111/and.12362
Summary Males with abnormal karyotypes and subgroups of fertile and infertile males with normal karyotypes may be at risk of producing unbalanced or aneuploid spermatozoa. Biological, clinical, environmental and other factors may also cause additional sperm aneuploidy. However, increased risk of sperm aneuploidy is directly related to chromosomally abnormal embryo production and hence to poor reproductive potential. This systemic literature review focuses on the identification of these males because this is an essential step in the context of assisted reproduction. This research may allow for a more personalised and, hence, more accurate estimation of the risk involved in each case, which in turn will aid genetic counselling for affected couples and help with informed decision-making.
Introduction Mature spermatozoa are the end products of a highly complex biological procedure known as spermatogenesis. During spermatogenesis, the diploid spermatocytes undergo two meiotic divisions before haploid spermatids are produced; spermatids will eventually transform into mature spermatozoa through a series of molecular and cellular events (De Jonge & Barratt, 2006). In humans, the mature spermatozoon contains a complement of 22 autosomal chromosomes and one sex chromosome, all in a highly compacted state (De Jonge & Barratt, 2006). However, during the first or the second meiotic division, incorrect chromosome segregation may occur, resulting in chromosomally abnormal spermatozoa (Carrell, 2007). In particular, this incorrect segregation may result in spermatozoa with an incorrect number of chromosomes, (aneuploid spermatozoa) or in spermatozoa with additional or deleted chromosomal material (unbalanced spermatozoa). Fertilisation with aneuploid or unbalanced spermatozoa will eventually lead to chromosomally abnormal embryos. Chromosomally abnormal embryos may arise from either affected oocytes or affected spermatozoa and are known as a major cause of implantation failure, pregnancy loss and foetal malformations (Hassold et al., 1993; Vialard et al., 2008). In general, the contribution of paternally derived aneuploidies compared with those that © 2014 Blackwell Verlag GmbH Andrologia 2014, xx, 1–14
are maternally derived is considered minor (Pacchierotti et al., 2007). However, published data have revealed that there are subgroups of males who may carry an increased risk of producing unbalanced or aneuploid spermatozoa (Tempest, 2011; Templado et al., 2013). This review study aims at identifying males who are at higher risk of producing unbalanced or aneuploid spermatozoa compared with the general population. The risk is estimated in both males with abnormal karyotypes, who have a biological predisposition to produce chromosomally abnormal spermatozoa, and males with normal karyotypes. Moreover, different biological, clinical and environmental parameters are presented as causative factors for an additional sperm aneuploidy load. Finally, the efficacy of available therapeutic options and sperm selection laboratory techniques is explored. Assessing sperm aneuploidy Currently, two techniques can be used to assess aneuploidy in human sperm cells. The first consists of the analysis of sperm karyotypes after the in vitro fusion of hamster egg and human sperm (Rudak et al., 1978), whereas the second technique visualises sperm chromosomes in interphase nuclei by the multicolour fluorescent in situ hybridisation (FISH) technique (Holmes & Martin, 1993). Both tests have clear limitations: only a small number of spermatozoa can be tested 1
Sperm aneuploidy in infertile men
with the hamster test, and only a restricted number of chromosomes are tested with the FISH technique. Neither test can assess nullisomy owing to the possible artefactual loss of chromosomes during slide preparation or in the absence of hybridisation. The sperm FISH technique is the most commonly used because it is less labour intensive and allows for the analysis of a large cohort of spermatozoa, thereby increasing the statistical accuracy and power of the outcomes. Sperm aneuploidy in the general population Segregation errors may account for 3–5% of the spermatozoa produced by fertile and normospermic males (Sarrate et al., 2010). In particular, in a study conducted by Templado et al. (2011b), all of the available published data on sperm aneuploidy rates obtained from FISH results on healthy donors aged 18–80 years were accumulated and analysed. The pooled data from 388 donors revealed disomy frequencies for 18 of the 24 chromosomes of sperm complement. In particular, it was estimated that for individual autosomes, the mean disomy frequency was approximately 0.1%, ranging from 0.03 (chromosome 8) to 0.47% (chromosome 22), and the estimated incidence of total aneuploidy (29 disomy of 2.26%) was 4.5%. The males who carry increased risk of producing chromosomally abnormal spermatozoa are primarily those with abnormal karyotypes, although certain subgroups of fertile and infertile males with normal karyotypes are also considered at risk (Templado et al., 2013). Males with abnormal karyotypes Constitutional chromosome abnormalities can be numerical or structural. Structural chromosome abnormalities involve alterations that may occur on the chromosomes’ structures while numerical chromosome abnormalities entail alterations that involve a missing or an extra chromosome; these conditions are known as aneuploidies. Males with abnormal karyotypes are prone to meiotic errors, and hence, they have a well-known biological predisposition for producing chromosomally abnormal spermatozoa (Carrell, 2007). The risk involved is directly related to the karyotypic abnormality observed. These males may have difficulties in establishing viable pregnancies, defined as failing to achieve any pregnancies or having history of repeated spontaneous abortions. Structural chromosome abnormalities commonly found among infertile males are: Reciprocal translocations, which are the most frequent structural alterations in humans and among infertile males. They involve the exchange of material between two or more chromosomes. Balanced reciprocal translocation carriers 2
A. Chatziparasidou et al.
in general show oligozoospermia or even azoospermia (Dong et al., 2012). FISH analyses of chromosome segregations have shown that the frequency of unbalanced chromosomes in reciprocal translocation male carriers is near 50% (Benet et al., 2005; Anton et al., 2008); this is less what was initially estimated (Martin & Spriggs, 1995; Geneix et al., 2002). Robertsonian translocations involve the fusion of two acrocentric chromosomes, which leads to a balanced state of 45, XY. Carriers of a balanced Robertsonian translocation show impaired gametogenesis to variable degrees. For Robertsonian translocation carriers, frequencies of 1–36% (average 15%) have been observed (Frydman et al., 2001; Ogur et al., 2006), which are much lower than would be theoretically expected. Inversion occurs when there are two chromosome breaks in the same chromosome and the segment heals in an inverted manner. For pericentric or paracentric inversion carriers, the risk of producing unbalanced gametes varies from very low to very high depending on the size of the inverted chromosome segment (Anton et al., 2005; Malan et al., 2006; Morel et al., 2007). In particular, the estimated prevalence of normal gametes ranges from 45.7% to 99.4%, meaning that some carriers may have the same prognosis as the general population whereas others may have their fertility reduced by half (Anton et al., 2007). Complex chromosome rearrangements are structural aberrations involving three or more break points on two or more chromosomes that result in a high rate of sperm chromosome imbalances, leading to subfertility and potential congenital abnormalities. Loup et al. (2010) reported only 14.8% of spermatozoa with normal or balanced chromosome complements, whereas Kirkpatrick & Ma (2012) reported a significantly lower frequency of unbalanced spermatozoa (15.8–24.3%). In structural rearrangement patients, sperm FISH studies have revealed an increased frequency of aneuploidies for chromosome pairs not involved in the chromosomal rearrangement. This finding was described as an interchromosomal effect (ICE) and has been postulated to be a potential consequence of meiotic disturbances produced by the rearrangements (Ferfouri et al., 2011; Alfarawati et al., 2012). A number of studies have been performed to assess the occurrence of ICE in structural reorganisation carriers by analysing the frequencies of numerical abnormalities in the gametes. According to Anton et al. (2011) 54% of men with Robertsonian translocations, 44% of reciprocal translocation carriers and 7% of men with inversions carry an added aneuploidy load in the form of an inter-chromosomal effect in the sperm, as analysed by FISH. However, the occurrence and the underlying mechanism of the inter-chromosomal effect © 2014 Blackwell Verlag GmbH Andrologia 2014, xx, 1–14
A. Chatziparasidou et al.
(ICE) are still controversial (Rogenhofer et al., 2012) given that increased frequencies of aneuploidy in the spermatozoa of males with abnormal sperm parameters have also been observed even among men with normal blood karyotypes (Douet-Guilbert et al., 2005). The most commonly identified numerical chromosome abnormalities among males are: Klinefelter syndrome (47,XXY) or mosaic variants (e.g. 47,XXY/46,XY). In general, these males have severe oligozoospermia or azoospermia. In nonmosaic patients, the frequency of observed sex chromosome aneuploidy averages from 4% to 6%, much lower than would be theoretically expected (Blanco et al., 2001; Fullerton et al., 2010; Tempest, 2011). In mosaic XY/XXY individuals, the average observed sex chromosome aneuploidy is even lower (Ferlin et al., 2005). However, in some individuals, a significantly higher frequency has been reported (Gonzalez-Merino et al., 2007). The difference between the expected and observed disomies may be explained either by the possible presence of an effective selection mechanism against disomic spermatozoa (Maiburg et al., 2012) or by focal spermatogenesis that originates from only euploid spermatocytes, as suggested by Sciurano et al., 2009; Vialard et al., 2012). Males diagnosed with 47,XYY karyotype. In theory, 50% of the sperm cells these males produce should be abnormal. However, Benet & Martin (1988) found no disomic sperm for sex chromosomes in 75 sperm karyotypes from one 47,XYY male, and Shi & Martin (2001), in a related study, reported 1% disomy risk for the sex chromosomes. The available data thus far support the hypothesis that the extra sex chromosome is eliminated during spermatogenesis. Mosaic karyotypes are the result of post-zygotic chromosome segregation errors during embryogenesis. In these mosaic cases, an increase in sex and autosome disomy (Collodel et al., 2007b; Perrin et al., 2009) was reported as a result of meiotic spermatogenetic impairment, but Giltay et al. (2000) failed to see an increased sex chromosome aneuploidy risk. Fertile males with normal karyotypes Males with normal karyotypes may also be at risk of producing sperm with aneuploid chromosome complement, which in turn may lead to a higher risk of producing embryos with aneuploid chromosome complement (Sanchez-Castro et al., 2009). From studies conducted with males who fathered paternally inherited aneuploid children, it was shown that a subgroup of fertile males from the general population may consistently produce higher levels of sperm aneuploidy (stable variants), at least for a number of disomies. In these cases, the risk © 2014 Blackwell Verlag GmbH Andrologia 2014, xx, 1–14
Sperm aneuploidy in infertile men
of fathering an aneuploid offspring or of recurrent miscarriages is moderately increased (Rubes et al., 2002, 2005; Tomascik-Cheeseman et al., 2006; Tempest et al., 2009; Uroz et al., 2011). A number of reports have focused on fathers of paternally inherited Down syndrome (Blanco et al., 1998; Soares et al., 2001a), Turner syndrome (Martınez-Pasarell et al., 1999; Soares et al., 2001b) and Klinefelter syndrome (Arnedo et al., 2006). At least a doubling of sperm disomy for chromosomes 21 and XY was observed in all 3 groups. Not all related studies, however, are consistent with these findings; neither Hixon et al. (1998), who studied Down syndrome fathers, nor Eskenazi et al. (2002), who studied Klinefelter syndrome fathers reported elevated aneuploidy. The role of the male partner genetics in recurrent pregnancy loss (RPL) is not always clear. Collodel et al. (2009) reported apoptosis, 1818YY diploidy and 18YY disomy scores to be significantly higher in men with a history of RPL compared with controls. In agreement, Rubio et al. (1999) reported a 2- to 3-fold increase in sperm sex chromosome disomy in men with histories of RPL compared with the controls. It seems likely from the studies conducted to date that in at least some patients with normal semen parameters, there is a moderate association between elevated sperm aneuploidy risk and fathering recurrent miscarriages. Infertile male patients with normal karyotypes After more than a decade of analysis and data collection, there is a consensus that infertile men with normal somatic karyotypes have an increased risk of sperm aneuploidy. However, with the advent of intracytoplasmic sperm injection (ICSI), it is possible to treat severe male infertility, allowing many infertile men the opportunity to father their own biological children (Palermo et al., 1992). Moreover, sperm extraction techniques such as microsurgical epididymal sperm aspiration and testicular sperm extraction can now be offered to azoospermic patients who would never have been able to father children (Esteves & Varghese, 2012). As these assisted reproduction techniques (ART) do not overcome the issues arised due to a deficient spermatogenesis, a careful estimation of the risk involved in each case is of utmost importance, to identify couples at risk of producing chromosomally abnormal embryos. The association between sperm concentration and sperm aneuploidy has been extensively studied, a strong and inverse relationship was found in the majority of the studies between sperm concentration and the mean frequencies of sex chromosome disomy and of diploidy. As a result, the risk of producing chromosomally abnormal embryos was found to be directly related to the 3
Sperm aneuploidy in infertile men
concentration of spermatozoa in the sample (SanchezCastro et al., 2009; McAuliffe et al., 2012b). Sarrate et al. (2010) reported a 2- to 3-fold increase in sex chromosome disomy and disomy of chromosome 21, as well as a 3-fold elevation of diploidy in oligospermic males compared with control donors. Severe oligospermia was more strongly correlated with increases in aneuploidy (Mougou-Zerelli et al., 2011; Durak Aras et al., 2012), whereas significantly elevated aneuploidy rates have been reported in the testicular sperm of patients with nonobstructive azoospermia (Sun et al., 2008; Rodrigo et al., 2011; Vozdova et al., 2012a); these findings indicate a dramatic increase in the frequency of meiotic errors (Gonsalves et al., 2004) in these patients. Data from the study conducted by Rodrigo et al. (2011) showed that, nonobstructive azoospermia patients had lower ongoing implantation and pregnancy rates than obstructive azoospermia patients, particularly those with abnormal FISH compared with testicular control samples. The relationship between chromosome abnormalities and sperm motility is still controversial. Most studies comparing disomy frequency and sperm motility have shown very consistent results, with no significant association between disomy frequency and sperm motility (Sarrate et al., 2010; Mougou-Zerelli et al., 2011). Others reported an increase in sperm chromosome abnormalities in selected groups of patients with asthenoteratozoospermia and normal sperm concentrations (Hristova et al., 2002; Templado et al.,2002; Collodel et al., 2007a). Severe asthenozoospermia and total sperm immotility are common features in males treated with ICSI. In cases of total sperm immotility, Zeyneloglu et al. (2000) reported that immotile spermatozoa that were morphologically normal but that tested positive on the hyposmotic swelling test did not have an increased aneuploidy risk for the chromosomes tested. Sperm immotility is also found in infertile patients with dysplasia of the fibrous sheath (DFS). In these cases, major alterations of the fibrous sheath are associated with the dysplastic development of the tail during spermatogenesis. Baccetti et al. (2005) and Ghedir et al. (2014) reported a high incidence of numeric disturbances in chromosome constitution, mainly diploidy and sex chromosomal aneuploidies, in males diagnosed with DFS. The correlation between chromosome aneuploidy and sperm morphology is not yet clear. Multiple reports show a higher risk of sperm aneuploidy in teratospermic samples (Kahraman et al., 2004; Dubey et al., 2008), including a 2- to 4-fold increase of sex chromosome disomy and a 2- to 3-fold increase of aneuploidy in teratozoospermic patients (Gole et al., 2001; Templado et al., 2002; Brahem et al., 2011a, 2012; Mougou-Zerelli et al., 2011). However, Dayal et al. (2010) and Sun et al. (2006) question whether sperm morphology is a valid 4
A. Chatziparasidou et al.
indicator for genetically normal sperm selection. Only in selected teratospermic subgroups are the data concerning sperm morphology more consistent. In particular, in cases of severe morphological abnormalities, such as with macrocephalic multiflagellated sperm syndrome (1% of infertile male patients), studies have reported aneuploidy levels of 10–30 times those of controls and a significant increase in the rates of diploidy, triploidy and tetraploidy (Perrin et al., 2008, 2011b; Brahem et al., 2011a). Moreover, patients with globozoospermia, also a rare condition that affects
Sperm aneuploidy in infertile male patients: a systematic review of the literature A. Chatziparasidou1,2, N. Christoforidis1,2, G. Samolada1 & M. Nijs1,2 1 Embryolab SA, IVF Unit, Kalamaria, Thessaloniki, Greece; 2 Embryolab Academy, Kalamaria, Thessaloniki, Greece
Keywords Chromosomal abnormalities—male infertility—sperm aneuploidy Correspondence Alexia Chatziparasidou, Embryolab Academy, Ethnikis Antistaseos. 173-175, Kalamaria, Thessaloniki, Greece. Tel.: +0030 2310 475 717 Fax: +0030 2310 475 718 E-mail: [email protected] Accepted: August 18, 2014 doi: 10.1111/and.12362
Summary Males with abnormal karyotypes and subgroups of fertile and infertile males with normal karyotypes may be at risk of producing unbalanced or aneuploid spermatozoa. Biological, clinical, environmental and other factors may also cause additional sperm aneuploidy. However, increased risk of sperm aneuploidy is directly related to chromosomally abnormal embryo production and hence to poor reproductive potential. This systemic literature review focuses on the identification of these males because this is an essential step in the context of assisted reproduction. This research may allow for a more personalised and, hence, more accurate estimation of the risk involved in each case, which in turn will aid genetic counselling for affected couples and help with informed decision-making.
Introduction Mature spermatozoa are the end products of a highly complex biological procedure known as spermatogenesis. During spermatogenesis, the diploid spermatocytes undergo two meiotic divisions before haploid spermatids are produced; spermatids will eventually transform into mature spermatozoa through a series of molecular and cellular events (De Jonge & Barratt, 2006). In humans, the mature spermatozoon contains a complement of 22 autosomal chromosomes and one sex chromosome, all in a highly compacted state (De Jonge & Barratt, 2006). However, during the first or the second meiotic division, incorrect chromosome segregation may occur, resulting in chromosomally abnormal spermatozoa (Carrell, 2007). In particular, this incorrect segregation may result in spermatozoa with an incorrect number of chromosomes, (aneuploid spermatozoa) or in spermatozoa with additional or deleted chromosomal material (unbalanced spermatozoa). Fertilisation with aneuploid or unbalanced spermatozoa will eventually lead to chromosomally abnormal embryos. Chromosomally abnormal embryos may arise from either affected oocytes or affected spermatozoa and are known as a major cause of implantation failure, pregnancy loss and foetal malformations (Hassold et al., 1993; Vialard et al., 2008). In general, the contribution of paternally derived aneuploidies compared with those that © 2014 Blackwell Verlag GmbH Andrologia 2014, xx, 1–14
are maternally derived is considered minor (Pacchierotti et al., 2007). However, published data have revealed that there are subgroups of males who may carry an increased risk of producing unbalanced or aneuploid spermatozoa (Tempest, 2011; Templado et al., 2013). This review study aims at identifying males who are at higher risk of producing unbalanced or aneuploid spermatozoa compared with the general population. The risk is estimated in both males with abnormal karyotypes, who have a biological predisposition to produce chromosomally abnormal spermatozoa, and males with normal karyotypes. Moreover, different biological, clinical and environmental parameters are presented as causative factors for an additional sperm aneuploidy load. Finally, the efficacy of available therapeutic options and sperm selection laboratory techniques is explored. Assessing sperm aneuploidy Currently, two techniques can be used to assess aneuploidy in human sperm cells. The first consists of the analysis of sperm karyotypes after the in vitro fusion of hamster egg and human sperm (Rudak et al., 1978), whereas the second technique visualises sperm chromosomes in interphase nuclei by the multicolour fluorescent in situ hybridisation (FISH) technique (Holmes & Martin, 1993). Both tests have clear limitations: only a small number of spermatozoa can be tested 1
Sperm aneuploidy in infertile men
with the hamster test, and only a restricted number of chromosomes are tested with the FISH technique. Neither test can assess nullisomy owing to the possible artefactual loss of chromosomes during slide preparation or in the absence of hybridisation. The sperm FISH technique is the most commonly used because it is less labour intensive and allows for the analysis of a large cohort of spermatozoa, thereby increasing the statistical accuracy and power of the outcomes. Sperm aneuploidy in the general population Segregation errors may account for 3–5% of the spermatozoa produced by fertile and normospermic males (Sarrate et al., 2010). In particular, in a study conducted by Templado et al. (2011b), all of the available published data on sperm aneuploidy rates obtained from FISH results on healthy donors aged 18–80 years were accumulated and analysed. The pooled data from 388 donors revealed disomy frequencies for 18 of the 24 chromosomes of sperm complement. In particular, it was estimated that for individual autosomes, the mean disomy frequency was approximately 0.1%, ranging from 0.03 (chromosome 8) to 0.47% (chromosome 22), and the estimated incidence of total aneuploidy (29 disomy of 2.26%) was 4.5%. The males who carry increased risk of producing chromosomally abnormal spermatozoa are primarily those with abnormal karyotypes, although certain subgroups of fertile and infertile males with normal karyotypes are also considered at risk (Templado et al., 2013). Males with abnormal karyotypes Constitutional chromosome abnormalities can be numerical or structural. Structural chromosome abnormalities involve alterations that may occur on the chromosomes’ structures while numerical chromosome abnormalities entail alterations that involve a missing or an extra chromosome; these conditions are known as aneuploidies. Males with abnormal karyotypes are prone to meiotic errors, and hence, they have a well-known biological predisposition for producing chromosomally abnormal spermatozoa (Carrell, 2007). The risk involved is directly related to the karyotypic abnormality observed. These males may have difficulties in establishing viable pregnancies, defined as failing to achieve any pregnancies or having history of repeated spontaneous abortions. Structural chromosome abnormalities commonly found among infertile males are: Reciprocal translocations, which are the most frequent structural alterations in humans and among infertile males. They involve the exchange of material between two or more chromosomes. Balanced reciprocal translocation carriers 2
A. Chatziparasidou et al.
in general show oligozoospermia or even azoospermia (Dong et al., 2012). FISH analyses of chromosome segregations have shown that the frequency of unbalanced chromosomes in reciprocal translocation male carriers is near 50% (Benet et al., 2005; Anton et al., 2008); this is less what was initially estimated (Martin & Spriggs, 1995; Geneix et al., 2002). Robertsonian translocations involve the fusion of two acrocentric chromosomes, which leads to a balanced state of 45, XY. Carriers of a balanced Robertsonian translocation show impaired gametogenesis to variable degrees. For Robertsonian translocation carriers, frequencies of 1–36% (average 15%) have been observed (Frydman et al., 2001; Ogur et al., 2006), which are much lower than would be theoretically expected. Inversion occurs when there are two chromosome breaks in the same chromosome and the segment heals in an inverted manner. For pericentric or paracentric inversion carriers, the risk of producing unbalanced gametes varies from very low to very high depending on the size of the inverted chromosome segment (Anton et al., 2005; Malan et al., 2006; Morel et al., 2007). In particular, the estimated prevalence of normal gametes ranges from 45.7% to 99.4%, meaning that some carriers may have the same prognosis as the general population whereas others may have their fertility reduced by half (Anton et al., 2007). Complex chromosome rearrangements are structural aberrations involving three or more break points on two or more chromosomes that result in a high rate of sperm chromosome imbalances, leading to subfertility and potential congenital abnormalities. Loup et al. (2010) reported only 14.8% of spermatozoa with normal or balanced chromosome complements, whereas Kirkpatrick & Ma (2012) reported a significantly lower frequency of unbalanced spermatozoa (15.8–24.3%). In structural rearrangement patients, sperm FISH studies have revealed an increased frequency of aneuploidies for chromosome pairs not involved in the chromosomal rearrangement. This finding was described as an interchromosomal effect (ICE) and has been postulated to be a potential consequence of meiotic disturbances produced by the rearrangements (Ferfouri et al., 2011; Alfarawati et al., 2012). A number of studies have been performed to assess the occurrence of ICE in structural reorganisation carriers by analysing the frequencies of numerical abnormalities in the gametes. According to Anton et al. (2011) 54% of men with Robertsonian translocations, 44% of reciprocal translocation carriers and 7% of men with inversions carry an added aneuploidy load in the form of an inter-chromosomal effect in the sperm, as analysed by FISH. However, the occurrence and the underlying mechanism of the inter-chromosomal effect © 2014 Blackwell Verlag GmbH Andrologia 2014, xx, 1–14
A. Chatziparasidou et al.
(ICE) are still controversial (Rogenhofer et al., 2012) given that increased frequencies of aneuploidy in the spermatozoa of males with abnormal sperm parameters have also been observed even among men with normal blood karyotypes (Douet-Guilbert et al., 2005). The most commonly identified numerical chromosome abnormalities among males are: Klinefelter syndrome (47,XXY) or mosaic variants (e.g. 47,XXY/46,XY). In general, these males have severe oligozoospermia or azoospermia. In nonmosaic patients, the frequency of observed sex chromosome aneuploidy averages from 4% to 6%, much lower than would be theoretically expected (Blanco et al., 2001; Fullerton et al., 2010; Tempest, 2011). In mosaic XY/XXY individuals, the average observed sex chromosome aneuploidy is even lower (Ferlin et al., 2005). However, in some individuals, a significantly higher frequency has been reported (Gonzalez-Merino et al., 2007). The difference between the expected and observed disomies may be explained either by the possible presence of an effective selection mechanism against disomic spermatozoa (Maiburg et al., 2012) or by focal spermatogenesis that originates from only euploid spermatocytes, as suggested by Sciurano et al., 2009; Vialard et al., 2012). Males diagnosed with 47,XYY karyotype. In theory, 50% of the sperm cells these males produce should be abnormal. However, Benet & Martin (1988) found no disomic sperm for sex chromosomes in 75 sperm karyotypes from one 47,XYY male, and Shi & Martin (2001), in a related study, reported 1% disomy risk for the sex chromosomes. The available data thus far support the hypothesis that the extra sex chromosome is eliminated during spermatogenesis. Mosaic karyotypes are the result of post-zygotic chromosome segregation errors during embryogenesis. In these mosaic cases, an increase in sex and autosome disomy (Collodel et al., 2007b; Perrin et al., 2009) was reported as a result of meiotic spermatogenetic impairment, but Giltay et al. (2000) failed to see an increased sex chromosome aneuploidy risk. Fertile males with normal karyotypes Males with normal karyotypes may also be at risk of producing sperm with aneuploid chromosome complement, which in turn may lead to a higher risk of producing embryos with aneuploid chromosome complement (Sanchez-Castro et al., 2009). From studies conducted with males who fathered paternally inherited aneuploid children, it was shown that a subgroup of fertile males from the general population may consistently produce higher levels of sperm aneuploidy (stable variants), at least for a number of disomies. In these cases, the risk © 2014 Blackwell Verlag GmbH Andrologia 2014, xx, 1–14
Sperm aneuploidy in infertile men
of fathering an aneuploid offspring or of recurrent miscarriages is moderately increased (Rubes et al., 2002, 2005; Tomascik-Cheeseman et al., 2006; Tempest et al., 2009; Uroz et al., 2011). A number of reports have focused on fathers of paternally inherited Down syndrome (Blanco et al., 1998; Soares et al., 2001a), Turner syndrome (Martınez-Pasarell et al., 1999; Soares et al., 2001b) and Klinefelter syndrome (Arnedo et al., 2006). At least a doubling of sperm disomy for chromosomes 21 and XY was observed in all 3 groups. Not all related studies, however, are consistent with these findings; neither Hixon et al. (1998), who studied Down syndrome fathers, nor Eskenazi et al. (2002), who studied Klinefelter syndrome fathers reported elevated aneuploidy. The role of the male partner genetics in recurrent pregnancy loss (RPL) is not always clear. Collodel et al. (2009) reported apoptosis, 1818YY diploidy and 18YY disomy scores to be significantly higher in men with a history of RPL compared with controls. In agreement, Rubio et al. (1999) reported a 2- to 3-fold increase in sperm sex chromosome disomy in men with histories of RPL compared with the controls. It seems likely from the studies conducted to date that in at least some patients with normal semen parameters, there is a moderate association between elevated sperm aneuploidy risk and fathering recurrent miscarriages. Infertile male patients with normal karyotypes After more than a decade of analysis and data collection, there is a consensus that infertile men with normal somatic karyotypes have an increased risk of sperm aneuploidy. However, with the advent of intracytoplasmic sperm injection (ICSI), it is possible to treat severe male infertility, allowing many infertile men the opportunity to father their own biological children (Palermo et al., 1992). Moreover, sperm extraction techniques such as microsurgical epididymal sperm aspiration and testicular sperm extraction can now be offered to azoospermic patients who would never have been able to father children (Esteves & Varghese, 2012). As these assisted reproduction techniques (ART) do not overcome the issues arised due to a deficient spermatogenesis, a careful estimation of the risk involved in each case is of utmost importance, to identify couples at risk of producing chromosomally abnormal embryos. The association between sperm concentration and sperm aneuploidy has been extensively studied, a strong and inverse relationship was found in the majority of the studies between sperm concentration and the mean frequencies of sex chromosome disomy and of diploidy. As a result, the risk of producing chromosomally abnormal embryos was found to be directly related to the 3
Sperm aneuploidy in infertile men
concentration of spermatozoa in the sample (SanchezCastro et al., 2009; McAuliffe et al., 2012b). Sarrate et al. (2010) reported a 2- to 3-fold increase in sex chromosome disomy and disomy of chromosome 21, as well as a 3-fold elevation of diploidy in oligospermic males compared with control donors. Severe oligospermia was more strongly correlated with increases in aneuploidy (Mougou-Zerelli et al., 2011; Durak Aras et al., 2012), whereas significantly elevated aneuploidy rates have been reported in the testicular sperm of patients with nonobstructive azoospermia (Sun et al., 2008; Rodrigo et al., 2011; Vozdova et al., 2012a); these findings indicate a dramatic increase in the frequency of meiotic errors (Gonsalves et al., 2004) in these patients. Data from the study conducted by Rodrigo et al. (2011) showed that, nonobstructive azoospermia patients had lower ongoing implantation and pregnancy rates than obstructive azoospermia patients, particularly those with abnormal FISH compared with testicular control samples. The relationship between chromosome abnormalities and sperm motility is still controversial. Most studies comparing disomy frequency and sperm motility have shown very consistent results, with no significant association between disomy frequency and sperm motility (Sarrate et al., 2010; Mougou-Zerelli et al., 2011). Others reported an increase in sperm chromosome abnormalities in selected groups of patients with asthenoteratozoospermia and normal sperm concentrations (Hristova et al., 2002; Templado et al.,2002; Collodel et al., 2007a). Severe asthenozoospermia and total sperm immotility are common features in males treated with ICSI. In cases of total sperm immotility, Zeyneloglu et al. (2000) reported that immotile spermatozoa that were morphologically normal but that tested positive on the hyposmotic swelling test did not have an increased aneuploidy risk for the chromosomes tested. Sperm immotility is also found in infertile patients with dysplasia of the fibrous sheath (DFS). In these cases, major alterations of the fibrous sheath are associated with the dysplastic development of the tail during spermatogenesis. Baccetti et al. (2005) and Ghedir et al. (2014) reported a high incidence of numeric disturbances in chromosome constitution, mainly diploidy and sex chromosomal aneuploidies, in males diagnosed with DFS. The correlation between chromosome aneuploidy and sperm morphology is not yet clear. Multiple reports show a higher risk of sperm aneuploidy in teratospermic samples (Kahraman et al., 2004; Dubey et al., 2008), including a 2- to 4-fold increase of sex chromosome disomy and a 2- to 3-fold increase of aneuploidy in teratozoospermic patients (Gole et al., 2001; Templado et al., 2002; Brahem et al., 2011a, 2012; Mougou-Zerelli et al., 2011). However, Dayal et al. (2010) and Sun et al. (2006) question whether sperm morphology is a valid 4
A. Chatziparasidou et al.
indicator for genetically normal sperm selection. Only in selected teratospermic subgroups are the data concerning sperm morphology more consistent. In particular, in cases of severe morphological abnormalities, such as with macrocephalic multiflagellated sperm syndrome (1% of infertile male patients), studies have reported aneuploidy levels of 10–30 times those of controls and a significant increase in the rates of diploidy, triploidy and tetraploidy (Perrin et al., 2008, 2011b; Brahem et al., 2011a). Moreover, patients with globozoospermia, also a rare condition that affects
