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Review |
,
From the * Division of Urology, Department of
Surgery, McGill University, Montreal, Quebec, Canada; and the
Division of Urology, Department of Surgery,
Brown University, Providence, Rhode Island.
| Correspondence to: Dr Armand Zini, St Mary's Hospital, 3830 Lacombe Ave, Room 2304, Montreal, Quebec, Canada H3T 1M5 (e-mail: ziniarmand{at}yahoo.com). |
| Received for publication September 23, 2008; accepted for publication December 1, 2008. |
The advent of assisted reproductive technologies, particularly
intracytoplasmic sperm injection (ICSI), has revolutionized the treatment of
male-factor infertility. However, there are many unanswered questions
regarding the safety of these techniques. These safety concerns are relevant
because 1) these technologies often bypass the barriers to natural selection;
2) infertile men, particularly those with severe male-factor infertility,
possess substantially more sperm DNA damage than do fertile men; and 3)
experimentally, sperm DNA damage has been shown to adversely affect the
developing embryo. This review discusses the etiology of sperm DNA damage,
describes the individual tests of sperm DNA damage, and explores the
relationship between sperm DNA damage and pregnancy outcomes. Based on a
systematic review of the literature, sperm DNA damage is associated with lower
natural, intrauterine insemination (IUI), and in vitro fertilization (IVF)
pregnancy rates, but not with ICSI pregnancy rates. The literature also
suggests that that sperm DNA damage is associated with an increased risk of
pregnancy loss in those couples undergoing IVF or ICSI. Nonetheless, the true
clinical utility of sperm DNA damage tests remains to be established, because
the available studies are small and few in number and the study
characteristics are heterogeneous. Although current data suggest that impaired
sperm DNA integrity may have the greatest effect on IUI pregnancy rates and
pregnancy loss by IVF and ICSI, further prospective studies are needed before
testing should become a routine part of patient management.
Key words: Fertility, ICSI, IVF, DNA integrity, meta-analysis
The study of sperm DNA damage is particularly relevant in an era in which advanced forms of assisted reproductive technologies (ARTs) are frequently used, because iatrogenic transmission of genetic defects is possible when natural selection barriers to fertilization are bypassed. Moreover, animal studies indicate that DNA damage is associated with both poor embryo development and poor pregnancy outcomes at in vitro fertilization (IVF; Fernández-Gonzalez et al, 2008).
To date, the short- and long-term ramifications of successful fertilization and development with DNA-damaged spermatozoa are unknown. Clearly, the understanding that sperm DNA damage is common in infertile men, together with the concerning preliminary reports on genetic and epigenetic abnormalities in the offspring associated with intracytoplasmic sperm injection (ICSI), urges us to explore the subject of sperm DNA damage further. DNA that possesses measurable damage (specifically, DNA oxidation) may cause misreading errors to occur during DNA replication, and this may result in the generation of de novo mutations (Kuchino et al, 1987). Although the concept has not been tested in the context of mammalian reproduction, we cannot dismiss the possibility that successful fertilization with DNA-damaged sperm may cause de novo mutations in the offspring (despite the ability of the oocyte and embryo to repair this DNA damage; Ahmadi and Ng, 1999). Studies have found that children of fathers who smoked cigarettes preconceptually have a higher risk of developing childhood cancers (Ji et al, 1997). These studies suggest that there may be a link between sperm DNA damage and the subsequent development of childhood diseases.
Human Sperm DNA and Chromatin Structure
Unlike the relatively loose structure of chromatin in somatic cells, sperm
chromatin is very tightly compacted by virtue of the unique associations
between the DNA and sperm nuclear proteins (predominantly protamines;
Ward and Coffey, 1991;
Brewer et al, 1999). During
the later stages of spermatogenesis, the spermatid nucleus is remodeled and
condensed, and this is associated with the displacement of histones by
transition proteins and then by protamines
(Steger et al, 2000). The DNA
strands are tightly wrapped around the protamine molecules, forming tight and
highly organized loops (Brewer et al,
1999). Intermolecular and intramolecular disulfide cross-links
between the cysteine-rich protamines are responsible for the compaction and
stabilization of the sperm nucleus, and it is thought that this nuclear
compaction is important to protect the sperm genome from external stresses
such as oxidation or temperature elevation
(Kosower et al, 1992).
In humans, sperm chromatin is tightly packaged by protamines, but up to 15% of the DNA remains packaged by histones at specific DNA sequences (ie, there is a nonrandom association between histones and DNA sequences; Gatewood et al, 1987). The histone-bound DNA sequences are less tightly compacted, and it is thought that these DNA sequences and/or genes may be involved in fertilization and early embryo development (Gatewood et al, 1987; Gineitis et al, 2000). Infertile men have a higher sperm histone to protamine ratio when compared with fertile controls (Oliva, 2006; Zhang et al, 2006). An excess of nuclear histones may result in poorer chromatin compaction and an increased susceptibility to DNA damage (Cho et al, 2001, 2003; Aoki et al, 2005, 2006).
Etiology of Sperm DNA Damage
The etiology of sperm DNA damage is multifactorial: it may be due to
intrinsic (eg, protamine deficiency, excess reactive oxygen species [ROS]
levels, apoptosis), or extrinsic factors (eg, testicular hyperthermia,
environmental toxins). Sperm DNA damage is clearly associated with male
infertility (and abnormal spermatogenesis) but a small percentage of
spermatozoa from fertile men also possess detectable levels of DNA damage
(Kodama et al, 1997;
Evenson et al, 1999;
Spano et al, 2000;
Zini et al, 2001).
Intrinsic Factors—
Sperm DNA damage has been associated with protamine deficiency
(Cho et al, 2001; Aoki et al,
2005,
2006). Infertile men have an
increased sperm histone to protamine ratio when compared with fertile
controls, and an important subset of infertile men (
5%–15%), but
not of fertile men, possesses a complete protamine deficiency
(Zhang et al, 2006). Protamine
deficiency (absolute or relative) can potentially result in defective
chromatin compaction (Aravindan et al,
1997b) and in an increased susceptibility to DNA damage
(Aoki et al, 2005). Studies on
transgenic animal models with targeted protamine deficiency demonstrate a link
between protamine deficiency, sperm DNA damage, and poor fertilizing capacity
at IVF (Cho et al, 2001,
2003). The association between
sperm DNA damage and protamine deficiency (Aoki et al,
2005,
2006) suggests that DNA damage
may in part be due to a defect in spermiogenesis (the period during which
sperm protamines are deposited; Steger et
al, 2000).
Sperm DNA damage has been associated with high levels of ROS (approximately 25% of infertile men have high levels of semen ROS; Zini et al, 1993; Irvine et al, 2000). Although the generation of low levels of ROS is necessary for normal sperm function, high levels of ROS (generated by defective spermatozoa and by semen leukocytes) can cause sperm dysfunction. The association between sperm DNA damage and sperm-derived ROS suggests that DNA damage may be due to a defect in spermiogenesis (Gomez et al, 1996), whereas the association between sperm DNA damage and leukocyte-derived ROS suggests that the DNA damage may be due to a posttesticular defect (eg, epididymitis; Ochsendorf, 1999).
Sperm DNA damage may be the result of an aborted apoptosis (programmed cell death), although this theory has been challenged (Muratori et al, 2000; Sakkas et al, 2003). During normal spermatogenesis, germ cell apoptosis prevents overproliferation and selectively aborts abnormal sperm forms (Sinha Hikin and Swerdloff, 1999). Sakkas et al (2003) have proposed that some of the spermatozoa with DNA damage have initiated and then subsequently escaped apoptosis ("abortive apoptosis"). In line with this theory, Marcon and Boissoneault (2004) have suggested that DNA damage may be the result of incorrect repair of transient DNA nicks that are introduced during spermiogenesis (the nicks are introduced to relieve the torsional strain on the DNA helix during the exchange of histones to protamines). Advancing age and gonadotoxins have been associated with reduced levels of germ cell apoptosis in the testicle, and an increase in the percentage of ejaculated spermatozoa with DNA damage, suggesting that in these men, both spermatogenesis and apoptosis have been disrupted (Brinkworth and Nieschlag, 2000; Singh et al, 2003).
Extrinsic Factors— Extrinsic factors that may cause sperm DNA damage include drugs (eg, chemotherapy), cigarette smoking, genital tract inflammation, testicular hyperthermia, and varicoceles.
Young men with cancer (eg, Hodgkin lymphoma and testicular cancer) typically have poor semen quality and sperm DNA damage even prior to cancer-specific therapy (O'Flaherty et al, 2008). They then experience cumulative dose damage during therapy (chemotherapy, radiation), often rendering them completely sterile (Fossa et al, 1997; Morris, 2002). The recovery of spermatogenesis may occur months to years after therapy, but evidence of sperm DNA damage may often persist beyond that period (Fossa et al, 1997). Patients who are scheduled to undergo definitive cancer therapy (surgery, chemotherapy, and/or radiation) are strongly encouraged to cryopreserve sperm for future use (Lee et al, 2006).
Studies have shown that cigarette smoking is associated with lower sperm counts and motility and with an increase in abnormal sperm forms and sperm DNA damage (Potts et al, 1999). It is postulated that smoking causes increased leukocyte-derived ROS production with subsequent adverse effects on mature sperm (Potts et al, 1999). Exposure to pesticides (organophosphates) and air pollution have also been associated with increased levels of sperm DNA damage (Sanchez-Pena et al, 2004; Rubes et al, 2005).
Posttesticular genital tract infection and inflammation, as seen clinically in epididymo-orchitis or prostatitis, result in leukocytospermia, and have been associated with increased levels of ROS and subsequent sperm DNA damage (Ereinpress et al, 2002).
Testicular hyperthermia has been shown experimentally to cause sperm DNA damage, as well, as an increase in the histone to protamine ratio (Sailer et al, 1997; Banks et al, 2005). Clinically, certain behaviors (eg, hot baths, saunas) and occupations (eg, welding, baking, occupations that involve prolonged driving) have been associated with increased scrotal temperatures (Jung et al, 2002). Moreover, an association between hyperthermia and reduced male fertility potential has also been demonstrated (Thonneau et al, 1998). Corroborative clinical studies on sperm DNA damage and hyperthermia are lacking.
Varicoceles have been associated with sperm DNA damage (Saleh et al, 2003). The level of sperm DNA damage is related to the high levels of oxidative stress found in the semen of these infertile men (Saleh et al, 2003). We have shown that varicoceles are associated with the abnormal retention of sperm cytoplasmic droplets (a morphologic feature associated with high levels of semen ROS) and that these retained droplets are correlated with sperm DNA damage in these infertile men (Zini et al, 2000; Fischer et al, 2003). Furthermore, sperm DNA integrity has been shown to improve after varicocele repair (Zini et al, 2005a).
There is experimental evidence to show that hormonal deficiency can cause sperm chromatin defects. FSH receptor knockout mice have reduced levels of sperm nuclear protamines, lower testosterone, impaired fertility, and increased levels of DNA damage as compared with wild-type mice (Xing et al, 2003). Recently, investigators have shown that serum testosterone levels are inversely related to sperm DNA damage in a cohort of infertile men (Meeker et al, 2008).
Tests of Sperm DNA Damage
A variety of assays have been developed to measure sperm DNA damage
(Aravindan et al, 1997a;
Evenson et al, 1999;
Chohan et al, 2006). The use
of these tests has been driven largely by the growing use of ARTs and the
concern that the integrity of the sperm genome is of importance in this
context. It is important to consider several issues when evaluating studies of
sperm DNA integrity. Although many assays profess to determine "DNA
integrity," it is important to understand what each assay actually
measures (Table 1). Some
procedures, such as the COMET and terminal deoxynucleotidyl
transferase-mediated dUTP nick end-labeling (TUNEL) assays, detect actual DNA
strand breaks. Other approaches measure the susceptibility of DNA to
denaturation—that is, the formation of single-stranded DNA from native
double-stranded DNA. These approaches depend on the fact that nicked DNA
denatures more easily than double-stranded DNA. Finally, some assays rely on
the differential binding of dyes to single-stranded and double-stranded DNA.
Despite differences in assay methodology, the results of most assays correlate
highly with each other, one exception being the manual acridine orange test
(Chohan et al, 2006). Current
assays are limited because they do not selectively differentiate clinically
important DNA fragmentation from clinically insignificant fragmentation. A
limited amount of single-stranded DNA breaks may be repaired by the oocyte,
whereas double-stranded DNA breaks are irreversible
(Ahmadi and Ng, 1999). In
addition, some DNA nicking occurs as a normal process during winding and
unwinding of DNA; current assays do not differentiate physiologic from
pathologic nicking. Finally, the assays generally do not evaluate the genes
that may be affected by the fragmentation; it is possible that fragmentation
in areas containing certain genes may be more detrimental than fragmentation
in relatively inactive regions of the genome. What the assays do attempt to do
is simply to determine the amount of DNA fragmentation. This approach is based
on the belief that more DNA nicking or fragmentation is pathologic. Most
studies define an upper normal level of the percentage of cells with DNA
fragmentation. Samples with assay results above this threshold percentage are
considered to have high DNA fragmentation. Each assay has advantages and
disadvantages that impact its availability and utility
(Table 2).
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Influence of Sperm DNA Damage on Natural and Assisted Pregnancy
Several studies suggest that sperm DNA damage is associated with lower
rates of natural insemination and intrauterine insemination (IUI) pregnancies.
Indeed, couples in whom the husband has a high percentage of spermatozoa with
DNA damage have very low potential for natural fertility and a prolonged time
to pregnancy (Evenson et al,
1999; Spano et al,
2000; Loft et al,
2003). A recent meta-analysis indicates a strong association
between sperm DNA damage and failure to achieve a natural pregnancy
(Evenson and Wixon, 2008).
High levels of sperm DNA damage have generally been associated with lower IUI
pregnancy rates (Duran et al
2002; Muriel et al,
2006; Bungum et al,
2007). An estimation of the diagnostic odds ratio (OR) can only be
obtained from the Bungum et al
(2007) study (a 2 x 2
table cannot be constructed from the data in the
Duran et al, 2002, and
Muriel et al, 2006, studies).
The OR derived from the Bungum et al
(2007) study (OR, 9.9; 95%
confidence interval [CI], 2.37–41.51; P < .001) indicates
that sperm DNA damage is associated with a significantly lower pregnancy rate
at IUI.
Numerous studies have examined the influence of sperm DNA integrity on pregnancy rates after standard IVF. A systematic review and meta-analysis of IVF studies indicates that sperm DNA damage is associated (albeit weakly) with lower IVF pregnancy rates with a combined OR of 1.57 (95% CI, 1.18–2.07; P < .05). The characteristics of the 9 evaluable IVF studies included in the meta-analysis are shown in Table 3. Nine otherwise valid studies were excluded from the meta-analysis because 1) they reported on a mixed population (IVF and IVF/ICSI) (Larson-Cook et al, 2003; Seli et al, 2004; Virro et al, 2004; Payne et al, 2005; Velez de la Calle et al, 2008) or 2) a 2 x 2 table could not be constructed (often because a cutoff or threshold DNA damage level was not reported; Tomlinson et al, 2001; Tomsu et al, 2002; Bakos et al, 2008; Meseguer et al, 2008). These observations are in keeping with a recent meta-analysis (Collins et al, 2008) and suggest that sperm DNA damage has a modest impact on pregnancy rates at IVF.
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A systematic review and meta-analysis of ICSI studies indicates that sperm DNA damage is not associated with ICSI pregnancy rates (combined OR, 1.14; 95% CI, 0.86–1.54, P = .65). The characteristics of the 11 evaluable ICSI studies are shown in Table 4. Seven otherwise valid studies were excluded from the meta-analysis because 1) they reported on a mixed population (IVF and IVF/ICSI; Larson-Cook et al, 2003; Seli et al, 2004; Virro et al, 2004; Payne et al, 2005; Velez de la Calle et al, 2008), 2) a 2 x 2 table could not be constructed (Bakos et al, 2008) or 3) the assay type used in the study is not widely recognized (Virant-Klun et al, 2002). These observations are in keeping with a recent meta-analysis (Collins et al, 2008) and suggest that sperm DNA damage has no measurable impact on pregnancy rates at ICSI. It is possible that the stringent process of sperm and embryo selection at ICSI (in humans) mitigates the potential adverse effect(s) of sperm DNA damage on reproductive outcomes (Gandini et al, 2004).
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Several studies have reported a relationship between sperm DNA damage and pregnancy loss after both standard IVF and IVF/ICSI (see Table 4). A systematic review and meta-analysis of IVF and ICSI studies shows that sperm DNA damage is associated with a significant increase in the rate of pregnancy loss after IVF and ICSI with a combined OR of 2.48 (95% CI, 1.52–4.04; P < .0001). The characteristics of the 11 evaluable studies (from 7 reports) are shown in Table 5. There was no significant difference in the OR according to treatment type (IVF or ICSI). These data suggest that the adverse effect of sperm DNA damage on live birth rates is probably more significant than is reflected by the clinical pregnancy rates alone.
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The value of tests of sperm DNA integrity must be evaluated by the same criteria as any diagnostic test using a combination of statistical parameters and clinical judgment. As a test to diagnose infertility, the assay must identify patients with infertility by having a high sensitivity. In addition, fertile patients should test negative; that is, the assays should have a high specificity. These 2 properties—infertile patients should test positive and fertile patients should test negative—mean that pregnancy should be less common in those with a positive test (high DNA fragmentation) than in those with a negative test. This relationship is commonly evaluated by examining ORs—the odds of pregnancy in those with a positive test divided by the odds of pregnancy in those with a negative test. It is important to understand that ORs tend to overestimate this relationship as compared with the likelihood ratio, which utilizes proportions instead of odds. Because ORs are not affected by the prevalence of the disease (infertility), a relatively high OR may have limited value in situations of low disease prevalence.
In addition to having appropriate statistical characteristics, a diagnostic test of infertility must have clinical utility to have value beyond a research tool. That means the results should be able to be used to affect clinical management. To be useful as a clinical tool, the results should be repeatable and consistent over time. Equally important, the test must be able to be performed far enough in advance to make management decisions. Lastly, the difference in prognosis must be clinically significant, not just statistically significant. With these concepts in mind, the value of DNA integrity assays should be examined as tests to predict failure of pregnancy by intercourse, IUI, IVF, or ICSI. As will become clear, these assays have much less value than they are often promulgated to have.
Clinical Value of Tests of Sperm DNA Damage
Three clinical scenarios are described below to illustrate the clinical
value of sperm DNA testing. The pro and con statements (for sperm DNA testing)
are based on 1) a systematic review of the literature, 2) the sperm DNA test
characteristics (eg, reproducibility, sensitivity, positivity rate), and 3)
disease prevalence (eg, pregnancy, pregnancy loss).
First-pregnancy planners— PRO argument: A.Z. These couples may benefit from testing because sperm DNA damage is associated with a significantly lower natural pregnancy rate (combined OR, 7.15; 95% CI, 3.07–16.68, P < .0001). An analysis of the 2 studies (with a median pregnancy rate of 64%), revealed a median positive predictive value (PPV) of 73% and median negative predictive value (NPV) of 68% (Evenson et al, 1999; Spano et al, 2000). This means that in populations with an overall pregnancy rate of 64%, the pregnancy rate is estimated at 27% when there is an abnormal test result and at 68% when the test result is normal. Thus, in this analysis, sperm DNA damage assessment provides clinically valuable information, because it can discriminate between pregnancy rates of 27% and 68%.
CON argument: M.S. The value of tests of sperm DNA integrity is often stated be greatest in predicting pregnancy by intercourse and IUI. In one of the most commonly quoted studies (Evenson et al, 1999) an OR of 7.6 was reported (Evenson and Wixon, 2008); although the OR is statistically significant, it ignores the prevalence of infertility in the study population. Although 25.6% of the patients failed to achieve pregnancy, the test was abnormal in only 6.2% of patients. The test failed to identify infertility in 4 out of 5 infertile patients because the sensitivity of the assay was only 19%. In addition, in an age of concern about cost-effectiveness, it is worrisome that out of the 132 patients tested, only 6 (3.7%) patients were found to have high DNA fragmentation and did not achieve pregnancy; the remaining 96.3% of patients derived no benefit from the test. Out of all patients with an abnormal test result, pregnancy still occurred in 40% of the spouses. Finally, in both studies of pregnancy by intercourse, the predictive ability was best if the test was done close to the time of intercourse; the test performed more poorly when it was performed farther ahead of time, further limiting the clinical value in this population.
IUI Candidates (Couples With Mild Male-Factor Infertility)— PRO argument: A.Z. These couples may benefit from testing because sperm DNA damage is associated with a significantly lower IUI pregnancy rate (OR, 9.9; 95% CI, 2.37–41.51, P < .0001). The study reported by Bungum et al (2007), with a pregnancy rate of 20%, revealed a PPV of 97% and NPV of 24%. This means that in populations with an overall IUI pregnancy rate of 20%, the pregnancy rate is estimated at 3% when there is an abnormal test result and at 24% when the test result is normal. Thus, in this analysis, sperm DNA damage assessment provides clinically valuable information, because it can discriminate between pregnancy rates of 3% and 24%. Couples with high levels of sperm DNA damage should consider IVF and/or ICSI rather than IUI.
CON argument: M.S. Although an OR of 9.9 may be impressive, it would be wrong to conclude that the Bungum study demonstrates that couples planning IUI should first be tested for sperm DNA integrity (Bungum et al, 2007). Out of all samples tested, abnormal results were obtained in only 17%, whereas overall 80% of patients did not conceive. This poor test performance is because the sensitivity of the assay was only 20.7%: it failed to diagnose failure to conceive in 4 out of 5 cases. Although it performed better with IUI than with intercourse, only 16.6% of patients would have benefited from the test. In addition, this is the only study of the relationship between pregnancy by IUI and sperm DNA integrity that allows for proper statistical evaluation. More studies are needed before a change in practice patterns should be instituted. More concerning is the fact that the DNA fragmentation assay was performed on the same sample that was used for IUI—hardly enough time to use the results to affect management. There has been no study demonstrating that sperm DNA integrity testing performed well in advance of IUI is predictive of pregnancy. Most worrisome, sperm DNA integrity is not always stable over time. A recent study examined a group of couples undergoing IUI, IVF, or ICSI for more than 1 cycle. In those couples with an initial normal DNA fragmentation, tests in subsequent cycles showed high DNA fragmentation in 15%. Even more worrisome was the finding that of those with initially high DNA fragmentation scores, 37% were found to have normal scores on subsequent testing (Erenpreiss et al, 2006).
IVF or ICSI Candidates (Couples With Severe Male-Factor Infertility)— PRO Argument: A.Z. These couples may benefit from testing because sperm DNA damage is associated with a significantly lower IVF pregnancy rate (combined OR, 1.57; 95% CI, 1.18–2.07; P < .05). An analysis of the 9 IVF studies (with a median pregnancy rate of 33%) revealed a median PPV of 71% and median NPV of 34% (Table 3). Thus, in populations with an overall IVF pregnancy rate of 33%, sperm DNA damage assessment can discriminate between IVF pregnancy rates of 29% (positive test) and 34% (negative test), a small difference with modest clinical value. Couples with high levels of DNA damage may be better served by proceeding to ICSI, in which pregnancy rates are not related to sperm DNA damage test results (combined OR, 1.14; 95% CI, 0.86–1.54; P = .65, see Table 4).
More importantly, these couples can benefit from testing because sperm DNA damage is associated with a significantly higher rate of pregnancy loss after IVF or ICSI (combined OR, 2.48; 95% CI, 1.52–4.04; P < .0001). An analysis of the pregnancy loss studies (with a median pregnancy loss rate of 18%), revealed a median PPV of 37% and median NPV of 90%. This means that in populations with an overall pregnancy loss of 18%, the rate of pregnancy loss is estimated at 37% when there is an abnormal test result and at 10% when the test result is normal. Thus, sperm DNA damage assessment provides clinically valuable information, because it can discriminate between pregnancy loss rates of 37% and 10%. The effect of DNA damage on pregnancy loss should be discussed with patients prior to undergoing ART.
CON Argument: M.S. The use of sperm DNA integrity testing in IVF candidates demonstrates the importance of understanding the difference between statistical significance and clinical significance. In the current meta-analysis, a statistically significant OR is obtained. However, the pregnancy rate in the normal (negative test) group was 34%, whereas in the abnormal result (positive test) group it was still 29%. It is unlikely that a 5% difference in pregnancy rates warrants the added expense (and increased potential risk) of ICSI. In addition, a recently published meta-analysis found no statistical significance to the OR in IVF cycles (Collins et al, 2008). This points out that the difference is so slight that different calculations with slightly different studies may give different statistical results. It is clear from the present analysis, as well as others, that in ICSI cycles, the assays have an OR no different from 1 and therefore have no predictive value for pregnancy.
The most interesting data involves the value of sperm DNA integrity testing in predicting pregnancy loss. The current analysis demonstrates a statistically significant OR of 2.48 corresponding to a pregnancy loss rate of 10% with a normal (negative) test and 37% with an abnormal (positive) test. It certainly may be argued that this difference is also clinically significant. Despite these impressive numbers, it should be understood that the assay failed to identify 60% of the pregnancy loss cases because of a sensitivity of only about 40%. On the flip side, because of a low PPV, 67% of patients with an abnormal (positive) test will have a successful pregnancy and delivery. One can hardly tell a couple not to proceed with IVF/ICSI because they have high DNA fragmentation when they have a two-thirds chance that any pregnancy will go to term. In addition, because there are no proven therapies to improve DNA integrity in most patients, the result of the test will not change management.
Summary
Successful human reproduction depends on the inherent integrity of the
sperm DNA. Indeed, there appears to be a threshold of sperm DNA damage beyond
which embryo development and subsequent pregnancy outcome are impaired. There
is now clinical evidence to show that, sperm DNA damage is detrimental to some
reproductive outcomes and that the spermatozoa of infertile men possess
substantially more DNA damage than that of fertile men. However, our
understanding of the etiology/etiologies of sperm DNA damage, and the full
impact of this sperm defect on reproductive outcomes in humans, remains
rudimentary. Additional studies are needed to fully define the clinical value
of sperm DNA damage testing and the optimal test to be used in this setting.
Finally, therapies for impaired DNA integrity need to be developed and
subsequent improvements in sperm DNA integrity from such therapies need to be
correlated with improved reproductive outcomes.
Footnotes
Dr Zini presents the "pro" viewpoint and Dr Sigman the
"con" viewpoint. 
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