2. Testicular Sperm Retrieval
Male infertile individuals with severe oligozoospermia or secretory azoospermia may be able to father children with the development of ICSI
[60][61][62] and testicular sperm extraction (TESE)
[63][64][65][66][67].
The existence of focal spermatogenesis in KS patients also has allowed for successful spermatozoa recovery (SSR) from the seminiferous tubules
[68][69][70]. The spermatozoa retrieval rate (SRR) in adolescents (15–19 y) and young adults (20–24 y) was 52%, 40–66% in adults and 30% in cases of cryptorchidism
[31][71][72][73]. The kind of spermatogenesis failure with the SRR was specified in some instances. Although 38 (76%) of 50 KS patients had tubular sclerosis and atrophy, 9 (18%) had complete or incomplete germ-cell aplasia (only SC), and 3 (6%) had complete or incomplete maturation arrest, authors were able to retrieve spermatozoa in 24 (48%) of these cases. Unfortunately, authors did not specify the testicular phenotype in relation to successful sperm retrieval
[74]. Another report of 47 KS patients revealed 34 cases with SCs alone (71% SRR), 9 with LC hyperplasia alone (33% SRR), 1 with maturation arrest (without sperm retrieval), and 3 with focal spermatogenesis (67% SRR)
[75]. In another study of 45 KS patients, 58% of total SRR was obtained, with 29 (64.4%) cases presenting tubular sclerosis and atrophy (59% SRR), 12 (26.7%) presenting complete germ cell aplasia–LC hyperplasia (50% SRR), and 4 (8.9%) presenting maturation arrest (75% SRR)
[76]. Another report of 6 KS patients with 35% of total SSR revealed 1 case with hypospermatogenesis and 5 cases with only SCs
[77]. In a study of 9 KS patients, 6 presented only SCs (64% SRR), 2 presented foci of spermatogenesis (100% SRR), and 1 evidenced only LC hyperplasia (without sperm retrieval)
[78]. These observations suggested that even in KS patients with a negative histopathological finding, a focus of spermatogenesis might be found.
2.1. Predictive Factors of Testicular Sperm Retrieval
Several markers were described in non-mosaic KS cases to characterize their androgen insufficiency and spermatogenesis dysfunction in comparison to the healthy population
[79][80][81][82][83][84][85].
There are currently no clinical or biological parameters that can predict an SSR with certainty in these KS patients. However, several patient characteristics were shown to be related to SSR cases as compared to unsuccessful sperm retrieval cases.
Several studies found a significant increase in SSR with lower age
[29][76][77][86][87][88][89][90][91][92][93][94], lower time of infertility
[29], lower age, lower FSH levels, and high T levels
[93], higher testicular volume and higher T levels
[95][96], higher T levels
[91][93][97], presence of 46,XY spermatogonia
[98], higher androgen-binding protein levels
[98], and with lower LH levels and higher T levels
[92]. Other studies, on the other hand, did not find a significant increase in the SSR with regard to age, testicular volume (decreased), FSH (increased), and T (normal) levels
[99][100], as well as in testicular echogenicity and intratesticular blood flow resistance
[101]; age, testicular volume, FSH, LH (increased), and T (normal) levels, as well as in the FSH:LH ratio or in the androgen sensitivity index (LH x T)
[74]; age, testicular volume, FSH, and T (decreased) levels
[102]; testicular volume, FSH, LH, and T (low-normal) levels
[86][103][104]; testicular volume, FSH, LH, and T (normal) levels
[76][104]; age, testicular volume, FSH, LH, T (decreased), PRL (normal), E2 (normal) and inhibin (decreased) levels
[105]; testicular volume, FSH, LH, T levels (low-normal), and PRL (normal) levels
[77]; testicular volume, FSH, and inhibin B (decreased) values
[89]; age, testicular volume, FSH, LH, and T (normal) values
[106]; FSH and LH levels or serum inhibin B (decreased) levels
[89][107]; FSH and LH levels
[91]; or age, time of infertility, hormone levels, number of fragments at TESE, time of search at TESE
[31].
Other studies were conducted to identify potential spermatogenesis markers, but without comparing cases with SSR versus cases with unsuccessful sperm retrieval. These included the findings of decreased testicular volume
[108], decreased testicular volume, increased FSH and LH levels, and decreased T levels
[70][109][110][111]; decreased testicular volume, high levels of FSH and LH, with normal T values
[112][113][114]; increased levels of FSH and LH, slightly increased levels of PRL, with normal values of T and E2
[115]; increased levels of FSH and LH, normal levels of PRL and decreased T levels
[116][117][118]; decreased testicular volume, high levels of FSH and LH, with normal PRL and T levels
[119]; and decreased testicular volume, increased FSH levels, and decreased inhibin B levels
[120].
The goal of T replacement therapy in young boys (early-to-mid-puberty) with KS is to promote linear growth, increase muscle mass, preserve bone density, and allow for the development of secondary sexual characteristics
[121]. Although T replacement therapy improves symptoms of androgen insufficiency caused by KS, it also inhibits spermatogenesis at the spermatogonia stage in adults. Furthermore, while T may aid in LH suppression, LC synthesis of the germ cell protector INSL3 will be decreased
[3][33]. Adult T replacement therapy should thus be used solely in patients who are not interested in infertility treatments and have androgen deficiency. It should be discontinued for at least 4–6 months prior to infertility treatment if used
[83][84].
2.2. Techniques of Testicular Sperm Retrieval
Many KS patients have sought infertility treatment as adults, with no other symptoms or signs besides infertility. These patients had decreased testicular volume, high FSH and LH mean serum levels, and normal or slightly lower T concentrations. This group of patients did not belong to the main group (65–85%) of KS patients reported as having low T levels
[82].
For patients, the testicular SRR is critical. Previous reviews showed a mean SRR of 44%
[9], with a range of 30–70%
[10]. This observed variability in the SRR suggests a possible effect of the different number of patients studied, retrieval technique, and differences in patient characteristics.
According to studies, non-mosaic KS patients with low T levels should be treated with aromatase inhibitors first to decrease E2 levels and therefore enhance T intratesticular availability. This was suggested to potentially improve spermatogenesis in KS cases with foci of spermatogenesis
[83]. When applied to men with low T levels or low T:E2 ratios, a higher retrieval rate (66%) has been reported using pre-treatment with aromatase inhibitors to equilibrate the T:E2 ratio
[70][75][88]. However, these success rates could also be attributed to the simultaneous use of microsurgical testicular sperm extraction (mTESE). Because of the scarcity of research in KS patients and the absence of comparisons between conventional TESE (cTESE) and mTESE in patients treated with aromatase inhibitors, this kind of treatment is not routinely followed in cases with low T levels and high FSH and LH values. In fact, there have been cases of SSR after cTESE in patients with slightly low T levels who did not receive aromatase pre-treatment (29, 31). Nevertheless, aromatase treatment should be administered in those circumstances
[88][93].
The mTESE
[122] is a very promising TESE procedure, presenting high rates of SSR (47–69%) in KS patients
[75][76][86][87][88][90][96][103][105][111][114][123][124], though none of these reports compared mTESE to cTESE. Although not in KS patients, both approaches were compared in the pioneering work of Schlegel
[122][125], with authors obtaining an SRR of 63% by mTESE vs. an SRR of 41% by cTESE. There have been very few reports comparing cTESE to mTESE in KS patients. A study compared 28 cases using cTESE (50% SRR) to 10 cases with mTESE (10% SRR)
[106]. Another report compared 23 cases using cTESE (0% SRR) to 20 cases with mTESE (33% SRR)
[97]. A third report compared 43 cases using cTESE (51% SRR) to 40 cases with mTESE (33% SRR)
[99].
In cTESE (37 reports), the SRR was 44% (228/516), with a range of 16–100%. There were 3 reports with ≥50 KS cases (SRR of 38, 40, and 48%)
[29][31][74], with none presenting an SRR greater than 50%. Of the other 34 cases, there were 16 case reports with 100% SRR
[20][23][65][70][110][111][115][116][117][118][119][126][127][128][129][130], one with 4 patients and 75% SRR
[120], one with 18 cases and 28% SRR
[107], one with 19 cases and 21% SRR
[101], another with 5 patients and 20% SRR
[131], one with 25 patients and 16% SRR
[102], and 13 reports exhibited an SRR of 30–57%
[68][69][72][77][89][95][98][112][132][133][134][135][136].
In mTESE (18 reports), the SRR was 43% (427/991), with an SRR range of 17–100%. There were 7 reports with ≥50 KS cases (SRR of 20, 28, 33, 43, 47, 57, and 66%)
[76][88][91][92][93][96], of which 2 cases presented an SRR of more than 50% (57, 66%)
[76][88]. The other 11 KS cases evidenced SRRs ranging from 17%
[104] to 40–74%
[75][78][90][105][123][137][138][139], with 2 cases displaying a 100% SRR, one with 2 patients
[114] and the other with 9 patients
[140].
The mTESE requires a surgical unit and specialized equipment, is aggressive (the testis is completely opened transversally), complex, time-consuming, and expensive. Many authors perform cTESE in a surgical unit, and the procedure is also time-consuming and expensive, as multiple testicular openings are performed if spermatozoa are not found
[94]. A very efficient modified cTESE procedure, on the other hand, involves spermatic cord block (local anesthesia) in an outpatient setting (without a surgical unit), with a single 1 cm scrotum excision to reach the tunica vaginalis space. Thereafter, a 0.5 cm incision is made to expose the seminiferous tubules, followed by a biopsy of a small fragment (1–2 mm) that is immediately examined for spermatozoa. Wherever necessary, the testis is simply rotated exposing its different faces, eliminating the need for additional scrotal incisions. The procedure takes about 30–45 min and no complications were observed
[29][31]. cTESE, like mTESE, requires the services of a highly skilled experienced urologist (
Figure 1).
Figure 1. Outpatient conventional TESE employing local anesthesia using the three-finger technique and spermatic cord block. Left. Exposure of the tunica albuginea after entering the tunica vaginalis space. Right. Exposure of the seminiferous tubules.
Recently, comparisons of both methods, cTESE and mTESE, were conducted. A meta-analysis involving 1248 KS patients found no statistically significant differences in SSR between the two methods, with a mean SRR of 44% (43% in cTESE, 45% in mTESE, and 41% in mixed cases)
[100]. A more recent comprehensive review of the literature on KS patients also revealed a mean SRR of 42–57% using both testicular sperm retrieval procedures
[141]. These differences highlight that SRR variability may be attributable to differences in patient characteristics as well as differences in the number of patients analyzed or the retrieval technique. Nevertheless, it would be relevant if the major American and European groups could conduct a prospective comparative study of mTESE vs. cTESE in a large number of KS cases.
2.3. Clinical and Newborn Outcomes
Several previous studies reported the use of cryopreserved testicular spermatozoa
[77][78][93][107][114][120][123][130][133][142], but the small number of cases prevented comparisons. Other studies comparing fresh with cryopreserved testicular spermatozoa reported similar rates of clinical pregnancy (CP) and newborns (NBs)
[77][106][124][133], whereas other studies have found lower CP and NB rates in cryopreserved testicular spermatozoa
[29][31].
Some studies provided larger numbers of patients enabling comparisons between fresh and cryopreserved spermatozoa treatment cycles. There were 10 fresh and 16 cryopreserved testicular spermatozoa treatment cycles in a report of 38 KS patients with an SRR of 39% using cTESE and mTESE. In ICSI cases with cryopreserved testicular spermatozoa, the authors observed a significantly higher embryo cleavage rate (ECR)
[106]. There were 20 fresh and 17 cryopreserved testicular spermatozoa treatment cycles in a report of 65 KS patients with an SRR of 39% using cTESE. In ICSI cycles using fresh testicular spermatozoa, the authors reported a significantly higher fertilization rate (FR), number of high-grade embryos, and CP rate
[29]. There were 32 fresh and 12 cryopreserved testicular spermatozoa treatment cycles in a study of 83 KS patients with an SRR of 42% using cTESE and mTESE. The implantation rate (IR) was significantly higher in ICSI cases with cryopreserved testicular spermatozoa
[99]. There were 25 fresh and 22 cryopreserved testicular spermatozoa treatment cycles in a recent report on 77 KS patients with a 40% SRR using cTESE. In ICSI cycles using fresh testicular spermatozoa, authors observed a higher FR, number of high-grade day-3 embryos, biochemical pregnancy rate, CP rate, IR and live birth delivery rate (LBDR)
[31]. In conclusion, two studies indicated that ICSI cycles using cryopreserved testicular spermatozoa had higher ECR and IR, while two studies revealed that ICSI cycles using fresh testicular spermatozoa had higher FR, ECR, number of high-quality embryos, IR, CP rate, and LBDR.
The authors of a meta-analysis of cases with secretory azoospermia first concluded that there were no significant differences in embryological and clinical outcomes using ICSI either with cryopreserved testicular spermatozoa or with fresh testicular spermatozoa. However, the authors also confirmed that when different pathologies, such in KS cases, were individually examined, fresh testicular sperm produced better outcomes
[143]. Thus, it is possible that the observations that using cryopreserved testicular spermatozoa yielded higher rates of embryo cleavage and implantation
[99][106] depends on a bias caused by the fact that only two parameters were evidenced and the number of cases analyzed was relatively low, with this data suggested to be inconclusive.
There has been some concern about the possibility of an increased risk of chromosome abnormalities in the offspring of KS patients, after increased rates of both autosomal aneuploidies
[16][112][144][145][146][147][148][149] and sex-chromosome aneuploidies were found in spermatozoa from KS men, albeit at a low rate
[150], and in preimplantation embryos
[132].
Up to the present, all children born after using testicular sperm from KS patients present a normal karyotype. This may be explained by previous observations that indicated that the majority of the 47,XXY germ cells are not meiotically competent, being thus unable to originate chromosomal abnormal sperm
[151], and by other reports that observed a normal pattern of sex chromosome segregation in most of the testicular sperm retrieved from KS patients
[112].
Until the present day, all published data have revealed that, with the exception of two cases, none of the children born from KS patients exhibited an abnormal chromosomal constitution
[29][31][87][88][96][99][100][106][141][152]. The prevalence of chromosomal abnormalities in the general population has been found to be at a 0.5–1% rate
[153][154]. The current research demonstrates that, as only two children (0.63%) were afflicted in 315 children, the risk of Klinefelter karyotype transmission is low. Thus, the present data reassures that KS men have no increased risk of transmitting their genetic problem to offspring. Nonetheless, patients with KS should be informed of the technical possibility of further genetic diagnosis procedures, even though the benefit of preimplantation genetic testing (PGT) or prenatal diagnosis (PND) is questionable in the light of these findings.