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Prospective assessment of Y-chromosome microdeletions and reproductive outcomes among infertile couples of Japanese and African origin

Paul E Kihaile1,2,3, Atsushi Yasui1 and Yoshihiro Shuto1

1Oita Medical University, Oita City, 879-5593 Japan

2St. Luke IVF Center, Oita City, 870-0497 Japan

3Muhimbili University College of Health Science, Box 65001, Dar Es Salaam, Tanzania

Journal of Experimental & Clinical Assisted Reproduction 2005, 2:9doi:10.1186/1743-1050-2-9

The electronic version of this article is the complete one and can be found online at: http://www.jexpclinassistreprod.com/content/2/1/9

Received: 15 September 2004
Accepted: 29 June 2005
Published: 29 June 2005

© 2005 Kihaile et al; licensee BioMed Central Ltd.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Background

To compare the frequency of Y-chromosome microdeletions in Japanese and African azoospermic and oligozoospermic men and describe embryo characteristics and reproductive outcome following in vitro fertilization (IVF) with intracytoplasmic sperm injection (ICSI).

Methods

Our study was performed prospectively at two centers, a private IVF clinic and a university hospital. Japanese and African (Tanzanian) men with nonobstructive azoospermia (NOA) and oligozoospermia (concentration < 5 × 106 /ml) were evaluated for Y-chromosome microdeletions (n = 162). Of the 47 men with NOA, 26 were Japanese and 21 were Africans. Of the 115 men with oligozoospermia, 87 were Japanese and 28 were Africans. Reproductive outcomes of patients with Y-chromosome microdeletions were then compared with those of 19 IVF+ICSI cycles performed on couples with Y-chromosome intact males/tubal factor infertility which served as a control group.

Results

Seven azoospermic and oligozoospermic patients had Y-chromosome deletions; the total number of deletions in the AZFc region was five. There was only one deletion in the AZFa region and one complete deletion involving all three regions (AZFa, b, and c) within AZF. In our study population, microdeletion frequency among Japanese men was 6.2% (95% CI, 4.25% – 14.45%), whereas no deletions were identified in the African group (95% CI, 0.0% – 7.27%). The difference between the two groups was not statistically significant, however. Embryos derived from ICSI utilizing sperm with Y-chromosome microdeletion showed reduced rates of fertilization, blastocyst development, implantation, and pregnancy compared to the Y-chromosome intact group, although these observed differences were not statistically significant.

Conclusion

The observed frequency of Y-chromosome microdeletion was 6.2% among Japanese azoospermic and oligozoospermic males; no microdeletions were identified among our African study patients. In this population of couples undergoing IVF+ICSI, there was no statistically significant difference in embryo characteristics or pregnancy outcome between patients with Y-chromosome microdeletion and those with an intact Y-chromosome.

Introduction

Approximately15% of the couples worldwide cannot conceive after one year of regular sexual intercourse, with the male factor accounting for ~40% of all infertility; however, in up to 30% of cases the etiology is unexplained [1,2]. Among these unknown cases of infertility, a genetic etiology for male infertility was long suspected. This was due to cytogenic evidence showing that 0.2% of azoospermic men, who were otherwise phenotypically normal, exhibited Y-chromosome microdeletions [3]. This evidence was supported by karyotyping which revealed autosomal translocations in 1.3% of infertile couples [4-7]. Researchers realized that many cases of male infertility might be genetic because of the failure of most clinical treatments to correct abnormal sperm parameters [8,9]. Observations of sperm counts in various species, including studies of naturally occurring deletions in drosophila via molecular analysis, also led to an intense search for human spermatogenesis gene(s) which might be deficient in some infertile males [10-13]. Recent advancements in molecular methodology have permitted careful mapping of Y-chromosome microdeletions in men with azoospermia and oligozoospermia; in Western populations this frequency varies between 1–35%, depending on inclusion criteria [14]. For Japanese males, a Y-chromosome microdeletion frequency range of 7.6–17% has been reported [15-22]. Such studies have identified three "azoospermic factor" regions (AZF) where deletions occur on the Y-chromosome long arm: AZFa, AZFb, and AZFc. AZFc was shown to contain the most frequently deleted gene cluster, known as the DAZ gene [23]. Several studies found AZFc deletions to be associated with successful retrieval of sperm during testicular sperm extraction (TESE), whereas deletions in AZFa and AZFb were not [23-25]. Histologically, these deletions are associated with various spermatogenetic alterations including Sertoli cell-only syndrome (SCOS), maturation arrest, and hypospermatogenesis.

Recently, several investigators have shown that embryo characteristics following intracytoplasmic sperm injection (ICSI) using sperm obtained from men with Y-chromosome microdeletions were not adversely affected by the deletion [26-31]. The central concern was that vertical transmission of the microdeletion via ICSI might be passed from father to son [32] or by natural (unassisted) conception [30,33]. Since very few studies concerning Y-chromosome microdeletion have been undertaken in Japanese males (and none in African males), we aimed to investigate the frequency of Y-chromosome microdeletion as well as selected embryo features and reproductive outcome in Japanese and African azoospermic and oligozoospermic men who underwent IVF+ICSI.

Materials and Methods

Between January 1998 and January 2003, male volunteers (n = 162) presenting for infertility evaluation and treatment at two centers were evaluated for Y-chromosome microdeletions via peripheral venipuncture. The study population consisted exclusively of Japanese (n = 113) and African (n = 49) males who, with their partners, sought infertility treatment either at St. Luke IVF Center (Japan) or Muhimbili National Hospital (Tanzania). Written informed consent was obtained from all study patients and the investigation was approved by the hospital's ethical committee. Subjects were partitioned into two groups based on sperm concentration: 1) nonobstructive azoospermia (NOA), and 2) oligozoospermia, defined as sperm concentration < 5 × 106 ml.

The first group consisted of 47 males (26 Japanese and 21 Africans); the second group consisted of 115 males (87 Japanese and 28 Africans). None of the study patients were diagnosed with obstructive azoospermia. Six couples from the Muhimbili center were excluded from the study due to active STD. The GFX Genomic Blood DNA Purification Kit (Amersham Biosciences, Buckinghamshire, United Kingdom) was used to extract DNA from peripheral venipuncture samples as previously described [34]. Y-chromosome microdeletions were detected using a polymerase chain reaction (PCR) amplification with a specific sequence tag site (STS) using 24 sets of primers which allowed evaluation of the following sites: sY14, sY18, sY78, sY81, sY83, sY85, sY84, sY90, sY100, sY131, sY134, sY139, sY145, sY143, sY153, sY147, sY156, sY149, sY254, sY157, sY202, sY243, sY158, and sY159. Deletion of the loci was confirmed if the product of the expected size was not obtained after three single STS PCR experiments.

Four patients with NOA and Y-chromosome microdeletion underwent TESE. The samples were microscopically examined to search for sperm, which was cryopreserved as described previously [24]. TESE was successful in 2 of 4 azoospermic cases; after cryopreservation these couples subsequently underwent two ICSI cycles. The three Japanese oligozoospermic patients with Y-chromosome microdeletion produced fresh ejaculated sperm which was subsequently used for 6 ICSI cycles. Sperm morphology in each laboratory was examined by 2 observers [35]; classification of normal sperm morphology at our centers is: <4% = severe teratozoospermia, 4–14% = moderate teratozoospermia and >14% = normal. No fathers or brothers of our male patients were available for testing. All Japanese couples who had a multifactoral diagnosis of oligozoospermia and tubal factor infertility were also assessed for Y-chromosome microdeletions and those found to have an intact Y-chromosome were assigned to the control group. Fourteen Japanese couples were initially considered for this group, but three were excluded because of endometriosis (n = 2) and leiomyoma (n = 1). These remaining couples (n = 11) constituted the control group and they underwent 19 ICSI cycles. Positive and negative controls were used for all AZF microdeletion tests. Thirteen fertile men with a sperm concentration of >20 × 106 /ml were used as positive controls, and twelve females served as negative controls.

Ovarian stimulation protocol, oocyte handling, laboratory procedures for insemination, measurement of sperm parameters, hormones, ICSI, and embryo and blastocyst grading were performed as previously described [35]. Using this protocol, only types I, II and III embryos were considered suitable for transfer and ≤ 3 embryos were transferred on day 3 after microinjection. For 6 cycles, embryos were cultured until day 5–6 and were transferred at the blastocyst stage. Clinical pregnancy was confirmed at 6 weeks via transvaginal ultrasound to establish embryonic cardiac activity.

Data were analyzed for equality of variance using the Levene's test. When p > 0.05 the variances were considered equal, a Student's t-test was performed, and p < 0.05 was considered significant. When p < 0.05, then the variances were considered unequal and a Wilcoxon signed ranked test was done, and p < 0.05 was considered significant. All computations were conducted using the SPSS statistical package (SPSS Inc., Chicago, USA).

Results

Of 162 azoospermic and oligozoospermic Japanese and African males who participated in the study, 47 were diagnosed with NOA and 115 as oligozoospermic. Of 47 NOA cases, 26 were Japanese and 21 were Africans. Of 115 oligozoospermic cases, 87 were Japanese and 28 were African. We identified seven cases with microdeletions and they were all within the azoospermia and oligozoospermia Japanese group. Five of these deletions were identified in the AZFc region, whereas only one deletion was identified in the AZFa region. There was also one complete deletion involving all three regions of AZF (AZFa, b, c). Therefore, the microdeletion frequency within the Japanese group was 6.2% (95% CI, 4.25% – 14.45%). No deletions were identified within the African group (95% CI, 0.0% – 7.27%); this difference was not statistically significant. The deletion frequency among azoospermic Japanese males was 15.4% (95% CI, 11.0% – 42.0%) whereas there were none among the African males (95%CI, 0.0% – 15.4%). Again, the difference did not reach statistical significance. The deletion frequency in oligozoospermic Japanese was 3.4% (95% CI, 1.18% – 9.6%) and there were none in oligozoospermic African males (95% CI, 0.0% – 12.0%); also with no statistical difference.

Two patients were diagnosed with SCOS and both exhibited one microdeletion in the AZFa and AZFabc regions. (Table 2). These two patients had characteristically high serum FSH levels (mean = 30.4 U/L, normal is < 10.0 U/L in our laboratory). Testicular volumes of males with Y-chromosome microdeletion and those with an intact Y-chromosome showed no statistically significant difference (average ± SD volumes were 11.14 ± 2.41 and 12.4 ± 3.40 ml, respectively).

Table 3 summarizes comparisons among various parameters in patients with and without Y-chromosome microdeletion. As expected, sperm concentration was significantly lower in the Y-chromosome microdeletion group than in the intact Y-chromosome group (p < 0.05).

Table 4 presents a comparison of embryo characteristics observed in AZFc microdeletion and Y-chromosome intact patients. Although the Y-chromosome microdeletion group showed a trend towards reduced rates of fertilization, implantation, and pregnancy when compared to the Y-chromosome intact group, this difference did not reach statistical significance. Screening for Y-chromosome microdeletions among our study patients' male offspring was not conducted in this investigation.

Discussion

This study shows the frequency of microdeletion in the AZF region of the Y-chromosome to be 6.2% among Japanese males with azoospermia and oligozoospermia. Our findings are consistent with prior reports which found a microdeletion frequency of 1% to 35%, depending on the male subfertility definition used for inclusion and on the choice of sequence tagged sites used for screening [6,14,28,36,37]. In our populaton, the majority of Y-chromosome microdeletions (~70%) occurred in the AZFc region of the AZF region and is in agreement with other investigations [27,38]. Previous studies on Y-chromosome microdeletion frequency in Japanese males [15-22] suggested a range of 7.6% – 17.0%. Separating these Japanese patients with deletions into azoospermic and oligozoospermic cases revealed frequencies of 15.4 % and 3.4%, respectively.

We excluded from analysis two study patients with Y-chromosome microdeletions at sY202 and sY243. Indeed, no known location has been ascertained so far for sY202 and sY243 is found in several locations both inside and outside DAZ. Nevertheless, the frequency observed in our population is consistent with previous data describing a 15%-20% microdeletion frequency in men with idiopathic azoospermia and a 7%-10% frequency in men with severe idiopathic oligozoospermia [15,23,38,39]. Interestingly, no microdeletions were documented among the 49 African males with azoospermia or severe oligozoospermia. Since ours is the first study of Y-chromosome microdeletion frequency to be undertaken on an African population, a comparison with earlier data sets from this group was not possible.

The absence of Y-chromosome microdeletions in our African study population may be due to limited sampling. However, this finding is in general agreement with the few studies conducted in other parts of Africa that found frequencies of male infertility secondary to oligozoospermia or azoospermia to be much lower (~20%) in Africa than elsewhere [40-48]. Unlike some other regions, the most common cause of male infertility in Africa was found to be infection. Yeboah et al. reported on 595 infertile African males and found ~70% of them to have inflammatory testicular lesion due to STD [40]. A multi-center study by Cates et al. demonstrated that >50% of African couples had secondary infertility due to STD [41], which was a rate much higher than in non-African countries (i.e., <30%).

In our study all active STD cases were excluded, although the association between male infertility and STD remains controversial. Some investigators have shown that treatment of infection directly improved the sperm quality in oligozoospermia [42,43] while others did not see any improvement in sperm quality after treatment [44,45]. It is difficult to know the precise frequency of azoospermia and oligozoospermia in Africa as certain cultural factors (e.g., polygamy) are more common than in other parts of the world [46]. Therefore, an azoospermic man may have children whose actual biological father was another man if the wife had extramarital intersourse with a fertile male [47,48]. Financial constraints did not enable testing to confirm paternity when babies were born after infertility treatments at our centers.

All 5 cases with Y-chromosome microdeletion in the AZFc region had successful outcomes following IVF+ ICSI. A comparison of reproductive outcomes between couples with AZFc microdeletion and couples with an intact Y-chromosome showed no statistically significant difference. Our results confirm previous studies showing that Y-chromosome microdeletions do not appear to adversely affect fertilization and pregnancy rates (either in azoospermic or severe oligozoospermic men) when sperm are successfully retrieved [26-33,36]. The concerns that IVF+ICSI might yield poorer results in the setting of Y-chromosome microdeletions were not seen in previous reports [26-30]. However, Van Volde et al. [29] found fertilization and embryo quality to be significantly lower in couples with Y-chromosome microdeletions compared to couples without Y-chromosome microdeletions; pregnancy and take home baby rates were not statistically different.

In conclusion, our investigation did not detect any Y-chromosome microdeletions in azoospermic or severely oligozoospermic men of African origin. This was in contrast to seven cases of Y-chromosome microdeletion identified in Japanese males. Furthermore, comparison of embryo characteristics in Japanese couples with Y-chromosome microdeletion and control couples (those with no Y-chromosome microdeletion) revealed no statistically significant difference. We regard it as premature to conclude definitively that Y-chromosome microdeletion in azoospermic and oligozoospermic African males is not as common as in other races, due to limited sampling. We hope to continue this investigations with a larger patient population to provide additional information on the overall frequency of azoospermia/oligozoospermia in African males, as well as the association of these conditions with Y-chromosome microdeletions.

Table 1. STS markers of the 7 infertile men with Y chromosome deletions.

Table 2. Findings in 7 infertile men with Y chromosome microdeletion

Table 3. Results of the various parameters of ejaculate sperm cycles in patients with AZFc region Y-deleted and Y-Intact chromosomes.

Table 4. ICSI attempts in 8 cycles with Y-chromosome microdeletions and 19 cycles without microdeletions.

Acknowledgements

We wish to thank Dr. Takafumi Utsunomiya, Yoko Kumasako and Keiko Hirotsuri of St. Luke hospital for their advice and technical help ; We also wish to thank Prof. Kensuke Yamamoto, Dr. Kazuo Aoki, Prof. Junichi Misumi and Akira Kono of Oita University school of Medicine for their help in study design and constant examination of our data; Drs. Ramzy E. Kisanga and Godfrey Lema of Muhimbili University of college science, Dar-es-salaam, Tanzania for their technical assistance while in Tanzania and San Francisco Edit http://www.sfedit.net for editing this manuscript.

References

  1. Thonneau P, Marchand S, Tallec A: Incidence of main causes of infertility in a resident population (1 850 000 inhabitants) of three French regions (1988–1989).

    Hum Reprod 1991, 6:811-81. PubMed Abstract OpenURL

  2. Abma JC, Chandra A, Mosher WD, Peterson LS: Fertility, Family Planning and Women's Health: New data from the 1995 national Survey of Family Growth.

    Vital heath statistics 1997, 23:1-114. OpenURL

  3. Tiepolo L, Zuffardi O: Localization of factors controlling spermatogenesis in nonfluorescent portion of the human chromosome Y long arm.

    Hum Genet 1976, 34:119-124. PubMed Abstract | Publisher Full Text OpenURL

  4. Van Assche E, Bonduelle M, Tournaye H, Joris H, Verheyen G, Devroey P, Van Steirteghem A, Liebaers I: Cytogenetics of infertile men.

    Hum Reprod 1996, 11:1-24. PubMed Abstract | Publisher Full Text OpenURL

  5. Bonduelle M, Aytoz A, Van Assche E: Incidence of chromosomal aberrations in children born after assisted reproduction through intracytoplasmic sperm injection.

    Hum Reprod 1998, 13:781-2. PubMed Abstract | Publisher Full Text OpenURL

  6. Bonduelle M, Camus M, De Vos A, Staessen C, Tournaye H, Van Assche E: Seven Years of Intracytoplasmic Sperm injection and follow up of 1987 subsequent children.

    Hum Reprod 1999, 14:243-264. PubMed Abstract OpenURL

  7. Egozcue S, Blanco J, Vendrell JM, García F, Veiga A, Aran B, Barri PN, Vidal F, Egozcue J: Human male infertility: chromosome anomalies, meiotic disorders, abnormal spermatozoa and recurrent abortion.

    Hum Reprod Update 2000, 6:93-105. PubMed Abstract | Publisher Full Text OpenURL

  8. Devroey P, Vandervorst M, Nagy P, Van Steirteghem AC: Do we treat the male or his gamete? In "Current Theory and Practice of ICSI". In Hum Reprod. Volume 13. Edited by: Devroey P, Tarlatzis B, Van Steirteghem A. Oxford, UK, Oxford University Press; 1998:178-185. PubMed Abstract | Publisher Full Text OpenURL

  9. Silber SJ, Van Sterteghem AC, Liu J, Nagy Z, Tournaye H, Devroey P: High fertilization and pregnacy rates after ICSI with spermatozoa obtained from testicle biopsy.

    Hum Reprod 1999, 10:148-152. OpenURL

  10. Obrien SJ, Wildt DE, Bush M: The Cheetah in genetic peril.

    Sci Am 1986, 254:84-92. PubMed Abstract OpenURL

  11. Ma K, Sharkey A, Kirsch S: Towards the molecular localisation of the AZF locus: mapping of microdeletions in azoospermic men within 14 subintervals of interval 6 of the human Y-chromosome.

    Hum Mol Genet 1992, 1:29-33. PubMed Abstract OpenURL

  12. Ma K, Inglis JD, Sharkey A, Bickmore WA, Hill RE, Prosser EJ: A Y chromosome gene family with RNA binding protein homology; candidate for the azoospermia factor AZF controlling human spermatogenesis.

    Cell 1993, 75:1287-1295. PubMed Abstract | Publisher Full Text OpenURL

  13. Eberhart CG, Maines JZ, Wasserman SA: Meiotic cell requirement for a fly homologue of human deleted in azoospermia.

    Nature 1996, 381:783-5. PubMed Abstract | Publisher Full Text OpenURL

  14. Simoni M, Bakker E, Eurlings MC: Laboratory guidelines for molecular diagnosis of Y-chromosomal microdeletions.

    Int J Androl 1999, 22:292-299. PubMed Abstract | Publisher Full Text OpenURL

  15. Tsujimura A, Matsumiya K, Takao T, Miyagawa Y, Koga M, Takeyama M, Fujioka H, Okuyama A: Clinical analysis of patients with azoospermia factor deletions by microdissection testicular sperm extraction.

    Int J Androl 2004, 27:76-81. PubMed Abstract | Publisher Full Text OpenURL

  16. Carvalho CM, Fujisawa M, Shirakawa T, Kamidono GA, Freitas S, Paulo T, Santos SE, Rocha J, Pena SD, Santos F: Lack of association between Y chromosome haplogroups and male infertility in Japanese men.

    American J Med Genet 2003, 116A(2):152-8. Publisher Full Text OpenURL

  17. Ewis AA, Lee J, Shinka T, Nakahori Y: Microdeletions of a Y-specific marker, Yfm1, and implications for a role in spermatogenesis.

    Journal of Hum Genet 2002, 47(5):257-61. Publisher Full Text OpenURL

  18. Nagafuchi S, Namiki M, Nakahori Y, Kondoh N, Okuyama A, Nakagome Y: A minute deletion of the Y chromosome in men with azoospermia.

    J Urol 1993, 150(4):1155-7. PubMed Abstract OpenURL

  19. Takao T, Akira T, Sada M, Goto R, Koga M, Miyagawa Y: Susceptibility gene for non azoospermia in the HLA 11 region ; Correlations with Y chromosome microdeletions and spermatogenesis.

    Inter J Androl 2004, 27:37-41. Publisher Full Text OpenURL

  20. Kobayashi K, Mizuno K, Hida A, Komaki R, Tomita K, Matsushita I, Namiki M, Iwamoto T, Tamura S, Minowada S: PCR analysis of the Y chromosome long arm in azoospermic patients: evidence for a second locus required for spermatogenesis published erratum appears in.

    Hum Mol Genet 1995, 4(5):974. PubMed Abstract OpenURL

  21. Kato H, Komori S, Nakata Y, Sakata K, Kanazawa R, Handa M, Kobayashi S, Koyama K, Isojima S: Screening for deletions in interval D16-22 of the Y chromosome in azoospermic and oligozoospermic Japanese men.

    J Hum Genet 2001, 46(3):110-4. PubMed Abstract | Publisher Full Text OpenURL

  22. Nakahori Y, Kuroki Y, Komaki R, Kondoh N, Namiki M, Iwamoto T, Toda T, Kobayashi K: The Y chromosome region essential for spermatogenesis.

    Hormone Research 1996, 46(Suppl 1):20-3. PubMed Abstract OpenURL

  23. Reijo R, Alagappan RK, Patrizio P, Page DC: Severe oligozoospermia resulting from deletions of azoospermia factor gene on Y chromosome.

    Lancet 1996, 347:1290-1293. PubMed Abstract | Publisher Full Text OpenURL

  24. Silber SJ, Alagappan R, Brown LG, Page DC: Y chromosome deletions in azoospermic and severely oligozoospermic men undergoing intracytoplasmic sperm injection after testicular sperm extraction.

    Hum Reprod 13:3332-3337. Publisher Full Text OpenURL

  25. Hopps CV, Mielnik A, Goldstein M, Palermo GD, Rosenwaks Z, Schlegel PN: Detection of sperm in men with Y chromosome microdeletions of the AZFa, AZFb and AZFc regions.

    Hum Reprod 2003, 18:1660-1665. PubMed Abstract | Publisher Full Text OpenURL

  26. Mulhall JP, Reijo R, Alagappan : Azoospermic men with deletion of the DAZ gene cluster are capable of completing spermatogenesis: fertilization, normal embryonic development and pregnancy occur when retrieved testicular spermatozoa are used for intracytoplasmic sperm injection.

    Hum Reprod 1997, 12:503-508. PubMed Abstract | Publisher Full Text OpenURL

  27. Oates RD, Silber S, Brown L, Page DC: Clinical characterization of 42 oligospermic or azoospermic men with microdeletion of the AZFc region of the Y chromosome, and of 18 children conceived via ICSI.

    Hum Reprod 2002, 17:2813-2824. PubMed Abstract | Publisher Full Text OpenURL

  28. Choi JM, Chung P, Veeck LA, Mielnik LA, Palermo GD, Schlegel PN: AZF microdeletions of the Y chromosome and in vitro fertilization outcome.

    Fertil Steril 2004, 81:337-341. PubMed Abstract | Publisher Full Text OpenURL

  29. Van Golde RJT, Wetzels AMM, de Graaf R: Decreased fertilization rate and embryo quality after ICSI in oligozoospermic men with microdeletions in the azoospermia factor c region of the Y chromosome.

    Hum Reprod 2001, 16:289-292. PubMed Abstract | Publisher Full Text OpenURL

  30. Silber SJ: pontaneous pregnancy in couples with very severe oligospermia (<0.5 × 10.6 sperm): implications for transmission of Y chromosome deletions.

    Fertil Steril 2001, 76:S10. Publisher Full Text OpenURL

  31. Kihaile PE, Kisanga RE, Aoki K, Kumasako Y, Misumi J, Utsunomiya T: Embryo Outcome in Y-chromosome Microdeleted Infertile Males after ICSI:.

    Mo Reprod Dev 2004, 68:176-181. Publisher Full Text OpenURL

  32. Page DC, Silber S, Brown LG: Men with infertility caused by AZFc deletion can produce sons by intracytoplasmic sperm injection but are likely to transmit the deletion and infertility.

    Hum Reprod 1999, 14:1722-1726. PubMed Abstract | Publisher Full Text OpenURL

  33. Rolf C, Gromoll J, Simoni M, Nieschlag1 E: Natural transmission of a partial AZFb deletion of the Y chromosome over three generations: Case report.

    Hum Reprod 2002, 17(9):2267-2271. PubMed Abstract | Publisher Full Text OpenURL

  34. Henegariu O, Hirschmann P, Kilian K: Rapid screening of the Y chromosome in idiopathic sterile men, diagnostic for deletions in AZF, a genetic Y factor expressed during spermatogenesis.

    Andrologia 1994, 26:97-106. PubMed Abstract OpenURL

  35. Utsunomiya T, Naitou T, Nagaki M: A prospective trial of blastocyst culture and transfer.

    Hum Reprod 2002, 17(7):1846-1851. PubMed Abstract | Publisher Full Text OpenURL

  36. Peterlin B, Kunej T, Sinkovec J, Gligorievska N, Zorn B: Screening for Y chromosome microdeletions in 226 Slovenian subfertile men.

    Hum Reprod 2000, 17(1):17-24. Publisher Full Text OpenURL

  37. Foresta C, Moro E, Ferlin A: Y chromosome microdeletions and alterations of spermatogenesis.

    Endocrine Reviews 2001, 22:226-239. PubMed Abstract | Publisher Full Text OpenURL

  38. Reijo R, Lee TY, Salo P, Alagappan R, Brown LG, Rosenberg M: Diverse spermatogenic defects in humans caused by Y chromosome deletions encompassing a novel RNA-binding protein gene.

    Nature Genetics 1995, 10:383-393. PubMed Abstract | Publisher Full Text OpenURL

  39. Foresta C, Ferlin A, Garolla A, Moro E, Pistorello M, Barbaux S, Rossato M: High frequency of well-defined Y-chromosome deletions in idiopathic Sertoli cell-only syndrome.

    Human Reproduction 1998, 13:302-307. PubMed Abstract | Publisher Full Text OpenURL

  40. Yeboah ED, Wadhwani JM, Wilson JB: Etiological factors of male infertility in Africa.

    International Journal of Fertility 1992, 37(5):300-7. PubMed Abstract OpenURL

  41. Cates W, Farley TM, Rowe PJ: Worldwide patterns of infertility: is Africa different?

    Lancet 1985, 2(8455):596-8. PubMed Abstract | Publisher Full Text OpenURL

  42. Imade GE, Towobola OA, Sagay AS, Otubu JA: Sexually transmitted diseases and medico-social factors associated with male infertility in Nigeria.

    Archives of AIDS Research 1993, 7(3–4):245-52. PubMed Abstract OpenURL

  43. Bornman MS, Crewe-brown HH, Reif S, Mahomed MF, Broomker D, Schulenburg GW: Sexually transmitted diseases (STD) in infertile males attending the andrology clinic at Ga-Rankuwa Hospital.

    Archives of AIDS Research 1993, 145-150. OpenURL

  44. Collet M, Reniers J, Frost E, Gass R, Yvert F, Leclerc A, Roth-Meyer C, Ivanoff B, Meheus A: Infertility in Central Africa: infection is the cause.

    International Journal of Gynaecol & Obstet 1988, 26:423-8. Publisher Full Text OpenURL

  45. Vigil P, Morales P, Tapia A, Riquelme R, Salgado AM: Chlamydia trachomatis infection in male partners of infertile couples: incidence and sperm function.

    Andrologia 2002, 34:155-61. PubMed Abstract | Publisher Full Text OpenURL

  46. Ness R, Markovic N, Carlson CL, Coughlin MT: Do men become infertile after having sexually transmitted urethritis? An epidemiologic examination.

    Fertil & Steril 1997, 68:205-13. PubMed Abstract | Publisher Full Text OpenURL

  47. Bambra CS: Current status of reproductive behaviour in Africa.

    Human Reproduction Update 1999, 5:1-20. PubMed Abstract | Publisher Full Text OpenURL

  48. Gausset Q: AIDS and cultural practices in Africa: the case of the Tonga (Zambia).

    Social Science & Medicine 2001, 52:509-18. Publisher Full Text OpenURL

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