1 Immunogénétique Humaine, Institut Pasteur, 25 rue du Dr Roux, 75724 Paris Cedex 15, France and 2 Andrology Unit, Department of Clinical Physiopathology, University of Florence, Viale Pieraccini 6, Florence, Italy
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Abstract |
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Key words: AZF deletions/azoospermia/genetic counselling/oligozoospermia/Y chromosome deletion
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Introduction |
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Y chromosome microdeletions are a common cause of spermatogenic failure (McElreavey et al., 1999). The incidence of Y microdeletions is 1520% in men with idiopathic azoospermia, falling to 710% in men with idiopathic severe oligozoospermia. Recurrent Y chromosome microdeletions define three non-overlapping regions of Yq, termed AZoospermia Factor (AZF) AZFa, AZFb and AZFc, that have been proposed to be associated with Sertoli cell-only syndrome, spermatogenic arrest and a variable phenotype (severe oligozoospermia or azoospermia) respectively (Vogt et al., 1996
). Although genotype/phenotype correlations have been difficult to establish, a number of studies support these general trends (Krausz and McElreavey, 1999
).
The type of deletion (AZFa, b or c) has been proposed as a potential prognostic factor for sperm retrieval in men undergoing TESE. Deletions including and extending beyond the AZFc region (AZFb+c and AZFa+b+c) are associated with a total absence of testicular spermatozoa (Silber et al., 1998; Table I) and the presence of an AZFb deletion is a significantly adverse prognostic finding for TESE (Brandell et al., 1998; Table I
). In contrast, in ~50% of azoospermic patients with AZFc deletions, mature spermatozoa have been found (Mulhall et al., 1997
).
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This case raises several questions regarding the correct management of couples where the male partner is affected by non-obstructive azoospermia. First, is it necessary to induce multiple follicular growth and carry out the retrieval of oocytes in the female partner considering that the general success rate of sperm retrieval by TESE is only 50%? Cryo-TESE is a good alternative to TESE/ICSI in azoospermic men and avoids unnecessary hormonal stimulation in the female partner. However, cryo-TESE is still a highly invasive technique which consists of multiple testis biopsies with possible adverse effect on the male (Manning et al., 1998), therefore, the need for a predictive diagnostic test before commencing cryo-TESE or TESE/ICSI procedures is clear. Only a few studies have attempted to develop a predictive diagnostic test pre-TESE/ICSI. Prior diagnostic testis biopsy analysed quantitatively (for the presence of mature spermatids) has been reported to be of value in the prediction of subsequent sperm retrieval (Silber et al., 1997
). Y chromosome screening (including the AZFb region) has also been reported as a potential prognostic test (Brandell et al., 1998
). The deletion of the patient mentioned above is consistent with previous reports of spermatogenic arrest either just prior to, or during meiosis, associated with an AZFb deletion (Vogt et al., 1996
; Girardi et al., 1997
; Brandell et al., 1998
; Kleiman et al., 1999
). To date, more than 30 studies have been published on Y chromosome screens of infertile men for microdeletions (for review, see Krausz and McElreavey, 1999). Unfortunately many of these studies did not report the extent of the deletions, testis histology was only available in a minority of cases and no matched phenotype was reported for the different type of AZFb deletions (Kent-First et al., 1999
). However, a careful analysis of the literature and of our own cases shows that different subtypes of AZFb deletions do exist (Tables I and II
). Deletions which remove the whole region (complete AZFb deletions (sY113-sY143), as described in the original article of Vogt et al. (1996) are associated with spermatogenic arrest at the spermatocyte (patient 1, 2, 3, 13, 15 in Table II
) or spermatid stage (patient 14 in Table II
). Deletions which remove the whole AZFb deletions + AZFa and/or AZFc are associated with Sertoli cell-only syndrome (patients 4, 16,17, 20, 26 in Table II
) or with spermatogenic arrest (patient 27 in Table II
). In contrast, deletions which remove only a part of the region or only a single marker (partial AZFb deletions) are associated with a more heterogeneous phenotype including oligozoospermia (patient 18, 22, 24, 40, 41, 47 in Table II
). Unless these atypical deletions are confirmed by Southern blotting their significance is uncertain. Some microdeletions may also represent irrelevant polymorphisms (patient 21 Table II
) (Kostiner et al., 1998
).
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Azoospermia has also been found in men with AZFa and AZFc deletions. AZFa deletions are exceedingly rare and are associated with Sertoli cell-only syndrome type I (Krausz and McElreavey, 1999).
The situation is different regarding azoospermic patients with deletions of the AZFc region. Deletions of the AZFc region are usually associated with hypospermatogenesis or Sertoli cell-only syndrome type II. It is known that hidden islands of normal spermatogenesis in Sertoli cell-only syndrome type II can be found if multiple biopsies are perfomed (Mulhall et al., 1997; Brandell et al., 1998
). Therefore in these cases cryo-TESE (but not TESE/ICSI) seems to be a correct approach.
The prognostic value of Y chromosome deletion analysis in cases of oligozoospermia is not at first apparent but it could have a clinical importance. Partial AZFb and complete AZFc deletions can be associated with oligozoospermia. On the basis of sperm number different types of assisted reproductive technique can be used since Y microdeletion does not preclude the normal fertilizing ability of the spermatozoa (Mulhall et al., 1997; Rossato et al., 1998
; Page et al., 1999
). However, a progressive decrease of sperm number over several months has been described in some men with AZFc deletions (Girardi et al., 1997
; Simoni et al., 1997
). Further follow-up studies on this group of men are urgently required to determine both quantative and qualitative changes in sperm production over time. Cryo-conservation of spermatozoa in these cases will avoid invasive techniques, e.g. TESE/ICSI, in the future.
Male offspring that are conceived by ICSI or IVF techniques from father with oligozoospermia or azoospermia would also benefit from knowledge of their Y status. Since AZFc deletions may be associated with a decline in sperm production over time, cryo-conservation of semen in early adulthood should be considered. Moreover, the identification of the genetic defect will render future medical or surgical therapies unnecessary.
In summary, Y microdeletion screening is important not only to define the aetiology of spermatogenic failure but also because it gives precious information for a more appropriate clinical management of both the infertile male and his future male child.
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Acknowledgments |
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Notes |
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This debate was previously published on Webtrack, May 19, 2000
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References |
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