AZFb Deletions Research Articles

RBMY genes and AZFb deletions.

Microdeletions of the AZFb region of the human Y chromosome usually result in severe consequences for spermatogenesis. AZFb contains at least four kinds of genes/gene families. These include a number of RBMY genes, which are clustered in the AZFb deletion interval. They are amongst the oldest genes on the mammalian Y chromosome, and are related to the gene encoding hnRNPG (RBMX) on the X chromosome. A retroposon-derived version of these genes is found on chromosome 11 that might replace the function of these genes during meiosis, during which time the X and Y chromosomes are transcriptionally inactivated. Each of these genes encodes proteins with an RNA binding motif, and interacts with more ubiquitously expressed proteins involved in pre-mRNA splice site selection. These findings imply that important pre-mRNA processing pathways might be disrupted in the germ cells of AZFb men.

Y chromosome microdeletion screening in infertile men.

Molecular analysis of Y-chromosomal microdeletions is routinely performed in the work-up of male infertility, in order to establish a diagnosis and for genetic counseling of the couple, since such microdeletions are transmitted to the male offspring. The review of published data shows that microdeletions are relatively common in patients with azoospermia or severe oligozoospermia, with wide variations in the reported deletion frequency depending mainly on the selection criteria. In general, patients with proximal deletions, involving the AZFa and/or the AZFb region show severe defects of spermatogenesis with a high prevalence of Sertoli cell only syndrome, while deletions of the distal AZFb and of the AZFc region can be compatible with residual spermatogenesis. Microdeletions have been only sporadically found in normozoospermic patients. For the time being the molecular analysis of microdeletions of the Y chromosome is indicated in infertile patients with sperm concentration <5 x 10(6)/ml and in men undergoing assisted reproduction techniques, since the genetic defect and, most probably, the related infertility problem will be transmitted to the sons.

The Prognostic Value of Y Chromosome Microdeletions Involving the AZFb Region in Testicular Sperm Extraction

Objectives: Testicular sperm extraction (TESE) for intracytoplasmic sperm injection (ICSI) is an effective treatment for men with non-obstructive azoospermia. Overall, approximately 35% of these men have no spermatozoa found in their testicular tissue. The success of TESE cannot be predicted based on preoperative hormonal profiles (FSH, testosterone), nor based on testicular volume. Even a prior diagnostic testis biopsy does not absolutely predict the success of TESE, due to the heterogeneous nature of sperm maturation within seminiferous tubules of the testicle. Preliminary data in recent literature suggest a correlation between microdeletions involving the AZFb of the Y-chromosome and the absence of spermatozoa with TESE (Brandell et al., Human Reprod., 1998). We hereby report our expanded experience of the relationship between microdeletions involving AZFb and TESE results in men with non-obstructive azoospermia.Design: A retrospective analysis of azoospermic men who underwent TESE from 1996 to 2000 was performed. The outcomes of men with AZFb microdeletion of the Y-chromosome were analyzed.Materials and Methods: All TESE were performed under local or general anesthesia by one surgeon. TESE were performed with either multiple biopsies or with a single large incision with multiple samples of the seminiferous tubules under microscopic vision (microdissection TESE). The procedures were performed in conjunction with planned in-vitro fertilization cycles with ICSI for the female partner. Y-chromosomal microdeletion was tested in all patients using DNA extracted from peripheral leukocytes with a series of 35 sequence-tagged sites on Yq using polymerase chain reaction.Results: Among 181 patients who undergone TESE, 10 (6%) were found to have microdeletion involving the AZFb regions and 5 of them (3%) have microdeletion in AZFb region only. For men with non-obstructive azoospermia and no detectable deletions of the AZFb region, 114/171 (67%) men had sperm retrieved with TESE, whereas none of the 11 patients with microdeletions involving the AZFb region had sperm found with TESE (p<0.001). The average duration of TESE in patients with deletions involving the AZFb region was 3.5 hours.Conclusions: Genetic studies may provide important prognostic information in the management of patients with severe male infertility, as illustrated by our observation that the presence of an AZFb deletion is a significantly adverse prognostic finding for TESE. When counseling men with AZFb deletions, clinicians should apprise them of these results before attempting TESE-ICSI. Objectives: Testicular sperm extraction (TESE) for intracytoplasmic sperm injection (ICSI) is an effective treatment for men with non-obstructive azoospermia. Overall, approximately 35% of these men have no spermatozoa found in their testicular tissue. The success of TESE cannot be predicted based on preoperative hormonal profiles (FSH, testosterone), nor based on testicular volume. Even a prior diagnostic testis biopsy does not absolutely predict the success of TESE, due to the heterogeneous nature of sperm maturation within seminiferous tubules of the testicle. Preliminary data in recent literature suggest a correlation between microdeletions involving the AZFb of the Y-chromosome and the absence of spermatozoa with TESE (Brandell et al., Human Reprod., 1998). We hereby report our expanded experience of the relationship between microdeletions involving AZFb and TESE results in men with non-obstructive azoospermia. Design: A retrospective analysis of azoospermic men who underwent TESE from 1996 to 2000 was performed. The outcomes of men with AZFb microdeletion of the Y-chromosome were analyzed. Materials and Methods: All TESE were performed under local or general anesthesia by one surgeon. TESE were performed with either multiple biopsies or with a single large incision with multiple samples of the seminiferous tubules under microscopic vision (microdissection TESE). The procedures were performed in conjunction with planned in-vitro fertilization cycles with ICSI for the female partner. Y-chromosomal microdeletion was tested in all patients using DNA extracted from peripheral leukocytes with a series of 35 sequence-tagged sites on Yq using polymerase chain reaction. Results: Among 181 patients who undergone TESE, 10 (6%) were found to have microdeletion involving the AZFb regions and 5 of them (3%) have microdeletion in AZFb region only. For men with non-obstructive azoospermia and no detectable deletions of the AZFb region, 114/171 (67%) men had sperm retrieved with TESE, whereas none of the 11 patients with microdeletions involving the AZFb region had sperm found with TESE (p<0.001). The average duration of TESE in patients with deletions involving the AZFb region was 3.5 hours. Conclusions: Genetic studies may provide important prognostic information in the management of patients with severe male infertility, as illustrated by our observation that the presence of an AZFb deletion is a significantly adverse prognostic finding for TESE. When counseling men with AZFb deletions, clinicians should apprise them of these results before attempting TESE-ICSI.

Prognostic value of Y deletion analysis: what is the clinical prognostic value of Y chromosome microdeletion analysis?

In many centres, Y chromosome deletion analysis is still not performed routinely and if so, the results are used for genetic counselling but are not considered as having a useful prognostic value. The type of deletion (AZFa, b or c) has been proposed as a potential prognostic factor for sperm retrieval in men undergoing TESE. AZFc deletions and partial AZFb deletions are associated with sperm retrieval in approximately 50% of cases while in the case of a patient with complete AZFb deletion the probability of finding mature spermatozoa is virtually nil. Therefore the extent and position of a Y microdeletion is important (complete or partial). The prognostic value of Y chromosome deletion analysis in cases of oligozoospermia is important when one considers the progressive decrease of sperm number over time in men with AZFc deletions. Cryo-conservation of spermatozoa in these cases could avoid invasive techniques, such as 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 the identification of the genetic defect will render future medical or surgical therapies unnecessary. Y microdeletion screening is therefore 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.

A High Frequency of Y Chromosome Deletions in Males With Nonidiopathic Infertility

Microdeletions of the long arm of the human Y chromosome are associated with spermatogenic failure and have been used to define three regions of Yq (AZFa, AZFb, and AZFc) that are recurrently deleted in infertile males. In a blind study we screened 131 infertile males (46 idiopathic and 85 nonidiopathic) for Y chromosome microdeletions. Nineteen percent of idiopathic males, with an apparently normal 46,XY chromosome complement had microdeletions of either the AZFa, AZFb, or AZFc region. There was no strict correlation between the extent or location of the deletion and the phenotype. The AZFb deletions did not include the active RBM gene. Significantly, a high frequency of microdeletions (7%) was found in patients with known causes of infertility and a 46,XY chromosome complement. These included deletions of the AZFb and AZFc regions, with no significant difference in the location or extent of the deletion compared with the former group. It is recommended that all males with reduced or absence sperm counts seeking assisted reproductive technologies be screened for deletions of the Y chromosome.

A high frequency of Y chromosome deletions in males with nonidiopathic infertility.

Microdeletions of the long arm of the human Y chromosome are associated with spermatogenic failure and have been used to define three regions of Yq (AZFa, AZFb, and AZFc) that are recurrently deleted in infertile males. In a blind study we screened 131 infertile males (46 idiopathic and 85 nonidiopathic) for Y chromosome microdeletions. Nineteen percent of idiopathic males, with an apparently normal 46,XY chromosome complement had microdeletions of either the AZFa, AZFb, or AZFc region. There was no strict correlation between the extent or location of the deletion and the phenotype. The AZFb deletions did not include the active RBM gene. Significantly, a high frequency of microdeletions (7%) was found in patients with known causes of infertility and a 46,XY chromosome complement. These included deletions of the AZFb and AZFc regions, with no significant difference in the location or extent of the deletion compared with the former group. It is recommended that all males with reduced or absence sperm counts seeking assisted reproductive technologies be screened for deletions of the Y chromosome.

Human male infertility and Y chromosome deletions: role of the AZF-candidate genes DAZ, RBM and DFFRY.

Microdeletions in Yq11 overlapping three distinct 'azoospermia factors' (AZFa-c) represent the aetiological factor of 10-15% of idiopathic azoospermia and severe oligozoospermia, with higher prevalence in more severe testiculopathies, such as Sertoli cell-only syndrome. Using a PCR-based screening, we analysed Yq microdeletions in 180 infertile patients affected by idiopathic Sertoli cell-only syndrome and different degrees of hypospermatogenesis, compared with 50 patients with known causes of testicular alteration, 30 with obstructive azoospermia, and 100 normal fertile men. In idiopathic severe testiculopathies (Sertoli cell-only syndrome and severe hypospermatogenesis), a high prevalence of microdeletions (34.5% and 24.7% respectively) was found, while milder forms were not associated with Yq alteration. No deletions were found in testiculopathies of known aetiology, obstructive azoospermia, normal fertile men and male relatives of patients with deletions. Deletions in the AZFc region involving the DAZ gene were the most frequent finding and they were more often observed in severe hypospermatogenesis than in Sertoli cell-only syndrome, suggesting that deletions of this region are not sufficient to cause complete loss of the spermatogenic line. Deletions in AZFb involving the RBM gene were less frequently detected and there was no correlation with testicular phenotype, with an apparent minor role for such gene in spermatogenesis. The DFFRY gene was absent in a fraction of patients, making it a candidate AZFa gene. Our data suggest that larger deletions involving more than one AZF-candidate gene are associated with a more severe testicular phenotype.

Male Infertility and the Y Chromosome

Although it has been established since the 1970s thatdeletions of the long arm of the Y chromosome are as-sociated with spermatogenic failure, only in the last fewyears have these regions been described at the molecularlevel. In parallel, Y-linked genes and gene families thatmay explain the phenotypes of men carrying these de-letions have been identified. The first association be-tween spermatogenic failure and an underlying geneticcause was demonstrated by Tiepolo and Zuffardi (1976)in a report of six azoospermic patients carrying micro-scopically detectable deletions of the distal portion ofYq. In four patients, the deletion was de novo—that is,their fathers were tested and were found to carry intactY chromosomes. On this basis, Tiepolo and Zuffardi(1976) proposed the existence of a spermatogenesis fac-tor, called the “azoospermia factor” (AZF), encoded bya gene on distal Yq. However, the assumption that AZFrepresented a single Y-linked gene was overturned whenVogt et al. (1996) observed that Y chromosome micro-deletions follow a certain deletion pattern, with threerecurrently deleted nonoverlapping subregions in prox-imal, middle, and distal Yq11, designated “AZFa,”“AZFb,” and “AZFc,” respectively. In addition, it be-came clear that these deletions were not exclusively as-sociated with azoospermia (Reijo et al. 1996

AZFb deletions predict the absence of spermatozoa with testicular sperm extraction: preliminary report of a prognostic genetic test.

Genetic abnormalities, including partial deletions of the Y-chromosome, are commonly detectable in men with non-obstructive azoospermia (NOA). NOA can be treated using testicular sperm extraction (TESE) with intracytoplasmic sperm injection (ICSI). Recent studies have shown that the presence of deletions involving the AZFc region do not appear to affect the chance of retrieving spermatozoa or have a significant impact on fertilization or pregnancy rates with ICSI. We investigated the effect of Y-chromosome partial deletions on the chance of sperm retrieval with TESE. Eighty attempts at sperm retrieval were performed using TESE on men who were previously evaluated for Y-chromosome partial deletions. Y-chromosome analysis was performed using a polymerase chain reaction (PCR)-based technique with 35 sequence-tagged-sites. Of the 80 men, nine (11%) had partial Y-chromosome deletions detected. Two azoospermic men with AZFc deletions had successful sperm retrieval, ICSI and a subsequent clinical pregnancy. Seven men had deletions involving the AZFb region (three men had isolated AZFb deletions, one had AZFa, AZFb and AZFc deleted, and three had AZFb and AZFc deleted). None of the seven men had spermatozoa extracted by TESE, a result that is significantly different from the overall 64% (47/73) sperm retrieval rate achieved at our centre (P = 0.001). Two men with AZFb deletions had cells consistent with round spermatids identified and injected into oocytes without effecting any normal fertilizations. Although preliminary, these results suggest that the presence of an AZFb deletion is a significantly adverse prognostic finding for TESE. Men with AZFb deletions should be apprised of these results before attempting TESE-ICSI. Alternatives such as donor insemination or adoption should be considered or therapy delayed until improved results with round spermatid injections are likely.