Clinical relevance of partial AZFc deletions

High frequencies of Non Allelic Homologous Recombination (NAHR) events at the AZF loci and male infertility risk in Indian men

Deletions in the AZoospermia Factor (AZF) regions (spermatogenesis loci) on the human Y chromosome are reported as one of the most common causes of severe testiculopathy and spermatogenic defects leading to male infertility, yet not much data is available for Indian infertile men. Therefore, we screened for AZF region deletions in 973 infertile men consisting of 771 azoospermia, 105 oligozoospermia and 97 oligoteratozoospermia cases, along with 587 fertile normozoospermic men. The deletion screening was carried out using AZF-specific markers: STSs (Sequence Tagged Sites), SNVs (Single Nucleotide Variations), PCR-RFLP (Polymerase Chain Reaction - Restriction Fragment Length Polymorphism) analysis of STS amplicons, DNA sequencing and Southern hybridization techniques. Our study revealed deletion events in a total of 29.4% of infertile Indian men. Of these, non-allelic homologous recombination (NAHR) events accounted for 25.8%, which included 3.5% AZFb deletions, 2.3% AZFbc deletions, 6.9% complete AZFc deletions, and 13.1% partial AZFc deletions. We observed 3.2% AZFa deletions and a rare long AZFabc region deletion in 0.5% azoospermic men. This study illustrates how the ethnicity, endogamy and long-time geographical isolation of Indian populations might have played a major role in the high frequencies of deletion events.

Early detection of Y chromosome microdeletions in infertile men is helpful to guide clinical reproductive treatments in southwest of China

The microdeletions of azoospermia factor (AZF) genes in Y chromosome are greatly associated with male infertility, which is also known as the second major genetic cause of spermatogenetic failure. Accumulating studies demonstrate that the different type of AZF microdeletions in patients reflect different clinical manifestations. Therefore, a better understanding of Y chromosome microdeletions might have broad implication for men health. In this study, we sought to determine the frequency and the character of different Y chromosome microdeletion types in infertile men in southwest of China.In total, 1274 patients with azoospermia and oligozoospermia were recruited in southwest of China and screening for Y chromosome microdeletions in AZF regions by multiplex polymerase chain reaction.The incidence of AZF microdeletions in southwest of China is 12.87%, which is higher than the national average. Further investigations unveiled that azoospermia factor c (AZFc) is the most frequent type of all the AZF microdeletions. Additionally, the number and also the quality of sperm in patients with AZFc microdeletion is decreasing with the age. Therefore, it is conceivable that the early testing for Y chromosome microdeletions in infertile men is crucial for fertility guidance.The early detection of Y chromosome microdeletions in infertile men can not only clearly explain the etiology of oligzoospermia and azoospermia, but also help for the clinical management of both infertile man and his future male offspring.

Transmissible microdeletion of the Y-chromosome encompassing two DAZ copies, four RBMY1 copies, and both PRY copies

OBJECTIVE

To study a transmissible partial AZFb and -c microdeletion.

DESIGN

Case report.

SETTING

Service of Reproductive Medicine, Molecular Biology, CHU Lyon, France.

PATIENT(S)

A case of oligoasthenospermia with partial spermatogenic failure. Screening for Yq microdeletions revealed the absence of sY143, suggesting an AZFb microdeletion.

INTERVENTION(S)

Sequence-tagged site mapping indicated that the deletion encompassed a portion of the AZFb and -c region. Genomic DNA from the patient's father gave the same pattern. During the course of these investigations, a pregnancy occurred. On the 46,XY amniocyte and cord blood DNA, the same microdeletion was found.

MAIN OUTCOME MEASURE(S)

Study of the fine structure of the Y-chromosome and the gene copy number.

RESULT(S)

The three males of this family have a rearrangement including a deletion encompassing r3 and r4, the palindrome P3, and its boundary regions: u3 and u1 in its distal part. This induced a reduction in DAZ and RBMY1 copy number and complete loss of PRY.

CONCLUSION(S)

PRY is not indispensable to complete spermatogenesis; and with two RBMY1 and two DAZ copies, complete spermatogenesis can be conserved.

Quantitative PCR technique for the identification of microrearrangements of the AZFc region

PURPOSE

The AZFc region spans about 3.5 Mb and contains many amplicons causing recombination events. Several papers have reported the occurrence of AZFc partial deletions resulting from non allelic homologous recombination (NAHR) ("gr-gr", "b1-b3" or "b2-b3" deletions), particularly in infertile patients. DAZ genes are present in 4 copies and rearrangements involve a modification of the number of DAZ genes.

METHODS

In addition to STS plus/minus PCR, we developed a quantitative technique using real time PCR (Q-PCR) to determine the number of DAZ genes. Fourteen DNA controls were selected to validate the use of Q-PCR to detect AZFc microrearrangements, and sperm DNA samples from 30 fertile men were studied.

RESULTS

Rearrangements of 14 controls were well identified with Q-PCR, and 2 AZFc partial deletions were detected in fertile men (1 "gr-gr" and 1 "b2-b3").

CONCLUSION

Q-PCR represents a well-adapted method to detect microrearrangements of the Y-chromosome, complementary to STS analysis.

Association of partial AZFc region deletions with spermatogenic impairment and male infertility

BACKGROUND

Complete deletions of the AZFc region in distal Yq are the most frequent molecular genetic cause of severe male infertility. They are caused by intrachromosomal homologous recombination between amplicons--large, nearly identical repeats--and are found in 5-10% of cases of azoospermia and severe oligozoospermia. Homologous recombination may also generate different partial deletions of AZFc, but their contribution to spermatogenic impairment has not been confirmed.

METHODS

In this study we analysed the prevalence and characteristics of different partial AZFc deletions and their association with spermatogenic failure. We studied 337 infertile men with different spermatogenic impairment and 263 normozoospermic fertile men using AZFc specific sequence tagged site markers and DAZ specific single nucleotide variants.

RESULTS

We identified 18 cases of partial AZFc deletions in the infertile group (5.3%) and one case in the control group (0.4%). Seventeen deletions had the "gr/gr" pattern, one the "b2/b3" pattern, and one represented a novel deletion with breakpoints in b3 and b4 amplicons. Partial AZFc deletions were associated with different spermatogenic phenotypes ranging from complete azoospermia to only moderate oligozoospermia.

CONCLUSIONS

Together with published data, our analysis of DAZ gene copy suggested that the contribution of the different deletions to male infertility varies: only partial AZFc deletions removing DAZ1/DAZ2 seem to be associated with spermatogenic impairment, whereas those removing DAZ3/DAZ4 may have no or little effect on fertility. These data show that, beside complete AZFc deletions, specific partial deletions represent a risk factor for male infertility, even if with different effect on spermatogenesis.

Copy number of DAZ genes in infertile men

The aim of the study was to define the relevance of deletions and duplications within the DAZ gene cluster to male factor infertility in a population of 90 infertile men and a control of 50 fertile men using real-time polymerase chain reaction (PCR). We conclude that partial deletions of the DAZ genes are associated with oligozoospermia but not with azoospermia; however, an increased number of DAZ genes does not seem to be a statistically significant risk factor for spermatogenic failure.

No partial DAZ deletions but frequent gene conversion events on the Y chromosome of fertile men

PURPOSE

Recently, partial DAZ deletions on the Y chromosome were identified in infertile men. To determine the clinical importance of partial DAZ deletion, we studied the number of DAZ copies in a well-defined population of 47 fertile men.

METHODS

The number of DAZ gene copies was determined by PCR assays, qualitative and quantitative DNA blot experiments.

RESULTS

Using semi-quantitative Southern blot, no partial DAZ deletion was detected in fertile men. In many cases, the results were discordant with the PCR assays and qualitative DYS1-blot experiments suggesting that the molecular events detected by the later methods could reflect gene conversion events. Many fertile men present four copies of the DAZ genes but an atypical organization of this DAZ locus. No difference in sperm concentration and motility in the fertile men were observed according to the different DAZ-haplotypes.

CONCLUSION

The different DAZ-haplotypes are compatible with normal spermatogenesis.

Role of the DAZ genes in male fertility

Males contribute to about 50% of infertility in humans and Y chromosome deletions are the major known genetic contribution to this. Amongst the genes encompassed by these deletions are the DAZ genes. The DAZ family of genes (consisting of homologues of BOULE, DAZL and DAZ) encode highly conserved RNA-binding proteins that are essential for gametogenesis in metazoans. They join the ranks of proteins that act to control this complex developmental process by regulating the translation of specific mRNAs. Advances in knowledge of how this gene family acts to regulate key meiotic events in model organisms will lead to a fuller understanding of their function in human fertility.

Sequence family variant loss from the AZFc interval of the human Y chromosome, but not gene copy loss, is strongly associated with male infertility

BACKGROUND

Complete deletion of the complete AZFc interval of the Y chromosome is the most common known genetic cause of human male infertility. Two partial AZFc deletions (gr/gr and b1/b3) that remove some copies of all AZFc genes have recently been identified in infertile and fertile populations, and an association study indicates that the resulting gene dose reduction represents a risk factor for spermatogenic failure.

METHODS

To determine the incidence of various partial AZFc deletions and their effect on fertility, we combined quantitative and qualitative analyses of the AZFc interval at the DAZ and CDY1 loci in 300 infertile men and 399 control men.

RESULTS

We detected 34 partial AZFc deletions (32 gr/gr deletions), arising from at least 19 independent deletion events, and found gr/gr deletion in 6% of infertile and 3.5% of control men (p>0.05). Our data provide evidence for two large AZFc inversion polymorphisms, and for relative hot and cold spots of unequal crossing over within the blocks of homology that mediate gr/gr deletion. Using SFVs (sequence family variants), we discriminate DAZ1/2, DAZ3/4, CDY1a (proximal), and CDY1b (distal) and define four types of DAZ-CDY1 gr/gr deletion.

CONCLUSIONS

The only deletion type to show an association with infertility was DAZ3/4-CDY1a (p = 0.042), suggesting that most gr/gr deletions are neutral variants. We see a stronger association, however, between loss of the CDY1a SFV and infertility (p = 0.002). Thus, loss of this SFV through deletion or gene conversion could be a major risk factor for male infertility.

EAA/EMQN best practice guidelines for molecular diagnosis of y-chromosomal microdeletions. State of the art 2004

Microdeletions of the Y chromosome are the second most frequent genetic cause of spermatogenetic failure in infertile men after the Klinefelter syndrome. The molecular diagnosis of Y-chromosomal microdeletions is routinely performed in the workup of male infertility in men with azoospermia or severe oligozoospermia. Since 1999, the European Academy of Andrology (EAA) and the European Molecular Genetics Quality Network (EMQN) support the improvement of the quality of the diagnostic assays by publication of the laboratory guidelines for molecular diagnosis of Y-chromosomal microdeletions and by offering external quality assessment trials. The present revision of the 1999 laboratory guidelines summarizes the results of a 'Best Practice Meeting' held in Florence (Italy) in October 2003. The basic protocol for microdeletion screening suggested in the 1999 guidelines proved to be very accurate, sensitive and robust. In the light of the recent advance in the knowledge of the Y chromosome sequence and of the mechanism of microdeletion it was agreed that the basic 1999 protocol, based on two multiplex polymerase chain reactions each covering the three AZF regions, is still fully valid and appropriate for accurate diagnosis.

Partial deletions in the AZFc region of the Y chromosome occur in men with impaired as well as normal spermatogenesis

BACKGROUND

Partial deletions of the AZFc region of the Y chromosome were reported to be a significant risk factor for oligo-/azoospermia. In this study, we assessed the occurrence and frequency of partial AZFc microdeletions in patients with spermatogenic failure and in controls with normal spermatogenesis.

METHODS

In a retrospective study design, gr/gr, b1/b3 and b2/b3 deletions were analysed by multiplex PCR in 170 men with normal spermatogenesis and 348 men with non-obstructive oligo-/azoospermia.

RESULTS

gr/gr deletions were found in 14 men with oligozoospermia or azoospermia (4.0%) and in three normozoospermic men (1.8%) (NS). b1/b3 deletions were found both in controls (n=1) and in patients (n=1). b2/b3 deletions were significantly more frequent in the normozoospermic (five out of 170) than in the oligo-/azoospermic men (two out of 348). Three novel partial AZFc deletion patterns were found in four oligo-/azoospermic men. No correlation with semen or other clinical parameters was found.

CONCLUSIONS

The frequency of gr/gr deletions is not significantly increased in men with oligo-/azoospermia, indicating that they are not sufficient per se to cause spermatogenetic impairment and infertility. b1/b3 and b2/b3 deletions are probably irrelevant for spermatogenesis. Novel deletion patterns found exclusively in infertile men suggest that other, still unexplored partial deletions might contribute to spermatogenic failure.

AZF and DAZ gene copy-specific deletion analysis in maturation arrest and Sertoli cell-only syndrome

Deletions of the AZFc region in Yq11.2, which include the DAZ gene family, are responsible for most cases of male infertility and were associated with severe oligozoospermia and also with a variable testicular pathology. To uncover the functional contribution of DAZ to human spermatogenesis, a DAZ gene copy-specific deletion analysis was previously established and showed that DAZ1/DAZ2 deletions associate with oligozoospermia. In this study we applied the same screening method to 50 control fertile males and 91 non-obstructive azoospermic males, 39 with Sertoli cell-only syndrome (SCOS) and 52 with meiotic arrest (MA). Samples were also screened with 24 sequence-tagged sites to the different AZF regions, including 114 control fertile males. After biopsy (testicular sperm extraction, TESE), residual spermiogenesis was found in 57.7% MA and 30.8% SCOS cases (incomplete syndromes). DAZ1/DAZ2 deletions were associated with the testicular phenotype of residual spermiogenesis as they were only found in two patients (8%) with incomplete MA. Differences between incomplete (23.3%) and complete (4.5%) MA cases regarding AZFc and DAZ1/DAZ2 deletion frequencies, and between incomplete (58.3%) and complete (11.1%) SCOS cases for AZFc deletions, suggest that incomplete syndromes might represent an aggravation of the oligozoospermic phenotype. As successful TESE was achieved in 87.5% of MA cases with AZFc and DAZ1/DAZ2 deletions and in 58.3% of SCOS cases with AZFc deletions, the present results also suggest that these molecular markers might be used for the establishment of a prognosis before TESE.

Analysis of the DAZ gene family in cryptorchidism and idiopathic male infertility

OBJECTIVE

To investigate whether partial deletions of the DAZ gene family on the Y chromosome are associated with cryptorchidism, similar to that found for complete AZF deletions.

DESIGN

Prospective study.

SETTING

University hospital.

PATIENT(S)

A total of 193 azoospermic and severely oligozoospermic men: 95 with a history of cryptorchidism and 98 classified as idiopathic.

INTERVENTION(S)

A two-part study for Y chromosome microdeletions was performed: a polymerase chain reaction (PCR)-based analysis for complete AZF deletions and partial DAZ gene analysis by PCR-restriction digestion assay for single-family variants.

MAIN OUTCOME MEASURE(S)

Presence and type of AZF deletions and number of DAZ genes present.

RESULT(S)

The frequency of complete AZF deletions was similar in idiopathic (13.3%) and cryptorchid men (11.6%), but partial DAZ deletions were found only in infertile subjects without cryptorchidism (7.1%). The testicular phenotype was similar in men with complete AZF deletions and partial DAZ deletions, therefore the contribution of the other AZF genes in determining the spermatogenic impairment is still unclear.

CONCLUSION(S)

Our findings suggest that the loss of only some copies of DAZ is sufficient to lead to severe male infertility, but it is not a frequent finding in cryptorchid men.

The pituitary-testicular axis in Klinefelter's syndrome and in oligo-azoospermic patients with and without deletions of the Y chromosome long arm

OBJECTIVE

The most frequent known genetic causes of severe oligospermia (< 5 million sperm/ml) or azoospermia in men are Klinefelter's syndrome (KS), and deletions in the Y chromosome long arm (Yq). We aimed to compare the function of the pituitary-testicular axis in patients with severe oligospermia or azoospermia, idiopathic or associated with Y chromosome deletions or Klinefelter's syndrome (KS) and in control subjects.

PATIENTS

We studied 47 men with idiopathic oligo-azoospermia, 42 with Yq deletions (27 AZFc, 13 AZFb and two AZFa) and oligo-azoospermia, 14 with KS and 39 control subjects (total 143).

MEASUREMENTS

We analysed levels of FSH, inhibin-B, LH, free testosterone and oestradiol in all subjects, and we calculated indexes based on those hormones.

RESULTS

Inhibin-B levels were indistinguishable between patients with idiopathic and Y deletion-associated oligo-azoospermia, lowest in the Klinefelter's patients and highest in controls. FSH levels followed the reverse pattern: indistinguishable between patients with idiopathic and deletion-associated oligo-azoospermia, highest in Klinefelter's patients and lowest in controls. Oestradiol, free testosterone and the derived indeces were not different in subjects with Yq deletions compared to those with idiopathic oligo-azoospermia. Among the Yq-deleted patients, no measured or derived parameter differed between the subjects with AZFc deletion and those with AZFb deletion. When non-KS oligo-azoospermic patients were classified according to histology [Sertoli cell-only (SCO), n = 18 or non-Sertoli cell only (non-SCO), n= 18] and compared to KS patients, the hormonal pattern did not differ between SCO and non-SCO subjects, but levels in KS patients were significantly different for FSH, inhibin-B and the FSH/inhibin-B ratio. KS patients not only had lower inhibin-B than SCO and non-SCO oligo-azoospermic men, but also higher FSH levels for any given inhibin-B concentration.

CONCLUSION

Our data show that Y-deleted patients do not have a lesser impairment of Sertoli cell function than patients with idiopathic oligo-azoospermia, and support the concept that the main determinant of inhibin-B production is the germ cell mass. Also, our results suggest that one or more other factors, apart from inhibin-B, may contribute to increased pituitary secretion of FSH in KS patients.

Partial DAZ deletions in a family with five infertile brothers

OBJECTIVE

To study the genetic cause of infertility in a family with five infertile brothers.

DESIGN

Case report.

SETTINGS

Center for reproductive medicine at a university medical center.

PATIENT(S)

Five brothers presenting with primary infertility due to severely impaired spermatogenesis; also, their parents and two other paternally related family members.

INTERVENTION(S)

Fluorescence in situ hybridization and sequence family variant analysis was performed in leukocyte DNA to determine the number of deleted in azoospermia (DAZ) genes. Linkage analysis was performed for X chromosome inheritance, and mitochondrial DNA (mtDNA) was screened for mutations.

MAIN OUTCOME MEASURE(S)

DAZ gene copy number, X chromosome linkage, and mtDNA sequence.

RESULT(S)

With conventional polymerase chain reaction (PCR) analysis, no deletions of the AZFc region were found, but with fluorescence in situ hybridization and sequence family variant analysis, only two DAZ genes instead of four were detected in all individuals tested. The five brothers did not share an identical X chromosomal locus, and no mutations were found in the mtDNA of the index patient.

CONCLUSION(S)

A reduced copy number of the DAZ genes is found in five infertile brothers with severely impaired spermatogenesis, as well as in their normospermic father and in two other fertile paternally related family members. This illustrates that the phenotype associated with a reduced copy number of the DAZ genes can be extremely variable.