Reduced copy number of DAZ genes in subfertile and infertile men

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.

A time- and cost-effective strategy to sequence mammalian Y Chromosomes: an application to the de novo assembly of gorilla Y

The mammalian Y Chromosome sequence, critical for studying male fertility and dispersal, is enriched in repeats and palindromes, and thus, is the most difficult component of the genome to assemble. Previously, expensive and labor-intensive BAC-based techniques were used to sequence the Y for a handful of mammalian species. Here, we present a much faster and more affordable strategy for sequencing and assembling mammalian Y Chromosomes of sufficient quality for most comparative genomics analyses and for conservation genetics applications. The strategy combines flow sorting, short- and long-read genome and transcriptome sequencing, and droplet digital PCR with novel and existing computational methods. It can be used to reconstruct sex chromosomes in a heterogametic sex of any species. We applied our strategy to produce a draft of the gorilla Y sequence. The resulting assembly allowed us to refine gene content, evaluate copy number of ampliconic gene families, locate species-specific palindromes, examine the repetitive element content, and produce sequence alignments with human and chimpanzee Y Chromosomes. Our results inform the evolution of the hominine (human, chimpanzee, and gorilla) Y Chromosomes. Surprisingly, we found the gorilla Y Chromosome to be similar to the human Y Chromosome, but not to the chimpanzee Y Chromosome. Moreover, we have utilized the assembled gorilla Y Chromosome sequence to design genetic markers for studying the male-specific dispersal of this endangered species.

Emerging evidence for the role of genomic instability in male factor infertility

Male infertility is a common and complex pathology affecting about 7% of men of reproductive age. Given its complexity, the underlying etiology for male infertility is often unknown. A growing amount of evidence suggests genomic instability may be an important factor in some cases of male factor infertility. While some specific manifestations of genomic instability, such as increased sperm aneuploidy rates and increased somatic translocations and inversions in infertile men, are well established, other facets of genomic instability associated with male infertility have not been thoroughly investigated. A limited body of recent work has identified a potential association between microsatellite instability and spermatogenic failure. In addition, mutations in mismatch repair and tumor suppressor genes, which could potentially lead to genomic instability, have been identified in some infertile men and animal models. In addition, results of two epidemiologic studies suggest spermatogenic defects might be just one aspect of a more systemic problem, possibly due to increased genomic instability. In this review we discuss well-established links between genomic instability and male infertility, as well as some of the emerging but less established data to support this relationship. We also propose some important areas of future research toward a more complete understanding of the underlying mechanisms for male infertility.

Genome instability in AZFc region on Y chromosome in leukocytes of fertile and infertile individuals following exposure to gamma radiation

PURPOSE

Men are exposed to various doses of ionizing radiation due to living in regions with high natural background radiation, accidentally, occupationally or for cancer treatment. To study genomic instability of AZFc region to gamma radiation, blood samples from normal, oligozoospermia, and azoospermia individuals were irradiated by a Co-60 source.

METHODS

Irradiated cells were kept for 48 h in order to repair initial DNA damages. Real time PCR was performed for three markers (SY 1206, SY 1197, SY 579) for testing copy number variation before and after irradiation. Copy number variations were compared by calculation of cycle threshold comparative method.

RESULTS

Copy number variations of studied markers in AZFc region (microdeletion and duplication) in all samples after exposure to radiation increased with a dose dependent fashion. The frequency of instability was significantly higher in samples from infertile men in comparison with fertile ones (p < 0.001).

CONCLUSION

No significant difference was seen between the two infertile groups (p > 0.05). This observation might be a possible explanation for induction of azoospermia and oligozoospermia after radiotherapy. Increased frequency of induced microdeletion and duplication in infertile men compared with normal might be attributed to the deficiency in repair systems and the genetic factors involved in incomplete spermatogenesis of infertile men.

The Y chromosome in the era of intracytoplasmic sperm injection: a personal review

The Y chromosome contains 60 multicopy genes composed of nine different gene families concentrated in regions of multiple repeat sequences called amplicons arranged in mirror images called palindromes. This pattern is susceptible to deletions caused by homologous recombination with itself, and can explain the presence of small numbers of sperm in otherwise azoospermic men.

The AZFc region of the Y chromosome: at the crossroads between genetic diversity and male infertility

BACKGROUND

The three azoospermia factor (AZF) regions of the Y chromosome represent genomic niches for spermatogenesis genes. Yet, the most distal region, AZFc, is a major generator of large-scale variation in the human genome. Determining to what extent this variability affects spermatogenesis is a highly contentious topic in human reproduction.

METHODS

In this review, an extensive characterization of the molecular mechanisms responsible for AZFc genotypical variation is undertaken. Such data are complemented with the assessment of the clinical consequences for male fertility imputable to the different AZFc variants. For this, a critical re-evaluation of 23 association studies was performed in order to extract unifying conclusions by curtailing methodological heterogeneities.

RESULTS

Intrachromosomal homologous recombination mechanisms, either crossover or non-crossover based, are the main drivers for AZFc genetic diversity. In particular, rearrangements affecting gene dosage are the most likely to introduce phenotypical disruptions in the spermatogenic profile. In the specific cases of partial AZFc deletions, both the actual existence and the severity of the spermatogenic defect are dependent on the evolutionary background of the Y chromosome.

CONCLUSIONS

AZFc is one of the most genetically dynamic regions in the human genome. This property may serve as counter against the genetic degeneracy associated with the lack of a meiotic partner. However, such strategy comes at a price: some rearrangements represent a risk factor or a de-facto causative agent of spermatogenic disruption. Interestingly, this precarious balance is modulated, among other yet unknown factors, by the evolutionary history of the Y chromosome.

AZFc partial deletions in Chilean men with severe spermatogenic failure

OBJECTIVE

To determine the prevalence of AZFc subdeletions in infertile Chilean men with severe spermatogenic impairment.

DESIGN

Prospective analysis.

SETTING

University infertility clinic.

PATIENT(S)

Ninety-five secretory azo/oligozoospermic men without AZFc Y chromosome microdeletions: 71 whose testicular histology showed severe spermatogenic impairment and 24 who exhibited reduced testicular volume and elevated serum FSH levels. As controls, we studied 77 men (50 fertile and/or normozoospermic, and 27 with azoospermia and normal spermatogenesis).

INTERVENTION(S)

Peripheral blood was drawn to obtain genomic DNA for polymerase chain reaction (PCR) digestion assays of DAZ-sequence nucleotide variants and for AZFc-STS PCR after a complete testicular characterization (biopsy, hormonal, and physical evaluation).

MAIN OUTCOME MEASURE(S)

DAZ genes and AZFc subdeletion types.

RESULT(S)

In cases we observed two "gr/gr" subdeletions (2.1%), one with absence of DAZ1/DAZ2 (g1/g2 subtype), and the other with absence of DAZ3/DAZ4 (r2/r4 subtype). Additionally, we found a g1/g3 subdeletion in a patient with Sertoli-cell-only syndrome. In controls, we observed two gr/gr subdeletions with absence of DAZ1/DAZ2 (2.6%) in a fertile/normozoospermic and in an obstructive azoospermic man.

CONCLUSION(S)

AZFc subdeletions do not seem to cause severe impairment of spermatogenesis. Moreover, gr/gr-DAZ1/DAZ2 subdeletions do not appear to affect fertility in Chilean men.

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.

Preliminary study of the relationship between DAZ gene copy deletions and spermatogenic impairment in Chinese men

Copy deletion screening of DAZ gene family on the Y chromosome in 485 patients with idiopathic azoospermia or oligozoospermia and 236 fertile men revealed that the prevalence of deletion patterns of the entire DAZ gene and DAZ1/DAZ2 gene were significantly higher in the patients than in fertile men. The deletion patterns correlate with spermatogenic impairment in a Chinese population.

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.

Polymorphisms associated with the DAZ genes on the human Y chromosome

The human Y chromosome is unique in that it does not engage in pairing and crossing over during meiosis for most of its length. Y chromosome microdeletions, a frequent finding in infertile men, thus occur through intrachromosomal recombination, either within a single chromatid or between sister chromatids. A recently identified polymorphism associated with increased risk for spermatogenic failure, the gr/gr deletion, removes two of the four Deleted in Azoospermia (DAZ) genes in the AZFc region on the Y-chromosome long arm. We found the likely reciprocal duplication product of gr/gr deletion in 5 (6%) of 82 males using a novel DNA-blot hybridization strategy and confirmed the presence of six DAZ genes in three cases by FISH analysis. Additional polymorphisms identified within the DAZ repeat regions of the DAZ genes indicate that sister chromatid exchange plays a significant role in the genesis of deletions, duplications, and polymorphisms of the Y chromosome.

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.

AZF deletions and Y chromosomal haplogroups: history and update based on sequence

AZF deletions are genomic deletions in the euchromatic part of the long arm of the human Y chromosome (Yq11) associated with azoospermia or severe oligozoospermia. Consequently, it can be assumed that these deletions remove Y chromosomal genes required for spermatogenesis. However, these 'classical' or 'complete' AZF deletions, AZFa, AZFb and AZFc, represent only a subset of rearrangements in Yq11. With the benefit of the Y chromosome sequence, more rearrangements (deletions, duplications, inversions) inside and outside the classical AZF deletion intervals have been elucidated and intra-chromosomal non-allelic homologous recombinations (NAHRs) of repetitive sequence blocks have been identified as their major cause. These include duplications in AZFa, AZFb and AZFc and the partial AZFb and AZFc deletions of which some were summarized under the pseudonym 'gr/gr' deletions. At least some of these rearrangements are associated with distinct Y chromosomal haplogroups and are present with similar frequencies in fertile and infertile men. This suggests a functional redundancy of the AZFb/AZFc multi-copy genes. Alternatively, the functional contribution(s) of these genes to human spermatogenesis might be different in men of different Y haplogroups. That raises the question whether, the frequency of Y haplogroups with different AZF gene contents in distinct human populations leads to a male fertility status that varies between populations or whether, the presence of the multiple Y haplogroups implies a balancing selection via genomic deletion/amplification mechanisms.

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.

A family of human Y chromosomes has dispersed throughout northern Eurasia despite a 1.8-Mb deletion in the azoospermia factor c region

The human Y chromosome is replete with amplicons-very large, nearly identical repeats-which render it susceptible to interstitial deletions that often cause spermatogenic failure. Here we describe a recurrent, 1.8-Mb deletion that removes half of the azoospermia factor c (AZFc) region, including 12 members of eight testis-specific gene families. We show that this "b2/b3" deletion arose at least four times in human history-likely on inverted variants of the AZFc region that we find exist as common polymorphisms. We observed the b2/b3 deletion primarily in one family of closely related Y chromosomes-branch N in the Y-chromosome genealogy-in which all chromosomes carried the deletion. This branch is known to be widely distributed in northern Eurasia, accounts for the majority of Y chromosomes in some populations, and appears to be several thousand years old. The population-genetic success of the b2/b3 deletion is surprising, (i) because it removes half of AZFc and (ii) because the gr/gr deletion, which removes a similar set of testis-specific genes, predisposes to spermatogenic failure. Our present findings suggest either that the b2/b3 deletion has at most a modest effect on fitness or that, within branch N, its effect has been counterbalanced by another genetic, possibly Y-linked, factor.

High frequency of gr/gr chromosome Y deletions in consecutive oligospermic ICSI candidates

BACKGROUND

The Y chromosome gr/gr microdeletion eliminates two copies of the DAZ gene and several additional transcriptional units and has been associated as a risk factor for infertility. Our objective was to study the presence of the gr/gr deletion in ICSI candidates in our population and to determine whether the laboratory, clinical and ICSI outcome were different in the gr/gr deleted patients.

METHODS

Two hundred and eighty-three ICSI candidates were studied. Semen analysis, serum FSH, LH, testosterone, inhibin B, karyotype and detection of sequence tagged sites in the Y chromosome were performed.

RESULTS

gr/gr deletions were detected in 11 (5.07%) of 217 oligospermic and in one (1.52%) of 66 azoospermic consecutive ICSI candidates, but in none of 232 controls (P=0.002). The fertility rate was not different in the four patients of the gr/gr deleted group treated by ICSI (64.38%; 47/73) as compared to average results at our center (65.49%; 2393/3654).

CONCLUSIONS

gr/gr deletions are a risk factor for spermatogenic failure at our population, but the prognosis of the four patients of the gr/gr deleted group treated by ICSI is not different from that of other ICSI patients.

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.

[Molecular detection of Y chromosome microdeletions: a new approach based on the denaturing gradient gel electrophoresis]

Ten percent of couples trying for a child fail to conceive. In approximately 50% of cases, infertility is due to the inability of the male partner to produce spermatozoa in sufficient numbers to effect conception. Over the past 5 years, molecular studies have suggested that interstitial microdeletions in Yq11 represent an etiological factor for male infertility. Y-microdeletions have been detected in 12% of non-obstructive azoospermia and 6% of severe oligozoospermia. In general, microdeletions were detected by separate multiplex-polymerase chain reaction (PCR) reactions using primer pairs for single tagged sites (STSs) of all three azoospermia factor (AZF) regions (AZFa, AZFb and AZFc). This review describes the molecular methods and laboratory guidelines for molecular diagnosis of Y-chromosomal microdeletions. The diagnostics of Y-chromosomal microdeletions should be performed in two steps: in any case, the routine diagnostic should include six STS loci, two STS loci localised in each AZF region, and once a deletion is detected, the analysis can be extended to STS loci known to cross the proximal and the distal borderlines of each AZF region. Other molecular techniques such as DGGE, Southern blot should be performed to detect partial deletions of gene copies or mosaicism. These different molecular approaches should allow explaining 10% of male infertility, to evaluate the risk to pass the defect onto their male offspring (by intracytoplasmic sperm injection) and improve the genetic counselling of couples undergoing micromanipulative assisted reproduction.

Polymorphism for a 1.6-Mb deletion of the human Y chromosome persists through balance between recurrent mutation and haploid selection

Many human Y-chromosomal deletions are thought to severely impair reproductive fitness, which precludes their transmission to the next generation and thus ensures their rarity in the population. Here we report a 1.6-Mb deletion that persists over generations and is sufficiently common to be considered a polymorphism. We hypothesized that this deletion might affect spermatogenesis because it removes almost half of the Y chromosome's AZFc region, a gene-rich segment that is critical for sperm production. An association study established that this deletion, called gr/gr, is a significant risk factor for spermatogenic failure. The gr/gr deletion has far lower penetrance with respect to spermatogenic failure than previously characterized Y-chromosomal deletions; it is often transmitted from father to son. By studying the distribution of gr/gr-deleted chromosomes across the branches of the Y chromosome's genealogical tree, we determined that this deletion arose independently at least 14 times in human history. We suggest that the existence of this deletion as a polymorphism reflects a balance between haploid selection, which culls gr/gr-deleted Y chromosomes from the population, and homologous recombination, which continues to generate new gr/gr deletions.

A fiber-FISH contig spanning the non-recombining region of the human Y chromosome

Using fluorescence in-situ hybridization on interphase chromatin fibers (fiber-FISH), we have constructed an overlapping fiber-FISH contig spanning the non-recombining region of the human Y chromosome (NRY). We first established a standard FISH-signal pattern for a distinct panel of DNA clones on prometaphase Y chromosomes in six healthy fertile men. Clones in the panel were selected from all R-bands as well as deletion intervals 1 through 7 plus PAR1 and PAR2 of the human Y chromosome. We next used signals of these marker clones to build a fiber-FISH contig for the multicopy gene families, CDY, DAZ, RBMY, TSPY and XKRY, along the NRY. Our fiber-FISH contig of human NRY may help to close the four gaps that still exist in the current physical map of the human Y chromosome. Furthermore, it provides a more complete picture with respect to the positions and arrangements of the multicopy gene families along the human NRY.

Y chromosome deletions in azoospermic men in India

Genetic factors cause about 10% of male infertility. Azoospermia factors (AZFa, AZFb, AZFc) are considered to be the most important for spermatogenesis. We therefore made an attempt to evaluate the genetic cause of azoospermia, Y chromosome deletion in particular, in Indian men. We have analyzed a total of 570 men, including 340 azoospermic men and 230 normal control subjects. DNA samples were initially screened with 30 sequence-tagged site (STS) markers representing AZF regions (AZFa, AZFb, AZFc). Samples, with deletion in the above regions were mapped by STS walking. Further, the deletions were confirmed by Southern hybridization using the probes from both euchromatic and heterochromatic regions. Of the total 340 azoospermic men analyzed, 29 individuals (8.5%) showed Y chromosome deletion, of which deletion in AZFc region was the most common (82.8%) followed by AZFb (55.2%) and AZFa (24.1%). Microdeletions were observed in AZFa, whereas macrodeletions were observed in AZFb and AZFc regions. Deletion of heterochromatic and azoospermic regions was detected in 20.7% of the azoospermic men. In 7 azoospermic men, deletion was found in more than 8.0 Mb spanning AZFb and AZFc regions. Sequence analysis at the break points on the Y chromosome revealed the presence of L1, ERV, and other retroviral repeat elements. We also identified a approximately 240-kb region consisting of 125 bp tandem repeats predominantly comprised of ERV elements in the AZFb region. Histological study of the testicular tissue of the azoospermic men, who showed Y chromosome deletion, revealed complete absence of germ cells and presence of only Sertoli cells.

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.

Clinical relevance of partial AZFc deletions

To determine the number of DAZ gene clusters in the Y-bearing spermatozoa of patients who underwent intracytoplasmic sperm injection (ICSI) and to compare the outcome with the number of clusters found in the spermatozoa of normospermic men. Prospective study. Academic hospital.Forty-seven patients with impaired spermatogenesis who were attending our clinic for ICSI and 56 semen donors. Peripheral blood was drawn to obtain somatic DNA for polymerase chain reaction (PCR) analysis and leukocytes for karyotyping and FISH analysis. Three-color FISH was performed on the spermatozoa remaining after ICSI and on the spermatozoa of semen donors to determine the presence of the X and Y chromosome as well as the number of DAZ gene clusters. Number of DAZ gene clusters in Y-bearing spermatozoa. Five patients had only one DAZ gene cluster, one patient had a complete AZFc deletion, and one patient had three clusters on average. One of the semen donors also showed three DAZ gene clusters in his Y-bearing spermatozoa. None of the semen donors had only one DAZ gene cluster. Besides complete AZFc deletions, partial deletions are also associated with impaired spermatogenesis. As a result, these partial deletions that are not recognized by routine PCR are reintroduced into the population by the ICSI technique.

Recombination between palindromes P5 and P1 on the human Y chromosome causes massive deletions and spermatogenic failure

It is widely believed that at least three nonoverlapping regions of the human Y chromosome-AZFa, AZFb, and AZFc ("azoospermia factors" a, b, and c)-are essential for normal spermatogenesis. These intervals are defined by interstitial Y-chromosome deletions that impair or extinguish spermatogenesis. Deletion breakpoints, mechanisms, and lengths, as well as inventories of affected genes, have been elucidated for deletions of AZFa and of AZFc but not for deletions of AZFb or of AZFb plus AZFc. We studied three deletions of AZFb and eight deletions of AZFb plus AZFc, as assayed by the STSs defining these intervals. Guided by Y-chromosome sequence, we localized breakpoints precisely and were able to sequence nine of the deletion junctions. Homologous recombination can explain seven of these deletions but not the remaining two. This fact and our discovery of breakpoint hotspots suggest that factors in addition to homology underlie these deletions. The deletions previously thought to define AZFb were found to extend from palindrome P5 to the proximal arm of palindrome P1, 1.5 Mb within AZFc. Thus, they do not define a genomic region separate from AZFc. We also found that the deletions of AZFb plus AZFc, as assayed by standard STSs heretofore available, in fact extend from P5 to the distal arm of P1 and spare distal AZFc. Both classes of deletions are massive: P5/proximal-P1 deletions encompass up to 6.2 Mb and remove 32 genes and transcripts; P5/distal-P1 deletions encompass up to 7.7 Mb and remove 42 genes and transcripts. To our knowledge, these are the largest of all human interstitial deletions for which deletion junctions and complete intervening sequence are available. The restriction of the associated phenotype to spermatogenic failure indicates the remarkable functional specialization of the affected regions of the Y chromosome.