A locus of the candidate gene family for azoospermia factor (YRRM2) is polymorphic with a null allele in Japanese males

Human Y chromosome microdeletion analysis by PCR multiplex protocols identifying only clinically relevant AZF microdeletions

PCR multiplex assays are the method of choice for quickly revealing genomic microdeletions in the large repetitive genomic sequence blocks on the long arm of the human Y chromosome. They harbor the Azoospermia Factor (AZF) genes, which cause male infertility when functionally disrupted. These protein encoding Y genes are expressed exclusively or predominantly during male germ cell development, i.e., at different phases of human spermatogenesis. They are located in three distinct genomic sequence regions designated AZFa, AZFb, and AZFc, respectively. Complete deletion of an AZF region, also called "classical" AZF microdeletion, is always associated with male infertility and a distinct testicular pathology. Partial AZF deletions including single AZF Y genes can cause the same testicular pathology as the corresponding complete deletion (e.g., DDX3Y gene deletions in AZFa), or might not be associated with male infertility at all (e.g., some BPY2, CDY1, DAZ gene deletions in AZFc). We therefore propose that a PCR multiplex assay aimed to reduce only those AZF microdeletions causing a specific testicular pathology-thus relevant for clinical applications. It only includes Sequence Tagged Site (STS) deletion markers inside the exon structures of the Y genes known to be expressed in male germ cells and located in the three AZF regions. They were integrated in a robust standard protocol for four PCR multiplex mixtures which also include the basic principles of quality control according to the strict guidelines of the European Molecular Genetics Quality Network (EMQN: http://www.emqn.org). In case all Y genes of one AZF region are deleted the molecular extension of this AZF microdeletion is diagnosed to be yes or no comparable to that of the "classical" AZF microdeletion by an additional PCR multiplex assay analyzing the putative AZF breakpoint borderlines.

CHROMOSOMAL ABNORMALITIES AND POLYMORPHISMS IN MEXICAN INFERTILE MEN

A cross-sectional study was conducted to estimate the prevalence of chromosome abnormalities and normal variable chromosome features (polymorphisms) in infertile men from northeastern Mexico. Karyotyping was carried out in 326 men with diagnosis of infertility. The sperm counts showed 204 patients with oligozoospermia, 87 with azoospermia and 35 normozoospermia. Five patients with oligozoospemia and two with azoospermia presented chromosome abnormalities. Nonzoospermic men did not show chromosomal abnormalities. Polymorphisms of heterochromatin and satellite length showed a significant increased in oligozoospermic and azoospermic men with respect to normozoospermic men, respectively. This study reports the prevalence of chromosome abnormalities, polymorphisms of heterochromatin length, and polymorphisms in satellites in Mexican infertile men. The prevalence in this study was similar to other studies in world literature.

Gonadotropin treatment of an azoospermic patient with a Y-chromosome microdeletion

OBJECTIVE

To report on the treatment with recombinant FSH of an azoospermic normogonadotropic patient with a Y-chromosome microdeletion.

DESIGN

Case report.

SETTING

An assisted reproduction center.

PATIENT(S)

A 32-year-old patient with azoospermia.

INTERVENTION(S)

Histological testicular biopsy, Y-chromosome screening, FSH treatment, and intracytoplasmic sperm injection.

MAIN OUTCOME MEASURE(S)

Fertilization, embryo development, pregnancy, and delivery.

RESULT(S)

After 6 months of treatment with gonadotropins, a small number of spermatozoa were found in the patient's ejaculate and used for IVF, resulting in a successful twin pregnancy and the delivery of two healthy girls.

CONCLUSION(S)

In this study, treatment with gonadotropins promoted the spermatogenesis process and led to the production of spermatozoa in a normogonadotropic azoospermic patient.

Cytogenetic and molecular analysis of the Y chromosome: absence of a significant relationship between CAG repeat length in exon 1 of the androgen receptor gene and infertility in Indian men

The genetic basis of male infertility remains unclear in the majority of cases. Recent studies have indicated an association between microdeletions of the azoospermia factor a (AZFa)-AZFc regions of Yq and severe oligospermia or azoospermia. Increased (CAG)n repeat lengths in the androgen receptor (AR) gene have also been reported in infertile men. Therefore, in order to assess the prevalence of these genetic defects to male infertility, 183 men with non-obstructive azoospermia (n = 70), obstructive azoospermia (n = 33), severe oligospermia (n = 80) and 59 fertile men were examined cytogenetically and at molecular level for Yq deletions, microdeletions, and AR-CAG repeat lengths along with hormonal profiles [luteinizing hormone (LH), follicle-stimulating hormone (FSH) and testosterone (T)]. We used high resolution cytogenetics to detect chromosome deletions and multiplex polymerase chain reaction (PCR) involving 27 sequence-tagged site (STS) markers on Yq to determine the rate and extent of Yq microdeletions. PCR amplification with primers flanking exon 1 of AR gene was used to determine the AR-(CAG)n repeat lengths. Hormonal profiles (LH, FSH and T levels) were also analysed in infertile and fertile men. Testicular biopsies showed Sertoli cell only (SCO) morphology, maturation arrests (MA) and hypospermatogenesis. No chromosome aberrations were found in infertile men but there was a significant increase (p < 0.001) in the association of acrocentric chromosomes including the Y chromosome. Yq microdeletions were found in 16 non-obstructive azoospermic men (16 of 70; 22%) and seven severe oligospermic individuals (seven of 80; 8.7%) and most of them had deletions in the sY240 locus. No Yq microdeletions were detected in patients with obstructive azoospermia. No statistically significant difference in the mean length of CAG repeats in AR gene was observed between infertile and fertile men (22.2 +/- 1.5 and 21.5 +/- 1.4 respectively). No significant increase or decrease in levels of LH, FSH and T was observed in infertile and fertile men. In some infertile men, significantly elevated levels of FSH alone or in combination with LH were found to be indicative of failure of spermatogenesis and/or suggestive of testicular failure. Y-chromosome microdeletions contribute to infertility in some patients but no relationship could be established with the (CAG)n repeat lengths in exon 1 of the AR gene in infertile Indian men.

A cost-effective screening test for detecting AZF microdeletions on the human Y chromosome

PCR-based screening of microdeletions in the azoospermic factor (AZF) on the Yq chromosome is an accepted means of identifying a common genetic cause of male infertility, responsible for 5-15% of cases associated with a low sperm count (</=5 x 10(6) sptz/ml). Based on an extensive analysis of the literature, we have established a cost-effective preliminary PCR-based diagnostic screening test, with a set of six pairs of primers ("set-of-6") that have the capability of detecting up to 95% of the Y microdeletion cases already published. These primers are: sY84 in AZFa, sY114, sY129, sY143 in AZFb, and sY149, sY254 in AZFc. Initially, the set-of-6 was tested with 13 other pairs of primers covering the three AZF subregions. A sample of 114 infertile men was tested and 10 (8.8%) microdeletions were found, 3 of which were among the 26 (11.5%) idiopathic azoospermic men. These results showed that all detected microdeletions would be identified using the set-of-6 only. Another sample of 34 patients was subsequently tested using the set-of-6 and 3 (8.8%) microdeletions were found in this group. A comparison of our results with those reported in the literature showed similar microdeletion detection frequencies, demonstrating that the set-of-6 primers provides a reliable, simple and cost-effective way of detecting AZF deletions.

Molecular biology of male infertility

About 15% of couples have reduced fertility and in approximately one-half of all cases the reason is male infertility, usually of genetic origin. Thus, in the context of research in genes involved in reproduction and sex determination, genetic anomalies in gametogenesis are being extensively studied. The most frequent pathogenic causes of male infertility are Y-chromosomal microdeletions (8-15%) in the long arm of the Y chromosome, which, by loss of specific DNA segments, leads to loss of vital genes for sperm production. Infertile men, who attend infertility clinics, rise to 15% among those with azoospermia or spermatogenesis problem. The new technique of intracytoplasmic sperm injection has allowed many infertile men to achieve their dreams of fatherhood. However, the spermatogenic defect is genetic anomalies, which might be a potential risk of transmitting this defect to future offspring. Therefore, genetic counseling of all couples with the diagnosis of male infertility is recommended before their enrolment in intrauterine insemination, in vitro fertilization, and intracytoplasmic sperm injection. The important role of genetic abnormalities in the causation of human male infertility is increasingly recognized. While much remains to be learned in this fast-moving field, considerable progress has been made in the clinical delineation of genetic forms of male infertility and in the characterization of the responsible genes and their mutations or deletions. This review should provide insight into the understanding of parthenogenesis of male infertility in the human.

Male infertility, genetic analysis of the DAZ genes on the human Y chromosome and genetic analysis of DNA repair

Many genes that are required for fertility have been identified in model organisms (). Mutations in these genes cause infertility due to defects in development of the germ cell lineage, but the organism is otherwise healthy. Although human reproduction is undoubtedly as complex as that of other organisms, very few fertility loci have been mapped (). This is in spite of the prevalence of human infertility, the lack of effective treatments to remedy germ cell defects, and the cost to couples and society of assisted reproductive techniques. Fifteen percent of couples are infertile and half of all cases can be traced to the male partner. Aside from defects in sperm production, most infertile men are otherwise healthy. This review is divided into two distinct parts to discuss work that: (i) led to the identification of several genes on the Y chromosome that likely function in sperm production; and (ii) implicates DNA repair in male infertility via increased frequency of mutations in DNA from men with meiotic arrest.

Defining regions of the Y-chromosome responsible for male infertility and identification of a fourth AZF region (AZFd) by Y-chromosome microdeletion detection

Cytogenetic and molecular deletion analyses of azoospermic and oligozoospermic males have suggested the existence of AZoospermia Factor(s) (AZF) residing in deletion intervals 5 and 6 of the human Y-chromosome and coinciding with three functional regions associated with spermatogenic failure. Nonpolymorphic microdeletions in AZF are associated with a broad spectrum of testicular phenotypes. Unfortunately, Sequence Tagged Sites (STSs) employed in screening protocols range broadly in number and mapsite and may be polymorphic. To thoroughly analyze the AZF region(s) and any correlations that may be drawn between genotype and phenotype, we describe the design of nine multiplex PCR reactions derived from analysis of 136 loci. Each multiplex contains 4-8 STS primer pairs, amplifying a total of 48 Y-linked STSs. Each multiplex consists of one positive control: either SMCX or MIC2. We screened four populations of males with these STSs. Population I consisted of 278 patients diagnosed as having significant male factor infertility: either azoospermia, severe oligozoospermia associated with hypogonadism and spermatogenic arrest or normal sperm counts associated with abnormal sperm morphology. Population II consisted of 200 unselected infertile patients. Population III consisted of 36 patients who had previously been shown to have aneuploidy, cytological deletions or translocations involving the Y-chromosome or normal karyotypes associated with severe phenotype abnormalities. Population IV consisted of 920 fertile (control) males. The deletion rates in populations I, II and III were 20.5%, 7% and 58.3%, respectively. A total of 92 patients with deletions were detected. The deletion rate in population IV was 0.87% involving 8 fertile individuals and 4 STSs which were avoided in multiplex panel construction. The ability of the nine multiplexes to detect pathology associated microdeletions is equal to or greater than screening protocols used in other studies. Furthermore, the data suggest a fourth AZF region between AZFb and AZFc, which we have termed AZFd. Patients with microdeletions restricted to AZFd may present with mild oligozoospermia or even normal sperm counts associated with abnormal sperm morphology. Though a definitive genotype/phenotype correlation does not exist, large deletions spanning multiple AZF regions or microdeletions restricted to AZFa usually result in patients with Sertoli Cell Only (SCO) or severe oligozoospermia, whereas microdeletions restricted to AZFb or AZFc can result in patients with phenotypes which range from SCO to moderate oligozoospermia. The panel of nine multiplexed reactions, the Y-deletion Detection System (YDDS), provides a fast, efficient and accurate method of assessing the integrity of the Y-chromosome. To date, this study provides the most extensive screening of a proven fertile male population in tandem with 514 infertile males, derived from three different patient selection protocols.

Polymerase chain reaction analysis of the Y chromosome long arm in azoospermic patients: lack of the Y chromosome recognition motif (YRRM1) gene

We analyzed DNA from a patient with azoospermia whose Y chromosome was cytogenetically normal. A total of 16 loci on the Y chromosome long arm were examined: 15 loci between DYS7E and DYZ1, and the Y chromosome RNA recognition motif (YRRM1) locus, a candidate gene for the azoospermic factor AZF. We did not detect the YRRM1 gene in this patient. This finding supports the theory that YRRM1 is an essential gene for spermatogenesis.

Genetics of idiopathic male infertility: Y chromosomal azoospermia factors (AZFa, AZFb, AZFc)

Y chromosomal spermatogenesis loci in Yq11 are disrupted with a frequency of 5-20% in men suffering from idiopathic infertility (azoospermia or severe oligozoospermia). They were designated azoospermia factors (AZFa, AZFb, AZFc). An efficient schedule for their molecular diagnosis in each infertility clinic is presented. In addition, I will include our current knowledge about their biological function during human germ cell development and a description of their pathology in men suffering from deletion of one or more AZF loci. Each Y gene expressed in testis tissue and located in Yq11, in a position overlapping one of the AZF loci, is an AZF candidate gene. Their diagnostic analysis will be described in a separate section. The clinical diagnosis of AZF candidate genes cannot substitute for diagnosis of the genetically defined AZF loci. Therefore, analysis of candidate genes is aimed at answering the question of whether mutations in their exon structures are able to induce the same pathological phenotypes as deletion of the corresponding AZF locus. Only after these gene mutations have been analysed can the AZF candidate gene be designated as a real AZF gene. Therefore, the basic aim of our current research is isolation and identification of all AZF genes.

Human Y chromosome deletions in Yq11 and male fertility

An overview is given about the current knowledge and research activities on the molecular analysis of interstitial deletions in the euchromatic part of the long arm of the human Y chromosome (Yq11). These mutations are associated with the male specific phenotype of azoospermia and severe oligozoospermia. The fact is stressed that only "de novo" microdeletions in Yq11 are of any diagnostic value in the infertility clinic because numerous polymorphic deletion events in Yq11 have also been reported. Three different "de novo" Yq11 microdeletions associated with male infertility are now found repeatedly (31 cases) in more than 700 patients. They strongly support the presence of at least three spermatogenesis loci in Yq11. They have been designated as AZFa, AZFb, and AZFc. Each of them should contain at least one Y gene functional in spermatogenesis and, if mutated, it should induce the same sterile phenotype as the corresponding AZF locus. These genes have not yet been found. However, some candidate genes exist: RBM for AZFb. DAZ and SPGY for AZFc. It is remarkable that all three encode testis specific RNA binding proteins with a similar sequence structure. Their structure and potential relationship is disussed.

Multiple functional copies of the RBM gene family, a spermatogenesis candidate on the human Y chromosome

The RBM (RNA-binding motif) gene family on the human Y chromosome encodes proteins with an RNA-binding domain. Its exclusive expression in germ cells and its partial deletion in some azoospermic or severely oligospermic males provide evidence of a role for RBM genes in spermatogenesis. There are approximately 30 RBM genes, found on both arms of the Y chromosome. Two RBM cDNA clones with slightly different sequences have been reported. To investigate the number of functional genes, we studied RBM expression by use of RT-PCR of RBM transcripts and by characterizing numerous RBM cDNA clones. A total of 27 RT-PCR and 19 cDNA clones were sequenced. Whereas the RT-PCR clones pointed to the existence of at least six RBM subfamilies (RBMI to RBMVI), the cDNA clones indicated that only RBMI is actively transcribed and encodes functional proteins. A total of six RBMI genes were identified, which produce four polypeptides due to some silent base substitutions. The transcripts of each gene are alternatively spliced to generate protein isoforms with three or four SRGY boxes, thus greatly increasing the complexity of the products of the RBM gene family. We also provide evidence suggesting that a 5-bp deletion in a previously reported RBM cDNA clone represents a processing irregularity.

Screening for deletions of the Y chromosome involving the DAZ (Deleted in AZoospermia) gene in azoospermia and severe oligozoospermia

OBJECTIVE

To evaluate the occurrence and prevalence of microdeletions of the Y chromosome involving the DAZ (Deleted in AZoospermia) gene in patients with azoospermia or severe oligozoospermia.

DESIGN

Controlled clinical study.

SETTING

University infertility clinic.

PATIENT(S)

Infertile men (n = 168) with nonobstructive, idiopathic azoospermia or severe oligozoospermia and normal LH. The control group consisted of proven fathers (n = 86).

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Semen analysis; polymerase chain reaction amplification of the loci sY84, sY143, sY254, and sY255; serum FSH, LH, and T; testicular volume.

RESULT(S)

Deletions involving the sY254 and sY255 DAZ loci were found in three azoospermic patients and two men with sperm concentration < 1 x 10(6)/mL. Serum FSH was elevated in four patients and was normal in one. All five patients had decreased testicular volumes compared with controls. No deletions involving the sY84 and sY143 loci were found. The four loci were amplified normally in the control group.

CONCLUSION(S)

The estimated frequency of deletions involving the DAZ locus is 3% in azoospermic-severely oligozoospermic men consulting an infertility clinic. Polymerase chain reaction amplification of the DAZ locus is useful for the diagnosis of microdeletions of the Y chromosome. Deletions involving more proximal regions of the Y chromosome seem to be rare.

Degeneracy in human multicopy RBM (YRRM), a candidate spermatogenesis gene

In order to search for mutations in the multicopy RBM genes that might be associated with male infertility, we have used sequence data from the reported cDNA clone to determine the intron exon boundaries of the YRRM 1 gene. This gene has 12 exons, three of which encode the putative RNA binding domain of the protein. Different copies of the gene contain sequence variations and, additionally, give rise to transcripts with different numbers of copies of the repeated SRGY motif. Since mutations in the RNA binding domain would seem likely to have an effect on the activity of the protein, we have scanned these exons for mutations by SSCP on DNA from normal and infertile men. Sequence differences in the exon encoding the N-terminal part of the RNA binding domain account for at least four different classes of the gene and give rise to different SSCP conformers. Sequence analysis shows that one of these classes is a pseudogene and that the members of another class are nonfunctional. RT-PCR shows that all classes are transcribed and that the A class is most abundant. We have found a point mutation that alters the highly conserved RNP2 motif in one infertile patient. This mutation is also found in his father. We have used PCR followed by SSCP analysis to map RBM on a Y Chromosome (Chr) YAC contig and have demonstrated a distribution that spans a major part of this chromosome's euchromatin.

The azoospermic factor on the Y chromosome

Azoospermia is the most frequent cause of male infertility. After excluding the obvious urological reasons and the effect of Klinefelter's syndrome, azoospermia may be caused by an abnormality in the crucial gene(s) expressed during male germ cell differentiation. Recently, two candidate genes for azoospermia have been cloned from the azoospermic factor (AZF) locus on the Y chromosome long arm (Yq). One is YRRM (Y chromosome RNA recognition motif) gene, and the other is DAZ (deletion in azoospermia) gene. Both genes encode RNA binding protein and their expression is restricted to the testis. Therefore they are good candidates for AZF, although their function remains unclear. Here, the genes on the Y chromosome possibly involved in spermatogenesis and the role of the Y chromosome in evolution are discussed.

Severe oligozoospermia resulting from deletions of azoospermia factor gene on Y chromosome

BACKGROUND

About 13% of cases of non-obstructive azoospermia are caused by deletion of the azoospermia factor (AZF), a gene or gene complex normally located on the long arm of the Y chromosome. Oligozoospermia is far more common than azoospermia, but little is known about genetic causes. We investigated whether severe oligozoospermia is caused by AZF deletions and, if so, whether those deletions are present in mature spermatozoa.

METHODS

By PCR, we tested leucocyte DNA, from 35 men who presented at infertility clinics and who had severe oligozoospermia, for the presence of 118 DNA landmarks scattered across the Y chromosome. In the two men in whom Y-chromosome deletions in leucocyte DNA were detected, we also tested leucocyte DNA from the individuals' fathers, and in one man we tested sperm DNA.

FINDINGS

In two men with ejaculate sperm counts of 40 000-100 000 per mL, we detected Y-chromosome deletions in leucocyte DNA similar in location to those previously reported in azoospermic individuals. No Y-chromosome deletions were detected in the fathers of the two men. For one of the two men, sperm DNA was tested, and it showed the same Y-chromosome deletion seen in leucocytes.

INTERPRETATION

The Y-chromosome deletions in these two men are de-novo mutations, and are therefore the cause of their severe oligozoospermia. Not only is the absence of AZF compatible with spermatogenesis, albeit at reduced rate, but also the resultant sperm bear the mutant Y chromosome. Because intracytoplasmic sperm injection is increasingly used as a means of circumventing oligozoospermia, AZF deletions could be transmitted by this practice, and would probably result in infertile sons. In cases of severe oligozoospermia, it may be appropriate to offer Y-DNA testing and genetic counselling before starting assisted reproductive procedures.

PCR haplotypes for the human Y chromosome based on alphoid satellite DNA variants and heteroduplex analysis

We have developed a system for revealing informative and useful haplotypes for the human Y chromosome using PCR. Variant alphoid satellite DNA subunits were amplified and analysed by digestion with HindIII to score a restriction site polymorphism, or on polyacrylamide gels to reveal 13 heteroduplex haplotypes. Heteroduplexes are double-stranded DNA molecules containing mismatches; the haplotype is the combination of alleles on the same chromosome. Structural studies showed that the heteroduplexes analysed here were formed from loci at the left (short arm) and right (long arm) edges of the centromeric alphoid array which differed by a 4-bp insertion/deletion and several point mutations. Consequently, many haplotypes may have arisen only once and are useful for evolutionary studies.

Fathers and sons: the Y chromosome and human evolution

It should be possible to use Y chromosome DNA polymorphisms to trace paternal lineages for evolutionary and other studies, but progress in these areas has been slow because it has been difficult to find suitable markers. However, it is now possible to use selected, slowly evolving polymorphisms to draw a rudimentary Y chromosome tree, while more rapidly evolving polymorphisms allow most independent Y chromosomes to be distinguished. Different populations often have characteristically different Y chromosomes, and Y chromosome studies are soon likely to make a major contribution to our understanding of the origins of modern humans.

Pericentric inversion with a minute deletion of the Y chromosome in a severely oligozoospermic man

An apparent pericentric inversion of the Y chromosome in a severely oligozoospermic infertile patient is described. The karyotype was 46,X,inv (Y) (p11.2 q11.23). DNA analysis, however, revealed a deletion involving nine loci within the most distal part of the euchromatic region of the long arm.