Three cases of genetic defects affecting sperm tail: a FISH study

Submicroscopic alterations in the cytoskeletal structure of sperm flagellum are associated with severely reduced or completely absent motility in subfertile or infertile men. Sometimes these alterations can be related to well known genotypic defects when the same anomaly affects the whole sperm population. Transmission electron microscopy (TEM) is the only tool able to specifically characterize the morphological features of genetic sperm defects. In this study, the frequencies of aneuploid and diploid spermatozoa were identified in three patients showing specific flagellar anomalies, each of them affecting the whole sperm population: dysplasia of the fibrous sheath, primary ciliary dyskinesia and absence of fibrous sheath. All these defects were highlighted by TEM. Fluorescence in situ hybridization (FISH) analysis was performed on decondensed sperm nuclei for chromosomes 18, X and Y, highlighting higher diploidies and sex chromosome disomies in cases of dysplasia of the fibrous sheath and primary ciliary dyskinesia, in agreement with other reports. We have also described FISH results in spermatozoa with absence of fibrous sheath. In this case, the only one reported due to the rarity of this defect, the aneuploidies and diploidies were within normal range. These data contribute to the growing evidence that genetic sperm defects of sperm flagella are generally correlated with meiotic segregation derangement. For this reason, genetic counseling is advisable, although all the genes involved and the possible mechanisms of these mutations have not yet been fully characterized.     

Y chromosome microdeletions: are they implicated in teratozoospermia?

BACKGROUND: Y chromosome microdeletions are known to impair spermatogenesis. Screenings for these microdeletions are performed mostly in patients with sperm count abnormalities. METHODS: We have screened the Y chromosome of 80 infertile patients with sperm morphological abnormalities. DNA from sperm, peripheral blood or single sperm following multiple displacement amplification (MDA) was utilized to amplify 20 specific sequence-tagged sites (STS) by PCR. RESULTS: Y chromosome microdeletions were detected in sperm DNA from four of the teratozoospermic patients; while none of the 53 men with normal sperm morphology had any deletions. Two of the four patients with deletions also provided peripheral blood and a fresh semen sample. Both patients had none of the STS deleted in the peripheral blood DNA. Y chromosome microdeletion analysis in the MDA amplified SRY-positive single sperm DNA confirmed the presence of the same deletion in all 10 sperm for one patient and eight out of 10 sperm in the second patient. CONCLUSIONS: Our observations suggest that some of the teratozoospermia might be related to gonadal mosaic Y chromosome microdeletions. Gonadal mosaicism can be a source of de novo transmissions of Y chromosome microdeletions. The application of MDA can yield enough DNA from a single sperm for genetic analyses.     

Screening for Y chromosome microdeletions in 226 Slovenian subfertile men.

BACKGROUND: The objective of this study was to estimate the frequency of Y chromosome microdeletions in the Slovenian population of infertile men and to analyse the consequences of mutation in respect to clinical severity and prognosis. METHODS: In a controlled clinical study at the university-based medical genetics service and infertility clinic, 226 infertile men undergoing ICSI were tested. The main outcome measures included polymerase chain reaction amplification of 16 genes and gene families and 42 sequence-tagged sites in the non-recombining region of the Y chromosome, semen, testicular volume and testicular histological analysis, serum FSH concentrations, fertilization and respective pregnancy rates. RESULTS: The incidence of deletions was 4.4%: 8.6% in men with azoospermia and 1.5% in men with oligoasthenoteratozoospermia. Isolated gene deletions were not identified. No statistically significant differences in clinical outcome measures were found in patients with mutations versus patients without mutations. High fertilization (49%) and pregnancy (43%) rates with sperm of patients with Y chromosome deletions were obtained. CONCLUSIONS: Testing for gene-specific microdeletions does not contribute significantly to the sensitivity of microdeletion test. Fertilization and pregnancy rates obtained using sperm of patients with Y chromosome deletions were comparable with those achieved in conventional IVF.     

Do we need to search for gr/gr deletions in infertile men in a clinical setting?

BACKGROUND: Partial deletions of the AZFc region of the Y chromosome suchas gr/gr deletions have been detected in infertile patientsas well as in control groups. The impact of these gr/gr deletionson the etiology of male infertility remains unknown. In thepresent study, we investigated the presence of gr/gr deletionsin Caucasian men. METHODS: gr/gr deletions were analyzed by using markers sY1291, sY1191and sY1197 and by investigating the presence of single nucleotidevariants (SNV) in DAZ and CDY1 genes in patients with azoospermia(n = 44), cryptozoospermia (n = 51) or severe oligozoospermia(n = 92). Control groups consisted of men with normal spermatogenesison testicular biopsy (n = 33), normozoospermia (n = 278) orproven fertility (n = 83). RESULTS: We observed 20 gr/gr deletions, with eight in infertile patients(4.3%) and 12 in the control groups (3.0%), which was not significantlydifferent. DAZ SNV analysis revealed eight different deletionpatterns in patients and controls. CONCLUSIONS: In the present study, no significant differences in the frequencyof gr/gr deletions between different patient and control groupswere observed. We concluded that the relationship between gr/grdeletions and male infertility remains unclear and that it istoo early to systematically test for gr/gr deletions for infertilecouples seeking assisted reproduction treatment.     

Ultrastructural sperm study in infertile males with microdeletions of Y chromosome

A retrospective study to detect specific Y chromosome microdeletions and to evaluate sperm ultrastructural characteristics in infertile men was set up. We selected 219 infertile men referred to Regional Referral Center for Male Infertility, Siena, Italy for semen analysis from January 1999 to April 2004. Family history, lymphocyte karyotype determination, Y microdeletion screening, physical examination, hormonal assays, semen analysis were carried out. Sperm concentration and progressive motility, ultrastructural analysis of sperm organelles, PCR amplification of sequence tagged sites for Y microdeletion screening were performed. Different Y-chromosome deletions were found, mainly in the AZFb and AZFc regions. Severe alterations of sperm ultrastructure, affecting whole sperm population, were detected in carriers of Y-deletions. Our data confirms the highest frequency of Y deletions in azoospermic patients. In all other patients with Y microdeletions, sperm ultrastructural defects affected the whole sperm population and were mainly related to apoptosis or immaturity.     

Sperm ubiquitination in patients with dysplasia of the fibrous sheath

BACKGROUND: Human sperm with structural abnormalities display an increased content of the cellular proteolytic marker peptide, ubiquitin. We investigated whether dysplasia of the fibrous sheath (DFS), a severe structural anomaly found in the sperm of some asthenozoospermic patients, is accompanied by (i) increased ubiquitination of the sperm surface and (ii) by increased ubiquitination of the sperm mitochondria. METHODS AND RESULTS: Five DFS patients and eight fertile donors were studied by immunocytochemistry with anti-ubiquitin antibodies. Increased cross-reactivity of the ubiquitinated mitochondrial epitopes was seen in 32-50% of DFS sperm, but only 2-4.1% of sperm from fertile donors. Sperm surface ubiquitination assessed by sperm-ubiquitin tag immunoassay (SUTI) and immunofluorescence demonstrated an increased sperm ubiquitination in all DFS patients. The average median value of ubiquitin-induced fluorescence in DFS patients was 25.8 counts (range 19.8-37.9), as opposed to 13.4 counts range (9.3-16.6) in fertile men. Sperm with 'stump tails', coiled tails, twin and triplet sperm, and clusters of immature spermatogenic cells were common. CONCLUSIONS: DFS sperm have increased cross-reactivity to anti-ubiquitin antibodies, a finding consistent with the ubiquitination of defective sperm shown in animal models. These results justify the use of ubiquitin-based assays for objective semen analysis in infertile men with heritable defects.     

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). Recentstudies have shown that the presence of deletions involvingthe AZFc region do not appear to affect the chance of retrievingspermatozoa or have a significant impact on fertilization orpregnancy rates with ICSI. We investigated the effect of Y-chromosomepartial deletions on the chance of sperm retrieval with TESE.Eighty attempts at sperm retrieval were performed using TESEon men who were previously evaluated for Y-chromosome partialdeletions. Y-chromosome analysis was performed using a polymerasechain reaction (PCR)-based technique with 35 sequence-tagged-sites.Of the 80 men, nine (11%) had partial Y-chromosome deletionsdetected. Two azoospermic men with AZFc deletions had successfulsperm retrieval, ICSI and a subsequent clinical pregnancy. Sevenmen had deletions involving the AZFb region (three men had isolatedAZFb deletions, one had AZFa, AZFb and AZFc deleted, and threehad AZFb and AZFc deleted). None of the seven men had spermatozoaextracted by TESE, a result that is significantly differentfrom the overall 64% (47/73) sperm retrieval rate achieved atour centre (P = 0.001). Two men with AZFb deletions had cellsconsistent with round spermatids identified and injected intooocytes without effecting any normal fertilizations. Althoughpreliminary, these results suggest that the presence of an AZFbdeletion is a significantly adverse prognostic finding for TESE.Men with AZFb deletions should be apprised of these resultsbefore attempting TESE-ICSI. Alternatives such as donor inseminationor adoption should be considered or therapy delayed until improvedresults with round spermatid injections are likely.     

A comparison of mitochondrial and nuclear DNA status in testicular sperm from fertile men and those with obstructive azoospermia

BACKGROUND: Mitochondria are vital to sperm as their motility powerhouses. They are also the only animal organelles with their own unique genome; encoding subunits for the complexes required for the electron transfer chain. METHODS: A modified long PCR technique was used to study mitochondrial DNA (mtDNA) in ejaculated and testicular sperm samples from fertile men undergoing vasectomy (n = 11) and testicular sperm from men with obstructive azoospermia (n = 25). Nuclear DNA (nDNA) fragmentation was measured by an alkaline gel electrophoresis (comet) assay. RESULTS: Wild-type mtDNA was detected in only 60% of fertile men's testicular sperm, 50% of their ejaculated sperm and 46% of testicular sperm from men with obstructive azoospermia. The incidence of mitochondrial deletions in testicular sperm of fertile and infertile men was not significantly different, but the mean size of the deletions was significantly less in testicular sperm from fertile men compared with men with obstructive azoospermia (P < 0.02). NDNA fragmentation in testicular sperm from fertile men and men with obstructive azoospermia was not significantly different. CONCLUSION: Multiple mtDNA deletions are common in testicular and ejaculated sperm from both fertile and infertile men. However, in males with obstructive azoospermia, the mtDNA deletions in testicular sperm are of a larger scale.     

Human sperm tail fibrous sheath undergoes phosphorylation during its development.

The phosphorylation of the human sperm tail fibrous sheath as a maturational step during its development is reported for the first time. This was demonstrated using GDA-J/F3 and RT97 monoclonal antibodies (MoAb) which recognize the fibrous sheath. In indirect immunofluorescence microscopy of frozen sections of human adult testes, the two antibodies reacted with the assembled fibrous sheath only, but the numbers of sperm tails stained with RT97 were consistently lower than those treated with GDA-J/F3. Furthermore, by using double indirect immunofluorescence, although the majority of spermatozoa were doubly stained with the two MoAbs, some GDA-J/F3-positive sperm tails were negative with RT97. In epididymal and ejaculated spermatozoa, the two antibodies stained all the tails. This indicated that the ontogenic appearance of the GDA-J/F3 epitope precedes that of RT97. In Western blotting and/or indirect immunofluorescence of spermatozoa, treatment of samples with alkaline phosphatase abolished the reactivity of RT97 while that of GDA-J/F3 MoAb was not affected. This finding indicated that the RT97 but not the GDA-J/F3 epitope was phosphorylated. Together, these results therefore reveal that during tail morphogenesis, the fibrous sheath undergoes phosphorylation as part of its structural maturation. Screening of sperm cell precursors recovered from oligozoospermic donors showed reaction of some abnormal germ cells with GDA-J/F3 MoAb but not with RT97, suggesting the possible failure of phosphorylation of the fibrous sheath protein in these cells. The significance of these findings is discussed together with the biological importance of phosphorylation to the fibrous sheath.     

Immunology: Identification of human sperm surface glycoproteins by sperm membrane-specific autoantibodies

In order to identify the surface antigens of human spermatozoarecognized by the sera of immune infertile men, sperm membrane-specificantibodies were obtained from three serum samples exhibitinghigh titres of antibodies with different sperm-binding patterns.Serum antibodies were adsorbed onto normal motile spermatozoaand subsequently eluted from the sperm membrane. Using the immunoblottingtechnique under renaturating conditions, the sperm-eluted antibodieswere tested against an electro-phoretically fractionated spermmembrane preparation. A total of 15 protein bands ranging from110 to 16 kDa were defined, but the immunoblot profiles differedquantitatively and qualitatively from one serum to another.Only two polypeptides were recognized by the three sperm membrane-specificantibody preparations; one of 90 kDa and another of 110 kDa.Blots were also used for the affinodetection of specific oligosaccharideside chains. Three lectins were tested (concanavalin A, Pisumsativum, and wheat germ agglutinin). Of the 15 protein zonesrecognized by the antibodies, 11 bound at least one lectin andshould contain glycopeptides with oligosaccharides of four differenttypes: N-linked biantennary complex type, N-linked fucosylatedcomplex type, N-linked lactosaminyl complex type with terminalsialic acid and polysialyl type oligosaccharides. Further analysisof these glycoproteins will be pursued with sperm-associatedantibodies eluted from the ejaculates of infertile men in orderto define those with a potential role in the fertilization process.     

AJ-FSI monoclonal antibody detects a novel group of non-glycostlated antigens within the human sperm tail fibrous sheath

AJ-FS1 is one of a new series of monoclonal antibodies (MoAbs)raised by immunizing mice with isolated human sperm tail fibroussheath. Usinjg indirect immunofluorescence (IIF), the AJ-FS1MoAb didnot react with the surface antigens of viable sperm,but didstain the falgellar principal piece of sperm dried ontoslides or those demenbranated with 1% Triton X-100. The specificityof the antibody for the fibrous sheatht was confirmed by immunogoldelectron microscopy which showed the distrobution of gold particleson the outer fibrous sheath surface, and its reaction with theWestern blots of purified fibrous sheath preparations wheremultiple protein bands with mol. wt ranging between 97 and 28kDa were identified. The same peptides were alsod detected inurea-dithiothreitol (DTT) fraction of sequentially extractedspermatozoa but not in Triton or Triton-DTT sperm lysates. Thefailure of sodium metaperiodate to abrogate the antobody reactionin both Western blotting and IIf indicated on the non-glycosylatednature of the antigens. IIF screening of human testicular cryosatatsections with AJ-FS1 MoAb showed its reactivity with the assembledfibrous sheath of maturing sperm tails only; thus indicatingthe late apperance of the antigens during spermatogensis. Theanti-body did not react with skin, oesophagus, tongue, liver,kidney, placenta, uterus, cervix or their blood vessels. Thesignificance of these results is discussedtogether with theimportnce of AJ-FS1 MoAb as a specific probe for the characterizationof the fibrous sheath antigens in both normal and abnormal falgella.     

Fertilization and early embrology: A sequential analysis of the effect of progesterone on specific sperm functions crucial to fertilization in vitro in infertile patients

The objective of these studies was to evaluate the modulatoryeffect(s) of progesterone on sperm functions crucial to fertilizationin infertile men with abnormal sperm parameters. A prospective,controlled study applying a sequential diagnostic analysis capableof identifying specific dysfunctions of the male gamete wasperformed. Patients (n = 14) were allocated to the study groupif they had a history of infertility of >1 year durationand after semen evaluation showed teratozoospermia (< 14%normal sperm forms as diagnosed by strict criteria) or terato-asthenozoospermia(< 50% progressive motility). After swim-up separation ofthe motile sperm fraction, the following functions were assessedwith and without previous exposure to progesterone (1.0 µg/ml):acrosome reaction (using Pisum sativum agglutinin), hyperactivatedmotility (using a computerized semen analyser), sperm-zona pellucidabinding (in the hemizona assay), sperm-zona pellucida penetration(in a sperm-zona penetration assay), and sperm-oocyte penetration(using the hamster zona-free oocyte/sperm penetration assay).Progesterone did not affect the percentage of acrosome-reactedspermatozoa after 1 or 3 h of incubation. Hyperactivated motilitywas significantly enhanced by progesterone after 1 h (12 ±4 versus 6 ± 2% in controls; P < 0.02). Although progesteronedid not affect sperm-zona binding, it significantly enhancedboth sperm-zona pellucida penetration (27 versus 12% in controls;P = 0.03) and sperm-oocyte penetration (15 versus 8% in controls;P < 0.05). Because those sperm functions enhanced by progesteroneare crucial to fertilization, the steroid may have value inthe treatment of some male-factor patients undergoing assistedreproductive therapy.     

A trial to restore defective human sperm centrosomal function

BACKGROUND: In human fertilization, sperm centrosome function is essential for male and female pronuclear movement and fusion. In this study, we investigated the possibility of restoring human sperm centrosomal function in sperm exhibiting abnormalities in microtubule organization. METHODS: Semen was obtained from both a fertile donor and a patient with dysplasia of the fibrous sheath (DFS). Following heterologous ICSI using human sperm, we examined microtubules and chromatin configuration in bovine oocytes. Sperm were treated with dithiothreitol (DTT) prior to ICSI, while the oocytes were treated with the cytoskeletal stabilizer paclitaxel after ICSI. RESULTS: The combination of DTT and paclitaxel treatment induced microtubule organization in dead sperm from the fertile donor following heterologous ICSI. This treatment, however, was not effective for DFS sperm. In addition, expression of centrin, a protein functioning within the sperm centrosome, was reduced in DFS sperm from that of the normal levels observed in fertile donor sperm. CONCLUSION: These results indicate that sperm centrosomal function could be induced by the treatment of sperm with DTT before ICSI and of oocytes with paclitaxel after ICSI. DFS sperm are likely to exhibit such severe dysfunction of sperm centrosome that cannot be compensated for by this treatment; therefore, this method may be a practical way to discern the degree of sperm centrosomal dysfunction.     

甘肃部分地区373例男性不育患者Y染色体AZF微缺失基因诊断的研究

目的研究甘肃地区男性不育患者Y染色体AZF区域微缺失的频率、分布情况方法采用多重PCR技术,对甘肃地区373例男性不育症患者进行Y染色体AZFa,AZFb,AZFc三个区域6个STS位点的微缺失检测。结果 373例男性不育患者中,42例发生了STS位点缺失,缺失率11.3%。其中无精子症因子AZFa(SY86,SY84)区未见缺失;AZFb(SY127,SY134)区缺失4例(9.52%);AZFc(SY254,SY255)区缺失32例(76.2%);AZFb+c区缺失5例(11.9%);AZFa+b+c缺失1例(2.38%)。结论甘肃部分地区AZF区域微缺失的频率、分布与国内其他报道一致,但是在本研究中未检测到AZFa区缺失患者。     

Detection of sperm in men with Y chromosome microdeletions of the AZFa,AZFb and AZFc regions

BACKGROUND: Y chromosome microdeletions are associated with severe male factor infertility. In this study, the success rate of testicular sperm retrieval was determined for men with deletions of AZF regions a, b or c. METHODS: AZF deletions were detected by PCR of 30 sequence-tagged sites within Yq emphasizing the AZFa, b and c regions. Semen analysis and diagnostic testis biopsy or testicular sperm extraction (TESE) findings were correlated with the specific AZF region deleted. RESULTS: A total of 78 men with AZF deletions included three with AZFa deletion, 11 with AZFb, 42 with AZFc, 16 with AZFb+c and six with Yq (AZFa+b+c). All men with AZFa, AZFb, AZFb+c and Yq deletions were azoospermic and no sperm were found with TESE or biopsy. Of men with isolated AZFc deletion, sperm were found in 75% (9/12) by TESE and 45% (9/20) on biopsy (56% overall); 62% (26/42) were azoospermic and 38% (16/42) severely oligozoospermic. A total of 7 patients with deletion patterns that included the complete AZFa region and 23 that included the complete AZFb region who underwent TESE or biopsy did not have sperm detected by these surgical measures. CONCLUSIONS: Microdeletion of the entire AZFa or AZFb regions of the Y chromosome portends an exceptionally poor prognosis for sperm retrieval, whereas the majority of men with AZFc deletion have sperm within the semen or testes available for use in IVF/ICSI.     

Incidence of tail structure distortions associated with dysplasia of the fibrous sheath in human spermatozoa

Dysplasia of the fibrous sheath (DFS) is an anomaly found in spermatozoa of severe asthenozoospermic patients. Marked hypertrophy and hyperplasia of the fibrous sheath is the common characteristic. Immunocytochemistry allowed us to visualize the distortions and incidence of tail structure abnormalities associated with this phenotype in six patients; four with a complete form and two with an incomplete form of this pathology previously diagnosed and studied by electron microscopy. Microtubules and fibrous sheaths were studied using monoclonal antibodies against alpha-acetylated tubulin and anti-FSC1 (the major protein component of the fibrous sheath). Mitochondrial sheaths were visualized using the mitochondrion-specific vital dye MitoTracker green FM(TM). Phase contrast and fluorescent microscopy of semen samples showed large numbers of spermatozoa with short, rigid, thick and irregular tails. As expected, anomalous and completely distorted fibrous sheaths, severe alterations of the axonemal microtubules and different patterns of mitochondrial sheath configurations were found. While ultrastructural studies of thin sections allow an in-depth knowledge of the internal organization of the sperm tail, fluorescence labelling of selected sperm components affords a unique view of the whole flagellum including topographical relationships of various organelles. The combination of these different approaches is essential for a comprehensive understanding of this particular pathology.     

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.     

Prognostic value of Y deletion analysis: How reliable is the outcome of Y deletion analysis in providing a sound prognosis?

Y chromosomal microdeletions at the azoospermia factor (AZF) locus have been implicated as one of the major causes of idiopathic male infertility. The availability of intracytoplasmic sperm injection (ICSI) in treating a variety of male infertility has raised the risk of the transmission of Y microdeletions from father to son. In many IVF centres, Y microdeletion analysis has been used as a diagnostic tool for genetic counselling of infertile couples. Presently, the only prognosis that can be derived from Y microdeletion analysis is that the affected male offspring would benefit from proper clinical management of their infertility. Prognoses based on the pattern of Y microdeletions in relation to phenotype are rather subjective and inconclusive because of insufficient data to derive a definitive correlation whose significance can be determined by statistical analysis. Standardization of the number and choice of sequence-tagged sites (STS), whose deletions result in defective spermatogenesis, for the polymerase chain reaction (PCR) analysis of Y microdeletions would enhance its reliability in the interpretation of the results which is crucial for therapeutic decision-making. Furthermore, in-depth understanding of the gene functions in male infertility, especially at the AZF locus, would contribute greatly to the quality of the prognostic value of Y microdeletion analysis.     

Sex chromosome mosaicism in males carrying Y chromosome long arm deletions

Microdeletions of the long arm of the Y chromosome (Yq) are a common cause of male infertility. Since large structural rearrangements of the Y chromosome are commonly associated with a 45,XO/46,XY chromosomal mosaicism, we studied whether submicroscopic Yq deletions could also be associated with the development of 45,XO cell lines. We studied blood samples from 14 infertile men carrying a Yq microdeletion as revealed by polymerase chain reaction (PCR). Patients were divided into two groups: group 1 (n = 6), in which karyotype analysis demonstrated a 45,X/46,XY mosaicism, and group 2 (n = 8) with apparently a normal 46,XY karyotype. 45,XO cells were identified by fluorescence in-situ hybridization (FISH) using X and Y centromeric probes. Lymphocytes from 11 fertile men were studied as controls. In addition, sperm cells were studied in three oligozoospermic patients in group 2. Our results showed that large and submicroscopic Yq deletions were associated with significantly increased percentages of 45,XO cells in lymphocytes and of sperm cells nullisomic for gonosomes, especially for the Y chromosome. Moreover, two isodicentric Y chromosomes, classified as normal by cytogenetic methods, were detected. Therefore, Yq microdeletions may be associated with Y chromosomal instability leading to the formation of 45,XO cell lines.