Chromosome abnormalities in sperm from infertile men with asthenoteratozoospermia

Research over the past few years has clearly demonstrated that infertile men have an increased frequency of chromosome abnormalities in their sperm. These studies have been further corroborated by an increased frequency of chromosome abnormalities in newborns and fetuses from pregnancies established by intracytoplasmic sperm injection. Most studies have considered men with any type of infertility. However, it is possible that some types of infertility have an increased risk of sperm chromosome abnormalities, whereas others do not. We studied 10 men with a specific type of infertility, asthenozoospermia (poor motility), by multicolor fluorescence in situ hybridization analysis to determine whether they had an increased frequency of disomy for chromosomes 13, 21, XX, YY, and XY, as well as diploidy. The patients ranged in age from 28 to 42 yr (mean 34.1 yr); they were compared with 18 normal control donors whose ages ranged from 23 to 58 yr (mean 35.6 yr). A total of 201 416 sperm were analyzed in the men with asthenozoospermia, with a minimum of 10 000 sperm analyzed per chromosome probe per donor. There was a significant increase in the frequency of disomy in men with asthenozoospermia compared with controls for chromosomes 13 and XX. Thus, this study indicates that infertile men with poorly motile sperm but normal concentration have a significantly increased frequency of sperm chromosome abnormalities.     

An increased frequency of human sperm chromosomal abnormalities after radiotherapy

13 cancer patients were studied before radiotherapy (RT) and at regular intervals after RT to determine the effect of RT on chromosomal abnormalities in sperm. The men were 19-47 years old and received testicular radiation doses of 0.4-5.0 Gray. Human pronuclear sperm chromosomes were analysed after penetration of zona-pellucida-free hamster eggs. Unfortunately the hamster egg penetration rates were exceedingly low, both before and after RT and this limited the number of sperm chromosome complements which could be analysed. Before RT, the frequency of abnormal sperm chromosome complements was 0% (0/9). After RT, the majority of men were azoospermic for 24 months but complements could be analysed from 4 men. In the first 12 months the frequency of abnormalities was 13% (1/8) and at 24 months it was 13% (7/55). By 36 months after RT, most men had recovered sperm production and the frequency of abnormalities in 8 men was 21% (18/86), which is significantly higher than the rate in control donors (8.5%). For individual men the range was 6-67%, and there was a significant correlation between testicular radiation dose and the frequency of sperm chromosomal abnormalities. The frequencies of both numerical and structural abnormalities were significantly increased after RT. This is the first evidence that radiation may increase the frequency of chromosomal abnormalities in human gametes.     

Chromosome analysis of human sperm

Summary A modified technique has been developed for the visualization of the chromosomes in human sperm. The cytogenetic analysis of 129 G-banded human sperm metaphases of 6 normal donors showed an incidence of structural and numerical chromosome abnormalities of 7.8%. Two out of 129 spermatozoa were aneuploid (1.6%). The frequency of sperms with chromatid-type aberrations was 2.3% (3/129). Chromosome-type aberrations were found in 5 out of 129 (3.9%) spermatozoa. X to Y ratio did not differ significantly from the expected one-to-one ratio. Twenty-six sperm complements from a patient 18–20 months after testes exposure to 30 Gy were examined. A significant increase of numerical and structural chromosome abnormalities was not observed. Chromatidtype aberrations were found in two sperm complements (7.7%) and chromosome-type aberrations in one sperm complement (3.9%). The cytogenetic analysis of 15 human sperms from a cancer patient 26 months after chemotherapy showed an increased frequency of aberrant sperm complements (33.4%). One chromatid-type (6.7%), three chromosometype aberrations (20.0%) and one (6.7%) hyperploid sperm complement could be observed. The sample size is still too small to answer the question whether chemical mutagens may increase the frequency of chromosomal abnormalities in human sperm.     

A comparison of the frequency of sperm chromosome abnormalities in men with mild,moderate, and severe oligozoospermia

Infertile men undergoing intracytoplasmic sperm injection have an increased frequency of chromosome abnormalities in their sperm. Men with low sperm concentration (oligozoospermia) have an increased risk of sperm chromosome abnormalities. This study was initiated to determine whether men with severe oligozoospermia (<10(6) sperm/ml) have a higher frequency of chromosome abnormalities in their sperm compared with men with moderate (1-9 x 10(6) sperm/ml) or mild (10-19 x 10(6) sperm/ml) oligozoospermia. Multicolor fluorescence in situ hybridization analysis was performed using DNA probes specific for chromosomes 13, 21, X, and Y (with chromosome 1 as an autosomal control for the sex chromosomes). Aneuploidy and disomy frequencies were assessed from a total of 603,011 sperm from 30 men: 10 in each of the categories. The mean frequencies of disomy for the patients with mild, moderate, and severe oligozoospermia were 0.17%, 0.24%, and 0.30%, respectively, for chromosome 13 and 0.22%, 0.44%, and 0.58%, respectively, for chromosome 21. For the sex chromosomes, the mean frequencies of disomy for mild, moderate, and severe oligozoospermia were 0.25%, 1.04%, and 0.68%, respectively, for XY, 0.047%, 0.08%, and 0.10%, respectively, for XX, and 0.04%, 0.06%, and 0.09%, respectively, for YY. The frequencies for diploidy also increased from 0.4% for mild to 1.20% for moderate to 1.24% for severe oligozoospermia. There was a significant inverse correlation between the frequency of sperm chromosome abnormalities and the sperm concentration for XY, XX, and YY disomy and diploidy. These results demonstrate that men with severe oligozoospermia have an elevated risk for chromosome abnormalities in their sperm, particularly sex chromosome abnormalities.     

Human sperm chromosome complements after microinjection of hamster eggs

A technique was developed for microinjection of human spermatozoa into golden hamster (Mesocricetus auratus) eggs to obtain human pronuclear chromosome complements. Before microinjection the spermatozoa were treated by brief sonication or incubation in TEST-yolk buffer to reduce motility. Very few sperm chromosome complements developed after sperm treatment with sonication and the frequency of spermatozoa with structural chromosomal abnormalities was exceedingly high (91%). The majority of sperm chromosome complements analysed had multiple breaks and rearrangements. Sperm incubation in TEST-yolk buffer before microinjection provided more analysable sperm karyotypes with a significantly lower frequency of structural chromosomal abnormalities (39%, P less than 0.001). Our results therefore suggest that sonication induces structural chromosomal abnormalities in spermatozoa. Since the frequency of chromosomal abnormalities after microinjection was higher than after sperm fertilization of hamster eggs, it appears that microinjection per se may also increase the frequency of chromosomal abnormalities in spermatozoa. These results are based on small numbers and must be confirmed on larger sample sizes, but our study suggests that microinjection of spermatozoa into eggs should not be recommended for clinical use until fully evaluated.     

Is there a relationship between sperm chromosome abnormalities and sperm morphology?

This review explores the relationship between sperm chromosomal constitution and morphology. With the advent of techniques for obtaining information on the chromosome complements of spermatozoa, this relationship has been studied in fertile men and in men with a high frequency of chromosomal abnormalities. Using human sperm karyotype analysis, no relationship between sperm chromosome abnormalities and morphology was found in fertile men, translocation carriers or post-radiotherapy cancer patients. Fluorescence in situ hybridization (FISH) analysis has not generally revealed a specific association between morphologically abnormal sperm and sperm chromosome abnormalities, but has indicated that teratozoospermia, like other forms of abnormal semen profiles (aesthenozoospermia, oligozoospermia) is associated with a modest increase in the frequency of sperm chromosome abnormalities. However, FISH studies on some infertile men and mouse strains have suggested that certain types of morphologically abnormal spermatozoa, such as macrocephalic multitailed spermatozoa, are associated with a very significantly increased frequency of aneuploidy. Thus, there may be an association between sperm morphology and aneuploidy in infertile men with specific abnormalities.     

Analysis of the chromosome complement in outbred mouse sperm fertilizing in vitro

The chromosome complements in a population of mouse sperm from random-bred ICR donors were analyzed at first-cleavage metaphase after in vitro fertilization (IVF) of oocytes from females of the same strain. The sperm were aged as donations occurred within an average of 31 days, either since last mating or at arrival at the animal facility in the case of virgin males. Of a total of 598 sperm complements studied from 22 sexually mature males aged 10–26 weeks old, there was one diploid complement (0.17%). The frequencies of hyperhaploidy and structural aberrations that were studied in 338 complements were 4.4% and 3.6%, respectively, giving an overall frequency of 8.0%. The hyperhaploid complements consisted of n + 1, n + 2, n + 3, and n + 7 counts, while the structural abnormalities were of the chromosome type and included large and small fragments and a possible translocation. This is the highest frequency of sperm chromosome abnormalities reported for mouse sperm obtained from males under physiological conditions and fertilized in vitro or in vivo. Sperm aging, strain, and/or technique differences are among the factors that may be responsible for this high frequency. Since the 8.0% frequency of hyperhaploidy and structural abnormalities is similar to the frequency reported for human sperm after IVF, the outbred murine in vitro fertilization system may be a useful model to study the origin of human sperm chromosome abnormalities.     

An analysis of structural aberrations in human sperm chromosomes

We have analyzed structural aberrations in 5,000 sperm chromosome complements obtained from 20 men over a 5-yr period by fusion of human sperm with hamster eggs. Detailed data are presented on 366 abnormal cells with 379 analyzable breakpoints. The frequency of cells with structural aberrations ranged from 1.9% to 14.5% among donors; this interindividual variability was statistically significant (p less than 0.0001). In contrast, repeat samples from individual men showed no significant variation over time. The number of sperm chromosome sets processed per hamster egg had no effect on the frequency with which structural aberrations occurred, nor were sperm chromosome abnormalities altered by varying capacitation or culture conditions. The spectrum of structural aberrations observed in human sperm chromosomes and a chi-square analysis of breakpoints based on DNA content are presented. Although human sperm chromosome abnormalities were visualized with a cross-species system, we believe that they represent an inherent, biologically significant phenomenon.     

A comparison of chromosomal aberrations induced by in vivo radiotherapy in human sperm and lymphocytes

Chromosomal aberrations in human sperm and lymphocytes were compared before and after in vivo radiation treatment of 13 cancer patients. The times of analyses after radiotherapy (RT) were 1, 3, 12, 24, 36, 48 and 60 months. The median total radiation dose was 30 Gy and the testicular dose varied from 0.4 to 5.0 Gy. Human sperm chromosome complements were analysed after fusion with golden hamster eggs. There were no abnormalities in sperm or lymphocytes before RT. Following RT there was an increase in the frequency of numerical and structural chromosomal abnormalities in both lymphocytes and sperm. For structural abnormalities there were more rejoined lesions (dicentrics, rings) in lymphocytes and more unrejoined lesions (chromosome breaks, fragments) in sperm. After RT there was a dramatic increase in the frequency of chromosomal abnormalities in lymphocytes: at 1 mo. the frequency was 42%, at 3 mo. 25%, at 12 mo. 14%, at 24 mo. 11%, at 36 mo. 9%, at 48 mo. 7% and at 6 mo. 4%. Since the majority of men were azoospermic after RT, there is little data on sperm chromosome complements before the analyses performed at 24 mo. post-RT. At 24 mo. the frequency of abnormalities was 13%, followed by 21% at 36 mo., 12% at 48 mo. and 22% at 60 mo. Thus it appears that the frequency of lymphocyte chromosomal abnormalities had an initial marked increase after RT followed by a gradual decrease with time whereas the frequency of sperm chromosomal abnormalities was elevated when sperm production recovered and remained elevated from 24 to 60 mo. post-RT. This difference in the effect of time makes it very difficult to compare abnormality rates in lymphocytes and sperm and to use analysis of induced damage in somatic cells as surrogates for germ cells since the ratio between sperm and lymphocytes varied from 1:1 (at 24 mo. post-RT) to 5:1 (at 60 mo. post-RT).     

Variation in the frequency and type of sperm chromosomal abnormalities among normal men

Summary The chromosomal constitution of 1582 human sperm from 30 normal men of proven fertility was investigated after sperm penetration of hamster eggs. A minimum of 30 sperm chromosome complements were analysed per donor so that the distribution and variation in the frequency and type of sperm chromosomal abnormalities could be assessed. The mean frequency of sperm chromosomal abnormalities in individual men was 10.4% (±6.0%) with a range of 0–24.7%. For numerical abnormalities the mean was 4.7% (±2.9%) with a range of 0–10% and for structural abnormalities the mean was 6.2% (±6.0%) with a range of 0–23.1%. The 95% confidence intervals for the mean of an individual male were 0–10.5% for numerical abnormalities, 0–18.2% for structural abnormalities, and 0–22.4% for total abnormalities. There was a significant excess of hypohaploid complements compared with hyperhaploid complements. Since hypohaploid complements could be caused by technical artefact, a conservative estimate of aneuploidy was obtained by doubling the frequency of hyperhaploid sperm, yielding an estimate of 2.4% aneuploidy. The proportion of X-bearing (53%) and Y-bearing (47%) sperm did not differ significantly. These results were compared to the other two large studies of sperm chromosome complements from normal men.     

Aneuploidy frequency in sperm of fertile men

Analysis of sperm aneuploidy in 11 healthy men using two-or three-color FISH permitted to determine the average frequency of disomy for chromosomes 13 and 21 (0.11% and 0.2%, respectively), disomy for chromosome 18 (0.05%) and to reveal gonosomal aneuploidy variants and their frequency. The frequency of XX disomy was 0.04%; XY, 0.17%; YY, 0.06%; and gonosomal nullisomy, 0.29%. We assessed the frequency of meiotic nondisjunction of 13, 21, 18, X, and Y chromosomes and the frequency of XX, XY, and YY diploid spermatozoa. The XY variant prevailed in gonosomal aneuploidy and diploidy and was associated with abnormal chromosomal segregation in meiotic anaphase I. The contribution of human sperm chromosomal imbalance to early embryonic lethality and to some forms of chromosomal abnormalities in the off-spring is discussed.     

Frequency and distribution of chromosome abnormalities in human spermatozoa

This study reviews the frequency and distribution of numerical and structural chromosomal abnormalities in spermatozoa from normal men obtained by the human-hamster system and by multicolor-FISH analysis on decondensed sperm nuclei. Results from large sperm karyotyping series analyzed by chromosome banding techniques and results from multicolor FISH in sperm nuclei (of at least 10(4) spermatozoa per donor and per probe) were reviewed in order to establish baseline values of the sperm chromosome abnormalities in normal men. In karyotyping studies, the mean disomy frequency in human sperm is 0.03% for each of the autosomes, and 0.11% for the sex chromosomes, lower than those reported in sperm nuclei by FISH studies using a similar methodology (0.09% and 0.26%, respectively). Both types of studies coincide in that chromosome 21 and sex chromosomes have a greater tendency to suffer segregation errors than the rest of the autosomes. The mean incidence of diploidy, only available from multicolor FISH in sperm nuclei, is 0.19%. Inter-donor differences observed for disomy and diploidy frequencies among FISH studies of decondensed sperm nuclei using a similar methodology could reflect real differences among normal men, but they could also reflect the subjective application of the scoring criteria among laboratories. The mean frequency of structural aberrations in sperm karyotypes is 6.6%, including all chromosome types of abnormalities. Chromosome 9 shows a high susceptibility to be broken and 50% of the breakpoints are located in 9q, between the centromere and the 9qh+ region. Structural chromosome aberrations for chromosomes 1 and 9 have also been analyzed in human sperm nuclei by multicolor FISH. Unfortunately, this assay does not allow to determine the specific type of structural aberrations observed in sperm nuclei. An association between advancing donor age and increased frequency of numerical and structural chromosome abnormalities has been reported in spermatozoa of normal men.     

Sperm chromosome analysis in a man heterozygous for a paracentric inversion of chromosome 7 (q11q22)

Summary Human sperm chromosomes were studied in a man heterozygous for a paracentric inversion of chromosome 7 (q11q22). The pronuclear chromosomes were analysed after in vitro penetration of golden hamster (Mesocricetus auratus) eggs. Ninety-four sperm chromosome spreads were examined, of which 34 contained the normal number 7 chromosome and 59 the inverted 6. This segregation was significantly different from the expected 1:1 ratio. The number of X- to Y-bearing sperm was 48 and 46 respectively. No sperm contained a recombinant chromosome caused by a crossover within the inversion. The frequency of chromosomal abnormalities in other chromosomes was 9.6%, which is not significantly different from the frequency observed in normal donors (8.9%) in our laboratory. These result suggest that the risk of chromosomally unbalanced sperm is not high for this paracentric inversion.     

Sequence analysis of long FMR1 arrays in the Japanese population: insights into the generation of long (CGG) n tracts

Sperm chromosome abnormalities were assessed in testicular cancer patients before and after treatment with BEP (bleomycin, etoposide, cisplatin). The frequencies of disomy for chromosomes 1, 12, X, Y and XY were assessed along with diploid frequencies and sex ratios by multicolour fluorescence in situ hybridization (FISH). For each cancer patient, a minimum of 10 000 sperm was assessed for each chromosome probe before and after chemotherapy (CT). Data was analysed “blindly” by coding the slides. A total of 161 097 sperm were analyzed, 80 445 before and 80 642 after treatment. The mean disomy frequencies were 0.11% pre-CT vs 0.06% post-CT for chromosome 1, 0.18% vs 0.15% for chromosome 12, 0.10% vs 0.9% for the X chromosome, 0.13% vs 0.10% for the Y chromosome and 0.25% vs 0.20% for XY sperm. There was no significant difference in the frequency of disomy pre-CT vs post-CT for any chromosome except that chromosome 1 demonstrated a significant decrease after CT. The “sex ratios” and frequency of diploid sperm were also not significantly different in pre- and post-CT samples with 50.2% X-bearing sperm pre-CT and 50.5% X post-CT and 0.14% diploid sperm pre-CT vs 0.15% diploid sperm post-CT. There was no significant donor heterogeneity among the cancer patients. None of the values in the cancer patients differed significantly from 10 normal control donors. Thus our study suggests that BEP chemotherapy does not increase the risk of numerical chromosomal abnormalities in human sperm. Received: 11 June 1996 / Revised: 8 August 1996     

Comparison of chromosomal abnormalities in hamster egg and human sperm pronuclei

One thousand human sperm and hamster egg haploid karyotypes were analyzed at the pronuclear stage after in vitro penetration. The frequency of abnormalities in human sperm was 8.5%, with 5.2% aneuploidy and 3.3% structural abnormalities. The hamster egg complements had an abnormality rate of 3.8%, with 3.3% aneuploidy and 0.5% structural abnormalities. In both human and hamster complements, chromosome abnormalities were observed in all chromosome groups, demonstrating that all chromosomes are susceptible to nondisjunction, not just acrocentric or small chromosomes. There is an intriguing difference between the frequency of hyperhaploid and hypohaploid complements in human sperm and hamster eggs. In the human complements, 2.4% were hyperhaploid and 2.7% hypohaploid. This is very close to the theoretical 1 to 1 ratio expected from nondisjunction. The hamster egg complements had more hypohaploid (2.2%) than hyperhaploid (0.9%) complements, despite identical treatment. Higher rates of hypohaploidy are generally ascribed to artificial loss of chromosomes, but may in fact reflect a predisposition of oocytes to anaphase lag during meiosis. The frequency of abnormalities (both numerical and structural) is higher in human complements than in hamster. This may reflect an innate propensity for meiotic chromosome abnormalities in humans or may result from greater exposure of humans to mutagenic agents.     

Aneuploid spermatozoa in infertile men: teratozoospermia.

We and others have demonstrated that infertile men who are candidates for intracytoplasmic sperm injection (ICSI) have an increased frequency of chromosomal abnormalities in their sperm. Reports based on prenatal diagnosis of ICSI pregnancies have confirmed the increased frequency of chromosomal abnormalities in offspring. Most studies to date have lumped various types of infertility together. However, it is quite likely that some subsets of infertility have an increased risk of sperm chromosomal abnormalities whereas others do not. We have studied nine men with severe teratozoospermia (WHO, 1992 criteria, 0-13% morphologically normal forms) by multicolour fluorescence in situ hybridisation (FISH) analysis to determine if they have an increased frequency of disomy for chromosomes 13, 21, XX, YY, and XY, as well as diploidy. All of the men also had aesthenozoospermia (< 50% forward progression) but none of the men had oligozoospermia (<20 x 10(6) sperm/ml). The patients ranged in age from 20 to 49 years (mean 33.2 years) in comparison to 18 normal control donors who were 23 to 58 years (mean 35.6 years). The control donors had normal semen parameters and no history of infertility. A total of 180,566 sperm were scored in the teratozoospermic men with a minimum of 10,000 sperm analyzed/donor/chromosome probe. There was a significant increase in the frequency of disomy in teratozoospermic men compared to controls for chromosomes 13 (.23 vs.13%), XX (.13 vs.05%), and XY (.50 vs.30%) (P <.0001, 2-tailed Z statistic). This study indicates that men with teratozoospermia and aesthenozoospermia but with normal concentrations of sperm have a significantly increased frequency of sperm chromosomal abnormalities.     

Individual variation in the frequency of sperm aneuploidy in humans

To examine interindividual differences in sperm chromosome aneuploidy, repeated semen specimens were obtained from a group of ten healthy men, aged 20-21 at the start of the study, and analyzed by multi-color fluorescence in situ hybridization (FISH) analysis to determine the frequencies of sperm aneuploidy for chromosomes X, Y, 8, 18 and 21 and of diploidy. Semen samples were obtained three times over a five-year period. Statistical analysis examining the stability of sperm aneuploidy over time by type and chromosome identified two men who consistently exhibited elevated frequencies of sperm aneuploidy (stable variants): one with elevated disomy 18 and one with elevated MII diploidy. Differences among frequencies of aneuploidy by chromosome were also seen. Overall, disomy frequencies were lower for chromosome X, 8 and 18 than for chromosomes 21 or Y and for XY aneuploidy. The frequency of chromosome Y disomy did not differ from XY sperm frequency. Also, the frequency of meiosis I (XY) and II (YY + XX) sex chromosome errors did not differ in haploid sperm, but the frequency of MII errors was lower than MI errors in diploid sperm. Frequencies of sperm aneuploidy were similar between the first sampling period and the second, two years later. However, the frequency of some types of aneuploidy (XY, disomy Y, disomy 8, total autosomal disomies, total diploidy, and subcategories of diploidy) increased significantly between the first sampling period and the last, five years later, while others remained unchanged (disomy X, 21 and 18). These findings confirm inter-chromosome differences in the frequencies of disomy and suggest that some apparently healthy men exhibit consistently elevated frequencies of specific sperm aneuplodies. Furthermore, time/age-related changes in sperm aneuploidy may be detected over as short a period as five years in a repeated-measures study.     

Chromosomes of human sperm: Variability among normal individuals

Summary The chromosomal constitution of 2468 human sperm cells been investigated by fusion of human sperm with hamster eggs. The overall frequency of cells with structural aberrations was 7.7%, ranging from 1.9% to 15.8%, and varying significantly among individuals. The highest frequency occurred in sperm from the oldest donor (49 years), who also had had a vasectomy reversal three years prior to sampling. The overall aneuploidy frequency was 1.7%, ranging from 0.6% to 3.1%. In nine out of ten donors from whom blood samples were available the frequency of sperm cells with structural aberrations was higher than that for lymphocytes. Two previously reported donors (Brandriff et al. 1984) were resampled after an interval of 14 and 16 months respectively, and were each found to have similar frequencies of sperm chromosome abnormalities at both sampling times. A father-son pair included in the study had several chromosome breakpoints in common, although no more frequently than unrelated individuals.     

Chromosomal breakage in human spermatozoa, a heterozygous effect of the Bloom syndrome mutation.

The chromosome complements of 662 spermatozoa produced by the three fathers of individuals with Bloom syndrome (BS) were analyzed to determine whether the BS mutation could affect chromosome segregation and the frequency of aneuploidy in sperm. The frequency of numerical abnormalities was not significantly different from that in normal controls studied in our laboratory, but the frequencies of structural abnormalities were significantly increased in two of the men, 14.3% and 15.9%, versus 8.6% in controls. More striking was the increase in these two men of cells with multiple structural abnormalities: 8.1% and 6.7% with multiple abnormalities, versus 2.3% in controls.     

Analysis of sex chromosome aneuploidy in sperm from fathers of Turner syndrome patients

Numerical sex chromosome abnormalities were analyzed in sperm from four fathers of Turner syndrome patients of paternal origin to determine whether there was an increased frequency of sex chromosome aneuploidy and to elucidate whether meiotic malsegregation mechanisms could be involved in the origin of Turner syndrome. Determination of the parental origin of the single X chromosome (maternal in all four cases) and exclusion of X and Y mosaicism were carried out by polymerase chain reaction amplification of five X chromosome polymorphisms and three Y chromosome segments. A total of 45,299 sperm nuclei from Turner fathers and 85,423 sperm nuclei from eight control donors was analyzed by three-color fluorescence in situ hybridization. The four patients showed a significant increase in the percentages of XY sperm (mean 0.22%; range 0.20% to 0.22%) compared with control donors (mean 0.11%; range 0.06% to 0.18%). These results suggest that the four individuals have an increased frequency of nondisjunctional errors in meiosis I, resulting in the production of an increased proportion of XY spermatozoa and of sperm lacking a sex chromosome. Received: 24 November 1998 / Accepted: 2 February 1999