Chromosomal abnormalities in human sperm

Comprehensive chromosome FISH assessment of sperm aneuploidy in normozoospermic males

PURPOSE

Sperm chromosomal abnormalities impact male fertility and pregnancy outcomes. However, the proportion of sperm with chromosomal abnormalities in normozoospermic men remains unclear. Herein, we evaluated sperm aneuploidy for 23 chromosomes to elucidate its incidence in normozoospermic men.

METHODS

Sperm from ten normozoospermic donors were obtained from a human sperm bank and analyzed using fluorescence in situ hybridization. The frequencies of nullisomy, disomy, and diploidy were analyzed along with trisomy, triploidy, tetraploidy, and other numerical abnormalities per chromosome and per donor levels.

RESULTS

A total of 248,811 sperm cells were analyzed (average: 24,881 ± 381 cells/donor), of which 246, 658 were haploid, 818 nullisomic, 393 disomic, 894 diploid, 13 triploid, 8 tetraploid, 3 trisomic, and 24 harbored multiple aneuploidies. Among the 22 autosomal and 2 sex chromosomes, the mean frequency of aneuploidy per chromosome was 0.49 ± 0.16%, including 0.33 ± 0.16% for nullisomy and 0.16 ± 0.08% for disomy. The mean frequencies of nullisomy, disomy, and aneuploidy per donor were 0.33 ± 0.13%, 0.16 ± 0.05%, and 0.49 ± 0.13%, respectively. The total frequencies of nullisomy, disomy, diploidy, and aneuploidy per donor were 7.62 ± 3.06%, 3.63 ± 1.12%, 0.36 ± 0.15%, and 11.25 ± 3.05%, respectively.

CONCLUSIONS

The dominant chromosome numerical abnormalities in normozoospermic men are nullisomy, disomy, and diploidy. Generally, the frequency of nullisomy is higher than that of disomy. The disomy or nullisomy frequencies for each chromosome being gained or lost were not unified and varied; some chromosomes (e.g., chromosomes 21 and 22 and sex chromosomes) are more prone to disomy while some others (e.g., chromosome 3) are more prone to nullisomy.

Detection of aneuploidy in human spermatozoa using fluorescence in situ hybridization (FISH)

Fluorescence in situ hybridization (FISH) with chromosome specific alpha-satellite DNA probes was used to estimate the rates of aneuploidy of chromosomes 1, 17, 18, X and Y in human ejaculated sperm. Sperm samples were collected from six donors, and biotinylated DNA probes, D1Z5, D17Z1, D18Z1, DXZ1 and DYZ3 were hybridized to interphase sperm which had been pretreated with dithiothreitol to expand their nuclei. A minimum of 3,000 sperm per donor were analyzed. The hybridization efficiency was 99.68% for all the five probes. The frequencies of aneuploidy for chromosomes 1, 17 and 18 were 0.65%, 0.66%, and 0.61%, respectively. For XX- and YY-sperm the frequencies were 0.28% and 0.27%, respectively. To estimate the diploidy and disomy rates, a mixture of D17Z1 and D18Z1 were used as probes, and the frequency of diploid sperm was calculated to be 0.27%. After subtraction of the diploidy rate, the disomy rates for chromosomes 1, 17, and 18 were estimated to be 0.38%, 0.39% and 0.33%, respectively. The proportion of X- and Y-bearing sperm were 49.90% and 49.66%, consistent with an expected 1:1 ratio.

Physiology and pathophysiology of the human spermatozoon: the role of electron microscopy

In this article, the major contributions of electron microscopy to the present understanding of the physiology and pathophysiology of the human spermatozoon are reviewed. The ultrastructural organization of sperm organelles playing a significant role for cell function and, therefore, for the reproductive process is described. Also, the major abnormalities and defects of the various organellar systems and how they impair the reproductive function and/or the viability of the cell are reviewed.

The meiotic segregation of human sperm chromosomes in two men with accessory marker chromosomes

Accessory marker chromosomes are occasionally discovered in normal individuals and they are presumed "clinically inert" since they do not appear to have any phenotypic effect. However, they do pose a theoretical risk at meiosis since they could disrupt the normal pairing and disjunction of homologous chromosomes. Sperm chromosome complements have been studied in two normal males, each of whom carry a small bisatellited accessory marker chromosome 47,XY, + mar (psps), to determine if these marker chromosomes are associated with an increased frequency of aneuploid gametes. Pronuclear chromosomes were visualized after in vitro fertilization of golden hamster eggs with human sperm. The frequency of sperm complements containing a marker chromosome was not significantly different from 50% as theoretically expected, in either male (17/43 and 13/31 with marker chromosomes). One male had 2/43 (4.7%) aneuploid sperm, which is very close to the average frequency of aneuploid sperm seen in control donors (5%). The other male had 6/31 complements with chromosomal abnormalities. One set of sperm chromosomes had structural abnormalities, and five (16.1%) had numerical abnormalities. This frequency of aneuploidy is significantly elevated over the frequency seen in control donors (P = .0002). It is particularly interesting that all the abnormalities involved small chromosomes, as would be expected if the marker chromosome participated in distributive pairing and thereby disrupted normal disjunction of chromosomes of similar size. These preliminary results suggest that accessory marker chromosomes may increase the risk of aneuploid gametes in some individuals.