Polymorphic Rearrangements of Human Chromosome 9 and Male Infertility: New Evidence and Impact on Spermatogenesis

Abstract

Chromosomal polymorphisms are structural variations in chromosomes that define the genomic variance of a species. These alterations are recurrent in the general population, and some of them appear to be more recurrent in the infertile population. Human chromosome 9 is highly heteromorphic, and how its rearrangement affects male fertility remains to be fully investigated. In this study, we aimed to investigate the association between the polymorphic rearrangements of chromosome 9 and male infertility via an Italian cohort of male infertile patients. Cytogenetic analysis was carried out, along with Y microdeletion screening, semen analysis, fluorescence in situ hybridization, and TUNEL assays using spermatic cells. Chromosome 9 rearrangements were observed in six patients: three of them showed a pericentric inversion, while the others showed a polymorphic heterochromatin variant 9qh. Of these, four patients exhibited oligozoospermia associated with teratozoospermia, along with a percentage of aneuploidy in the sperm of above 9%, in particular, an increase in XY disomy. Additionally, high values for sperm DNA fragmentation (≥30%) were observed in two patients. None of them had microdeletions to the AZF loci on chromosome Y. Our results suggest that polymorphic rearrangements of chromosome 9 might be associated with abnormalities in sperm quality due to incorrect spermatogenesis regulation.

Keywords: chromosome 9 polymorphism; chromosome inversion; genetic infertility; heterochromatin; male infertility; oligozoospermia; sperm DNA fragmentation; sperm aneuploidy; sperm quality.

Figure 1

Karyotype analysis showing a pericentric inversion of chromosome 9: 46, XY, inv(9) (p11q12) (a). Karyogram including the bands of chromosome 9; in red those involved in the rearrangement (b).

Figure 2

Karyotype analysis showing a pericentric inversion of chromosome 9: 46, XY, inv(9) (p11q13) in a heterozygous condition (a). Karyogram including the bands of chromosome 9; in red those involved in the rearrangement (b).

Figure 3

Polymorphic chromosome 9 variant 9qh (n: normal; a: qh++; b: qh+; c: qh−).

Figure 4

Multiplex PCR products obtained using a mixture of primers. Lane 1: Phi-X174 RF DNA Hae III Digest molecular weight marker; lane 2: water; lane 3: control female DNA; lanes 4 and 5: DNA of a patient examined amplified with multiplexes A and B, respectively. The presence of all investigated bands indicates the absence of microdeletions.

Figure 5

Representative image of FISH signals on aneuploid spermatozoa of patients carrying chromosome 9 rearrangements, analyzed by fluorescence microscope. CEP 18/X/Y probes were used to detect alpha satellite sequences in the centromeric regions of chromosomes 18, X and Y. Chromosome X appears in green, chromosome Y in red, and chromosome 18 in sky-blue (a). LSI 13/21 probes were instead utilized to detect the 13q14 region and the 21q22.13 to 21q22.2 regions. Chromosome 13 appears in green, while chromosome 21 appears in red (b).

Figure 6

Representative image of sperm cells with fragmented DNA (green fluorescence) and sperm cells with intact DNA (blue fluorescence), analyzed by fluorescence microscope.