An infertile patient with Y chromosome b1/b3 deletion presenting with congenital bilateral absence of the vas deferens with normal spermatogenesis

Repetitive DNA Sequences in the Human Y Chromosome and Male Infertility

The male-specific Y chromosome, which is well known for its diverse and complex repetitive sequences, has different sizes, genome structures, contents and evolutionary trajectories from other chromosomes and is of great significance for testis development and function. The large number of repetitive sequences and palindrome structure of the Y chromosome play an important role in maintaining the stability of male sex determining genes, although they can also cause non-allelic homologous recombination within the chromosome. Deletion of certain Y chromosome sequences will lead to spermatogenesis disorders and male infertility. And Y chromosome genes are also involved in the occurrence of reproductive system cancers and can increase the susceptibility of other tumors. In addition, the Y chromosome has very special value in the personal identification and parentage testing of male-related cases in forensic medicine because of its unique paternal genetic characteristics. In view of the extremely high frequency and complexity of gene rearrangements and the limitations of sequencing technology, the analysis of Y chromosome sequences and the study of Y-gene function still have many unsolved problems. This article will introduce the structure and repetitive sequence of the Y chromosome, summarize the correlation between Y chromosome various sequence deletions and male infertility for understanding the repetitive sequence of Y chromosome more systematically, in order to provide research motivation for further explore of the molecules mechanism of Y-deletion and male infertility and theoretical foundations for the transformation of basic research into applications in clinical medicine and forensic medicine.

Sequence Read Depth Analysis of a Monophyletic Cluster of Y Chromosomes Characterized by Structural Rearrangements in the AZFc Region Resulting in DYS448 Deletion and DYF387S1 Duplication

The azoospermia factor c region (AZFc), located in the long arm of the human Y chromosome, is frequently involved in chromosome rearrangements, mainly due to non-allelic homologous recombination events that occur between the nearly identical sequences (amplicon) that comprises it. These rearrangements may have major phenotypic effects like spermatogenic failure or other pathologies linked to male infertility. Moreover, they may also be relevant in forensic genetics, since some of the Y chromosome short tandem repeats (Y-STRs) commonly used in forensic analysis are located in amplicons or in inter-amplicon sequences of the AZFc. In a previous study, we identified four phylogenetically related samples with a null allele at DYS448 and a tetrallelic pattern at DYF387S1, two Y-STRs located in the AZFc. Through NGS read depth analysis, we found that the unusual Y-STR pattern may be due to a 1.6 Mb deletion arising concurrently or after a 3.5 Mb duplication event. The observed large genomic rearrangement results in copy number reduction for the RBMY gene family as well as duplication of other AZFc genes. Based on the diversity of 16 additional Y-STRs, we estimated that the duplication/deletion event occurred at least twenty generations ago, suggesting that it has not been affected by negative selection.