DDX3Y is likely the key spermatogenic factor in the AZFa region that contributes to human non-obstructive azoospermia

Abstract

Non-obstructive azoospermia, the absence of sperm in the ejaculate due to disturbed spermatogenesis, represents the most severe form of male infertility. De novo microdeletions of the Y-chromosomal AZFa region are one of few well-established genetic causes for NOA and are routinely analysed in the diagnostic workup of affected men. So far, it is unclear which of the three genes located in the AZFa chromosomal region is indispensible for germ cell maturation. Here we present four different likely pathogenic loss-of-function variants in the AZFa gene DDX3Y identified by analysing exome sequencing data of more than 1,600 infertile men. Three of the patients underwent testicular sperm extraction and revealed the typical AZFa testicular Sertoli cell-only phenotype. One of the variants was proven to be de novo. Consequently, DDX3Y represents the AZFa key spermatogenic factor and screening for variants in DDX3Y should be included in the diagnostic workflow.

Fig. 1. Overview of the Y-chromosomal azoospermia factor A region.

a Schematic illustration of the Y chromosome and the AZF microdeletions. The genes localizing within the AZFa region are shown as well as typical break points leading to the classic complete AZFa deletion. b Exon/intron structure of DDX3Y. Identified loss-of-function (LoF) variants are located in exon 6 and 13 as well as in the donor splice site of intron 15 and affect at least the sequence of the C-terminal helicase domain.

Fig. 2. Characterization of patients M2171, M2185, and M3086.

a Pedigree of M2171 with de novo variant c.1609+1del in DDX3Y. b Sequencing of cDNA derived from splicing assay based on a minigene construct. c.1609+1del causes a shift of the splice donor site of intron 15 at position c.1609+1 to position c.1609, resulting in a frameshift. c Pedigree of patient M2185 with hemizygous variant c.1272dup p.(Lys425*). DNA of further family members was not available for analysis. d Pedigree of M3086 carrying the hemizygous variant c.428dup p.(Glu145Glyfs*13). DNA of additional family members was not available for segregation analyses. e Hematoxylin and eosin (HE) staining of testicular sections of M2171, M2185, and M3086, demonstrating SCO. Example Sertoli cells (SC) are indicated by arrows.