gr/gr-DAZ2-DAZ4-CDY1b deletion is a high-risk factor for male infertility in Tunisian population

The azoospermia factor c (AZFc) region harbors multi-copy genes that are expressed in the testis. Deletions of this region lead to reduced copy numbers of these genes. In this present study we aimed to determine the frequency of AZFc subdeletion in infertile and fertile men from Tunisia and to identify whether deletions of DAZ and CDY1 gene copies are deleterious on spermatogenesis and on semen quality. We studied a group of 241 infertile men and 115 fertile healthy males using a sequence tagged site (STS)±method. To gain insight into the molecular basis of the heterogeneous phenotype observed in men with the deletion we defined the type of DAZ and CDY1 genes deleted. We reported in the present study and for the first time a new type of AZFc deletion (gr/gr-DAZ2-DAZ4-CDY1b) and hypothesis that this new deletion is the result of two successive events. We also demonstrated that this deletion constitutes a relative high-risk factor for male infertility in Tunisian population.

DAZ duplications confer the predisposition of Y chromosome haplogroup K* to non-obstructive azoospermia in Han Chinese populations

STUDY QUESTION

What are the genetic causes for the predisposition of certain Y chromosome haplogroups (Y-hgs) to spermatogenic impairment?

SUMMARY ANSWER

The AZFc(azoospermia factor c)/DAZ (deleted in azoospermia) duplications might underlie the susceptibility of Y-hg K* to spermatogenic impairment.

WHAT IS KNOWN ALREADY

The roles of Y chromosomal genetic background in spermatogenesis are controversial and vary among human populations. Individuals in predisposed Y-hgs may carry some genetic factors, which might be a potential genetic modifier for the Y-hg-specific susceptibility to spermatogenic impairment.

STUDY DESIGN, SIZE, DURATION

A total of 2444 individuals with azoospermia or oligozoospermia and 2456 healthy controls were recruited to this study from March 2004 and January 2011.

PARTICIPANTS/MATERIALS, SETTING, METHODS

We performed a two-stage association study to investigate the risk and/or protective Y-hgs for spermatogenic impairment. In addition, the genetic causes for the predisposition of certain Y-hg to spermatogenic impairment were investigated. Deletion typing and DAZ gene copy number quantification were performed for individuals in predisposed Y-hgs.

MAIN RESULTS AND THE ROLE OF CHANCE

Y-hgs K* and O3e* showed significantly different distribution between cases and controls consistently in two-stage studies. Combined analyses identified significant predisposition to non-obstructive azoospermia in Y-hg K* [odds ratio (OR) 8.58; 95% confidence interval (CI) 3.31-22.28; P = 1.40 × 10⁻⁵], but a protecting effect in Y-hg O3e* (OR 0.64; 95% CI 0.53-0.78; P = 4.20 × 10⁻⁵). Based on the dynamic nature of the Y chromosome, we hypothesized that Y-hgs K* and O3e* may be accompanied by modifying genetic factors for their predisposing or protecting effects in spermatogenesis. Accordingly, we quantified the multi-copy DAZ gene, which has variable copy numbers between individuals and plays an important role in spermatogenesis. In combined analysis, we found that the over-dosage of DAZ was significantly more frequent in Y-hg K* than in O3e* (OR 4.79; 95% CI 1.67-13.70; P = 6 × 10⁻³).

LIMITATIONS, REASONS FOR CAUTION

Owing to the inconsistency of genetic background, it remains to be determined whether the results derived from Han Chinese populations are applicable to other ethnic groups.

WIDER IMPLICATIONS OF THE FINDINGS

The findings of this study can advance the etiology of spermatogenic impairment, and also shed new light on Y chromosome evolution in human populations. Y-hg-specific genetic factors of modifying spermatogenic phenotypes deserve further investigation in larger and diverse populations.