The Y chromosome harbors a number of genes essential for testis development and function. Its highly repetitive structure predisposes this chromosome to deletion/duplication events and is responsible for Y-linked copy-number variations (CNVs) with clinical relevance. The AZF deletions remove genes with predicted spermatogenic function en block and are the most frequent known molecular causes of impaired spermatogenesis (5-10% of azoospermic and 2-5% of severe oligozoospermic men). Testing for this deletion has both diagnostic and prognostic value for testicular sperm retrieval in azoospermic men. The most dynamic region on the Yq is the AZFc region, presenting numerous NAHR hotspots leading to partial losses or gains of the AZFc genes. The gr/gr deletion (a partial AZFc deletion) negatively affects spermatogenic efficiency and it is a validated, population-dependent risk factor for oligozoospermia. In certain populations, the Y background may play a role in the phenotypic expression of partial AZFc rearrangements and similarly it may affect the predisposition to specific deletions/duplication events. Also, the Yp contains a gene array, TSPY1, with potential effect on germ cell proliferation. Despite intensive investigations during the last 20 years on the role of this sex chromosome in spermatogenesis, a number of clinical and basic questions remain to be answered. This review is aimed at providing an overview of the role of Y chromosome-linked genes, CNVs, and Y background in spermatogenesis.

Purpose: Azoospermia affects 1% of men and it can be the consequence of spermatogenic maturation arrest (MA). Although the etiology of MA is likely to be of genetic origin, only 13 genes have been reported as recurrent potential causes of MA. Methods: Exome sequencing in 147 selected MA patients (discovery cohort and two validation cohorts). Results: We found strong evidence for 5 novel genes likely responsible for MA ( ADAD2 , TERB1 , SHOC1 , MSH4 , and RAD21L1 ), for which mouse knockout (KO) models are concordant with the human phenotype. Four of them were validated in the two independent MA cohorts. In addition, 9 patients carried pathogenic variants in 7 previously reported genes - TEX14 , DMRT1 , TEX11 , SYCE1 , MEIOB , MEI1 and STAG3 - allowing to upgrade the clinical significance of these genes for diagnostic purposes. Our meiotic studies provide novel insight into the functional consequences of the variants, supporting their pathogenic role. Conclusions: Our findings contribute substantially to the development of a pre-TESE prognostic gene panel. If properly validated, the genetic diagnosis of complete MA prior to surgical interventions is clinically relevant. Wider implications include the understanding of potential genetic links between NOA and cancer predisposition, and between NOA and premature ovarian failure.

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The standard FSH treatment is based on a 3 months period, after which both quantitative/qualitative improvement of sperm parameters and increased pregnancy rate were reported. In this prospective clinical trial, for the first time, we studied (i) Sperm hyaluronic acid binding capacity after highly purified FSH (hpFSH) treatment; (ii) the effect after short-term and standard treatment on this functional parameter. As secondary objective, we analyzed three SNPs on FSHβ and FSHR genes to define their potential predictive value for responsiveness. From a total of 210 consecutive patients, 40 oligo- and/or astheno- and/or teratozoospermic patients fulfilled the inclusion criteria. Treatment consisted in hpFSH 75 IU/L every other day for 3 months. To avoid potential biases derived from the lack of placebo, we analyzed each patient after 4-6 months of 'wash-out' period. After FSH treatment, we observed a statistically significant (p < 0.001) improvement of the percentage of hyaluronic acid bound spermatozoa from basal to T1 (after 1 month) and to T3 (after 3 months). Importantly, these values returned to near-baseline value after the wash-out. The same results were detected for total motile sperm count after 3 months with return to baseline after wash-out. Forty-two percent of patients responded to the therapy with increasing hyaluronic acid binding capacity above the double of the Intraindividual Variation (IV) while 24% of patients reached above the normal Sperm-Hyaluronan Binding Assay (HBA) value. Further increase in 'responders' was observed at T3. The responsiveness to treatment resulted independent from FSHR/FSHβ polymorphisms. The significant positive effect on sperm maturity after 1 month opens novel therapeutic perspectives. In view of both the high cost and the relative invasiveness of treatment, the short protocol (1 month) could represent a viable FSH treatment option prior Assisted Reproductive Techniques since FSH, by acting on sperm maturation, increases the proportion of functionally competent cells.

The association between impaired spermatogenesis and TGCT has stimulated research on shared genetic factors. Y chromosome-linked partial AZFc deletions predispose to oligozoospermia and were also studied in TGCT patients with controversial results. In the largest study reporting the association between gr/gr deletion and TGCT, sperm parameters were unknown. Hence, it remains to be established whether this genetic defect truly represents a common genetic link between TGCT and impaired sperm production. Our aim was to explore the role of the following Y chromosome-linked factors in the predisposition to TGCT: (i) gr/gr deletion in subjects with known sperm parameters; (ii) other partial AZFc deletions and, for the first time, the role of partial AZFc duplications; (iii) DAZ gene dosage variation. 497 TGCT patients and 2030 controls from two Mediterranean populations with full semen/andrological characterization were analyzed through a series of molecular genetic techniques. Our most interesting finding concerns the gr/gr deletion and DAZ gene dosage variation (i.e., DAZ copy number is different from the reference sequence), both conferring TGCT susceptibility. In particular, the highest risk was observed when normozoospermic TGCT and normozoospermic controls were compared (OR = 3.7; 95% CI = 1.5-9.1; p = 0.006 for gr/gr deletion and OR = 1.8; 95% CI = 1.1-3.0; p = 0.013 for DAZ gene dosage alteration). We report in the largest European study population the predisposing effect of gr/gr deletion to TGCT as an independent risk factor from impaired spermatogenesis. Our finding implies regular tumour screening/follow-up in male family members of TGCT patients with gr/gr deletion and in infertile gr/gr deletion carriers.