Daniela Zuccarello

Male infertility: role of genetic background.

Male infertility represents one of the clearest examples of a complex disease with a substantial genetic basis. Numerous male mouse models, mutation screening and association studies reported over the last few years reveal the high prevalence of genetic causes of spermatogenic impairment, accounting for 10-15% of severe male infertility, including chromosomal aberrations and single gene mutations. Natural selection prevents the transmission of mutations causing infertility, but this protective mechanism may be overcome by assisted reproduction techniques. Consequently, the identification of genetic factors is important for appropriate management of the infertile couple. However, a large proportion of infertile males are diagnosed as idiopathic, reflecting poor understanding of the basic mechanisms regulating spermatogenesis and sperm function. Furthermore, the molecular mechanisms underlying spermatogenic damage in cases of genetic infertility (for example Yq microdeletions) are not known. These problems can be addressed only by large scale association studies and testicular or spermatozoal expression studies in well-defined alterations of spermatogenesis. It is conceivable that these studies will have important diagnostic and therapeutic implications in the future. This review discusses the genetic causes of male infertility known to date, the genetic polymorphisms possibly associated with male infertility, and reports novel results of global gene expression profiling of normal human testis by microarray technology.

Role of hormones, genes, and environment in human cryptorchidism.

Cryptorchidism is the most frequent congenital birth defect in male children (2-4% in full-term male births), and it has the potential to impact the health of the human male. In fact, although it is often considered a mild malformation, it represents the best-characterized risk factor for reduced fertility and testicular cancer. Furthermore, some reports have highlighted a significant increase in the prevalence of cryptorchidism over the last few decades. Etiology of cryptorchidism remains for the most part unknown, and cryptorchidism itself might be considered a complex disease. Major regulators of testicular descent from intraabdominal location into the bottom of the scrotum are the Leydig-cell-derived hormones testosterone and insulin-like factor 3. Research on possible genetic causes of cryptorchidism has increased recently. Abundant animal evidence supports a genetic cause, whereas the genetic contribution to human cryptorchidism is being elucidated only recently. Mutations in the gene for insulin-like factor 3 and its receptor and in the androgen receptor gene have been recognized as causes of cryptorchidism in some cases, but some chromosomal alterations, above all the Klinefelter syndrome, are also frequently involved. Environmental factors acting as endocrine disruptors of testicular descent might also contribute to the etiology of cryptorchidism and its increased incidence in recent years. Furthermore, polymorphisms in different genes have recently been investigated as contributing risk factors for cryptorchidism, alone or by influencing susceptibility to endocrine disruptors. Obviously, the interaction of environmental and genetic factors is fundamental, and many aspects have been clarified only recently.

Male infertility and androgen receptor gene mutations: clinical features and identification of seven novel mutations.

Objective  Androgens and a functioning androgen receptor (AR) are essential for development and maintenance of the male phenotype and spermatogenesis. Consistent with this, mutations in the AR gene cause a variety of defects related to androgen insensitivity, ranging from complete feminization to phenotypic males with infertility. The aim of his study was to analyse the prevalence of AR gene mutations in male infertility and to clarify the genotype‐phenotype relation.

Genetic Alterations Associated With Cryptorchidism

CONTEXT Cryptorchidism is the most frequent congenital birth defect in male children and represents an important risk factor for infertility and testicular cancer. Major regulators of testicular descent are the hormones insulin-like factor 3 (INSL3) and testosterone, and disruption of these pathways might cause cryptorchidism. OBJECTIVE To determine the frequency of genetic alterations in cryptorchidism. DESIGN AND SETTING Case-control study in 2 departments of pediatric surgery in Italy between January 2003 and March 2005. PATIENTS Six hundred male infants with cryptorchidism. Boys were followed up for 2 to 3 years (through January 2008) and orchidopexy was performed in those who were persistently cryptorchid. We analyzed 300 noncryptorchid male children aged 1 to 4 years as controls. MAIN OUTCOME MEASURES Karyotype anomalies and INSL3, INSL3 receptor, and androgen receptor gene mutations. RESULTS The frequency of genetic alterations in boys with cryptorchidism was low (17/600 [2.8%; 95% confidence interval {CI}, 1.7%-4.5%]) and was significantly higher in participants with persistent cryptorchidism (16/303 [5.3%; 95% CI, 3.0%-8.4%]; P = .001) and those with bilateral cryptorchidism (10/120 [8.3%; 95% CI, 4.1%-14.8%]; P = .001) than in controls (1/300 [0.3%; 95% CI, 0.1%-0.8%]). Boys with persistent cryptorchidism had a 17-fold greater odds of having a genetic alteration (odds ratio, 16.7; 95% CI, 2.2-126.5). The most common genetic findings in those with cryptorchidism were 8 cases of Klinefelter syndrome and 5 cases of mutations in the INSL3 receptor gene. Genetic alterations were not found in boys with low birth weight or low gestational age, who had frequent spontaneous descent of the testes. CONCLUSION In a small percentage of the study population, there was a statistically significant association between bilateral and persistent cryptorchidism and genetic alterations, including Klinefelter syndrome and INSL3 receptor gene mutations.

Androgens stimulate endothelial progenitor cells through an androgen receptor-mediated pathway

Background and objective  Testosterone (T) treatment has recently been shown to induce an increase in the number of endothelial progenitor cells (EPCs) through a possible effect on bone marrow. Hypogonadotrophic hypogonadal (HH) men have low circulating EPCs that increase significantly after T treatment. Moreover, expression of the androgen receptor (AR) has been demonstrated by immunohistochemistry in these cells, suggesting that T might also have a direct effect on EPC function. In the present study we investigated the expression and function of the AR in human EPCs and the in vitro effect of androgens on EPC function.

Human papillomavirus found in sperm head of young adult males affects the progressive motility

OBJECTIVE To evaluate the prevalence of human papillomavirus (HPV) sperm infection and its correlation with sperm parameters in a cohort of young adult males. DESIGN Cross-sectional clinical study. SETTING Andrology and Microbiology sections at a university hospital. PATIENT(S) A cohort of 200 young adult male volunteers (18 years old), 100 with previous sexual intercourse and 100 without previous sexual intercourse. MAIN OUTCOME MEASURE(S) Seminal parameters, sperm culture for HPV and fluorescence in situ hybridization (FISH) analysis for HPV detection in the sperm head. Statistical analysis was performed with a two-tailed Students t-test. RESULT(S) Results of HPV investigation were compared to sperm parameters and results of FISH analysis. HPV infection was present in sperm cells of 10 subjects among those 100 young adults who already had unprotected intercourse and its presence was associated with reduced sperm motility. Furthermore, infected samples showed that about 25% of sperm had an HPV DNA positivity at the head site, but it is unclear whether it was integrated in the nucleus or not. CONCLUSION(S) This is the first report estimating the percentage of HPV-positive sperm in infected subjects and the association between HPV infection and sperm motility.

Detailed functional studies on androgen receptor mild mutations demonstrate their association with male infertility.

Context   Mutations in the androgen receptor (AR) gene can cause the androgen insensitivity syndrome (AIS). For complete and severe partial AIS, well‐characterized in vitro functional assays can be used for genotype–phenotype correlation; however, for mild forms of AIS, as associated with male infertility, experimental evidence is scarce or lacking. In particular, optimal in vitro functional tests informative about the genotype–phenotype relation have not been described.

Mutations in dynein genes in patients affected by isolated non-syndromic asthenozoospermia

BACKGROUND Asthenozoospermia (AZS) is a common cause of male infertility characterized by reduced forward motility (WHO grade A+B sperm motility <50% or A < 25%) or absent sperm motility in fresh ejaculate. AZS may exist as an isolated disorder, in combination with other sperm anomalies or as part of a syndromic association. Up to date, only a few genes, constituting the cilia/flagella structure, have been associated with isolated AZS in humans, whereas several other genes are known to be involved in syndromic form of AZS, including primary ciliary dyskinesia (PCD) and Kartagener syndrome (KS). Axonemal ultrastructural defects, including absent or shortened arms of dyneins, can be found in >50% of PCD/KS patients. Approximately 90% of KS male patients are affected by AZS. The majority of KS patients can be ascribed to dynein genes mutations. METHODS Mutation screening of DNAI1, DNAH5 and DNAH11 genes was performed in 90 patients with isolated non-syndromic AZS and 200 controls. RESULTS We found three mutations (one in each gene) specifically associated with AZS in seven patients (7.8%). Mutations are inherited from the mothers and may be found in familial clusters. No ultrastructural axonemal anomaly was detected in sperm. CONCLUSIONS We report for the first time a possible association between mutations in dynein genes and isolated AZS. Male carriers of the mutations always exhibit AZS, whereas female carriers manifest no alterations in either fertility or pulmonary clearance.

Paracrine and endocrine roles of insulin-like factor 3

Insulin-like factor 3 (INSL3) is expressed in Leydig cells of the testis and theca cells of the ovary. This peptide affects testicular descent by acting on gubernaculum via its specific receptor leucine-rich repeat-containing G proteincoupled receptor 8 (LGR8). From initial animal data showing the cryptorchid phenotype of Insl3/ Lgr8 mutants, an extensive search for mutations in INSL3 and LGR8 genes was undertaken in human patients with cryptorchidism, and a frequency of mutation of 4–5% has been detected. However, definitive proofs of a causative role for some of these mutations are still lacking. More recent data suggest additional paracrine (in the testis and ovary) and endocrine actions of INSL3 in adults. INSL3 circulates at high concentrations in serum of adult males and its production is dependent on the differentiation effect of LH. Therefore, INSL3 is increasingly used as a specific marker of Leydig cell differentiation and function.

ORIGINAL RESEARCH—BASIC SCIENCE: The PDE5 Inhibitor Sildenafil Increases Circulating Endothelial Progenitor Cells and CXCR4 Expression

INTRODUCTION Endothelial progenitor cells (EPC) are a specific subtype of progenitor cells that can be isolated from circulating mononuclear cells, able to migrate from the bone marrow to the peripheral circulation where they contribute to vascular repair. CXC-motif chemochine receptor 4 (CXCR4) receptor seems to play a critical role in this process. AIM To assess the effects of sildenafil (a type 5 phosphodiesterase [PDE5] inhibitor) administration in 20 healthy young men. METHODS Evaluation of CXCR4 expression in circulating EPC before and 4 hours after in vivo administration of 100 mg sildenafil by flow cytometry and colony-forming unit. RESULTS We found that sildenafil increases circulating EPC number, the relative expression of CXCR4 on these cells and the ability to generate colonies in vitro. CONCLUSIONS These data allow us to suppose an involvement of PDE5 in bone marrow release and peripheral homing of EPC.