Micropenis and the AR Gene: mutation and CAG repeat-length analysis

Relationships among androgen receptor CAG repeat polymorphism, sex hormones and penile length in Han adult men from China: a cross-sectional study

This study aimed to investigate the correlations among androgen receptor (AR) CAG repeat polymorphism, sex hormones and penile length in healthy Chinese young adult men. Two hundred and fifty-three healthy men (aged 22.8 ± 3.1 years) were enrolled. The individuals were grouped as CAG short (CAG_S) if they harbored repeat length of ≤20 or as CAG long (CAG_L) if their CAG repeat length was >20. Body height/weight, penile length and other parameters were examined and recorded by the specified physicians; CAG repeat polymorphism was determined by the polymerase chain reaction (PCR) method; and the serum levels of the sex hormones were detected by radioimmunoassay. Student's t-test or linear regression analysis was used to assess the associations among AR CAG repeat polymorphism, sex hormones and penile length. This investigation showed that the serum total testosterone (T) level was positively associated with the AR CAG repeat length (P = 0.01); whereas, no significant correlation of T or AR CAG repeat polymorphism with the penile length was found (P = 0.593). Interestingly, an inverse association was observed between serum prolactin (PRL) levels and penile length by linear regression analyses (β= −0.024, P = 0.039, 95% confidence interval (CI): −0.047, 0). Collectively, this study provides the first evidence that serum PRL, but not T or AR CAG repeat polymorphism, is correlated with penile length in the Han adult population from northwestern China.

Reference standard of penile size and prevalence of buried penis in Japanese newborn male infants

The present study set forth the reference values for penile size and determined the prevalence of buried penis in Japanese full-term newborns. The stretched penile length was measured and the presence of buried penis was assessed at 1-7 days of age in 547 Japanese full-term newborn infants born between 2008 and 2012 in Tokyo. The stretched penile lengths were compared at 1-12 hours and 1-7 days of age in 63 infants and by two observers in 73 infants to estimate postnatal changes and interobserver variation, respectively. The mean stretched penile length was 3.06 cm (SD, 0.26; 95% confidence interval [CI], 3.04-3.08) and the mean ratio of penile length to body length was 6.24 × 100(-1) (SD, 0.55 × 100(-1)), both of which were significantly smaller than those in Caucasian newborn infants. Buried penis was identified in 20 of 547 infants (3.7%; 95% CI, 2.1-5.2%). The first measurements of penile length at 1-12 hours were significantly smaller than the next measurements at 1-7 days (95% CI of the difference, 0.22-0.34). The 95% CI for the limits of agreement in the penile lengths measured by the two observers was -0.58 to -0.40 for the lower limit and 0.33 to 0.51 for the upper limit. These findings indicate that the penile length should be assessed after 24 hours of age by the reference standard of the same ethnicity for identifying micropenis and that buried penis is not uncommon in Japanese full-term newborns.

Isolated micropenis reveals partial androgen insensitivity syndrome confirmed by molecular analysis

Partial androgen insensitivity syndrome (PAIS) is the milder variant of androgen receptor (AR) defects. The subtle effects of AR mutations present in a patient with micropenis, peno-scrotal hypospadias, infertility, clitoromegaly and posterior labial fusion. We studied the association of isolated micropenis with the genetic defects resulting in androgen resistance, that is, AR gene defects and 5-alpha reductase type 2 (SRD5A2) deficiency. We describe two cases of isolated micropenis: one in a 14-year-old boy and the other in a 3-year-old boy who was followed until he was 10 years old. There were no findings of hypospadias, cryptorchidism or gynecomastia in either of these patients. Serum gonadotrophin and androgen levels were obtained and karyotyping was done. Human chorionic gonadotropin (hCG) stimulation testing assessed the functional capacity of the testes. DNA was extracted from peripheral leukocytes, and all exons of the SRD5A2 and AR genes were amplified by polymerase chain reaction and sequenced. In both patients, baseline testosterone (T) level was low and the values were elevated after hCG testing. The sequence of the SRD5A2 gene was normal in patient 1, and a heterozygous polymorphism, V89L, was found in patient 2. Two known mutations, P390S and A870V, were identified in patients 1 and 2, respectively. Mutations in the AR gene can be associated with isolated micropenis without other features of PAIS, such as hypospadias or gynecomastia. This underlines the importance of including AR gene analysis in the evaluation of isolated micropenis with normal plasma T to ensure proper management of the patient and appropriate genetic counseling for the family.

Pharmacogenetics and pharmacogenomics of sexual dysfunction: current status, gaps and potential applications

Although treatment of different types of sexual dysfunction has improved in the past decade with the introduction of phosphodiesterase type 5 inhibitors and selective serotonin reuptake inhibitors, response rates to these targeted therapies are variable. There are a number of studies in the published literature that provide proof-of-concept that genetic variation contributes to the variable response. Pharmacogenomics will most likely be one part of our therapeutic armamentarium in the future and will provide a stronger scientific basis for optimizing drug therapy on the basis of each patient’s genetic constitution. This article will review English language medical literature on the state-of-the-art genetic polymorphisms of drug targets, transporters and signaling molecules as well as pharmacogenetic studies of sexual dysfunction and suggested possible applications. Collectively, the data demonstrate that pharmacogenomics in the field of sexual medicine is still in its infancy. More research will provide further intriguing new discoveries in years to come.

Haplotype analysis of the estrogen receptor 1 gene in male genital and reproductive abnormalities

BACKGROUND

We have recently suggested that homozygosity for a specific 'AGATA' haplotype within a approximately 50 kb linkage disequilibrium (LD) block of the gene for estrogen receptor alpha (ESR1) may raise the susceptibility to cryptorchidism by enhancing estrogenic effects of environmental endocrine disruptors (EEDs).

METHODS

Haplotype analysis of ESR1 was performed in 328 Japanese subjects, i.e. 70 patients with micropenis (MP), 43 patients with hypospadias (HS), 80 patients with spermatogenic failure (SF) and 135 control males. Genotyping was performed by the 5' nuclease assay.

RESULTS

The LD block was identified in each of the patient groups and in the control males. The frequency of homozygotes for the specific 'AGATA' haplotype was markedly higher in the HS patients [P = 0.0000033, odds ratio [OR] = 11.26] and slightly higher in the MP patients (P = 0.034, OR = 3.64) than in the control males, and the 'AGATA' haplotype was strongly associated with HS (P = 0.0000022, OR = 11.26) and weakly associated with MP (P = 0.040, OR = 3.64) in a recessive mode. There was no significant difference between the SF patients and the control males.

CONCLUSIONS

Our results support the hypothesis that homozygosity for the specific ESR1 'AGATA' haplotype may increase the susceptibility to the development of male genital abnormalities in response to estrogenic EEDs.

Developmental model for the pathogenesis of testicular carcinoma in situ: genetic and environmental aspects

Carcinoma in situ testis (CIS), also known as intratubular germ cell neoplasia (ITGCN), is a pre-invasive precursor of testicular germ cell tumours, the commonest cancer type of male adolescents and young adults. In this review, evidence supporting the hypothesis of developmental origin of testicular germ cell cancer is summarized, and the current concepts regarding aetiology and pathogenesis of this disease are critically discussed. Comparative studies of cell surface proteins (e.g. PLAP and KIT), some of the germ cell-specific markers (e.g. MAGEA4, VASA, TSPY and NY-ESO-1), supported by studies of regulatory elements of the cell cycle (e.g. p53, CHK2 and p19-INK4d) demonstrated a close similarity of CIS to primordial germ cells and gonocytes, consistent with the pre-meiotic origin of CIS. Recent gene expression profiling studies showed that CIS cells closely resemble embryonic stem cells (ESCs). The abundance of factors associated with pluripotency (NANOG and OCT-3/4) and undifferentiated state (AP-2gamma) may explain the remarkable pluripotency of germ cell neoplasms, which are capable of differentiating to various somatic tissue components of teratomas. Impaired gonadal development resulting in the arrest of gonocyte differentiation and retention of its embryonic features, associated with an increasing genomic instability, is the most probable model for the pathogenesis of CIS. Genomic amplification of certain chromosomal regions, e.g. 12p, may facilitate survival of CIS and further invasive progression. Genetic studies, have so far not identified gene polymorphisms predisposing to the most common non-familial testicular cancer, but this research has only recently begun. Association of CIS with other disorders, such as congenital genital malformations and some forms of impaired spermatogenesis, all rising in incidence in a synchronous manner, led to the hypothesis that CIS might be a manifestation of testicular dysgenesis syndrome (TDS). The aetiology of TDS including testicular cancer remains to be elucidated, but epidemiological trends suggest a primary role for environmental factors, probably combined with genetic susceptibility.

Gene-environment interactions: a review of effects on reproduction and development

Polymorphisms in genes can lead to differences in the level of susceptibility of individuals to potentially adverse effects of environmental influences, such as chemical exposure, on prenatal development or male or female reproductive function. We have reviewed the literature in this area, with the caveat that papers involving straight gene knock-outs in experimental animals, without a clear human relevance, were largely excluded. This review represents current knowledge in this rapidly moving field, presenting both human epidemiological and animal data, where available. Among the polymorphic genes and environmental interactions discussed with respect to prenatal development are those for P-glycoprotein (multidrug resistance protein) and the avermectins; methylenetetrahydrofolate reductase (MTHFR), an enzyme in folate metabolism, and dietary folic acid; transforming growth factor alpha (TGFalpha) and cigarette smoke; and alcohol dehydrogenase (ADH) and cytochrome P-450 (CYP) 2E1 in association with alcohol consumption. Effects on male reproduction attributable to gene-environment interaction involve infertility seen as a result of either organophosphorous (OP) pesticide interaction with the polymorphic paraoxonase (PON1) gene or antiandrogenic agent interaction with the androgen receptor (AR). MTHFR, folate metabolism, and dietary folic acid are also considered in conjunction with preeclampsia and early pregnancy loss, and the effect of the interaction of glutathione S-transferase (GST) with exposure to benzene or cigarette smoke on pregnancy maintenance is explored. As a conclusion, we offer a discussion of lessons learned and suggested research needs.

Association of micropenis with Pro185Ala polymorphism of the gene for aryl hydrocarbon receptor repressor involved in dioxin signaling

The prevalence of undermasculinized external genitalia has increased in several countries including Japan, and this phenomenon has primarily been ascribed to the deleterious effects of environmental endocrine disruptors such as dioxins. To examine a possible role of the genetic susceptibility to dioxins in the development of micropenis (MP), we studied the Arg554Lys polymorphism of the gene for aryl hydrocarbon receptor (AHR) and the Pro185Ala polymorphism of the gene for aryl hydrocarbon receptor repressor (AHRR), in 73 boys with MP (34 boys with mild MP from -2.1 to -2.5 SD and 39 boys with severe MP below -2.5 SD) and 80 control males (50 boys and 30 fertile adult males). The allele and genotype frequencies of the AHR polymorphism were comparable between the two groups of males, but those of the AHRR polymorphism were significantly different, with the Pro allele and the Pro/Pro genotype being more frequent in boys with MP than in control males (P-value: 0.0029 for the allele frequency and 0.011 for the genotype frequency). In addition, both polymorphisms were comparable in the allele and genotype frequencies between boys with mild MP and those with severe MP and between control boys and control fertile adult males. The results suggest that the AHRR Pro185Ala polymorphism may constitute a susceptibility locus for the development of MP in response to dioxins.

Molecular epidemiology of hypospadias: Review of genetic and environmental risk factors

Hypospadias is one of the most common congenital anomalies in the United States, occurring in approximately 1 in 125 live male births. It is characterized by altered development of the urethra, foreskin, and ventral surface of the penis. In this review, the embryology, epidemiology, risk factors, genetic predisposition, and likely candidate genes for hypospadias are described. Recent reports have identified increases in the birth prevalence of mild and severe forms of hypospadias in the United States from the 1960s to the present. Studies in consanguineous families and small case series have identified allelic variants in genes controlling androgen action and metabolism that cause hypospadias, but the relevance of these findings to the general population is unknown. Concern has also focused on whether exposure to endocrine disrupting chemicals (EDC) with antiandrogenic activity is the cause of this increase. Hypospadias is believed to have a multifactorial etiology in which allelic variants in genes controlling androgen action and metabolism predispose individuals to develop this condition. When genetic susceptibility is combined with exposure to antiandrogenic agents, a threshold is surpassed, resulting in the manifestation of this birth defect. A clear role for exposure to antiandrogenic environmental chemicals has yet to be established in the etiology of hypospadias, although results from laboratory animal models indicate that a number of environmental chemicals could be implicated. Molecular epidemiology studies that simultaneously examine the roles of allelic variants in genes controlling androgen action and metabolism, and environmental exposures are needed to elucidate the risk factors for these anomalies and the causes of the increased rate of hypospadias.

Counting CAG repeats in the Huntington's disease gene by restriction endonuclease EcoP15I cleavage

Huntington's disease (HD) is a progressive neurodegenerative disorder with autosomal-dominant inheritance. The disease is caused by a CAG trinucleotide repeat expansion located in the first exon of the HD gene. The CAG repeat is highly polymorphic and varies from 6 to 37 repeats on chromosomes of unaffected individuals and from more than 30 to 180 repeats on chromosomes of HD patients. In this study, we show that the number of CAG repeats in the HD gene can be determined by restriction of the DNA with the endonuclease EcoP15I and subsequent analysis of the restriction fragment pattern by electrophoresis through non-denaturing polyacrylamide gels using the ALFexpress DNA Analysis System. CAG repeat numbers in the normal (30 and 35 repeats) as well as in the pathological range (81 repeats) could be accurately counted using this assay. Our results suggest that this high-resolution method can be used for the exact length determination of CAG repeats in HD genes as well as in genes affected in related CAG repeat disorders.