Steroid 5alpha-reductase 1 polymorphisms and testosterone/dihydrotestosterone ratio in male patients with hypospadias

BACKGROUND/AIM: Defects in the steroid 5alpha-reductase type 2 (SRD5A2) activity cause decreased formation of dihydrotestosterone (DHT) from testosterone (T), resulting in defective masculinization of external genitalia; the T/DHT ratio is increased. We investigated 10 patients with elevated T/DHT ratios in whom mutations in the SRD5A2 and AR genes had been excluded to find out whether structural alterations of the SRD5A1 gene could contribute to their genital malformations. METHODS: Single-strand conformation polymorphism analysis and direct sequencing were used to detect variations in the SRD5A1 gene of the patients and of 49 adult fertile men who served as controls. RESULTS: The sequence analysis of exon 3 of the SRD5A1 gene indicated an adenine-to-guanine change (ACA vs. ACG), both triplets encoding the amino acid residue threonine. The ACG sequence was detected in 57% of all subjects and was equally distributed in patients and controls. The T/DHT ratio was significantly higher in controls with the ACG variant as compared with those having the ACA variant. However, no particular sequence aberration was found in the SRD5A1 genes of either group. CONCLUSION: Mutant SRD5A1 isoenzyme does not seem to play a crucial role in the development of hypospadias.     

Phenotypic feminization in a genetic male dog caused by nonfunctional androgen receptors

A dog raised as a female pup did not have utero-ovarian structures when ovariohysterectomy was attempted at 6 mo of age. Three months later, the dog exhibited male-like behavior, and 2 symmetrical testicular-shaped structures arose bilateral to the vulva. Intersex cases such as this one may involve chromosomal abnormalities, defects in testicular secretions or androgen insensitivity in tissues of the sex accessories. Serum concentrations of testosterone and dihydrotestosterone were measured in the intersex and in intact normal male (control; n=7) dogs. In addition, 5alpha-reductase enzyme activity was determined in the gonadal tissue of the intersex dog and control dogs. Androgen receptors were studied in cultured fibroblasts from the genital skin of the intersex and control dogs. The cytogenetic studies identified the animal's karyotype to be 78 XY. All complete cells from the gonadal tissue showed an XY sex chromosome complement. Serum testosterone concentrations before and after challenge with hCG were not different between the intersex and control dogs (6.2 vs 5.72 +/- 1.8 ng/ml and 9.5 vs 8.69 +/- 2.39 ng/ml before and after hCG challenge, respectively). Similarly serum dihydrotestosterone concentrations were not different between the intersex and control dogs before and after challenge with hCG (158 vs 162 +/- 1.4 pg/ml and 270 vs 278.71 +/- 45.98 pg/ml before and after hCG challenge, respectively). The 5alpha-reductase enzyme activity of the gonads was not different between the intersex and control dogs (105 pmol/h/mg protein vs 110 +/- 2.4 pmol/h/mg protein). The Bmax values of binding in the control dogs fibroblast strains were 25 +/- 3.5 fmol/mg protein. However, specific binding of dihydrotestosterone was virtually undetectable in the fibroblasts cultured from the intersex dog. These results exclude chromosomal abnormalities and deficient secretion of testosterone and dihydrotestosterone as causative factors. Because fibroblasts cultured from genital skin lacked any ability to specifically bind dihydrotestosterone, it is suggested that nonfunctional androgen receptors in some tissues of the sex accessories contributed to the feminine phenotype of this particular dog.     

Characterization and chromosomal mapping of a human steroid 5 alpha-reductase gene and pseudogene and mapping of the mouse homologue.

The enzyme steroid 5 alpha-reductase catalyzes the conversion of testosterone into the more powerful androgen, dihydrotestosterone. We previously described the cloning of rat and human cDNAs that encode steroid 5 alpha-reductase and their expression in oocytes and cultured cells. Here, we report the isolation, characterization, and chromosomal mapping of two human steroid 5 alpha-reductase genes. One gene (symbol SRD5A1) is functional, contains five exons separated by four introns, and maps to the distal short arm of chromosome 5. Two informative restriction fragment length polymorphisms are present in exons 1 and 2 of this gene. A second gene (symbol SRD5AP1) has all of the hallmarks of a processed pseudogene and was mapped to the q24-qter region of the X chromosome. In the mouse, a single steroid 5 alpha-reductase gene (Srd5 alpha-1) is linked to Xmv-13 on chromosome 13.     

Expression of androgen-responsive properties in human skin fibroblast strains of genital and nongenital origin

Specific 5alpha-dihydrotestosterone (DHT) binding capacity (Bmax) has been determined for human skin fibroblast strains from non-genital areas of males and females (N = 8), as well as prepuce and labium majus (N = 9). Genital strains had a mean three times that of non-genital ones (32 vs. 11 fmol/mg cell protein). There were no sex differences. Variation among strains was not simply correlated with donor age; that within strains was unrelated to in vitro age. The lowest values for genital strains overlapped the nongenital ones; those of the nongenital strains approached the limit of detectability. These results parallel those for delta4-3-ketosteroid 5alpha-reductase activity. Thus, serially cultured genital and nongenital skin fibroblasts express their relative differentiative ancestry as androgen target cells. This expression may affect the diagnosis of androgen insensitivity and certain inborn errors of metabolism; its variability is discussed in terms of clonal heterogeneity.     

Differential gene-expression patterns in genital fibroblasts of normal males and 46,XY females with androgen insensitivity syndrome: evidence for early programming involving the androgen receptor

Background  

Androgen insensitivity syndrome (AIS) comprises a range of phenotypes from male infertility to complete feminization. Most individuals with AIS carry germline mutations of the androgen receptor (AR) that interfere with or ablate its function. As genital fibroblasts retain expression of the AR in vitro, we used genital skin fibroblasts from normal males and 46,XY females with complete AIS due to known AR mutations to gain insights into the role of the AR in human genital differentiation.     

L712V mutation in the androgen receptor gene causes complete androgen insensitivity syndrome due to severe loss of androgen function

Inability to respond to the circulating androgens is named as androgen insensitivity syndrome (AIS). Mutations in the androgen receptor (AR) gene are the most common cause of AIS. A cause and effect relationship between some of these mutations and the AIS phenotype has been proven by in vitro studies. Several other mutations have been identified, but need to be functionally validated for pathogenicity. Screening of the AR mutations upon presumptive diagnosis of AIS is recommended. We analyzed a case of complete androgen insensitivity syndrome (CAIS) for mutations in the AR gene. Sequencing of the entire coding region revealed C > G mutation (CTT–GTT) at codon 712 (position according to the NCBI database) in exon 4 of the gene, resulting in replacement of leucine with valine in the ligand-binding domain of the AR protein. No incidence of this mutation was observed in 230 normal male individuals analyzed for comparison. In vitro androgen binding and transactivation assays using mutant clone showed approximately 71% loss of ligand binding and about 76% loss of transactivation function. We conclude that CAIS in this individual was due to L712V substitution in the androgen receptor protein.     

Novel and recurrent mutations in patients with androgen insensitivity syndromes

BACKGROUND/AIMS: Androgen insensitivity syndrome (AIS) caused by mutations within the androgen receptor gene represents a variety of phenotypes from females with 46,XY karyotype over individuals with ambiguous genitalia to infertile males. METHODS: We studied 24 patients with AIS by sequencing androgen receptor gene. 19 of the investigated patients were affected by complete androgen insensitivity syndrome (CAIS) and 5 suffered from partial androgen insensitivity syndrome (PAIS). RESULTS: So far we have detected 12 unreported mutations as well as 9 recurrent mutations (3 recurrent mutations were detected twice) in exons 2-8 of the androgen receptor gene. Three of the novel mutations cause a frameshift with subsequent premature termination and were found in patients with CAIS. These frameshifts were induced by single nucleotide deletion or insertion, or in one case by a 13-bp deletion, respectively. Another premature stop codon found in a CAIS patient results from an already reported nucleotide substitution in exon 5. Furthermore, in a CAIS patient we found a novel duplication of codon 788. All other mutations caused single base substitutions spread through exons 2-8 and were associated with CAIS or PAIS. CONCLUSIONS: We report a broad spectrum of different mutations within the AR gene leading to various manifestations of AIS. Apart from truncating mutations, a reliable genotype/phenotype correlation cannot be established. Therefore, modifying factors must be effective.     

Expression of the androgen receptor and 5α-reductase type 2 in the developing human fetal penis and urethra

Normal penile development is dependent on testosterone, its conversion via steroid 5 alpha-reductase type 2 to dihydrotestosterone, and a functional androgen receptor (AR). The goal of this study was to investigate the distribution of AR and 5 alpha-reductase type 2 in the developing human fetal external genitalia with special emphasis on urethra formation. Twenty fetal genital specimens from normal human males (12-20 weeks gestation) were sectioned serially and stained by avidin-biotinylated peroxidase complex method with antigen retrieval. Stained sections throughout male genital development documented the expression of AR and 5 alpha-reductase type 2 in the phallus. Between 12 and 14 weeks of gestation, AR was localized to epithelial cells of the urethral plate in the glans, the tubular urethra of the penile shaft, and stromal tissue surrounding the urethral epithelium. In the fetal penis between 16 and 20 weeks gestation, the density of AR expression was greatest in urethral epithelial cells versus the surrounding stromal tissues. There was a characteristic pattern of AR expression in the glandular urethral epithelium between 16 and 20 weeks gestation. AR expression was greater along the ventral aspect of the glandular urethra than along the dorsal aspect of the urethral epithelium. The expression of 5 alpha-reductase type 2 was localized to the stroma surrounding the urethra, especially along the urethral seam area in the ventral portion of the remodeling urethra. These anatomical studies support the hypothesis that androgens are essential for the formation of the ventral portion of the urethra and that abnormalities in either the AR or 5 alpha-reductase type 2 can explain the occurrence of hypospadias.     

Prenatal prediction of androgen insensitivity syndrome using exon 1 polymorphism of the androgen receptor gene.

Exon 1 polymorphism of the androgen receptor (AR) gene is characterized by a (CAG)n(CAA) repeat at position 172 following the translation start codon. The aim of this study was to determine whether AR gene exon 1 polymorphism could be used to perform prenatal diagnosis in high risk families with complete or partial androgen insensitivity syndrome. After enzymatic amplification of a 1 kilobase exon 1 fragment, each DNA was simultaneously digested by MspI and PstI restriction enzymes. After electrophoresis on a 15% electrophoresis on a 15% acrylamide gel or a 6% Nusieve gel, we measured the size of the obtained fragments and determined the number of CAG repeats since a 282 basepair fragment corresponds to 21 CAG. We previously showed that the number of CAG repeats within the AR gene exon 1 in 23 families with complete or partial androgen insensitivity syndrome was 19 +/- 4. By this method, we detected heterozygosity in 50% of the mothers. We present here 2 exclusion prenatal diagnoses using exon 1 polymorphism of the AR gene. Family A presented a boy with a severe form of partial androgen insensitivity syndrome. The mother had 2 uncles with ambiguous genitalia. In family B, the affected child had a complete androgen insensitivity syndrome. In both families, analysis of the AR gene exon 1 polymorphism of the trophoblastic DNA showed the presence of the normal maternal X chromosome. The parents decided to carry on the gestation. In family A, the newborn had normal male external genitalia. In family B, sonography confirmed the presence of normal male external genitalia. These data suggest that exon 1 polymorphism of the AR gene could be prenatally used to predict androgen insensitivity syndrome.     

Age-dependent expression of 5alpha-reductase and androgen receptors mRNA by the canine prostate

The growth of the prostate gland is androgen-dependent. Testosterone is converted to the most potent dihydrotestosterone (DHT) by 5alpha-reductase within the prostate. Androgen interacts with androgen receptors (AR) to regulate normal growth of the prostate and has also been implicated in both the progression of benign prostate hyperplasia and prostate cancer. This study was conducted to compare the mRNA expression of AR and 5alpha-reductase by the prostate gland from three age categories: immature, young-mature and old dogs. Quantitative gene expression was assessed by the real-time PCR and the results were expressed as a relative mRNA expression of the target gene. This study revealed that there was no significant difference in the mRNA expression of the AR gene by the prostate gland of immature, young and old dogs. In contrast, there is a highly significant (P<0.001) down-regulation in 5alpha-reductase gene by the prostate of young and old dogs as compared with immature dogs. However, there is no significant difference in mRNA expression of the 5alpha-reductase gene by the prostate gland from young and old dogs. This differential expression of AR and 5alpha-reductase genes, which are involved in the regulation of androgen effect on prostate gland, might reflect an age-dependent growth requirement of the gland for androgens.     

A floxed allele of the androgen receptor gene causes hyperandrogenization in male mice.

We previously generated a conditional floxed mouse line to study androgen action, in which exon 3 of the androgen receptor (AR) gene is flanked by loxP sites, with the neomycin resistance gene present in intron 3. Deletion of exon 3 in global AR knockout mice causes androgen insensitivity syndrome, characterized by genotypic males lacking normal masculinization. We now report that male mice carrying the floxed allele (AR(lox)) have the reverse phenotype, termed hyperandrogenization. AR(lox) mice have increased mass of androgen-dependent tissues, including kidney, (P < 0.001), seminal vesicle (P < 0.001), levator ani muscle (P = 0.001), and heart (P < 0.05). Serum testosterone is not significantly different. Testis mass is normal, histology shows normal spermatogenesis, and AR(lox) males are fertile. AR(lox) males also have normal AR mRNA levels in kidney, brain, levator ani, liver, and testis. This study reaffirms the need to investigate the potential phenotypic effects of floxed alleles in the absence of cre in tissue-specific knockout studies. In addition, this androgen hypersensitivity model may be useful to further investigate the effects of subtle perturbations of androgen action in a range of androgen-responsive systems in the male.     

Loss of androgen dependency with preservation of functional androgen receptors in androgen-dependent mouse tumor (Shionogi Carcinoma 115).

Shionogi Carcinoma 115 (SC 115) is an androgen-dependent mouse tumor. Chiba Subline 2 (CS 2) is an androgen-independent subline derived from SC 115. CS 2 contains androgen receptors (AR), but is refractory to androgen and does not exhibit androgen-related responses which are observed in SC 115. In the present study the structure and function of AR in SC 115 and CS 2 are examined using cloned cells. There were no gross rearrangements or deletions in the AR genes of these cell lines when compared by Southern blot analysis with the AR gene in the mouse seminal vesicle. SC 115 and CS 2 expressed AR mRNA of normal size. When the cDNA containing DNA- and androgen-binding domains of the AR genes of both cell lines were amplified by polymerase chain reaction, no mutations were found in these regions. SC 115 and CS 2 were transfected with a plasmid containing a long terminal repeat of mouse mammary tumor virus linked to the chloramphenicol acetyltransferase (CAT) gene. Androgen stimulation of these transfectants resulted in equal elevation of CAT activity. These results indicated that the androgen-independent CS 2 contained functionally normal AR which were identical to those in the androgen-dependent parent tumor.