E. L. Yong

Linkage between male infertility and trinucleotide repeat expansion in the androgen-receptor gene

BACKGROUND Androgens acting via the androgen receptor bring about stimulation and maintenance of spermatogenesis. If mutations in the androgen-receptor gene interfere with the receptors function, this effect may partly account for impaired spermatogenesis. We aimed to find out whether expansion of a trinucleotide repeat in the androgen-receptor gene is associated with male infertility. METHODS We analysed 67 coded semen and blood samples from a predominantly white group of male infertility patients and controls. Clinical analyses included cause of infertility, sperm count, and reproductive hormone concentrations. Analysis of trinucleotide (CAG) repeat length and point mutations in the androgen-receptor gene was done by PCR, single-stranded conformational polymorphism, and DNA sequencing. FINDINGS Screening and characterisation of the androgen-receptor gene in 35 patients and 32 controls showed no point mutations in the gene. 30 of the infertile patients had idiopathic azoospermia or oligozoospermia, and these men had significantly longer CAG repeat tracts than controls (mean 23.2 [SE 0.7] vs 20.5 [0.3], p=0.0001). The odds of having CAG repeat lengths of 20 were six-fold higher for fertile men than for men with a spermatogenic disorder. INTERPRETATION Our results indicate a relation between CAG repeat length in the androgen-receptor gene and the risk of defective spermatogenesis. With the use of intracytoplasmic sperm injection, this mutation could be inherited, possibly leading to an increase in male infertility in future generations. Should further elongation of the CAG repeat occur in these future generations, there is an added risk of increased severity of male infertility, and potentially an increased incidence of neurodegenerative disease.

Analysis of the transactivation domain of the androgen receptor in patients with male infertilitv

Wang Q, Ghadessy FJ, Yong EL. Analysis of the transactivation domain of the androgen receptor in patients with male infertility. Clin Genet 1998: 54: 185–192. 0 Munksgaard, 1998

Partial androgen insensitivity and correlations with the predicted three dimensional structure of the androgen receptor ligand-binding domain.

Genetic defects of the human androgen receptor (AR) can cause a wide spectrum of androgen insensitivity syndromes (AIS) ranging from phenotypic females in those with complete AIS; ambiguous genitalia in partial AIS; to male infertility in minimal AIS. The majority of these defects are due to point mutations resulting in amino acid substitutions. It is however unclear why certain mutations result in partial AIS, whereas others in the same exon cause the complete syndrome. We present a case of partial AIS due to a point mutation affecting codon 758 of the AR ligand-binding domain (LBD) that changed the sense of the codon from asparagine to threonine (N758T). The mutant receptor displayed normal binding affinity to DHT but abnormal dissociation kinetics in both patients fibroblasts and transfected COS-7 cells. The mutant AR was thermolabile, and resulted in approximately 50% reduction in receptor transactivation capacity when examined with a reporter gene incorporating an androgen-response-element. Although the 3-D structure of AR LBD is not known, the homologous region in a member of the steroid receptor superfamily, retinoid-X receptor (RXR-alpha), has been crystallized, allowing comparison of aligned amino-acid sequences of RXR-alpha and AR. The mutation, N758T, lies in a predicted linker region between the fifth alpha-helix (H5) and the first beta-strand (S1). Generally, mutations leading to partial AIS tend to cluster in the predicted linker regions located between the structural helices of the AR LBD. Most strikingly, the predicted linker regions contain over 70% of the mutant ARs associated with prostate cancer in the LBD. The occurrence of mutations associated with both partial AIS and prostate cancer in the same predicted linker regions, suggest that this clustering is not coincidental and that the predicted linker regions are likely to have important, but subtle, roles in defining androgen binding and ligand specificity.

Directed pharmacological therapy of ambiguous genitalia due to an androgen receptor gene mutation

We report a 46,XY infant with an M807T mutation in his androgen receptor that abrogated cellular responses to testosterone, but not to dihydrotestosterone (DHT), resulting in ambiguous genitalia. Treatment with a topical DHT gel restored male genital development allowing the infant to be reared in accordance with his chromosomal sex.

A novel splice site mutation in the androgen receptor gene results in exon skipping and a non-functional truncated protein

Mutations of the androgen receptor (AR) gene and protein are associated with complete androgen insensitivity syndromes (CAIS) in individuals with XY genotypes causing them to develop as phenotypic females. Splice site mutations of the AR gene are very rare and in this report we describe the consequences of a novel G --> A mutation at the exon 7/intron 7 splice junction of the AR gene that resulted in CAIS in two siblings. Reverse transcriptase-polymerase chain reaction (RT-PCR) of the AR transcript in patients fibroblasts was performed and sequencing of the product showed omission of exon 7, with exon 6 being spliced directly to exon 8. This resulted in a shift of the reading frame and the introduction of a premature stop codon 10 amino acids into exon 8. Immunoblot analyses showed that the resultant AR protein was partially deleted in its C-terminal region and was approximately 1.5 kDa smaller than the wild type. This truncated AR was non-functional as it was unable to bind its physiological ligand (dihydrotestosterone) in androgen-binding assays. This is the first documentation of a point mutation in the AR gene which causes exon skipping and proves that the mutation is the cause of CAIS in our two subjects.

Chronic low-dose follicle-stimulating hormone compared with clomiphene/human menopausal gonadotropin for induction of ovulation

Concurrent administration of clomiphene can reduce the amount of gonadotropins required for induction of ovulation. Recently, follicle-stimulating hormone (FSH) administered in a chronic, low-dose fashion has been reported to give satisfactory pregnancy rates. We compared the conventional clomiphene/human menopausal gonadotropin (hMG) with the chronic, low-dose FSH regimen for induction of ovulation in 87 patients over 110 cycles. The clomiphene/hMG regimen required half the amount of gonadotropin compared to the chronic FSH regimen to achieve follicular maturation. Despite the reduced amount of gonadotropin, the clomiphene/hMG regimen induced a mean fourfold higher level of estradiol production and was associated with significantly greater numbers of large and intermediate-sized follicles compared to the chronic FSH regimen. The proportion of clomiphene/hMG cases with multifollicular development and overstimulation was therefore high (30%). In contrast, the chronic FSH regimen, despite requiring larger amounts of gonadotropin and longer periods of treatment, resulted in unifollicular development, low rates of overstimulation and improved pregnancy rates. We conclude that although clomiphene can reduce the requirement for gonadotropins, the relative safety and effectiveness of the chronic low-dose FSH regimen makes it the method of choice for ovulation induction.

The First 2 Case Reports of Frozen Embryo Donation Twin Pregnancies in Singapore: Hormonal Profiles and Obstetrical Outcome

A 35‐year‐old woman with premature ovarian failure and another 30‐year‐old woman with gonadal dysgenesis were the recepients of donated supernumerous frozen embryos after successfully prepared with cyclic steroid replacement therapy as described previously.1,2)

Responses of polycystic ovarian syndrome and related variants to low-dose follicle stimulating hormone

Objective: To determine whether patients with classical polycystic ovarian syndrome (PCOS) respond differently to low‐dose FSH therapy in comparison with anovulatory patients (PCOS‐like) where only some features of PCOS are present. Methods: Two groups of patients were studied. The PCOS group (25 patients, 51 cycles) and the PCOS‐like group (38 patients, 57 cycles) were treated with the same protocol of purified FSH, commencing with an initial dosage of 75 IU/day and increasing by 37.5 IU/day after 14 days, where necessary. Estradiol levels and ultrasonographic evidence of follicular development were used for monitoring. Results: PCOS patients required more ampules of FSH, needed more days of gonadotropin stimulation, secreted higher levels of E2 and had increased numbers of intermediate follicles compared to the PCOS‐like group. Conclusions: This study demonstrated significant differences between PCOS and other PCOS‐like conditions when treated with low‐dose FSH. Classification of the subvariants of PCOS may have therapeutic implications.