The CAG repeat polymorphism within the androgen receptor gene and maleness

The androgen receptor's CAG/glutamine tract in mouse models of neurological disease and cancer

The androgen receptor (AR) is a ligand-activated transcription factor that is central to androgen-dependent development and diseases. Activity of the receptor is influenced by the length of a CAG/glutamine tract in its N-terminal transactivating domain. Expansions of this tract cause Kennedy disease, a protein aggregation degenerative disorder of motor neurons that occurs only in men, and shorter length tracts have been linked to increased risk of prostate cancer. Here we review recent data from mouse models in which gene targeting was used to humanize the mouse Ar gene and introduce CAG/glutamine tracts of varying lengths. Insertion of an expanded tract encoded by 113 CAG repeats modeled Kennedy disease and revealed an important myopathic contribution to the disease phenotype. Variations in CAG tract length within the range of normal human alleles influenced the onset and progression of prostate cancer when targeted Ar mice were crossed to a transgenic prostate cancer model. This series of mice with different Ar alleles has provided insights into the mechanisms by which variations in the CAG/glutamine tract length influence the occurrence of human disease.

Androgen receptor gene CAG repeat length in women with metabolic syndrome

OBJECTIVE

The length of the androgen receptor gene CAG repeat [AR (CAG)(n)] modulates the activity of the androgen receptor (AR), and this polymorphism has been shown to modulate body fat mass and serum concentrations of insulin in men. We hypothesized that shorter AR (CAG)(n) is associated with metabolic syndrome (MBS) or its components in women.

DESIGN, PATIENTS AND MEASUREMENTS

In a cross-sectional controlled study we studied 52 Finnish women aged 34-55 years with MBS and 69 age-matched controls. All participants were recruited from a sample of women drawn from the Finnish population register. We compared the mean AR (CAG)(n) in the two groups. Furthermore, we correlated the AR (CAG)(n) with serum testosterone, androstenedione, dehydroepiandrosterone sulfate and several parameters of glucose and lipid metabolism in each group and in all 121 women.

RESULTS

There was no difference in the biallelic mean AR (CAG)(n) between the MBS and the control group (21.6+/-0.2 vs. 21.8+/-0.2, not significant). The AR (CAG)(n) did not correlate significantly with any of the clinical or biochemical parameters of glucose or fat metabolism. However, it correlated negatively with serum testosterone (-0.195, p = 0.04) and androstenedione concentrations (-0.205, p = 0.03) in all studied women.

CONCLUSIONS

The AR (CAG)(n) is not a major determinant of MBS in women but it contributes to ovarian androgen production.

Androgen receptor variants and prostate cancer in humanized AR mice

Androgen, acting via the androgen receptor (AR), is central to male development, differentiation and hormone-dependent diseases such as prostate cancer. AR is actively involved in the initiation of prostate cancer, the transition to androgen independence, and many mechanisms of resistance to therapy. To examine genetic variation of AR in cancer, we created mice by germ-line gene targeting in which human AR sequence replaces that of the mouse. Since shorter length of a polymorphic N-terminal glutamine (Q) tract has been linked to prostate cancer risk, we introduced alleles with 12, 21 or 48 Qs to test this association. The three "humanized" AR mouse strains (h/mAR) are normal physiologically, as well as by cellular and molecular criteria, although slight differences are detected in AR target gene expression, correlating inversely with Q tract length. However, distinct allele-dependent differences in tumorigenesis are evident when these mice are crossed to a transgenic prostate cancer model. Remarkably, Q tract variation also differentially impacts disease progression following androgen depletion. This finding emphasizes the importance of AR function in androgen-independent as well as androgen-dependent disease. These mice provide a novel genetic paradigm in which to dissect opposing functions of AR in tumor suppression versus oncogenesis.

Gene polymorphisms and male infertility--a meta-analysis and literature review

Many genetic polymorphisms have been studied extensively to elucidate their role in the pathophysiology of male infertility. This article presents a review of the literature following a thorough search of PubMed, a compilation of meta-analyses of studies reporting an association with male fertility where the population(s) could be clearly identified as fertile and/or infertile, and a summary of all polymorphisms that have been investigated in single case-control studies to date. The meta-analyses revealed significant associations between polymorphism and male fertility only for AZF gr/gr deletions (OR 1.81, 1.46-2.24 CI, P<0.00001) and MTHFR 677C-->T (OR 1.39, 1.15-2.69 95% CI, P=0.0006) but not for POLG, DAZL, USP26 or FSHR. The influence of CAG repeat length in AR remains open and debated. Genes encoding nuclear proteins (PRM1/2, TNP1/2) and ER1 are possible candidates for further examination, while the role of TAF7L remains unclear. Polymorphisms in 16 other genes have been investigated in single studies, but the results remain doubtful due to often small and heterogeneous cohorts and in the absence of independent replications. The genetic studies performed so far emphasize the complexity of male infertility as a presumably polygenetic trait amended by environmental, lifestyle or occupational factors.

The paradox dividing testosterone deficiency symptoms and androgen assays: a closer look at the cellular and molecular mechanisms of androgen action

INTRODUCTION

Central to the diagnosis and treatment of testosterone deficiency syndrome in the adult male is the remarkable paradox that there is a very poor correlation between the characteristic symptoms and levels of serum androgens.

AIM

Because androgen deficiency can be associated with severe symptomatology, as well as diverse conditions such as coronary heart disease, diabetes, and metabolic syndrome, the aim was to present an evidence-based working hypothesis to resolve this confusing clinical paradox.

METHODS

A review of the possible mechanisms in testosterone deficiency syndrome was carried out, and a hypothesis to explain this paradox and associated problems in the diagnosis and clinical management of androgen deficiency was established on the basis of a review of the literature.

MAIN OUTCOME MEASURES

The mechanisms by which androgen deficiency could arise were studied at five different levels: 1. Impaired androgen synthesis or regulation. 2. Increased androgen binding. 3. Reduced tissue responsiveness. 4. Decreased androgen receptor activity. 5. Impaired transcription and translation.

RESULTS

As with insulin in maturity onset diabetes mellitus, there can be both insufficient production and variable degrees of resistance to the action of androgens operating at several levels in the body simultaneously, with these factors becoming progressively worse with aging, adverse lifestyle, other disease processes, and a wide range of medications.

CONCLUSIONS

Using this model, androgen deficiency can be redefined as an absolute or relative deficiency of androgens or their metabolites according to the needs of that individual at that time in his life. There are important ways in which the considerations raised by this hypothesis affect the etiology, terminology, diagnosis, and treatment of androgen-deficient states.

Prevalence of symptomatic androgen deficiency in men

CONTEXT

Despite recognition that androgen deficiency in men should be defined according to biochemical and clinical criteria, most prevalence estimates are based on low testosterone levels alone.

OBJECTIVE

The objective of this study was to examine the association between symptoms of androgen deficiency and low total and calculated free testosterone levels and estimate the prevalence of symptomatic androgen deficiency in men.

DESIGN

This study was a population-based, observational survey.

PARTICIPANTS

A total of 1,475 Black, Hispanic, and white men, between the ages of 30-79 yr, with complete data on testosterone, SHBG, and symptoms of androgen deficiency, and who are not taking medications that impact sex steroid levels were randomly selected from the Boston Area Community Health Survey.

OUTCOME

Outcomes were measured as symptomatic androgen deficiency, defined as low total (<300 ng/dl) and free (<5 ng/dl) testosterone plus presence of low libido, erectile dysfunction, osteoporosis or fracture, or two or more of following symptoms: sleep disturbance, depressed mood, lethargy, or diminished physical performance.

RESULTS

Mean age of the sample was 47.3 +/- 12.5 yr. Approximately 24% of subjects had total testosterone less than 300 ng/dl, and 11% of subjects had free testosterone less than 5 ng/dl. Prevalence of symptoms were as follows: low libido (12%), erectile dysfunction (16%), osteoporosis/fracture (1%), and two or more of the nonspecific symptoms (20%). Low testosterone levels were associated with symptoms, but many men with low testosterone levels were asymptomatic (e.g. in men 50+ yr, 47.6%). Crude prevalence of symptomatic androgen deficiency was 5.6% (95% confidence interval: 3.6%, 8.6%), and was not significantly related to race and ethnic group. Prevalence was low in men less than 70 yr (3.1-7.0%) and increased markedly with age to 18.4% among 70 yr olds. Projection of these estimates to the year 2025 suggests that there will be as many as 6.5 million American men ages 30-79 yr with symptomatic androgen deficiency, an increase of 38% from 2000 population estimates.

CONCLUSIONS

Prevalence of symptomatic androgen deficiency in men 30 and 79 yr of age is 5.6% and increases substantially with age. The aging of the U.S. male population will cause a large increase in the burden of symptomatic androgen deficiency. Future work should address the clinical significance of low testosterone levels in asymptomatic men.

Avian Clock gene polymorphism: evidence for a latitudinal cline in allele frequencies

In comparison with most animal behaviours, circadian rhythms have a well-characterized molecular genetic basis. Detailed studies of circadian clock genes in 'model' organisms provide a foundation for interpreting the functional and evolutionary significance of polymorphic circadian clock genes found within free-living animal populations. Here, we describe allelic variation in a region of the avian Clock orthologue which encodes a functionally significant polyglutamine repeat (ClkpolyQcds), within free-living populations of two passerine birds, the migratory bluethroat (Luscinia svecica) and the predominantly nonmigratory blue tit (Cyanistes caeruleus). Multiple ClkpolyQcds alleles were found within populations of both species (bluethroat: 12 populations, 7 alleles; blue tit: 14 populations, 9 alleles). Some populations of both species were differentiated at the ClkpolyQcds locus as measured by F(ST) and R(ST) values. Among the blue tit, but not bluethroat populations, we found evidence of latitudinal clines in (i) mean ClkpolyQcds repeat length, and (ii) the proportions of three ClkpolyQcds genotype groupings. Parallel analyses of microsatellite allele frequencies, which are considered to reflect selectively neutral processes, indicate that interpopulation allele frequency variation at the ClkpolyQcds and microsatellite loci does not reflect the same underlying demographic processes. The possibility that the observed interpopulation ClkpolyQcds allele frequency variation is, at least in part, maintained by selection for microevolutionary adaptation to photoperiodic parameters correlated with latitude warrants further study.

Androgen receptor gene CAG repeat length and body mass index modulate the safety of long-term intramuscular testosterone undecanoate therapy in hypogonadal men

CONTEXT

A reliable form of androgen substitution therapy regarding kinetics, tolerance, and restoration of androgenicity is paramount in hypogonadal men. Intramuscular injection of the long-acting ester testosterone undecanoate (TU) offers a new modality.

OBJECTIVE

The objective of the study was to assess the safety of TU regarding metabolic and pharmacogenetic confounders.

DESIGN

This was a longitudinal one-arm open observation trial. A minimum of five individual assessments was a prerequisite. Putative modulators of safety parameters entering regression models were nadir and/or delta total testosterone concentrations, body mass index, androgen receptor (AR) gene CAG repeat length, and age.

SETTING

The study was conducted at an andrological outpatient clinic.

PATIENTS

Patients included 66 hypogonadal men (mean age 38 +/- 9.9 yr).

MAIN OUTCOME MEASURES

A total of 515 data time points each related to prostate, erythropoiesis, lipoproteins, and circulation during 118 treatment-years with 1000 mg TU at 10- to 14-wk intervals.

RESULTS

Testosterone substitution resulted in significant decrements of serum levels of low-density lipoprotein-cholesterol, resting diastolic and systolic blood pressure, and heart rate. Erythropoiesis was stimulated and concentrations of high-density lipoproteincholesterol increased. Parameters remained stable after four injections. No adverse effects regarding the prostate were observed. Significantly increased hematocrit greater than 50% was predicted by enhanced androgen action (shorter AR CAG repeats per higher testosterone levels). However, insufficient androgen action (longer AR CAG repeats per lower testosterone levels) caused pathological safety parameters (high blood pressure, adverse lipid profiles). In addition, a body mass index 30 kg/m(2) or greater represents a clinically relevant factor for the occurrence of all pathological safety parameters. Risk calculations for obese patients and nonlinear pharmacogenetic models to tailor androgen substitution are presented.

CONCLUSIONS

Testosterone substitution with im TU is generally well tolerated. Modifications of androgen action are due to both AR CAG repeats and testosterone levels. Adverse observations are mostly seen in obese patients.

Glutamine tract length of human androgen receptors affects hormone-dependent and -independent prostate cancer in mice

The androgen receptor (AR) is involved in the initiation and progression of prostate cancer and its transition to androgen independence. Genetic variation in AR may contribute to disease risk and has been studied for a polymorphic N-terminal glutamine (Q) tract that shows population heterogeneity. While the length of this tract is known to affect AR in vitro, association with disease is complicated by genetic and environmental factors that have led to discordant epidemiological findings. To clarify the effect of Q tract polymorphism on prostate cancer, we created mice bearing humanized AR genes (h/mAr) varying in Q tract length. ARs with short Q tracts (12Q), which are transcriptionally more active, induce earlier disease in the transgene-induced TRAMP prostate cancer model than alleles with median (21Q) or long (48Q) tracts. Disease length varies within each genotype, with greater differentiation and AR expression in slower growing tumors. Remarkably, following androgen ablation, Q tract length has effects that are also allele-dependent and in directions opposite to those in hormone intact mice. Differences in AR activity conferred by Q tract length thus appear to direct distinct pathways of androgen-independent as well as androgen-dependent progression, and highlight substantial risk that may be associated with alterations in the androgen axis. This AR allelic series in humanized mice provides an experimental paradigm to dissect the role of AR in prostate cancer initiation and progression, to model response to treatment and to test therapies targeted specifically to the human AR.

Part of the interindividual variation in serum testosterone levels in healthy men reflects differences in androgen sensitivity and feedback set point: contribution of the androgen receptor polyglutamine tract polymorphism

CONTEXT

There is a large interindividual variation in serum (free) testosterone (FT) levels in men, underlain in part by genetic components.

OBJECTIVE

The objective of the study was to explore the hypothesis that this variability results in part from differences in androgen sensitivity and feedback loop set point and assess the role of the androgen receptor (AR) polyglutamine tract polymorphism encoded by a CAG repeat of variable length in exon 1 of the AR gene.

DESIGN/SETTING/PARTICIPANTS

We performed a cross-sectional analysis in two independent populations of healthy men, consisting of 2322 men aged 35-59 yr (Belstress study) and 358 men aged 25-45 yr (Siblos study), respectively.

MAIN OUTCOME MEASURES

Serum hormonal levels and the AR gene CAG repeat length were determined.

RESULTS

In the Belstress population, serum testosterone and calculated FT showed a positive linear association with LH (P < 0.001). In the 200 men with lowest FT, CAG repeat number was lower than in the 200 men with highest FT (P = 0.004). As studied in a larger subset of the population consisting of 857 men covering the whole FT range, FT increased progressively with CAG repeat length (P = 0.003). These findings of a positive relation of FT with both LH and CAG repeat length were confirmed in the Siblos study population (both P < or = 0.001). Difference in FT between extreme quartiles of CAG repeat was 10 and 14% in the Belstress and Siblos study, respectively. In both study populations, CAG repeat length was also positively associated with serum total testosterone (P < or = 0.004).

CONCLUSIONS

The data support the view that between-subject variability in serum FT in healthy men is underlain in part by differences in androgen sensitivity and feedback set point, with a contributory role of AR polymorphism. These findings have potential implications for the interpretation of epidemiological studies, diagnosis of hypogonadism, and pharmacogenetics of androgen treatment in men.

The validity of androgen assays

Problems in the measurement of androgens and in interpreting results have been reviewed and classified as follows: PREANALYTICAL FACTORS: The exact sampling conditions in relation to circadian and seasonal variations, diet, alcohol, physical activity and posture.

PHYSIOLOGICAL AND MEDICAL FACTORS

Androgen levels vary according to the patient's general health, stress, sexual activity and smoking habits. Analytical variables. Sample preservation and storage variables are often unknown. The different androgen assays used have widely differing accuracy and precision and are subject to large inter-laboratory variation, which especially in women and children can render the results of routinely available direct immunoassays meaningless.

INTERPRETATION OF RESULTS

Laboratory reference ranges vary widely, largely independent of methodology, and fail to take into account the log-normal distribution of androgen values, causing errors in clinical diagnosis and treatment. Other unknowns are antagonists such as SHBG, estrogens, catecholamines, cortisol, and anti-androgens. As well as age, androgen receptor polymorphisms play a major role in regulating androgen levels and resistance to their action.

CONCLUSIONS

Though laboratory assays can support a diagnosis of androgen deficiency in men, they should not be used to exclude it. It is suggested that there needs to be greater reliance on the history and clinical features, together with careful evaluation of the symptomatology, and where necessary a therapeutic trial of androgen treatment given.

Polymorphisms of androgen receptor gene in childhood and adolescent males with first-onset major depressive disorder and association with related symptomatology

This study was designed to explore the association between CAG repeats in AR gene and major depressive disorder (MDD) in male children and adolescents. The results showed that there were differences between adolescent depressive patients and adolescent controls in CAG repeats' length and alleles' distributions, and the severity of depression and anxiety was negatively correlated with the length of CAG repeats in adolescent patients. This suggested that AR gene might be involved in the depressive upset in adolescents, and the age- and sex-related prevalent differences might also be associated to CAG repeats.

Hypogonadism and androgen deficiency symptoms in testicular cancer survivors

OBJECTIVES

To investigate the prevalence of hypogonadism in correlation with androgen deficiency symptoms in testicular cancer survivors.

METHODS

Luteinizing hormone, follicle-stimulating hormone, serum testosterone, dehydroepiandrosterone, and sex hormone binding globulin levels were determined in patients who had undergone treatment for unilateral testicular cancer. Patients with serum testosterone levels less than 3.0 ng/mL were classified as hypogonadal; all other testosterone levels signified eugonadism. Additionally, all patients completed the Aging Males' Symptoms scale: scores of less than 26 indicated no androgen deficiency symptoms and scores greater than 27 indicated symptoms.

RESULTS

According to testosterone level, 18 (26.5%) of 68 patients were hypogonadal and 50 (73.5%) were eugonadal (P = 0.456). According to the Aging Males' Symptoms scale, 23 (33.8%) of the 68 patients had androgen deficiency symptoms and 45 (66.2%) had no symptoms (P = 0.267). The median testosterone level was 3.6 ng/mL in all patients with androgen deficiency symptoms, 2.4 ng/mL in patients with androgen deficiency symptoms who were hypogonadal, and 4.7 ng/mL in those with androgen deficiency symptoms who were eugonadal.

CONCLUSIONS

Testicular cancer survivors are at risk of developing hypogonadism and androgen deficiency symptoms. However, no specific testosterone threshold could be detected at which symptoms start, indicating that each patient has an individual testosterone threshold for androgen deficiency symptoms.

Mechanisms of Disease: pharmacogenetics of testosterone therapy in hypogonadal men

A defective, mutated androgen receptor may lead to variable phenotypes of androgen insensitivity in humans. Also, the CAG repeat polymorphism in exon 1 of the androgen receptor gene modulates androgen effects; in vitro, transcription of androgen-dependent target genes is attenuated with increasing length of triplet residues. Clinically, the CAG repeat polymorphism causes significant modulations of androgenicity in various tissues and psychological traits in healthy eugonadal men: the longer the repeat tracts, the less pronounced is the androgen effect when individuals with similar testosterone concentrations are compared. Furthermore, as effects of testosterone substitution are markedly influenced by the number of CAG repeats, the pharmacogenetic implications of this polymorphism are likely to have a significant role in future testosterone treatment of hypogonadal men. Thresholds at which testosterone treatment should be initiated, as well as androgen dosage, might be tailored according to the receptor polymorphism.

Androgen resistance

Androgen resistance causes the androgen insensitivity syndrome in its variant forms and is a paradigm of clinical syndromes associated with hormone resistance. In its complete form, the syndrome causes XY sex reversal and a female phenotype. Partial resistance to androgens is a common cause of ambiguous genitalia of the newborn, but a similar phenotype may result from several other conditions, including defects in testis determination and androgen biosynthesis. The biological actions of androgens are mediated by a single intracellular androgen receptor encoded by a gene on the long arm of the X chromosome. Mutations in this gene result in varying degrees of androgen receptor dysfunction and phenotypes that often show poor concordance with the genotype. Functional characterization and three-dimensional modelling of novel mutant receptors has been informative in understanding the mechanism of androgen action. Management issues in syndromes of androgen insensitivity include decisions on sex assignment, timing of gonadectomy in relation to tumour risk, and genetic and psychological counselling.

Genetic features of the X chromosome affect pubertal development and testicular degeneration in adolescent boys with Klinefelter syndrome

OBJECTIVE

To investigate how genetic features of the X chromosome influence growth, pubertal development and testicular degeneration in adolescent boys with Klinefelter syndrome (KS). Previous studies have suggested that genetic features of the X chromosome may contribute to the wide phenotypic variation in KS.

DESIGN

A prospective clinical study.

PATIENTS

Fourteen nonmosaic 47,XXY boys, aged 10-13.9 years.

MEASUREMENTS

The relationship of genetic features of the X chromosome, including parental origin of X chromosomes, the CAG repeat length of the androgen receptor (AR) gene, and X inactivation with progression of pubertal development, growth and testicular function in KS boys.

RESULTS

Paternal (47,XmXpY, n = 3) as compared to maternal (47,XmXmY, n = 11) origin of the supernumerary X chromosome was associated with a later onset of puberty. In 47,XmXpY patients, serum LH concentrations increased above 1.0 IU/l at 12.5 +/- 0.6 years (mean +/- SD), Tanner stage P2 occurred at 12.5 +/- 0.7 years, and pubertal acceleration of growth was noted at 13.9 +/- 1.4 years and peak velocity at 14.5 +/- 0.8 years. All of these occurred 1.3-1.9 years later than in 47,XmXmY patients (P = 0.01-0.09). In 47,XmXmY subjects, CAG repeat length (range 17-26) correlated with age at which serum LH level first exceeded 1.0 IU/l (rs = 0.63, P = 0.06, n = 10) and testosterone 1.0 nmol/l (28.8 ng/dl) (rs = 0.78, P = 0.02, n = 10).

CONCLUSIONS

Paternal origin of the supernumerary X chromosome is associated with later onset of puberty and longer CAG repeats of the AR with later pubertal reactivation of the pituitary-testicular axis in KS boys. Identifying genetic factors that affect the phenotype may lead to a better understanding of the pathogenesis of KS.

The relationship between libido and testosterone levels in aging men

CONTEXT

Although it is known that serum testosterone (T) concentrations are related to libido, the strength of that relationship in community-dwelling men has not yet been determined.

OBJECTIVE

Our objective was to assess the strength and significance of the association between aging men's self-reports of libido and serum T concentrations.

DESIGN

Our study was a community-based evaluation of men's health and aging, including three data collection waves: baseline (T1, 1987-1989) and follow-ups (T2, 1995-1997; T3, 2002-2004). Libido was measured on a 14-point scale assessing self-reported frequency of desire and thoughts/fantasies; low libido was defined as a score of less than 7 of 14.

SETTING

We conducted an epidemiological study in greater Boston, Massachusetts.

PARTICIPANTS

There were 1632 men aged 40-70 yr at baseline, with follow-up on 922 (56%) at 9 yr (T2) and 623 (38%) at 15 yr (T3).

MAIN OUTCOME MEASURES

We assessed total and calculated bioavailable T .

RESULTS

Three hundred eighteen (19%) subjects reported low libido at baseline. Libido and T displayed a significant association. However, the difference in mean T levels between those subjects with low libido and those without was small; analyses indicated a 3.4 ng/dl (0.12 nmol/liter) increase in total T per unit increase in libido. Subjects reporting low libido exhibited an increased but modest probability of exhibiting low T. Dividing T concentrations by the number of androgen receptor gene cytosine, adenine, guanine repeats did not enhance associations.

CONCLUSIONS

Libido and T concentrations are strongly related at the population level. However, the value of individual patient reports of reduced libido as indicators of low T levels is open to question.

New facets of androgen replacement therapy during childhood and adolescence

The goals of androgen therapy for adolescents are to promote linear growth and secondary sexual characteristics, at the same time as permitting the normal accrual of muscle mass and bone mineral content. Secondary goals are mainly in the psychosocial sphere, in which pubertally delayed boys feel that they look too young, are not considered a 'peer' in their age group and have difficulty competing in athletic endeavours. These goals are irrespective of the causes of delayed pubertal development: constitutional delay of growth and puberty (CDGP), a transient but very common form of pubertal delay and, much less commonly, primary or secondary permanent hypogonadism. Not all boys with CDGP require testosterone therapy, but those that come to a referral practice are likely candidates, as the watchful waiting period has finished. Although a range of androgen preparations is available for adults (injectable, oral, implantable and cutaneous patches and gels), most are drug delivery devices that are appropriate for full adult androgen replacement. These doses are too large for the induction of puberty. Therefore, at present, the injectable form is the only one that is easily adaptable for the increasing amounts of androgen necessary for the various stages of pubertal development. All preparations deliver testosterone that is readily converted to dihydrotestosterone by 5-alpha reductase. The author's practice is to begin with injecting 50-75 mg of one of the long-acting esters (enanthate or cypionate) per month, and gradually escalate to 100-150 mg/month, before changing to twice monthly dosage. As most adolescents have delayed puberty, the therapy is needed for 6-18 months before the hypothalamic-pituitary-gonadal axis functions at the late adolescent/adult level in those with CDGP. Those with permanent hypogonadism will require lifelong therapy. Once adequate virilisation is induced, and virtually full adult height is reached, any of the therapies noted above can be used in those permanently hypogonadal, whether primarily or secondarily.

Replacing the mouse androgen receptor with human alleles demonstrates glutamine tract length-dependent effects on physiology and tumorigenesis in mice

Polymorphism in the length of the N-terminal glutamine (Q) tract in the human androgen receptor (AR) has been implicated in affecting aspects of male health ranging from fertility to cancer. Extreme expansion of the tract underlies Kennedy disease, and in vitro the AR Q tract length correlates inversely with transactivation capacity. However, whether normal variation influences physiology or the etiology of disease has been controversial. To assess directly the functional significance of Q tract variation, we converted the mouse AR to the human sequence by germline gene targeting, introducing alleles with 12, 21, or 48 glutamines. These three "humanized" AR (h/mAR) mouse lines were grossly normal in growth, behavior, fertility, and reproductive tract morphology. Phenotypic analysis revealed traits that varied subtly with Q tract length, including body fat amount and, more notably, seminal vesicle weight. Upon molecular analysis, tissue-specific differences in AR levels and target gene expression were detected between mouse lines. In the prostate, probasin, Nkx3.1, and clusterin mRNAs trended in directions predicted for inverse correlation of Q tract length with AR activation. Remarkably, when crossed with transgenic adenocarcinoma of mouse prostate (TRAMP) mice, striking genotype-dependent differences in prostate cancer initiation and progression were revealed. This link between Q tract length and prostate cancer, likely due to differential activation of AR targets, corroborates human epidemiological studies. This h/mAR allelic series in a homogeneous mouse genetic background allows examination of numerous physiological traits for Q tract influences and provides an animal model to test novel drugs targeted specifically to human AR.

Genetic mechanisms of fetal male undermasculinization: a background to the role of endocrine disruptors

Fetal male sex development proceeds along an orderly sequence of events coordinated by an interplay of genetic and hormonal events. These operate in a time- and concentration-dependent manner. Once a testis is formed (the female sex being constitutive in nature), differentiation of the internal and external male genitalia is androgen dependent. A number of genetic syndromes of sex reversal are well characterized at the biochemical and molecular levels. They fall into three principal categories: defects in formation of the testis, defects in production of androgens, and defects in the action of androgens. In many instances, the precise cause is not established, although the investigative evidence points in the direction of one of the three stated classifications. Polymorphic variants in several of the genes involved in male development are associated with certain degrees of male undermasculinization. While the genetic background is essentially static, it is plausible that the effect of endocrine disruptors during fetal life acting through epigenetic mechanisms may partly explain the observed changing trends in male reproductive tract disorders.

Androgen receptor in prostate cancer: cause or cure?

Growth of prostate tumours is dependent on androgens. Hence, therapy involves removing androgens and opposing their effects using antiandrogens. This is initially successful but inevitably fails and tumours recur. The cause of this transition to hormone-independence, and the precise role of the androgen receptor in this, is a matter of considerable debate. A recent study used a mouse model to assess the effects of increased androgen receptor expression in the prostate and found that, whereas increased expression of wild-type receptor had no effect, a mutation of the androgen receptor caused it to have oncogenic properties. This goes some way to elucidating how the androgen receptor affects tumour growth, and provides an exciting model for further study of androgen receptor mutations in prostate cancer.

Timing of pubertal maturation and the onset of sexual behavior among Zimbabwe school boys

The relationship between reproductive maturation and the onset of sexual behavior in boys across cultures is unclear. To explore the relative timing of pubertal events and their relationship to the onset of sexual behavior, we used data collected from 442 Zimbabwe school boys aged 12-18 years. Measures of reproductive maturation included self-reported spontaneous nocturnal emission, secondary sexual characteristics, and salivary testosterone. Behavioral measures included age at first sexual fantasies, non-coital sexual behavior, and coitus. Sigmoid interpolation curve techniques indicated a median age of first erection at 10.75 +/- 0.11 years, first sexual fantasy at 12.66 +/- 0.03 years, first spontaneous nocturnal emission at 13.02 +/- 0.03 years, and adult levels of blood testosterone at 17.2 +/- 0.7 years. First reported spontaneous nocturnal emission was significantly related to all measures of sexual behavior. Multiple regression models indicated that first reported spontaneous nocturnal emission was a stronger predictor of sexual behavior than variation in secondary sexual characteristics. In addition, testosterone was a significant predictor of sexual fantasies and intercourse, independent of first reported spontaneous nocturnal emission. These results confirm earlier findings in other populations that self-reported spontaneous nocturnal emissions can be used as a marker of pubertal timing among adolescent boys. They also suggest that variation in testosterone plays a role in the onset of sexual behavior among boys, beyond its relationship to developmental timing. The behavioral mechanisms represented by the significant effects of testosterone reported here remain to be investigated.

Natural history of seminiferous tubule degeneration in Klinefelter syndrome

Klinefelter syndrome (47,XXY) is characterized by small, firm testis, gynaecomastia, azoospermia and hypergonadotropic hypogonadism. Degeneration of the seminiferous tubules in 47,XXY males is a well-described phenomenon. It begins in the fetus, progresses through infancy and accelerates dramatically at the time of puberty with complete hyalinization of the seminiferous tubules, although a few tubules with spermatogenesis may be present in adult life. Activation of the pituitary-gonadal axis at 3 months of age is seen in Klinefelter boys similar to healthy boys. However, the level of testosterone in Klinefelter boys is significantly lower than in controls. After this 'minipuberty', the hormone levels decline to normal prepubertal levels until puberty. In puberty, an initial rise in testosterone, inhibin B, LH and FSH occurs in Klinefelter boys. However, the rise in testosterone levels off and ends at a low-normal level in young adults. Likewise, serum concentration of inhibin B exhibits a dramatic decline to a low, often undetectable level, concomitantly with a rise in FSH, reflecting the degeneration of the seminiferous tubules. Many hypotheses about the underlying mechanism of the depletion of the germ cells in Klinefelter males have been reported and include insufficient supranumerary X-chromosome inactivation, Leydig cell insufficiency and disturbed regulation of apoptosis of Sertoli and Leydig cells. However, at present, the exact mechanism remains unclear. In this article, we summarize current knowledge on the development of the classical endocrinological and histological features of 47,XXY males from fetus to adulthood and review the literature concerning the degeneration of the seminiferous tubules in this syndrome.

Androgen receptor polymorphism (CAG repeats) and androgenicity

Objective Polymorphism of the androgen receptor (AR) has been related to various pathophysiological conditions, such as osteoporosis and infertility. The objectives of this study were to evaluate the frequency of distribution in a normal Italian population and to assess CAG repeats (CAGr) in other conditions, such as hypoandrogenism, potentially influenced by AR polymorphism. Patients and measurements CAGr polymorphism was determined in a group of 91 healthy normoandrogenized subjects, 29 hypoandrogenized patients (hypoplasia of prostate and seminal vesicles, reduced beard or body hair, etc.) and 29 infertile patients by direct sequencing. Results The mean (+/- SD) number of CAG repeats [(CAGr)n] was 21.5 (+/- 1.7) in the control group, 21.4 (+/- 2.0) in the infertile patients and 24.0 (+/- 2.9) in the hypoandrogenic males. The difference was statistically significant between this last group and the other two (P < 0.0001), while there was no difference between normal controls and infertile patients. The frequency distribution showed a shift towards higher CAG length in hypoandrogenized patients compared to controls and infertile patients. If we used a cut-off point of 24.9 (2 SD above the mean), the percentage of patients with 25 or more CAGr repeats was 38% among hypoandrogenized patients, 7% among infertile patients and 5% among the control group. In hypoandrogenized subjects (CAGr)n correlated slightly with testis and prostate volume. The number of CAG repeats was not associated with any of the hormonal parameters, including testosterone, evaluated in the three groups. Conclusions Our normal population, representing subjects from Central Italy, is superimposable on other European populations with regard to (CAGr)n distribution. Hypoandrogenic males have a shift in the frequency distribution towards longer (CAGr)n. Infertile patients are not statistically different from the control group. These findings suggest that, given the same amount of circulating testosterone, as in our hypoandrogenized and control group, the final net androgenic phenotypical effect is due to AR polymorphism.

CAG repeat length in an infertile male population of Irish origin

The androgen receptor (AR) gene, located on the X chromosome, is an important regulator of human spermatogenesis. In the past decade, the link between the CAG polyglutamine tract, situated on exon one of the AR gene, and reduced spermatogenesis has become a controversial one. Alterations in the length of the CAG polyglutamine tract have been associated with prostate cancer at a reduced intrinsic length and neuromuscular diseases at a CAG repeat length of > or = 40. Minimal intermediate increases have been linked with depressed spermatogenesis in infertile males. Asian and Australian groups have published an association between increased CAG repeat length and reduced spermatogenesis while many European studies have found no such association. The aim of this study was to document the association between increased CAG repeat length and reduced spermatogenesis in a group of Irish infertile males and controls known to have fathered at least one child. The study employed the ABI 377 DNA sequencer to size the CAG repeat region of exon one of the AR gene in each group. Statistical analysis revealed no actual link between the length of the CAG tract and a reduction of spermatogenesis in a cohort of infertile patients (n = 66) of Irish ethnic origin when compared to a fertile control group (n = 77) (p = 0.599).

The CAG Repeat Polymorphism in the Androgen Receptor Gene Is Associated with HDL-Cholesterol but Not with Coronary Atherosclerosis or Myocardial Infarction

Background: Age-adjusted morbidity and mortality rates from coronary heart disease (CHD) are higher in men than in women. Androgens are suspected to be responsible for the male disadvantage. The genomic effect of androgens is mediated by the androgen receptor (AR), which has a polymorphic CAG repeat in exon 1. The number of repeats is inversely related to the transcriptional activity of the AR on target genes.

Methods: We investigated the association of this CAG repeat polymorphism with CHD and myocardial infarction (MI) in 2 independent case–control studies involving 544 Caucasian men.

Results: The number of CAG repeats in the AR gene correlated significantly with HDL-cholesterol (HDL-C) in controls (r = 0.21; P = 0.015). This effect was independent of triglycerides, body mass index, alcohol intake, smoking, and age in a multiple regression model (R2 = 50%). Despite decreased HDL-C, lower CAG repeat numbers were not associated with increased risk for CHD (odds ratio = 0.82; 95% confidence interval, 0.50–1.36; P = 0.44) or MI in carriers of AR genes with lower CAG repeat numbers (odds ratio = 0.72; 95% confidence interval, 0.37–1.39; P = 0.33).

Conclusions: Shorter, more androgenic AR alleles with fewer CAG repeats are associated with lower HDL-C, but not with an increased risk for CHD or MI, which argues against a detrimental androgen effect on cardiovascular risk under physiologic conditions.

Association between androgen receptor gene CAG repeat polymorphism and plasma testosterone levels in postmenopausal women

OBJECTIVES

The biologic action of androgens in target cells depends on plasma androgen levels and receptor transcriptional activity. We investigated the relationship between androgen receptor (AR) CAG repeat polymorphism, serum androgen levels, and anthropometric, metabolic, and hormonal variables in 39 postmenopausal women, taking into consideration the patterns of X-chromosome inactivation.

METHODS

Genomic DNA was extracted from peripheral leukocytes. Polymerase chain reactions (PCRs) were performed to amplify the polymorphic (CAG)n repeat of the human AR gene, which were analyzed with GeneScan software (Applied Biosystems, Foster City, CA). The X-chromosome inactivation analysis was based on the AR gene methylation patterns.

RESULTS

The mean age of participants was 54.7 years; mean age at menopause was 48 years. The number of CAG repeats ranged from 15 to 30, with a median length of 23. Analysis of X-chromosome inactivation patterns showed 19 cases with a degree of skewing (DS) > or =70% and seven with a DS > or =90%. The X-weighted CAG repeat biallelic mean was significantly lower in individuals with total testosterone (TT) greater than 0.56 ng/mL (group mean) than in the group with TT < or =0.56 (P=.018). No difference was observed between the groups regarding dehydroepiandrosterone sulfate (DHEA-S). Plasma TT was significantly higher in the group with the smaller X-weighted CAG repeat biallelic mean (P=.01). Free androgen index (FAI) was also significantly higher in this group (P=.033). Testosterone levels and FAI were inversely correlated to X-weighted CAG repeat biallelic mean.

CONCLUSION

Our data indicate an association between testosterone plasma levels and AR CAG repeats in postmenopausal women, and suggest that plasma levels of androgens in postmenopausal women may be related to variants of the AR gene.

Sex Steroid Level, Androgen Receptor Polymorphism, and Depressive Symptoms in Healthy Elderly Men

OBJECTIVES

To determine the prevalence of depression in a cohort of elderly men as assessed using a 30-item Geriatric Depression Scale (GDS) score and to describe the association between this score and sex steroids, androgen receptor (AR) polymorphism, and general health status.

DESIGN

Observational study on the relationship between sex steroid status and health-related parameters.

SETTING

Community-based.

PARTICIPANTS

Ambulatory men (n=236 in 1997, n=192 in 2000) aged 70 and older at inclusion in 1996, interviewed in 1997 and 2000.

MEASUREMENTS

Serum levels of testosterone, estradiol, sex hormone binding globulin (SHBG), dehydroepiandrosterone-sulfate (DHEAS), cortisol, and the AR gene cytosine, adenine, guanine (CAG)-repeat length polymorphism were determined. Free testosterone and free estradiol were calculated. Questionnaires included GDS, 36-item Short Form, and Rapid Disability Rating Scale-2.

RESULTS

Median age was 75.3 years (interquartile range=73.5-78.5). A GDS score of 11 or greater was found in 30 (12.7%) men. Age and GDS score were significantly interrelated (P<.01), as were all health-assessment scores. GDS scores were not related to (free) testosterone or AR polymorphism in 1997 or 2000. In 1997 only (n=236), higher GDS scores were related to higher estradiol, free estradiol, and DHEAS levels.

CONCLUSION

The data did not support a role for testosterone in depression in elderly community-based men as assessed using the GDS.

Andropause: invention, prevention, rejuvenation

There is a growing interest, as well as a booming industry, in the use of testosterone therapy for middle-aged and older men. This interest has led to the definition of a new condition, termed 'andropause', meaning the putative somatic consequences of gradually falling blood testosterone concentrations during male aging. This trend risks replicating both the rejuvenation fads of a century ago and the recent experience in estrogen therapy for menopause that has been propelled for decades by advocacy substituting for reliable scientific evidence. The current status and prospects for androgen therapy in middle-aged and older men should be evaluated critically from the perspective of male reproductive health during aging. This review appraises current knowledge with a focus on the questionable basis for using androgen therapy to improve male reproductive health during aging.

Lack of association between androgen receptor polymorphisms and bone mineral density or physical function in older men

Individuals whose androgen receptors have short polyglutamine tracts (resulting from CAG repeats) may have greater receptor signaling activity of the androgen receptor. We evaluated the association between bone mineral density (BMD) and CAG repeats in 91 older men with normal (control) and low femoral neck (EN) BMD (OP) or a history of femoral fracture (FX). Bioavailable testosterone (BioT) and physical performance, including composite score (EPESE) and physical activity (PASE), were also measured. Comparing FX, OP, and control subjects, we observed BMD Tscores of -2.16 +/- 1.08, -2.26 +/- 0.74, and -0.20 +/- 0.40 (p < 0.001); CAG repeat lengths of 21.9 +/- 2.7, 22.5 +/- 2.4, and 22.3 +/- 2.9 (p = 0.63); BioT levels of 2.29 +/- 1.25, 2.19 +/- 1.11, and 3.99 +/- 1.25 nmol/L (p < 0.001); EPESE scores of 8.0 +/- 3.0, 9.7 +/- 2.0, and 11.3 +/- 0.9 (p < 0.001); and PASE scores of 91 +/- 66, 122 +/- 66, and 200 +/- 55 (p < 0.001), respectively. There were no significant correlations between CAG repeats and BioT or physical performance. Men with osteoporosis or fracture had lower BioT, physical performance, and physical activity than controls. This study found no association between CA G repeats and FN BMD in older men with normal or low BMD or FX.

X-chromosome inactivation patterns and androgen receptor functionality influence phenotype and social characteristics as well as pharmacogenetics of testosterone therapy in Klinefelter patients

Klinefelter syndrome is characterized by a vast range of phenotypes related to androgen effects. Testosterone (T) acts via the X-linked androgen receptor gene carrying the CAG repeat (CAGn) polymorphism, the length of which is inversely associated with androgen action and might account for the marked variation in phenotypes. In 77 newly diagnosed and untreated Klinefelter patients with a 47,XXY karyotype we assessed phenotype and social traits in relation to X-weighted biallelic CAGn length using X-chromosome inactivation analysis after digestion of leukocyte DNA with methylation-sensitive HpaII. Forty-eight men were hypogonadal and received T substitution therapy; in these, pharmacogenetic effects were investigated. The shorter CAGn allele was preferentially inactive. CAGn length was positively associated with body height. Bone density and the relation of arm span to body height were inversely related to CAGn length. The presence of long CAGn was predictive for gynecomastia and smaller testes, whereas short CAGn were associated with a stable partnership and professions requiring higher standards of education also when corrected for family background. There was a trend for men with longer CAGn to be diagnosed earlier in life. Under T substitution, men with shorter CAGn exhibited a more profound suppression of LH levels, augmented prostate growth, and higher hemoglobin concentrations. A significant genotype-phenotype association exists in Klinefelter patients: androgen effects on appearance and social characteristics are modulated by the androgen receptor CAGn polymorphism. The effects of T substitution are pharmacogenetically modified. This finding is magnified by preferential inactivation of the more functional short CAGn allele.

Polymorphisms in androgen and estrogen receptor genes: effects on male aging

Besides lifestyle and environmental factors, the life-long exposure to the endocrine milieu of gonadal steroids is a determining factor to gender specific features of aging. In contrast to women, men do not experience a sudden cessation of gonadal function comparable to menopause. However, cross-sectional and longitudinal population studies demonstrate that the hormones with anabolic actions (e.g. testosterone [T], growth hormone, insulin-like growth factor [IGF]-1, dehydroepiandrosterone) do decrease progressively with aging in healthy men, and chronic systemic illnesses accelerate this process. In addition, estrogen has recently been established to be essential for normal physiology of the male. The slow progressive decline of the hypothalamic-pituitary-gonadal (HPG) function is thought to be responsible for many common signs and symptoms of aging men, such as general weakness, sexual dysfunction, and increased fat mass. There is a large inter-individual variation in sex hormone levels cross-sectionally within given age groups as well as longitudinally with aging. A contributing factor to this variability are the numerous functionally significant polymorphisms that have been detected in the receptors for androgen and estrogen. In this review, we summarize the recent information on some common polymorphisms in androgen and estrogen receptor genes and their effect on gender specific and aging-related symptoms and diseases of men.

No association of the A260G and A386G DAZL single nucleotide polymorphisms with male infertility in a Caucasian population

BACKGROUND

The human DAZ gene family includes two autosomal genes, BOULE and DAZL, and a Y-chromosomal DAZ gene cluster. All are RNA-binding proteins and assumed to be master regulators of germline gene expression. We have investigated the impact of two DAZL polymorphisms, located at nucleotide positions 260 (SNP 260) and 386 (SNP 386), on the fertility of Caucasian men. These single nucleotide polymorphisms (SNPs) have been described previously to be associated with spermatogenic failure.

METHODS

Blood samples were collected and genomic DNA was extracted from 165 normozoospermic men and 202 oligo- or azoospermic patients, of whom 28 displayed an AZFc deletion. The frequencies of A or G allelic variants in SNP 260 and 386 were analysed via TaqMan allelic discrimination assays. In both cases, the A to G transition leads to a threonine to alanine change.

RESULTS

A total of 24.2% of the controls showed a heterozygous nucleotide variant (AG) for the SNP 260 and the remaining 75.8% were homozygous for A. In the AZFc-deleted group, this distribution was significantly different, with 39.3% for AG, 57.1% for AA and 3.6% for GG. However, the increased heterozygosity was not correlated with sperm counts and morphology. The patients without deletions displayed a similar allelic pattern to the controls (24.1% AG/75.9% AA). For SNP 386, only the AA nucleotide variant was found in all subjects studied and in no case was the previously described heterozygous AG variant found.

CONCLUSION

In a selected Caucasian population, the DAZL SNP 386 is completely absent and SNP 260 is not associated with spermatogenic failure and therefore does not represent a molecular marker for genetic diagnosis of male infertility.

A polymorphic CA repeat in the IGF-I gene is associated with gender-specific differences in body height, but has no effect on the secular trend in body height

OBJECTIVE

A polymorphism near the promoter region of the IGF-I gene has been associated with serum IGF-I levels, age-related decline of serum IGF-I levels, body height, birth weight and intima media thickness in hypertensive subjects.

DESIGN AND METHODS

We investigated the association between the length of the IGF-I alleles of this promoter polymorphism and IGF-I levels and body height. Furthermore, we investigated the potential influence of this polymorphism on final height in relationship to the secular trend of individuals born between 1917 and 1945. All subjects were participants of the Rotterdam Study.

RESULTS

We observed, in analyses including only homozygous carriers, the highest IGF-I levels in homozygous carriers of the 192-bp allele (18.7 nmol/l +/- 0.6) and homozygous carriers of the 194-bp allele (17.7 nmol/l +/- 1.4). IGF-I levels were significantly lower in individuals with homozygous longer alleles [> 194-bp (12.0 nmol/l +/- 1.2; P < 0.001)] and homozygous shorter alleles [< 192-bp (15.6 nmol/l +/- 1.4; P < 0.05)] compared to homozygous carriers of the 192-bp and the 194-bp allele. In males and females separately, an optimum for serum IGF-I was also observed in homozygous carriers of the 192-bp and 194-bp allele. Only in males, homozygous carriers of the 192-bp allele were significantly taller than homozygous carriers of the shorter alleles (174.9 cm +/- 0.2 vs. 171.5 cm +/- 1.4; P = 0.01). When all subjects genotyped for the IGF-I promoter polymorphism were included in the analysis, a clear optimum for IGF-I levels and body height was observed in carriers of the 192-bp and/or 194-bp allele in the total population. Between 1917 and 1945, a secular trend in body height was observed in our Dutch population. Mean final body height was significantly higher in carriers of the most frequent alleles (192-bp and/or the 194-bp), than carriers of the remaining shorter and longer genotypes (P-trend < 0.01).

CONCLUSIONS

In conclusion, we observed an optimum in IGF-I levels and final body height for the 192-bp and 194-bp allele of the IGF-I gene. A gender-specific effect of the IGF-I alleles on body height was observed. The secular trend in body height observed in our elderly Dutch population was similar for the different genotypes; carriers of the 192-bp and/or the 194-bp allele remained significantly taller throughout time.

Klinefelter's syndrome

Klinefelter's syndrome is the most common genetic cause of human male infertility, but many cases remain undiagnosed because of substantial variation in clinical presentation and insufficient professional awareness of the syndrome itself. Early recognition and hormonal treatment of the disorder can substantially improve quality of life and prevent serious consequences. Testosterone replacement corrects symptoms of androgen deficiency but has no positive effect on infertility. However, nowadays patients with Klinefelter's syndrome, including the non-mosaic type, need no longer be considered irrevocably infertile, because intracytoplasmic sperm injection offers an opportunity for procreation even when there are no spermatozoa in the ejaculate. In a substantial number of azoospermic patients, spermatozoa can be extracted from testicular biopsy samples, and pregnancies and livebirths have been achieved. The frequency of sex chromosomal hyperploidy and autosomal aneuploidies is higher in spermatozoa from patients with Klinefelter's syndrome than in those from normal men. Thus, chromosomal errors might in some cases be transmitted to the offspring of men with this syndrome. The genetic implications of the fertilisation procedures, including pretransfer or prenatal genetic assessment, must be explained to patients and their partners.

Androgen Replacement Therapy

The major goal of androgen substitution is to replace testosterone at levels as close to physiological levels as is possible. For some androgen-dependent functions testosterone is a pro-hormone, peripherally converted to 5alpha-dihydrotestosterone (DHT) and 17beta-estradiol (E2), of which the levels preferably should be within normal physiological ranges. Furthermore, androgens should have a good safety profile without adverse effects on the prostate, serum lipids, liver or respiratory function, and they must be convenient to use and patient-friendly, with a relative independence from medical services. Natural testosterone is viewed as the best androgen for substitution in hypogonadal men. The reason behind the selection is that testosterone can be converted to DHT and E2, thus developing the full spectrum of testosterone activities in long-term substitution. The mainstays of testosterone substitution are parenteral testosterone esters (testosterone enantate and testosterone cipionate) administered every 2-3 weeks. A major disadvantage is the strongly fluctuating levels of plasma testosterone, which are not in the physiological range at least 50% of the time. Also, the generated plasma E2 is usually supraphysiological. A major improvement is parenteral testosterone undecanoate producing normal plasma levels of testosterone for 12 weeks, with normal plasma levels of DHT and E2 also. Subcutaneous testosterone implants provide the patient, depending on the dose of implants, with normal plasma testosterone for 3-6 months. However, their use is not widespread. Oral testosterone undecanoate dissolved in castor oil bypasses the liver via its lymphatic absorption. At a dosage of 80 mg twice daily, plasma testosterone levels are largely in the normal range, but plasma DHT tends to be elevated. For two decades transdermal testosterone preparations have been available and have an attractive pharmacokinetic profile. Scrotal testosterone patches generate supraphysiological plasma DHT levels, which is not the case with the nonscrotal testosterone patches. Transdermal testosterone gel produces fewer skin irritations than the patches and offers greater flexibility in dosage. Oromucosal testosterone preparations have recently become available. Testosterone replacement is usually of long duration and so patient compliance is of utmost importance. Therefore, the patient must be involved in the selection of type of testosterone preparation. Administration of testosterone to young individuals has almost no adverse effects. With increasing age the risk of adverse effects on the prostate, the cardiovascular system and erythropoiesis increases. Consequently, short-acting testosterone preparations are better suited for aging androgen-deficient men.

Testosterone metabolism, dose-response relationships and receptor polymorphisms: selected pharmacological/toxicological considerations on benefits versus risks of testosterone therapy in men

In this review selected toxicological problems related to testosterone therapy in hypogonadal men are discussed. Applying "classical" pharmacological/toxicological findings (e.g. animal studies on short- and long-term toxicity) to clinical situations is not very helpful. Molecular biological knowledge and especially evaluation of epidemiological studies, as well as intervention studies, on testosterone therapy in hypogonadal men are more useful. Potential risks include overdosage for lifestyle reasons, e.g. excessive muscle building and reduction of visceral obesity, when erythrocytosis occurs concomitantly. Modern galenic formulations of testosterone administration (e.g. transdermal gel, suitable testosterone esters for intramuscular application and newer oral preparations) avoid supraphysiological serum concentrations, therefore significantly reducing the toxicological risk. A hypothetical model of the toxicological risks of testosterone therapy is given that is based on the influence of testosterone metabolism (aromatization vs. reduction) of the respective parameter/target chosen. Finally, the great influence of polymorphisms of the androgen receptor on the assessment of toxicological risk and on the individualization of androgen therapy is shown. Already existing national, continental and international guidelines or recommendations for the testosterone therapy should be harmonized.

Androgens and male fertility

Androgens play a crucial role in the development of male reproductive organs such as the epididymis, vas deferens, seminal vesicle, prostate and the penis. Furthermore, androgens are needed for puberty, male fertility and male sexual function. High levels of intratesticular testosterone, secreted by the leydig cells, are necessary for spermatogenesis. Intratesticular testosterone is mainly bound to androgen binding protein and secreted into the seminiferous tubules. Inside the sertoli cells, testosterone is selectively bound to the androgen receptor and activation of the receptor will result in initiation and maintenance of the spermatogenic process and inhibition of germ cell apoptosis. The androgen receptor is found in all male reproductive organs and can be stimulated by either testosterone or its more potential metabolite dihydrotestosterone. Severe defects of the androgen receptor may result in abnormal male sexual development. More subtle modulations can be a potential cause of male infertility. Treatment of an infertile man with testosterone does improve spermatogenesis, since exogenous administrated testosterone and its metabolite estrogen will suppress both GnRH production by the hypothalamus and Luteinising hormone production by the pituitary gland and subsequently suppress testicular testosterone production. Also, high levels of testosterone are needed inside the testis and this can never be accomplished by oral or parenteral administration of androgens. Suppression of testosterone production by the leydig cells will result in a deficient spermatogenesis, as can be seen in men taking anabolic-androgenic steroids. Suppression of spermatogenesis by testosterone administration is also the basis for the development of a male contraceptive. During cytotoxic treatment or irradiation suppression of intratesticular testosterone production cells may prevent irreversible damage to the spermotogonial stem cells.