5[alpha]-reductase type 2 gene variant associations with prostate cancer risk, circulating hormone levels and androgenetic alopecia

Int. J. Cancer: 120, 776–780 (2006)' 2006 Wiley-Liss, Inc.
5a-Reductase type 2 gene variant associations with prostate cancerrisk, circulating hormone levels and androgenetic alopecia Vanessa M. Hayes1,2*#, Gianluca Severi3,4*, Emma J.D. Padilla1, Howard A. Morris5, Wayne D. Tilley5,6,Melissa C. Southey7,8, Dallas R. English3,4, Robert L. Sutherland1,2, John L. Hopper4, Peter Boyle8 and Graham G. Giles3,41Cancer Research Program, Garvan Institute of Medical Research, St Vincent's Hospital, Sydney, Australia 2University of New South Wales, Sydney, Australia 3Cancer Epidemiology Centre, Cancer Council of Victoria, Melbourne, Australia 4Centre for Molecular, Environmental, Genetic and Analytic Epidemiology, University of Melbourne, Melbourne, Australia 5Hanson Institute, Adelaide, Australia 6Dame Roma Mitchell Cancer Research Laboratories, University of Adelaide, Adelaide, Australia 7Department of Pathology, University of Melbourne, Melbourne, Australia 8International Agency for Research on Cancer, Lyon, France Controversy exists over the significance of associations between cancer risk and male patterned balding. However, only one pro- the SRD5A2 (5a-reductase type 2) polymorphisms, A49T and spective epidemiological study has been able to demonstrate such V89L, and risk of prostate cancer. These potentially functional an association.7 Two recent studies have challenged this hypothe- polymorphisms may alter life-long exposure to androgens with sis, reporting an association between increased risk of aggressive subsequent effects on male health and aging. The aim of this study prostate cancer and reduced circulating levels of testosterone.8,9 In was to examine the association of these variants with prostate can-cer risk, plasma hormone levels and androgenetic alopecia. Sub- addition, we have argued that the observed increase in prostate jects include 827 cases and 736 controls from an Australian popu- cancer incidence with increased age may be related to the andro- lation-based case–control study of prostate cancer. Information on cline age associated decreasing levels of androgens.9 prostate cancer risk factors and patterns of balding were col- SRD5A2, is encoded by the SRD5A2 gene located at band p23 on lected. Plasma levels of testosterone, 3a-diol glucuronide (3a- chromosome 2.10 Two single nucleotide polymorphisms (SNPs) diolG), dehydroepiandrosterone sulfate, androstenedione, sex hor- identified within the coding region of SRD5A2, rs9282858 (G>A) mone-binding globulin and estradiol were measured for controls.
No associations with the V89L polymorphism were found. Car- and rs523349 (G>C), have been implicated in influencing prostate riers of the rarer A49T A allele were at a 60% higher risk of pros- cancer risk via altering androgen levels. The alanine to threonine tate cancer (OR 5 1.60; 95% CI 1.09–2.36; p 5 0.02) and 50% amino acid change at codon 49 (A49T, GCC to ACC) increases 5a- lower risk of vertex and frontal balding (p 5 0.03) compared with reductase activity 5-fold in vitro,11 while the valine to leucine sub- men homozygous for the more common G allele. Although we stitution at codon 89 (V89L, GTA to CTA) results in an almost found little evidence of association between this variant and 30% reduction in enzyme activity both in vitro and in vivo.12 The plasma levels of 5 measured androgens, circulating 3a-diolG levels commonly used amino acid substitution nomenclature, A49T and were 34% lower in A49T A allele carriers (p < 0.0001). Our study V89L, will be used to identify these genetic markers in this study.
provides evidence that the SRD5A2 A49T A variant is associated with an increased risk of prostate cancer, lower levels of circulat- Molecular epidemiological studies of these dimorphic markers ing 3a-diolG and decreased risk of baldness. These findings raise have reported inconsistent findings with respect to their role in important questions with respect to previous assumptions con- prostate cancer risk and/or clinicopathological behavior. A meta- cerning hormonal influences on prostate cancer risk in ageing analysis has reported a modest effect of the A49T polymorphism on prostate cancer risk, but no role for V89L.13 Reports of associa- 2006 Wiley-Liss, Inc.
tions between the A49T and V89L polymorphisms and plasmaandrogen levels, including testosterone and 3a-diolG, have been Key words: SRD5A2; limited.14–17 A single study has reported a null association between population-based case-control study; plasma androgens; androgenetic the V89L variant and balding patterns in European men.18 To further examine associations between these two well-defined polymorphisms and prostate cancer risk, plasma hormone levels Membrane-bound 5a-reductase type 2 (SRD5A2) is responsible for the irreversible conversion of testosterone into its more activemetabolite, dihydrotestosterone (DHT) and is essential for the nor- Abbreviations: 3a-diolG, 3a-diol glucuronide; 3b-diolG, 3b-diol glucu- mal growth and development of the prostate gland.1 This hor- ronide; CI, confidence interval; DHEAS, dehydroepiandrosterone-sulfate; mone-regulator has been implicated in male pathophysiology, DHT, dihydrotestosterone; E2, estradiol; H–N, Hamilton–Norwood; H–W,Hardy–Weinberg; LD, linkage disequilibrium; OR, odds ratio; RFPC, Risk including prostate cancer and balding (androgenetic alopecia).
Factors for Prostate Cancer; SRD5A1, 5a-reductase type 1; SRD5A2, 5a- The ratio of DHT to testosterone has been reported to be highest reductase type 2; SHBG, sex hormone-binding globulin.
for African–Americans, intermediate for Europeans and lowest for Grant sponsors: National Health and Medical Research Council (grant Asian–Americans, which corresponds to reported ethnic-based numbers: 251533, 940394, 991129, 299955, 396407); Cancer Institute of risk of prostate cancer for these groups, suggesting an association New South Wales; Tattersall Family Foundation; Whitten Foundation; with prostate cancer risk.2 Prostate cancer risk has been associated Armati Family Foundation, Australia; and BNP Paribas Foundation, Aus-tralia and France. Infrastructure was provided by the Australian Cancer with vertex pattern balding.3 Increased levels of DHT have been Research Foundation Unit for the Molecular Genetics of Cancer and The demonstrated in the male balding scalp,4 while lack of balding is Cancer Council Victoria.
seen in pseudohermaphrodites (men with congenital 5a reductase *These authors contributed equally to the manuscript.
deficiency) with a concomitant reduced ability to convert testos- Correspondence to: Cancer Research Program, Garvan Institute of terone to DHT.5 DHT in turn is metabolized to 5a-androstane-3a- Medical Research, 384 Victoria Street, Darlinghurst, NSW 2010, Aus-tralia. Fax: 161-2-92958321. E-mail: [email protected] 17b-diol glucuronide (3a-diolG), a predictor of both cutaneous Received 1 August 2006; Accepted after revision 12 September 2006 and intraprostatic serum 5a-reductase levels.6 These observations DOI 10.1002/ijc.22408 support the ‘‘androgen hypothesis'' that increases in active andro- Published online 29 November 2006 in Wiley InterScience (www.interscience.
gens (and their metabolites) are associated with increased prostate Publication of the International Union Against Cancer SRD5A2 SNPS, PROSTATE CANCER, SERUM ANDROGENS AND BALDING and androgenetic alopecia, we genotyped the A49T and V89L var- the Sequenom MassARRAYTM Compact system (Sequenom, San iants in a large population-based case–control study of Australian Diego, CA), using matrix-assisted laser desorption/ionization men (827 cases, 736 controls).
time-of-flight (MALDI-TOF) mass spectrometry. PCR and exten-sion primer sequences were designed using Sequenom RealSNP(www.RealSNP.com). PCR was performed in duplex in 384-well Subject and methods plates with a final volume of 5 ll containing 2.5 ng of DNA, 103 Qiagen HotStar Taq PCR buffer, 25 mM MgCl2, 25 mM dNTPs, Subjects were participants in the Melbourne and Perth arms of 200 nM of each of the 4 PCR primers (primer sequences available the Risk Factors for Prostate Cancer (RFPC) study, an Australian upon request) and 0.15 U Qiagen HotStar Taq Polymerase. PCR population-based case–control study of prostate cancer conducted cycling was executed using an Eppendorf Mastercycler, under the between 1994 and 1998 and described in detail elsewhere.19,20 The following conditions: 95°C for 15 min, 45 cycles of 95°C for 20 study focus was the prevention of prostate cancers likely to contrib- sec, 56°C for 30 sec and 72°C for 1 min, followed by a final exten- ute to premature mortality and, consequently, recruitment was re- sion step of 3 min at 72°C. The MassEXTEND reaction was per- stricted to men with tumors diagnosed at an early age and of more formed using the 13 ACT termination mix (ddATP, ddCTP, aggressive histopathology. To this end, tumors that were well-dif- ddTTP, dGTP), 600 nM of each extension primer (primer sequen- ferentiated and those with Gleason scores less than 5 were ces available upon request) and 0.063 U of Thermosequenase. The excluded. Eligible cases with histopathologically-confirmed adeno- cycling conditions were as follows: 94°C for 2 min, 40 cycles of carcinoma of the prostate diagnosed before age 70 years were 94°C for 5 sec, 52°C for 5 sec and 72°C for 5 sec. To assess reli- ascertained from the Cancer Registries of Victoria and Western ability of the genotyping, 31% of the study samples were ran- Australia. Random samples of 100%, 50% and 25%, respectively, domly regenotyped for both A49T and V89L with a concordance of the cases diagnosed in the age groups younger than 60 years, 60– rate of 100% and 99.4%, respectively.
64 years and 65–69 years were asked to participate in the study. Eli-gible controls were randomly selected from males on the StateElectoral Rolls (registration to vote is compulsory for adult Austra- Statistical analysis lian citizens) and were frequency-matched to the expected age dis- Estimates of allele/genotype frequencies and tests of deviation tribution of the prostate cancer cases in a ratio of 1 control per case.
from Hardy–Weinberg (H–W) equilibrium were carried out using A total of 1,047 cases and 1,058 controls participated in the study standard procedures based on asymptotic likelihood theory.23 (65% and 50%, respectively, of those eligible).3 A face-to-face Linkage disequilibrium (LD) between the 2 variants was assessed interview was conducted using structured questionnaires to obtain by using Lewontin's D0, and tests for significance were based on information on potential risk factors including age, history of pros- asymptotic likelihood theory.24 Fisher's exact test was used to test tate cancer in first-degree relatives, country of birth, life-style for independence between the SNPs and categorized risk factors, (including diet) and other potential risk factors for prostate cancer.
namely, age (<55, 55–64, 65–69), country of birth (Australia, The interviewer also scored the subject's androgenetic alopecia others), family history of prostate cancer (affected first-degree rel- according to an adapted Hamilton–Norwood (H–N) scale,21 as no atives, no affected relatives) and tumor stage (stage I to IV) and balding (H–N stages I and II), frontal balding (H–N stages II, III, grade (moderate and high). Tests for association between geno- IIIa and IVa), vertex balding (H–N stage III vertex-V) and frontal types and the various outcome of interest (i.e., prostate cancer baldness concurrent with vertex baldness (H–N stage IV, V, Va, VI risk, circulating hormone levels and androgenetic alopecia) were and VII).3 Tumor stage (stage I to IV according to the American performed under codominant, dominant and recessive models.
Joint Committee on Cancer 2002) and grade (moderate, Gleason 5– Case–control analyses were conducted using unconditional logis- 7 or moderately differentiated; high, Gleason 8–10 or poorly differ- tic regression and odds ratio (OR) estimates and their 95% confi- entiated) was recorded from histopathology reports. Informed con- dence intervals (CI) were derived under likelihood theory.25 sent was obtained from all study participants. Blood samples were Adjustment for country of birth, age, history of smoking, history available from 831 cases (79% of participants) and 738 controls of prostate cancer in first-degree relatives (family history), body (70%). A detailed description of participant characteristics has mass index (BMI) and alcohol consumption did not materially been published.22 The study was approved by the Human Research change the OR estimates from the logistic models. Polytomous Ethics Committee of the Cancer Council of Victoria (HREC 9500).
logistic regression models were used to estimate ORs by tumorstage (dependent variable with 3 categories: 0, 1 and 2 for con- Plasma hormone levels trols, stage I–II and stage III–IV tumors, respectively) and grade Plasma samples of controls only were sent to the laboratory of (dependent variable with 3 categories: 0, 1 and 2 for controls, one of us (HAM) in randomly assigned batches of around 80 sam- moderate-grade and high-grade tumors, respectively).
ples each. The laboratory was blinded to the status of the samples As plasma levels of testosterone, 3a-diolG, DHEAS, androstene- (genotype). One scientist performed all measurements with 10% dione, SHBG and E2 were skewed, linear regression of the trans- sample pooling per batch for quality control purposes. Plasma formed levels to test the possible association with genotypes was dehydroepiandrosterone-sulfate (DHEAS) and sex hormone-bind- used. Levels of 3a-diolG and E2 were log-10 transformed, while ing globulin (SHBG) levels were measured using a competitive the others were square-root transformed. The linear regression mod- immunometric assay (IMMULITE analyzer, DPC, CA). The inter- els were adjusted for age and laboratory assay and were fitted using assay coefficient of variation (CV) was 12.4% at 2.1 lmol/l for all the controls. Results are presented as adjusted back-transformed DHEAS and 6% at 26 nmol/l for SHBG. Testosterone and estra- means and their corresponding 95% CI derived from the fitted diol (E2) levels were measured using electrochemiluminescence regression models. These statistical analyses were performed using immunoassay (Elecsys 2010 analyzer, Roche Diagnostics GmbH, Stata/SE 8.2 (Stata Corporation, College Station, TX).
Mannheim, Germany). The CV was 1.6% at 36 nmol/l for testos- The association between genotype and androgenetic alopecia terone and 11.1% at 93 pmol/l for E2. Plasma androstenedione was tested using a maximum-likelihood multinomial (polytomous) and 3a-diolG levels were measured using a radioimmunoassay logistic regression model (mlogit function in Stata/SE 8.2). The (DSL-4200 and DSL-6000 respectively, TX). The CV was 10.7% model, with alopecia as outcome, was fitted adjusting for age and at 3.3 nmol/l for A and 4.3% at 21.1 nmol/l for 3a-diolG.
including an indicator variable to adjust for the case/control status,because we previously found in this study an association between alopecia and prostate cancer.3 Finally, an interaction term was Genomic DNA was extracted from whole blood and genotyped added to test whether the effect of genotype in cases differed from in a blinded manner for the A49T (rs9282858) and V89L the effect in controls. Two separate models were fitted for the 2 (rs523349) SRD5A2 variants. Genotyping was performed using HAYES ET AL.
TABLE I – SRD5A2 GENE POLYMORPHISMS IN CONTROLS II). Circulating levels of 3a-diolG for carriers of the GA genotype AND PROSTATE CANCER CASES (adjusted mean 5 9.2 nmol/l) were 34% lower than for carriers of the GG genotype (14.0 nmol/l, p < 0.0001). Similarly, DHEAS levels for carriers of the GA genotype (2.17 lmol/l) were lower than for carriers of the GG genotype (2.61 lmol/l), but the differ- ence was only marginally significant (p 5 0.05). We found no evi- 1.60 (1.09–2.36) dence of association between V89L and the levels of any analyte measured (all p  0.1).
Androgenetic alopecia 1.09 (0.89–1.35) 0.90 (0.64–1.28) For A49T the model including the interaction between genotype and case–control status showed that the ORs for baldness in con- trols were lower than the corresponding ORs for cases. The ORs Number of subjects with at least one of the two variants measured.
for vertex baldness and for vertex and frontal baldness combined –2Odds ratios and 95% confidence intervals from unconditional logis- were significantly lower than one for controls but not for cases.
tic regression analysis.–3Test for association between genotype andprostate cancer risk (likelihood ratio test).
However, the statistical evidence of an interaction between A49Tand case/control status was only marginal (p 5 0.03) and there isno obvious reason why the association between genotype and The likelihood ratio test was used to test nested hypotheses and baldness would be dependent on case/control status. In Table III, the Wald test to assess statistical significance of individual param- we present the ORs for cases and controls combined. We found eters. All tests were two-sided. Following convention, nominal marginal evidence of an association between A49T and alopecia statistical significance was based on p < 0.05. No attempt was (p 5 0.04) with carriers of the GA allele being at lower risk of ver- made to adjust for multiple comparisons.
tex baldness (OR 0.56, 95% CI 0.31–1.01) and vertex and frontal baldness (OR 0.52, 95% CI 0.29–0.94).
Although we found little evidence of an overall association Genotyping of both A49T and V89L variants was successful in between V89L and alopecia (p 5 0.1 and 0.3 from the codominant over 99% of the samples yielding 827 cases and 736 controls with and recessive models, respectively), the ORs associated with the at least 1 of the 2 variants determined (826 cases and 734 controls CC genotype compared with the GG genotype were all higher with both variants determined, Table I). Only 5 cases (<1%) and than 1 and were statistically significant for vertex baldness (OR 7 controls (
1%) were not European in origin, with the great ma- 1.92, 95% CI 1.04–3.54) and vertex and frontal baldness com- jority of subjects (98.5%) being born in Australia, the British Isles, bined (OR 1.98, 95% CI 1.08–3.64). We did not find statistical or Western Europe. Median age at diagnosis for the cases was 62 evidence of different ORs between cases and controls (P for inter- years. The proportion of cases that were diagnosed at age <55, action between V89L and case/control status 5 0.05).
55–64 and 65–69 was 14% (n 5 113), 52% (n 5 435) and 34%(n 5 279), respectively. Two hundred and fifty-four cases (31%)had a stage III or stage IV tumor and 223 (27%) were poorly dif- ferentiated or had a Gleason score 8 or higher.
Our study suggests that carriers of the SRD5A2 A49T variant The distribution of the genotypes was consistent with H–W have a 34% lower circulating level of 3a-diolG, a 60% higher risk equilibrium for both loci in cases and controls, and for cases and of developing prostate cancer and a 50% lower risk of alopecia controls combined (all p > 0.2). The 2 loci were in strong LD and than men homozygous for the more common variant. We found D0 was 0.74 for controls (p 5 0.001), 0.99 for cases (p < 0.0001) no association between V89L and risk of prostate cancer, baldness and 0.92 for cases and controls combined (p < 0.0001). There was or circulating hormone levels.
no association between either genotype and age, or country of Strengths of our study include its large sample size and detailed birth or family history of prostate cancer (all p > 0.05).
data on tumor stage and grade and risk factors for prostate cancerincluding the direct assessment of the baldness status of partici- Prostate cancer risk pants. Another strength of our study is the evaluation of hormone The frequency of the A allele in A49T (G > A) was 4.5% for levels in controls to test whether the genetic variants in SRD5A2 cases and 2.9% for controls, with no subjects homozygous AA modulate circulating hormone levels, thus facilitating interpreta- (Table I). The proportion of carriers of the GA genotype was tion of associations between the SRD5A2 gene variants and risk of slightly higher in cases (9%) than for controls (6%, p 5 0.02) and prostate cancer, and androgenetic alopecia. A major limitation of the corresponding OR was 1.60 (95% CI 1.09–2.36). The propor- our study is its retrospective nature (case–control design) preclud- tion of GA carriers was similar for stage I–II (47/569, 8%) and ing meaningful testing of associations between circulating hor- stage III–IV (28/254, 11%) tumors (p 5 0.2; OR 1.38, 95% CI mone levels and prostate cancer.
0.84–2.25). There was no difference in the genotype distribution Although a meta-analysis,13 and a large (n 5 2,216) multiethnic by tumor grade, with the portion of GA carriers being similar for population case-control study,26 failed to support an increased risk both moderate 56/604 (9%) and high 19/223 (8.5%) Gleason conferred by the V89L polymorphism, studies since 2003 continue grades (p 5 0.7; OR 0.91, 95% CI 0.53–1.57).
to report associations between this variant and prostate cancer risk The frequency of the C allele in V89L (G>C) was 31% for both in European populations.27–30 In our study, we confirm a lack of cases and controls (Table I). There was no evidence of association association between V89L and risk of prostate cancer. The meta- between genotype and prostate cancer risk as the OR was very analysis could not exclude the possibility of an association close to 1 (p 5 0.5). There was no significant difference in the fre- between the A49T polymorphism and risk of prostate cancer, as quency of the C allele (both 31%) or genotype distribution for tu- confirmed in our study.13 The discrepancies between studies may mor stage I–II (8% CC, 45% GC) versus stage III–IV (10% CC, be due to the relatively low frequency of the A49T risk allele in 41% GC) or for moderate (8% CC, 45% GC) versus high (12% European populations (3% allele frequency/6% genotype fre- CC, 39% GC) tumor grade (both p > 0.1).
quency, controls); thus, many small studies will have lackedadequate statistical power to address this question.
The effect of these polymorphic markers on prostate cancer There was no association between the A49T variant and levels incidence and clinicopathological behavior has been investigated.
of testosterone, androstenedione, SHBG or E2 (all p  0.18, Table An increase in the risk of more aggressive disease27 and metastatic SRD5A2 SNPS, PROSTATE CANCER, SERUM ANDROGENS AND BALDING TABLE II – HORMONE LEVELS1 BY GENOTYPE IN THE CONTROLS OF THE RFPC STUDY 3a-diolG (nmol/l) 12.6 (12.3–13.0) 14.0 (13.4–14.6) 2.61 (2.50–2.73) 2.31 (2.22–2.40) 29.3 (28.3–30.3) 90.2 (88.5–92.0) 13.5 (12.0–15.0) 2.17 (1.78–2.61) 2.06 (1.74–2.42) 28.4 (24.5–32.6) 93.8 (86.7–101.4) 12.5 (12.0–13.0) 13.7 (13.0–14.5) 2.58 (2.42–2.74) 2.27 (2.14–2.39) 28.7 (27.4–30.1) 90.8 (88.3–93.4) 12.9 (12.4–13.5) 14.0 (13.2–14.9) 2.61 (2.44–2.79) 2.32 (2.19–2.46) 29.5 (27.9–31.0) 90.2 (87.5–92.9) 12.9 (11.8–14.0) 12.1 (10.7–13.6) 2.50 (2.17–2.85) 2.27 (2.01–2.55) 30.8 (27.7–34.1) 88.3 (83.2–93.8) 1Adjusted back-transformed means and their corresponding 95% CI derived from linear regression of the transformed levels. Levels of 3a- diol G and E2 were log 10 transformed, while the others were square-root transformed. The models were adjusted for age and laboratory assay.
–2Two had missing genotype for A49T.–3Likelihood ratio test for association between genotype and circulating hormone levels. Abbreviations:T, testosterone; 3a-diolG, 3a-diol glucuronide; DHEAS, dehydroepiandrosterone-sulfate; A, androstenedione; SHBG, sex hormone-binding globulin; E2, estradiol.
TABLE III – SRD5A2 POLYMORPHISMS AND ANDROGENETIC ALOPECIA No balding (n 5 278) Frontal (n 5 516) Frontal and vertex (n 5 389) 0.92 (0.56–1.51) 0.56 (0.31–1.01) 0.52 (0.29–0.94) OR (95% CI) GC vs. GG 1.09 (0.81–1.49) 1.06 (0.76–1.48) 1.26 (0.91–1.74) OR (95% CI) CC vs. GG 1.48 (0.82–2.70) 1.92 (1.04–3.54) 1.98 (1.08–3.64) OR (95% CI) any C vs. GG 1.43 (0.80–2.55) 1.86 (1.03–3.38) 1.78 (0.99–3.21) 1Test for association between genotype and baldness status (i.e., the three ORs for the different baldness categories are all 1); the likelihood ratio test was used.–2ORs are from a generalized logit model fitted through a log-linear model for multiway contingency tables. Two separatemodels were fitted for the two variants. The models were adjusted for age and case–control status because the prevalence of vertex baldness incases was slightly higher than in controls (p 5 0.04).–3Test for association between genotype and the specific category of baldness (i.e., both ORs for GC and CC are 1).
disease,31 for patients carrying the V89L C allele or CC genotype, sis that high levels of androgens would be associated with an respectively, and a trend for more advanced stage disease for increase in prostate cancer risk. In contrast, we found an associa- patients carrying the A49T A allele (GA genotype)11,31,32 has tion between the SRD5A2 A49T variant and decreased 3a-diolG been reported. In agreement with other studies, we found no asso- levels, as well as increased prostate cancer risk. More recently, 2 ciation between either tumor stage or grade and the V89L or large prospective studies have shown that high circulating levels A49T variant.27,32–34 of androgens decrease the risk of aggressive prostate cancer.8,9 It has been suggested that genetic polymorphisms of SRD5A2 The involvement of androgens in androgenetic alopecia is well mediate their effects via changes in androgen levels, including 3a- accepted, implicating hormone regulatory genes in predisposing diolG, a major metabolite of DHT synthesized in the prostate. As men to this predominantly male condition.36 In addition, a moder- DHT is largely derived from the SRD5A2 isoform SRD5A1 activity ate association between prostate cancer and vertex type baldness in the skin, circulating 3a-diolG concentration is believed to be a compared with no balding has been described.3 Two independent more accurate marker of SRD5A2 activity. A study of 604 British studies have shown an association between the presence of a non- men participating in the European Prospective Investigation into functional androgen receptor (AR) polymorphism (AR-E211 Cancer and Nutrition (EPIC) study showed that V89L was not asso- G>A) and reduced risk of alopecia,22,37 while no association be- ciated with serum androgen levels, while carriers of the A49T vari- tween the SRD5A2 V89L variant has been observed.18 We found ant had 24% lower serum levels of 3a-diolG than individuals little evidence of an increased risk of vertex or vertex and frontal homozygous for the common allele (p 5 0.0003).14,15 This strong balding combined for carriers of the V89L variant, but we did association between A49T and levels of 3a-diolG was confirmed in observe a marginally significant association between the presence our study, in which we measured levels of this DHT metabolite in of the A49T variant and decreased risk of vertex or vertex plus plasma. After adjusting for age and assay/batch, levels of 3a-diolG frontal balding combined. This association with decreased balding were 34% lower for carriers of the A49T variant than for men is surprising as balding is usually associated with increased DHT homozygous for the common variant. The latter finding is in con- levels, which in turn is associated with increased SRD5A2 activity trast with the results from a study that showed that the A49T variant in the presence of the A49T variant. Our findings that the A49T increases the activity of SRD5A2 in vitro.11 However, one cannot variant is associated with lower 3a-diolG plasma levels and, thus, exclude the possibility that the rarely studied 3b-diolG, an alternate decreased DHT (assuming 3a-diolG is a true indicator of circulat- metabolite of DHT,35 together with other hormones, may not have ing DHT levels) supports our observed association between A49T influenced these findings thus providing an explanation for the and decreased balding. Thus, contrary to current understanding, apparent inconsistency between our results and the in vitro study.
our findings suggest an alternative functional effect of the A49T The interpretation of these results in terms of prostate cancer variant on enzymatic activity. Once again we cannot exclude the risk is further complicated by the historically prevailing hypothe- possibility that circulating 3a-diolG plasma levels are not being HAYES ET AL.
influenced by the enzymatic activity of SRD5A1 (known to be questions; including the perceived functional consequences of the active in the skin), by the hydroxysteroid dehydrogenases which A49T variant and whether 3a-diolG is a true indicator of circulating convert DHT and dehydroepiandrosterone to 3a-diolG, or by the DHT levels. It readdresses issues surrounding limitations of assess- production of 3b-diolG. The interplay between hormones in the ing circulating androgens as a true reflection of tissue-specific skin (i.e., scalp and hair follicles), in the circulation and in the pros- androgen levels and lends weight to the historically less accepted tate is not well understood. Thus, further studies are needed to ‘‘androcline hypothesis'' of prostate cancer risk.
investigate whether androgen levels in the circulation are trulymarkers of androgen levels within tissues like the prostate and skin.
In this large population-based, case–control study we confirm previous observations that the SRD5A2 A49T variant is associatedwith increased prostate cancer risk, as well as a decrease in the cir- We would like to thank the study participants and the many urolo- culating hormone 3a-diolG in European men. This is also the first gists, nurses, and histopathologists who kindly facilitated the recruit- study to suggest an association between this polymorphism and ment and collection of patient information and pathologist reports.
decreased male patterned balding. These findings raise a number of V.M.H. is a Fellow of the Cancer Institute of New South Wales.
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