BJUI. Second to fourth digit ratio, adult testosterone level and testosterone deficiency

Transcription

1 Sexual Medicine SECOND TO FOURTH DIGIT RATIO, ADULT TESTOSTERONE LEVEL AND TESTOSTERONE DEFICIENCY GARCÍA-CRUZ ET AL. BJUI Second to fourth digit ratio, adult testosterone level and testosterone deficiency Eduardo García-Cruz, Jorge Huguet, Marta Piqueras, María J. Ribal and Antonio Alcaraz Hospital Clínic de Barcelona Urology Department, Barcelona, Spain Accepted for publication 20 January 2011 Study Type Diagnostic (exploratory cohort) Level of Evidence 2b OBJECTIVES The ratio of the second and fourth finger lengths (2D/4D) is related to intrauterine exposure to testosterone. The relationship between 2D/4D and adult hormonal pattern is controversial. The aim of our study was to determine if there was a relationship between adult serum testosterone levels and the 2D/4D ratio. What s known on the subject? and What does the study add? 2D/4D digit ratio is inversely related to intrauterus exposure to androgens. Our experience suggests that 2D/4D digit ratio inversely predicts adult testosterone levels and is directly related to hypogonadism. The hormonal profile (testosterone and sexual hormone binding globulin) of the patients was determined between 7.00 am and am. Age, weight, height, body mass index, toxic habits, digital rectal examination, prostate-specific antigen and 2D and 4D measurements were recorded prospectively. biochemical hypogonadism (testosterone <346 ng/dl). Mean 2D/4D ratio in patients with testosterone >346 ng/dl was lower than in patients with testosterone <346 ng/dl (2D/4D 0.97 ± vs 0.99 ± depending on their hormonal status, P = 0.05). High 2D/4D ratio was associated with low testosterone serum levels (P = 0.046). PATIENTS AND METHODS We prospectively recruited 204 consecutive patients referred for transrectal prostate biopsy between January 2008 and June The same physician performed clinical examinations, 2D/4D measurements and the transrectal biopsy in all cases. Cut-off points of 231 and 346 ng/dl testosterone (8 and 12 nmol/l) were used. 2D/4D determination was done with a vernier calliper on the left hand. RESULTS The mean age was 67 ± 7 years and the mean testosterone level was 413 ± 18 ng/dl (14.33 ± 0.62 nmol/l). The percentages of patients with testosterone <231 ng/dl (8 nmol/l) and testosterone <346 ng/dl (12 nmol/l) were 6.1 and 30.6 respectively. Univariate analysis showed that low 2D/ 4D ratios were related to higher levels of testosterone (B = ; β = 0.165, P = 0.045) and also with low prevalence of CONCLUSIONS The 2D/4D ratio is related to adult testosterone levels and the presence of testosterone deficiency syndrome. Patients with high 2D/4D ratios have lower testosterone levels and higher risk of testosterone deficiency syndrome. KEYWORDS testosterone, digit ratio, testosterone deficiency syndrome INTRODUCTION The ratio of the length of the second finger (index) to fourth finger (ring) 2D/4D is different depending on \gender in humans [1,2]. On average, this ratio is 25% higher in females than in males [3]. Evidence suggests that foetal sex hormones, mainly androgens, are involved in sexual 2D/ 4D variability. Thus, males tend to have longer 4D (and subsequently a lower 2D/4D ratio) and females a shorter 4D (and thus a higher 2D/4D ratio). Moreover, it seems that androgen variability also affects intrasexual variation of this relationship [1]. The 2D/4D ratio does not change with ageing. Stability of the digit ratio relationship has been established throughout childhood and puberty [4 7]. The 2D/4D ratio at the age of 2 was found to be negatively correlated with the testosterone/oestrogen ratio as measured by amniocentesis in the second trimester [7]. For example, children with congenital adrenal hyperplasia, a condition that results in abnormally high testosterone levels during gestation, have lower 2D/4D values than controls [8,9]. Females with male co-twins, exposed to higher testosterone levels in utero, have lower 2D/4D values than females with female co-twins [10]. The 2D/4D ratio negatively correlates with testosterone sensitivity in androgen receptors as measured by the number of CAG repeats in the androgen receptor gene [11]. As prenatal , doi: /j x x

2 SECOND TO FOURTH DIGIT RATIO, ADULT TESTOSTERONE LEVEL AND TESTOSTERONE DEFICIENCY TABLE 1 Main clinical and biochemical data of 204 patients enrolled in the study Age (years) mean, SD 67 ± 7 Tobacco use (packs/year) 21 ± 7 Current smoker (%) 41.6 Former smoker (%) 24.9 Non-smoker (%) 33.5 Alcohol (daily intake, g), mean, SD 18 ± 23 Weight (kg), mean, SD 76 ± 10 Height (m), mean, SD 1.68 ± 0.06 BMI (kg/m 2 ), mean, SD 26 ± 3 2D length (cm), mean, SD 7.23 ± D length (cm), mean, SD 7.35 ± D/4D mean, SD 0.98 ± 0.04 Testosterone [ng/dl (nmol/l)], mean, SD 413 ± 18 (14.33 ± 0.62) % of patients with <231 ng/dl (<8 nmol/l) 6.1 % of patients with ng/dl (8 12 nmol/l) 24.5 % of patients with >346 ng/dl (>12 nmol/l) 69.4 SHBG (nmol/l), mean, SD 42.5 ± D ratio was obtained by dividing 2D by 4D. Moreover, patients were subclassified into two categories regarding their 2D/4D ratio: those with a ratio lower than one (index shorter) and those with a ratio equal to or higher than one (ring shorter). We performed a univariate analysis to determine which variables were related to testosterone and SHBG levels. A multivariate analysis was performed with variables with statistical significance in the univariate analysis. Moreover, age, BMI and presence of diabetes mellitus were included in the multivariate analysis because of their wellestablished relationship with testosterone levels and testosterone deficiency syndrome (TDS), regardless of the result of the univariate analysis. Finally, we used a receiver operator characteristic (ROC) curve analysis to predict the accuracy of 2D/4D in identifying TDS. testosterone affects human behaviour and cognition and since other ways of studying these effects in humans are laborious and pose various difficulties [12,13], 2D/4D has become popular as a means to study the effects of prenatal androgenization in humans, especially with regard to sex-linked behaviours and traits [1,14]. Moreover, some authors found that 2D/4D seemed to be related not only to foetal but also to adult hormonal patterns [3]. Additionally, differences in adult hormonal status in the same gender could be related to the 2D/4D ratio [1]. Data on how this 2D/4D ratio reflects the adult sexual hormone pattern have been incomplete and inconsistent [1]. In this context, our aim was to analyse the relationship, if any, between the 2D/4D ratio and circulating testosterone levels in males undergoing prostate biopsy. PATIENTS AND METHODS We prospectively evaluated 204 patients submitted to TRUS prostate biopsy because of PSA elevation or abnormal DRE between February 2008 and February Screening was carried out with 5+5 core TRUS-guided prostate biopsy. As part of our clinical protocol, we determined the hormonal pattern (testosterone [automated electroimmunoassay method, Cobas, Roche Diagnostics, Burgess Hill, West Sussex, UK] and sexual hormone binding globulin [SHBG] [automated immunometric chemoluminescence method, Cobas]) in these patients. Patients were informed about the study and verbal consent was obtained. Free and bioavailable testosterone were calculated using the Vermeulen formula [15]. All biopsies and digit length determinations were done by one urologist (E.G.C.). A vernier calliper was used to measure digit length on the left hand. Although right hand ratios are slightly more related to hormonal profile [3], we chose to size non-dominant hand ratios as there is evidence that supports the use of the left hand in the determination of the 2D/4D ratio [4]. Hormonal pattern (testosterone and SHBG) was determined between 7.00 am and am. Patients who were receiving LHRH analogues or testosterone replacement therapy were excluded from the analysis. Following ISA, ISSAM, EAU, EAA and ASA recommendations (International Society of Andrology, International Society for the Study of the Aging Male, European Association of Urology, European Academy of Andrology, American Society of Andrology) [16], we considered testosterone cut-off points of 231 and 346 ng/dl (8 12 nmol/l) as a diagnosis of biochemical hypogonadism. We prospectively recorded age, body mass index (BMI) and medical history. Testosterone was analysed as a continuous variable and as a categorical variable using ISA, ISSAM, EAU, EAA and ASA recommendations [16]. The 2D/ RESULTS Table 1 shows the clinical and hormonal data of the 204 patients of the study. The mean age was 67 ± 7 years and the mean testosterone level was 413 ± 18 ng/dl (14.33 ± 0.62 nmol/ L). The percentages of patients with testosterone <231 ng/dl (8 nmol) and testosterone <346 ng/dl (12 nmol/l) were 6.1 and 30.6 respectively. Mean 2D/4D ratio was 0.98 ± A total of 129 patients (63%) had the fourth finger longer than the second (2D < 4D). In Table 2 univariate analysis between hormonal status (total, free and bioavailable testosterone and SHBG) and clinical variables is shown. Univariate analysis showed that low 2D/4D ratios correlated with higher levels of testosterone (B = ; β = 0.165, P = 0.045) and also with low prevalence of biochemical hypogonadism (testosterone <346 ng/dl, or 12 nmol/l). Linear regression between testosterone and 2D/4D is displayed in Fig. 1. The levels of free testosterone (B ; β 0.223, P = 0.008) and bioavailable testosterone (B ; β 0.221, P = 0.009) were related to the 2D/4D ratio in the univariate analysis, as shown in Table 2. The relationship between free testosterone levels and bioavailable testosterone levels and 2D/4D are displayed in Figs 2 and 3. No relationship was found between SHBG levels, height, tobacco or alcohol use and 2D/ 4D. The SHBG levels were related to age, weight and BMI

3 GARCÍA-CRUZ ET AL. TABLE 2 Main clinical variables and their relationship with testosterone levels in the univariate analysis Total testosterone P SHBG P Free testosterone P Bioavailable testosterone P Age B B B B β β β 0.35 β Weight B B B B β β β β Height B B B B β β 0.1 β β 0.90 BMI B B B B β β β β Diabetes mellitus 456 ± 178 ng/dl (15.82 ± 6.17 nmol/l) No 410 ± 172 ng/dl (14.22 ± 5.96 nmol/l) ± nmol/l No ± nmol/l ± 2.41 ng/dl No ± 2.56 ng/dl ± ng/dl No ± ng/dl Tobacco B B B B β β 0.41 β β Alcohol B B B B β β β β D/4D B B B B β β 0.69 β β The second, fourth, sixth and eighth columns show B and β values of the linear regression test between total testosterone, SHBG, free testosterone, bioavailable testosterone and independent variables The mean 2D/4D ratio in patients with testosterone <346 ng/dl (12 nmol/l) was lower than in patients with testosterone >346 ng/dl (12 nmol/l) (2D/4D 0.97 ± vs 0.99 ± 0.043, P = 0.05). Patients with 2D > 4D had a lower testosterone level and a higher rate of biochemical hypogonadism (testosterone <346 ng/dl, or 12 nmol/l) than patients with 2D < 4D (404 ± 158 vs 476 ± 185 ng/dl [14.02 ± 5.48 vs ± 6.42 nmol/l], P = 0.017; 41.7% vs 23%, P = 0.013). Graphical representations are given in Figs 4 and 5. Patients with biochemical TDS (testosterone <346 ng/dl, or 12 nmol/l) had a higher 2D/4D ratio than patients with testosterone >346 ng/dl (12 nmol/l) (0.993 ± in patients with testosterone <346 ng/dl [12 nmol/l] vs ± in patients with testosterone <346 ng/dl [12 nmol/l], P = 0.049). This relationship is displayed in Fig. 6. In patients with testosterone level <231 ng/dl (8 nmol/l) no statistical differences were found between testosterone and 2D/4D ratio (0.98 ± 0.04 in patients with testosterone Ratio D2:D Sq r lineal = Testosterone, ng/dl >231 ng/dl [8 nmol/l] vs 0.99 ± 0.05 in patients with testosterone <231 ng/dl [8 nmol/l]; P = 0.593). Finally, we aimed to analyse the ability of the 2D/4D ratio to predict biochemical hypogonadism (testosterone <346 ng/dl, or 12 nmol/l). In Fig. 7 we show the ROC curve for the 2D/4D ratio and the presence of testosterone <346 ng/ml, with an area under the curve of DISCUSSION FIG. 1. Relationship between testosterone levels and 2D/4D ratio. Linear regression showing the inverse relationship between testosterone levels and the 2D/4D ratio (B = ; β = 0.165; P = 0.045). The relationship between 2D/4D and foetal testosterone is clearly established. However, previous evidence of the correspondence between the 2D/4D ratio and adult testosterone values is erratic and controversial [1]. In our work, we suggest that the relationship between 2D and 4D is related to adult testosterone levels. To our knowledge this is the first study in the

4 SECOND TO FOURTH DIGIT RATIO, ADULT TESTOSTERONE LEVEL AND TESTOSTERONE DEFICIENCY FIG. 2. Relationship between free testosterone levels and 2D/4D ratio. Linear regression showing the inverse relationship between testosterone levels and the 2D/4D ratio (B = ; β = 0.223; P = 0.008). FIG. 3. Relationship between bioavailable testosterone levels and 2D/4D ratio. Linear regression showing the inverse relationship between testosterone levels and 2D/4D ratio (B = ; β = 0.221; P = 0.009). Ratio D2:D4 Ratio D2:D Sq r lineal = FIG. 4. Testosterone levels depending on 2D and 4D. The left box plot represents testosterone levels in patients with 2D < 4D, while the right box plot represents testosterone levels in patients with 2D > 4D (476 ± 185 ng/dl [16.51 ± 6.41 nmol/l] vs 404 ± 158 ng/dl [14.01 ± 5.48 nmol/l], P = 0.017). Testosterone, ng/dl D<4D Free Testosterone, ng/dl Sq r lineal = Bioavailable Testosterone, ng/dl D>4D literature in which the 2D/4D ratio is related to the presence of biochemical hypogonadism (testosterone <346 ng/dl, or 12 nmol/l). There are some studies in the literature regarding 2D/4D in relation to adult total testosterone levels. In a study conducted with patients recruited in a fertility clinic [3], the 2D/4D ratio was found to correlate with testosterone, luteinizing hormone, oestrogen and prolactin. That study, however, was conducted with a very specific population of 131 patients (69 males and 62 females) with fertility problems. In another study, Manning et al. [17] analysed 96 males (44 males undergoing elective surgical sperm retrieval [mean age 39 years] and 52 controls recruited through family doctors [mean age 56 years]). They found positive associations between luteinizing hormone, FSH and testis volume, but did not find an association between testosterone and 2D/4D. In the discussion, it was pointed out that a relation between the 2D/4D ratio and adult testosterone levels had only been found in biased study populations (fertility clinic males) but not in normative populations [17]. In a study with 370 young Danish males (range years old) Bang et al. [18] did not find a relationship between adult sex hormone levels and 2D/4D. Their study was conducted with a population of healthy males (medical examination before military service). The methodology of that study has been criticized since the blood samples were not collected following current standards and because 2D/4D measurements were carried out outlining their right hand. Hönekopp et al. [1] published a meta-analysis including three studies analysing total testosterone and 2D/4D, in which it was concluded that there was no evidence of any relation between the 2D/4D ratio and adult hormonal levels. It was pointed out that the main data to sustain the 2D/4D ratio and adult hormone link were from a highly biased study [3,19]. In this meta-analysis, the authors also added their data in a cohort of 102 males. Mean age in this cohort of males was 22.4 years. Hönekopp et al. [1] did not find any relationship between hormonal profile and 2D/4D relationship. In the present study, the 2D/4D ratio correlates with total, free and bioavailable testosterone levels. Moreover, the digit ratio is also related to biochemical hypogonadism (41% in males with 2D > 4D compared with 23% in males with 2D < 4D). Thus, our experience underlines the relationship between in utero androgen exposure and adult hormonal levels and the probability of suffering TDS. There are some remarkable differences between the present study and previous evidence. In previous publications the studied population was recruited from males in fertility centres [2,17] or young males [1,17,18]. The relationship between testosterone and fertility is obvious, but it is also remarkable that the majority of subfertile males are rather young people, clearly younger than in our study, where late-onset hypogonadism is more prevalent. In this regard, it is important to note that mean age in most of the studies was much

5 GARCÍA-CRUZ ET AL. lower than in our report, ranging from 19.5 [16] to 39 years [17]. In only one paper was the mean age 56 years [17]. Interestingly, studies with older populations obtained statistically significant relationships between the 2D/4D ratio and hormonal levels [3,17]. In the present study we aimed to examine a more representative population of the clinical setting, which is why our series includes mainly patients over 50 years old who could be assumed to have a higher probability of having low testosterone levels than a younger population [16]. In our opinion age is a key issue in the study design, since it is well established that testosterone decreases with age [15,19 21], and aging males are more prone to chronic illnesses [16]. On the other hand, the 2D/4D ratio has been shown to be stable through life [4 7]. Thus, 2D/4D may not be related to testosterone levels in young adult males simply because they have not yet developed TDS. It is possible that the relationship between the 2D/4D ratio and testosterone levels increases with time. Young males tend to have high testosterone levels and a low TDS rate. On the other hand, older males are more likely to suffer TDS as testosterone declines with decades. Then, if we are searching for a relationship between testosterone levels and 2D/4D, it might be that older males could be a more representative population of the relationship between 2D/4D and testosterone levels and/or TDS. Using the 2D/4D ratio, we were able to diagnose more than 60% of patients with biochemical hypogonadism (area under the curve [AUC] 0.603). We compared 2D/4D with other well-known risk factors for low testosterone like aging, obesity or presence of factors for metabolic syndrome. Surprisingly, a very simple examination was the most powerful clinical factor to predict hypogonadism (data not shown: aging AUC 0.54; BMI AUC 0.571; hypertension AUC 0.47; diabetes mellitus AUC 0.534; dyslipidaemia AUC 0.508). There are some limitations to our study. First, as commented above, our population is a highly biased sample of males. In this sense, the important bias in the study population might explain some surprising results. For example, the bias and the relatively small sample could be the reason why no relationship between testosterone and FIG. 5. Biochemical hypogonadism prevalence depending on the 2D/4D ratio (41.7% in 2D > 4D vs 23% in 2D < 4D patients, P = 0.013) D2<D4 23 D2>D4 % Biochemical Hypogonadism FIG. 6. 2D/4D ratio depending on hormonal status. Patients with testosterone <346 ng/dl (12 nmol/l) had higher 2D/4D ratio (right box plot) than those with testosterone >346 ng/dl (12 nmol/l) (left box plot) (0.993 ± vs ± 0.037, P = 0.049). Ratio 2D:4D T>346 T<346 TDS, Testosterone >346 ng/dl diabetes was found. Moreover, we think this bias in the sample explains the high 2D/4D ratio shown in the present study. Second, we do not have any period of follow-up. Thus, it is risky to extract long-term conclusions from an observational study. To boost the understanding of the relationship between 2D/4D, foetal and adult testosterone, a multicentre prospective trial should be planned in the general population. Furthermore, ours is a biased population since the relationship between the prostate and testosterone is well established [21 24]. Finally, the determination of the digit ratio involves many problems that make its clinical application complicated. Nevertheless, the link between digit ratio and testosterone levels and risk for TDS derived from our study encourages us to deepen the relationship between 2D/4D and testosterone. FIG. 7. ROC curve showing the 2D/4D ratio relationship and the presence of testosterone <346 ng/dl. Sensibility Specificity The 2D/4D ratio is related to adult testosterone levels and the presence of TDS. Patients with high 2D/4D ratios have lower testosterone levels and higher risk of suffering TDS. ACKNOWLEDGEMENTS The authors would like to acknowledge Dr Nizam Mamode from Guy s and St Thomas for reviewing the manuscript. CONFLICT OF INTEREST None declared. REFERENCES 1 Hönekopp J, Bartholdt L, Beier L, Liebert A. Second to fourth digit length ratio (2D:4D) and adult sex hormone levels: new data and a meta-analytic review. Psychoneuroendocrinology 2007; 32: McIntyre MH. The use of digit ratios as markers for perinatal androgen action. Reprod Biol Endocrinol 2006; 4: 10 3 Manning JT, Scutt D, Wilson J, Lewis- Jones DI. The ratio of 2nd to 4th digit length: a predictor of sperm numbers and concentrations of testosterone, luteinizing hormone and oestrogen. Hum Reprod 1998; 13: McIntyre MH, Ellison PT, Lieberman DE, Demerath E, Towne B. The development

6 SECOND TO FOURTH DIGIT RATIO, ADULT TESTOSTERONE LEVEL AND TESTOSTERONE DEFICIENCY of sex differences in digital formula from infancy in the Fels Longitudinal Study. Proc Biol Sci 2005; 272: Trivers R, Manning J, Jacobson A. A longitudinal study of digit ratio (2D:4D) and other finger ratios in Jamaican children. Horm Behav 2006; 49: Malas MA, Dogan S, Evcil EH, Desdicioglu K. Fetal development of the hand, digits and digit ratio (2D:4D). Early Hum Dev 2006; 82: Lutchmaya S, Baron-Cohen S, Raggatt P, Knickmeyer R, Manning JT. 2nd to 4th digit ratios, fetal testosterone and estradiol. Early Hum Dev 2004; 77: Ökten A, Kalyoncu M, Yari ş N. The ratio of second- and fourth-digit lengths and congenital adrenal hyperplasia due to 21- hydroxylase deficiency. Early Hum Dev 2002; 70: Brown WM, Hines M, Fane BA, Breedlove SM. Masculinized finger length patterns in human males and females with congenital adrenal hyperplasia. Horm Behav 2002; 42: Van Anders SM, Vernon PA, Wilbur CJ. Finger-length ratios show evidence of prenatal hormone-transfer between opposite-sex twins. Horm Behav 2006; 49: Manning JT, Bundred PE, Newton DJ, Flanagan BF. The second to fourth digit ratio and variation in the androgen receptor gene. Evol Hum Behav 2003; 24: Collaer ML, Hines M. Human behavioral sex differences: a role for gonadal hormones during early development? Psychol Bull 1995; 118: Cohen-Bendahan CC, van de Beek C, Berenbaum SA. Prenatal sex hormone effects on child and adult sex-typed behavior: methods and findings. Neurosci Biobehav Rev 2005; 29: Manning JT. Digit Ratio: A Pointer to Fertility, Behavior, and Health. New Brunswick: Rutgers University Press, Vermeulen A, Kaufman JM. Diagnosis of hypogonadism in the aging male. Aging Male 2002; 5: Wang C, Nieschlag E, Swerdloff R et al. Investigation, treatment, and monitoring of late-onset hypogonadism in males: ISA, ISSAM, EAU, EAA, and ASA recommendations. Eur Urol 2009; 55: Manning JT, Wood S, Vang E et al. Second to fourth digit ratio (2D:4D) and testosterone in men. Asian J Androl 2004; 6: Bang AK, Carlsen E, Holm M, Petersen JH, Skakkebaek NE, Jørgensen N. A study of finger lengths, semen quality and sex hormones in 360 young men from the general Danish population. Hum Reprod 2005; 20: Morley JE, Kaiser FE, Perry HM III et al. Longitudinal changes in testosterone, luteinizing hormone, and folliclestimulating hormone in healthy older men. Metabolism 1997; 46: Harman SM, Metter EJ, Blackman MR, Landis PK, Carter HB, Baltimore Longitudinal Study on Aging. Serum levels of insulin-like growth factor I (IGF-I), IGF-II, IGF-binding protein-3, and prostate-specific antigen as predictors of clinical prostate cancer. J Clin Endocrinol Metab 2000; 85: Leifke E, Gorenoi V, Wichers C, Von Zur Mühlen A, Von Büren E, Brabant G. Age-related changes of serum sex hormones, insulin-like growth factor-1 and sex-hormone binding globulin levels in men: cross-sectional data from a healthy male cohort. Clin Endocrinol (Oxf) 2000; 53: Huggins C, Hodges CV. Studies on prostatic cancer. I: the effect of castration, of estrogen, and of androgen injection on serum phosphatases in metastatic carcinoma of the prostate. Cancer Res 1941; 1: Huggins C, Stevens R, Hodges CV. Studies on prostatic cancer. II: the effects of castration on advanced carcinoma of the prostate gland. Arch Surg 1941; 43: Isbarn H, Pinthus JH, Marks LS et al. Testosterone and prostate cancer: revisiting old paradigms. Eur Urol 2009; 56: Correspondence: Eduardo García-Cruz, Hospital Clínic de Barcelona Urology, Villarroel 170, Barcelona, Spain. edu_garcia_cruz@yahoo.com; ecruz@clinic.ub.es Abbreviations: 2D, second finger (index) length; 4D, fourth finger (ring) length; SHBG, sexual hormone binding globulin; BMI, body mass index; TDS, testosterone deficiency syndrome; ROC, receiver operator characteristic