Correlations between digit ratio and infertility in Chinese men

The association and underlying mechanism of the digit ratio (2D:4D) in hypospadias

The second-to-fourth digit (2D:4D) ratio is thought to be associated with prenatal androgen exposure. However, the relationship between the 2D:4D ratio and hypospadias is poorly understood, and its molecular mechanism is not clear. In this study, by analyzing the hand digit length of 142 boys with hypospadias (23 distal, 68 middle, and 51 proximal) and 196 controls enrolled in Shanghai Children's Hospital (Shanghai, China) from December 2020 to December 2021, we found that the 2D:4D ratio was significantly increased in boys with hypospadias ( P < 0.001) and it was positively correlated with the severity of the hypospadias. This was further verified by the comparison of control mice and prenatal low testosterone mice model obtained by knocking out the risk gene (dynein axonemal heavy chain 8 [ DNAH8 ]) associated with hypospadias. Furthermore, the discrepancy was mainly caused by a shift in 4D. Proteomic characterization of a mouse model validated that low testosterone levels during pregnancy can impair the growth and development of 4D. Comprehensive mechanistic explorations revealed that during the androgen-sensitive window, the downregulation of the androgen receptor (AR) caused by low testosterone levels, as well as the suppressed expression of chondrocyte proliferation-related genes such as Wnt family member 5a ( Wnt5a ), Wnt5b , Smad family member 2 ( Smad2 ), and Smad3 ; mitochondrial function-related genes in cartilage such as AMP-activated protein kinase ( AMPK ) and nuclear respiratory factor 1 ( Nrf-1 ); and vascular development-related genes such as myosin light chain ( MLC ), notch receptor 3 ( Notch3 ), and sphingosine kinase 1 ( Sphk1 ), are responsible for the limitation of 4D growth, which results in a higher 2D:4D ratio in boys with hypospadias via decreased endochondral ossification. This study indicates that the ratio of 2D:4D is a risk marker of hypospadias and provides a potential molecular mechanism.

The ratio of 2nd to 4th digit length and reproductive function of infertile male patients

Purpose

To investigate the relationship between the ratio of index to ring finger lengths (2D:4D ratio), reflecting androgen exposure in utero, and reproductive function among men.

Methods

Male patients (N = 180) who consulted for fertility issues participated in the study. The palms of both hands were scanned, and the 2D:4D ratio was calculated. Data on semen volume, sperm concentration and total motility, total and motile sperm counts, and serum hormone concentrations were obtained. Spearman correlation coefficients between the 2D:4D ratio and hormone and semen quality parameters were calculated.

Results

The total sperm count was significantly negatively correlated with the 2D:4D ratio of the left hand (r = -0.154, p  = 0.039) but not with that of the right hand (r = -0.045, p  = 0.548). Testosterone showed weak negative correlations with the 2D:4D ratio in the left (r = -0.142, p  = 0.058) and right (r = - 0.149, p  = 0.046) hands. Follicle-stimulating hormone levels were negatively correlated with the 2D:4D ratios of the left (r = -0.173, p  = 0.020) and right (r = -0.164, p  = 0.027) hands. Other semen quality parameters or luteinizing hormone levels showed no significant correlation with the 2D:4D ratios.

Conclusions

No clear associations were observed between the 2D:4D ratios and reproductive function.

Adolescent Transgender Females Present Impaired Semen Quality That Is Suitable for Intracytoplasmic Sperm Injection Even Before Initiating Gender-Affirming Hormone Treatment

The present study aimed to determine the semen quality and cryopreservation outcomes among adolescent transgender females at the time of fertility preservation (FP) before initiating gender-affirming hormone (GAH) treatment. This retrospective cohort study included 26 adolescent transgender females who underwent FP in our Fertility Institute between 06/2013 and 10/2020. Pre-freezing semen parameters were compared to WHO 2010 reference values. Post-thaw semen parameters were used to determine the adequate assisted reproductive technology (ART). A multivariate linear regression analysis was performed to assess the impact of medical and lifestyle factors on semen quality. The mean age at which adolescent transgender females underwent FP was 16.2 ± 1.38 years. The median values of all semen parameters in our study group were significantly lower compared to the WHO data, including volume (1.46 mL vs 3.2 mL, respectively, P = 0.001 ), sperm concentration (28 × 10⁶/mL vs 64 × 10⁶/mL, P < 0.001), total sperm number (28.2 × 10⁶ vs 196 × 10⁶, P < 0.001), total motility (51.6% vs 62%, P < 0.001), and normal morphology (2% vs 14%, P < 0.001). The frequency of semen abnormalities was teratozoospermia 72%, hypospermia 52%, oligozoospermia 28%, and azoospermia 4%. The median post-thaw total motile count was 0.17 × 10⁶/vial, and the quality was adequate only for ICSI in 87.7% of the thawed semen samples. No correlation was found between selected medical and lifestyle factors and poor semen parameters. Semen quality is strongly reduced among adolescent transgender females before hormone therapy and their stored sperm samples are suitable for intracytoplasmic sperm injection (ICSI) rather than conventional IVF/intrauterine insemination (IUI).

Decreased digit ratio (2D:4D) and gastric cancer in Chinese men

BACKGROUND

The development of finger length is influenced by the level of hormones during pregnancy in the womb. The relative length of 2nd to 4th digit (2D:4D) is considered as a putative marker for prenatal hormone exposure and may represent an individual susceptibility to certain diseases, particularly those hormone-related cancers (e.g., gastric cancer).

AIMS

The aim of this study is to investigate whether there is a possible relationship between 2D:4D ratio and gastric cancer (GCA) in Chinese men.

METHODS

94 male patients with GCA and 91 controls were chosen to participate in this study. Photographs of both hands were collected and then the lengths of second and fourth digits of both hands were measured. Left hand, right hand, mean hand, and right minus left hand (∆R-L) 2D:4D ratios were analyzed and compared.

RESULTS

In GCA group, 2D:4D ratios were significantly lower (right hand: p<0.01; left hand, mean hand: p<0.001) than controls. No association was observed between 2D:4D ratio and tumor staging (neither in tumor size (T) nor in lymph node involvement (N) or distant metastases (M)). There was also no correlation between 2D:4D ratio and age of onset.

CONCLUSIONS

Decreased 2D:4D ratio may be an indicator for forecasting the susceptibility to develop GCA.

Digit ratio (2D:4D) in a Chinese population with schizophrenia

BACKGROUND

Prenatal gonadal hormones may play a major role in pathogenesis of schizophrenia. It has been reported that second to fourth digit ratio (2D:4D) was influenced by the levels of exposure to prenatal testosterone and estrogen. So, 2D:4D may help to predict the disease susceptibility to schizophrenia.

AIMS

The aim of this study was to investigate the relationship between the digit ratio (2D:4D) and schizophrenia in Chinese population.

METHODS

We recruited 178 schizophrenics (males: 76; females: 102) and 365 controls (males: 218; females: 147) in this study. Photocopies of both hands were collected and left hand, right hand, mean hand and left minus right hand (DL-R) 2D:4D were analyzed.

RESULTS

The right and mean hand 2D:4D ratios were significantly higher in schizophrenics compared to that of controls in both males and females. The left hand 2D:4D ratio in female schizophrenics was also significantly higher than in controls. Compared to controls, the DL-R 2D:4D in male schizophrenics was obviously higher. There was a weakly (but not significantly) negative correlation between the mean hand 2D:4D ratio and the age of onset.

CONCLUSIONS

The 2D:4D ratio may correlate with the schizophrenia in Chinese population, and it may be an indicator of schizophrenia.

Does human ejaculate quality relate to phenotypic traits?

A given man's phenotype embodies cues of his ancestral ability to effectively defend himself and his kin from harm, to survive adverse conditions, and to acquire status and mating opportunities. In this review, we explore the hypothesis that a man's phenotype also embodies cues to fertility or the probability that an ejaculate will fertilize ova. Female mate choice depends on the ability to discern the quality of a male reproductive partner through his phenotype, and male fertility may be among the traits that females have evolved to detect. A female who selects as mates males that deliver higher quality ejaculates will, on average, be more fecund than her competitors. Data on several non-human species demonstrate correlations between ejaculate quality and secondary sexual characteristics that inform female mate choice, suggesting that females may select mates in part on the basis of fertility. While the non-human literature on this topic has advanced, the human literature remains limited in scope and there is no clear consensus on appropriate methodologies or theoretical positions. We provide a comprehensive review and meta-analysis of this literature, and conclude by proposing solutions to the many issues that impede progress in the field. In the process, we hope to encourage interest and insight from investigators in other areas of human mating and reproductive biology. Am. J. Hum. Biol. 28:318-329, 2016. © 2015 Wiley Periodicals, Inc.

Second to fourth digit ratio (2D:4D) and coronary heart disease

INTRODUCTION

Sex steroid exposure during human development may influence disease susceptibility. Second to fourth digit ratio (2D:4D) is thought to be a putative biomarker for prenatal hormone level during foetal life. Recently there has been a great deal of interest in 2D:4D and risk of disease in adulthood.

METHODS

We explored the relationship between 2D:4D ratio and coronary heart disease. Photocopies of the two hands of 310 males (controls: 155; patients: 155) were collected at Yin chuan city, in the Ningxia province of China. Left hand, right hand, mean hand and right minus left 2D:4D (Dr-l) were analysed.

RESULTS

The mean values of 2D:4D ratio in patients were higher than those of CSIN controls. The patients showed significantly higher 2D:4D (left hand: P < 0.01; right hand, mean hand: P < 0.05) than controls. In patients, 2D:4D (especially left hand 2D:4D) were inversely associated with age at diagnosis (left hand: P < 0.001; right hand, mean hand: P < 0.05). No association between Dr-l and age or age at presentation of disease was observed in the groups.

CONCLUSION

2D:4D may correlate particularly with risk of coronary heart disease in Chinese men.

Penile length, digit length, and anogenital distance according to birth weight in newborn male infants

PURPOSE

Anogential distance (AGD) and the 2:4 digit length ratio appear to provide a reliable guide to fetal androgen exposure. We intended to investigate the current status of penile size and the relationship between penile length and AGD or digit length according to birth weight in Korean newborn infants.

MATERIALS AND METHODS

Between May 2013 and February 2014, among a total of 78 newborn male infants, 55 infants were prospectively included in this study. Newborn male infants with a gestational age of 38 to 42 weeks and birth weight>2.5 kg were assigned to the NW group (n=24) and those with a gestational age<38 weeks and birth weight<2.5 kg were assigned to the LW group (n=31). Penile size and other variables were compared between the two groups.

RESULTS

Stretched penile length of the NW group was 3.3 ± 0.2 cm, which did not differ significantly from that reported in 1987. All parameters including height, weight, penile length, testicular size, AGD, and digit length were significantly lower in the LW group than in the NW group. However, there were no significant differences in AGD ratio or 2:4 digit length ratio between the two groups.

CONCLUSIONS

The penile length of newborn infants has not changed over the last quarter century in Korea. With normal penile appearance, the AGD ratio and 2:4 digit length ratio are consistent irrespective of birth weight, whereas AGD, digit length, and penile length are significantly smaller in newborns with low birth weight.

Stability of proposed biomarkers of prenatal androgen exposure over the menstrual cycle

The prenatal hormonal milieu is widely believed to shape health later in life; however, there are considerable methodological challenges associated with measuring the in utero hormonal environment. Two potential biomarkers of prenatal androgen exposure that can be measured postnatally have been proposed: anogenital distance (AGD) and the ratio of the second to fourth digits of the hand (2D:4D). Although both measures are widely used research tools, their use in adult women may be complicated by the dramatic fluctuations in reproductive hormones across the menstrual cycle. To determine whether there is cyclical variation in these biomarkers, we conducted a longitudinal study of 12 naturally cycling, nulliparous adult women. Trained examiners assessed two measures of AGD [anus to clitoris (AGD-AC) and anus to fourchette (AGD-AF)] and 2D:4D in both hands for the duration of three menstrual cycles, taking measurements during the follicular, peri-ovulatory and luteal phases of each cycle. Despite the small sample size, longer (more masculine) AGD was associated with lower (more masculine) digit ratios, as predicted by the literature. Using multi-level linear regression models, we found that AGD and 2D:4D measurements did not differ significantly across cycle phases. AGD-AF and digit ratios in both hands were associated with age at menarche, suggesting a possible common developmental trajectory. These results demonstrate that AGD and 2D:4D are stable across the menstrual cycle. In addition, research is needed to determine how reliably these measures reflect the in utero hormonal milieu.

Second to fourth digit ratio, handedness and testicular germ cell tumors

BACKGROUND

Research on early life exposures and testicular germ cell tumors (TGCT) risk has focused on a possible perinatal etiology with a well-known hypothesis suggesting that hormonal involvement during fetal life is associated with risk. Second-to-fourth digit ratio (2D:4D) and left-hand dominance have been proposed as markers of prenatal hormone exposure.

AIM

To evaluate associations between 2D:4D digit ratio, right minus left 2D:4D (ΔR-L), and left-hand dominance and TGCT in the U.S. Servicemen's Testicular Tumor Environmental and Endocrine Determinants Study.

METHODS

A total of 246 TGCT cases and 236 non-testicular cancer controls participated in the current study, and completed a self-administered questionnaire. Associations between digit ratio, hand dominance and TGCT were estimated using unconditional logistic regression adjusting for identified covariates.

RESULTS

Right 2D:4D was not associated with TGCT [odds ratio (OR) for a one-standard deviation (SD) increase in right-hand 2D:4D: 1.12, 95% confidence interval (CI): 0.93-1.34]. The results were consistent when evaluating the association based on the left hand. The difference between right and left-hand 2D:4D was also not associated with TGCT risk [OR for a one-SD increase in ΔR-L: 1.03, 95% CI: 0.87-1.23]. Compared to men who reported right-hand dominance, ambidexterity [OR (95% CI)=0.65 (0.30-1.41)] and left-hand dominance [OR (95% CI)=0.79 (0.44-1.44)] were not associated with risk.

CONCLUSIONS

These results do not support the hypothesis that prenatal hormonal imbalance is associated with TGCT risk. Given the limited sample size, further evaluation of the relationship between TGCT and prenatal hormonal factors using digit ratio, ΔR-L, or left-hand dominance and larger sample size are warranted.

Clinical review: Anogenital distance or digit length ratio as measures of fetal androgen exposure: relationship to male reproductive development and its disorders

CONTEXT

Male reproductive disorders evident at birth or in young adulthood are remarkably common. They are hypothesized to comprise a testicular dysgenesis syndrome (TDS), with a fetal origin involving mild androgen deficiency.

EVIDENCE ACQUISITION

Testing this hypothesis requires "seeing back in time." Two ways have been proposed: measurement of anogenital distance (AGD), or measurement of the 2:4 digit length ratio. This review assesses the evidence that they reflect fetal androgen exposure and might be used to provide insight into the origin of TDS disorders.

EVIDENCE SYNTHESIS

Supporting evidence for AGD derives from rat experimental studies that identified a fetal masculinization programming window, within which androgen action determines adult reproductive organ size, TDS disorders, and AGD. In humans, AGD is positively correlated to testis size, sperm count/fertility, penis length, and T levels, consistent with rat experimental data. The 2:4 digit ratio also shows associations with these parameters, but inconsistently between studies; evidence that the 2:4 digit ratio accurately reflects fetal androgen exposure is also equivocal.

CONCLUSIONS

AGD appears to provide a reliable guide to fetal androgen exposure, although available data are limited. The next steps are to: standardize AGD measurement; obtain age-specific population data; and use AGD to evaluate the importance of fetal androgens in determining reproductive disorders and variation in testis/penis size and sperm count in the normal population. These studies should identify what, if any, clinical applications of AGD measurement are feasible--for example, its ability to predict adult-onset reproductive function and disorders.