Genome-wide association study identifies nine novel loci for 2D:4D finger ratio, a putative retrospective biomarker of testosterone exposure in utero

Variations in gender identity and sexual orientation of university students

Background

Previous studies have shown that a small percentage of people in the general population have atypical gender identity and/or sexual orientation.

Aim

This study aimed to explore variations in gender identity and sexual orientation in university students and determine genetic factors associated with these variations.

Methods

Deviations from complete gender congruence and exclusive heterosexual orientation in 736 Japanese university students were quantitatively assessed with self-assessment questionnaires. Next, we conducted genetic tests for 80 participants who showed relatively low gender identity scores and/or atypical sexual orientation. These genetic tests consisted of repeat number analysis of the androgen receptor gene (AR) and a SKAT-O: an optimal unified sequence kernel association test, which is an exome-based rare variant association study. The results of the genetic tests were compared with the Japanese reference data and the results of our 637 control samples.

Outcomes

We calculated the gender identity and sexual orientation scores of all participants and analyzed the molecular data of 80 selected participants.

Results

The gender identity scores of 736 participants were broadly distributed: only ~15% of natal males and ~5% of natal females had the maximum score that corresponds to complete gender congruence. The sexual orientation scores also varied: ~80% of natal males and ~60% of natal females showed exclusive heterosexual orientation. We found no association between gender characteristics and AR repeat numbers. The SKAT-O showed that rare damaging variants of TDRP and 3 other genes were more common in the 80 participants than in the control group.

Clinical Implications

Our data support the view that gender is a phenotypic continuum rather than a binary trait.

Strength and Limitations

This study quantitatively assessed the gender characteristics of a large cohort of university students. Moreover, we conducted systematic screening for genetic factors associated with gender variations. The weaknesses of the study were the limited analytic power of the questionnaires, the relatively small sample for molecular analyses, and incomplete clinical information and relatively advanced ages of the control group.

Conclusion

This study revealed significant variations in gender identity and sexual orientation in university students, which may be partly associated with variants in TDRP or other genes.

In support of 2D:4D: More data exploring its conflicting results on handedness, sexual orientation and sex differences

In the last few years, several studies have questioned the value of the second-to-fourth digit ratio (2D:4D) as a measure of exposure to sex hormones before birth. Controversy has also extended to the 2D:4D association with individual features previously related to this exposure such as handedness and sexual orientation. Given that it has been argued that sex differences in 2D:4D could be a consequence of body-size differences, we have tested in a large sample the allometric relationship between finger lengths and body size. Our results show that the association is either allometric or isometric, depending on the analyses performed. In any case, the deviation from isometry is not large enough to explain the typically observed sex difference in this trait. We have also tested the association between sexual orientation and 2D:4D, finding a relationship between 2D:4D and sexual orientation in men but not in women. We attribute this discordance with previously published meta-analysis to differences in genetic background, a variable that has gained relevance in recent years in studies involving 2D:4D. Finally, we did not find any relationship between 2D:4D and handedness, evaluated through self-reported preference and hand performance. Our main conclusion is that 2D:4D shows differences between sexes beyond their disparity in body size. In our opinion, 2D:4D can be used cautiously as an indicator of intrauterine exposure to sex hormones taking into account some considerations, such as analysing a very large sample and taking careful measurements of the ethnicity of the sample.

Born to be wild: Second-to-fourth digit length ratio and risk preferences

The second-to-fourth digit length ratio of an individual's hand (digit ratio) is a putative biomarker for prenatal exposure to testosterone. We examine the hypothesized negative association between the digit ratio and the preference for risk taking within a large U.S. population survey. Our statistical framework provides a cardinal proxy for the true digit ratio based on ordinal digit ratio measurements and accounts for measurement error under the assumptions of Gaussianity and time-invariant true digit ratios. Our empirical findings support the hypothesis and suggest a meaningful biological basis for risk preferences.

A genome-wide association study with tissue transcriptomics identifies genetic drivers for classic bladder exstrophy

Classic bladder exstrophy represents the most severe end of all human congenital anomalies of the kidney and urinary tract and is associated with bladder cancer susceptibility. Previous genetic studies identified one locus to be involved in classic bladder exstrophy, but were limited to a restrict number of cohort. Here we show the largest classic bladder exstrophy genome-wide association analysis to date where we identify eight genome-wide significant loci, seven of which are novel. In these regions reside ten coding and four non-coding genes. Among the coding genes is EFNA1, strongly expressed in mouse embryonic genital tubercle, urethra, and primitive bladder. Re-sequence of EFNA1 in the investigated classic bladder exstrophy cohort of our study displays an enrichment of rare protein altering variants. We show that all coding genes are expressed and/or significantly regulated in both mouse and human embryonic developmental bladder stages. Furthermore, nine of the coding genes residing in the regions of genome-wide significance are differentially expressed in bladder cancers. Our data suggest genetic drivers for classic bladder exstrophy, as well as a possible role for these drivers to relevant bladder cancer susceptibility.

A genome-wide association study on classic bladder exstrophy reveals eight genome-wide significant loci, most of which contained genes expressed in embryonic developmental bladder stages.

Giving science the finger-is the second-to-fourth digit ratio (2D:4D) a biomarker of good luck? A cross sectional study

OBJECTIVES

To explore whether random chance, weak research methodology, or inappropriate reporting can lead to claims of statistically significant (yet, biologically meaningless) biomarker associations, using as a model the relation between a common surrogate of prenatal testosterone exposure, second-to-fourth digit ratio (2D:4D), and a random indicator of good luck.

DESIGN

Cross sectional study.

SETTING

University sports performance laboratory in the United States. Data were collected from May 2015 to February 2017.

PARTICIPANTS

176 adults (74 women, 102 men), including university students, faculty, and staff with no history of injuries, disease, or medical conditions that would affect digit length.

MAIN OUTCOME MEASURES

2D:4D, body composition parameters potentially influenced by androgens (bone mineral content, bone mineral density, body fat percentage), and good luck (using poker hands from randomly selected playing cards as a surrogate).

RESULTS

2D:4D significantly correlated with select body composition parameters (Spearman's r _s range -0.26 to 0.23; P<0.05), but the correlations varied by sex, participant hand measured, and the method of measuring 2D:4D (by photocopy or radiography). However, the strongest correlation observed was between right hand 2D:4D in men measured by radiograph and poker hand rank (r _s=0.28, P=0.004).

CONCLUSIONS

Greater prenatal exposure to testosterone, as estimated by a lower 2D:4D, significantly increases good luck in adulthood, and also modulates body composition (albeit to a lesser degree). While these findings are consistent with a wealth of research reporting that 2D:4D is related to many seemingly disparate outcomes, they are not meant to provide confirmatory evidence that 2D:4D is a universal biomarker of nearly everything. Instead, the associations between 2D:4D and good luck are simply due to chance, and provide a "handy" example of the reproducibility crisis within medical and scientific research. Biologically sound hypotheses, pre-registration of trials, strong methodological and statistical analyses, transparent reporting of negative results, and unbiased interpretation of data are all necessary for biomarker studies and other areas of clinical research.

A genome-wide association study of interhemispheric theta EEG coherence: implications for neural connectivity and alcohol use behavior

Aberrant connectivity of large-scale brain networks has been observed among individuals with alcohol use disorders (AUDs) as well as in those at risk, suggesting deficits in neural communication between brain regions in the liability to develop AUD. Electroencephalographical (EEG) coherence, which measures the degree of synchrony between brain regions, may be a useful measure of connectivity patterns in neural networks for studying the genetics of AUD. In 8810 individuals (6644 of European and 2166 of African ancestry) from the Collaborative Study on the Genetics of Alcoholism (COGA), we performed a Multi-Trait Analyses of genome-wide association studies (MTAG) on parietal resting-state theta (3-7 Hz) EEG coherence, which previously have been associated with AUD. We also examined developmental effects of GWAS findings on trajectories of neural connectivity in a longitudinal subsample of 2316 adolescent/young adult offspring from COGA families (ages 12-30) and examined the functional and clinical significance of GWAS variants. Six correlated single nucleotide polymorphisms located in a brain-expressed lincRNA (ENSG00000266213) on chromosome 18q23 were associated with posterior interhemispheric low theta EEG coherence (3-5 Hz). These same variants were also associated with alcohol use behavior and posterior corpus callosum volume, both in a subset of COGA and in the UK Biobank. Analyses in the subsample of COGA offspring indicated that the association of rs12954372 with low theta EEG coherence occurred only in females, most prominently between ages 25 and 30 (p < 2 × 10-9). Converging data provide support for the role of genetic variants on chromosome 18q23 in regulating neural connectivity and alcohol use behavior, potentially via dysregulated myelination. While findings were less robust, genome-wide associations were also observed with rs151174000 and parieto-frontal low theta coherence, rs14429078 and parieto-occipital interhemispheric high theta coherence, and rs116445911 with centro-parietal low theta coherence. These novel genetic findings highlight the utility of the endophenotype approach in enhancing our understanding of mechanisms underlying addiction susceptibility.

Associations Between Cytochrome P450 (CYP) Gene Single-Nucleotide Polymorphisms and Second-to-Fourth Digit Ratio in Chinese University Students

BACKGROUND Cytochrome P450 (CYP) genes are necessary for the production or metabolism of fetal sex hormones during pregnancy. The second-to-fourth digit ratio (2D: 4D) is formed in the early stage of human fetal development and considered an indicator reflecting prenatal sex steroids levels. We explored the association between 2D: 4D and single-nucleotide polymorphisms (SNPs) of CYP. MATERIAL AND METHODS Correlation analysis between 2D: 4D and 8 SNPs, rs2687133 (CPY3A7), rs7173655 (CYP11A1), rs1004467, rs17115149, and rs2486758 (CYP17A1), and rs4646, rs2255192, rs4275794 (CYP19A1), was performed using data from 426 female and 412 male Chinese university students. SNP genotyping was conducted using PCR. Digit lengths were photographed and measured by image processing software. RESULTS rs2486758 (CYP17A1) correlated with left hand 2D: 4D in men (P=0.026), and rs1004467 (CYP17A1) correlated with right hand 2D: 4D in men (P=0.008) and the whole population (P=0.032). In men, allele G rs1004467 decreased right hand 2D: 4D, while allele C of rs2486758 increased left hand 2D: 4D. In women, left hand 2D: 4D was higher in genotypes with allele A of SNP rs4646 (CYP19A1) under the dominant genetic model; female DR-L was higher in genotypes with allele T of rs17115149 (CYP11A1). SNPs rs2687133 (CYP3A7) and rs1004467 (CYP17A1) were significantly correlated with right hand 2D: 4D (P=0.0107). CONCLUSIONS SNPs rs1004467 and rs2486758 of CYP17A1 are significant in the relationship between 2D: 4D and CYP gene polymorphisms under different conditions. SNP interactions between CYP genes probably impact 2D: 4D. The correlation between 2D: 4D and some sex hormone-related diseases may be due to the effect of CYP variants on the 2 phenotypes.

The evolutionary biology of endometriosis

We provide the first analysis and synthesis of the evolutionary and mechanistic bases for risk of endometriosis in humans, structured around Niko Tinbergen's four questions about phenotypes: phylogenetic history, development, mechanism and adaptive significance. Endometriosis, which is characterized by the proliferation of endometrial tissue outside of the uterus, has its phylogenetic roots in the evolution of three causally linked traits: (1) highly invasive placentation, (2) spontaneous rather than implantation-driven endometrial decidualization and (3) frequent extensive estrogen-driven endometrial proliferation and inflammation, followed by heavy menstrual bleeding. Endometriosis is potentiated by these traits and appears to be driven, proximately, by relatively low levels of prenatal and postnatal testosterone. Testosterone affects the developing hypothalamic-pituitary-ovarian (HPO) axis, and at low levels, it can result in an altered trajectory of reproductive and physiological phenotypes that in extreme cases can mediate the symptoms of endometriosis. Polycystic ovary syndrome, by contrast, is known from previous work to be caused primarily by high prenatal and postnatal testosterone, and it demonstrates a set of phenotypes opposite to those found in endometriosis. The hypothesis that endometriosis risk is driven by low prenatal testosterone, and involves extreme expression of some reproductive phenotypes, is supported by a suite of evidence from genetics, development, endocrinology, morphology and life history. The hypothesis also provides insights into why these two diametric, fitness-reducing disorders are maintained at such high frequencies in human populations. Finally, the hypotheses described and evaluated here lead to numerous testable predictions and have direct implications for the treatment and study of endometriosis. Lay summary: Endometriosis is caused by endometrial tissue outside of the uterus. We explain why and how humans are vulnerable to this disease, and new perspectives on understanding and treating it. Endometriosis shows evidence of being caused in part by relatively low testosterone during fetal development, that 'programs' female reproductive development. By contrast, polycystic ovary syndrome is associated with relatively high testosterone in prenatal development. These two disorders can thus be seen as 'opposite' to one another in their major causes and correlates. Important new insights regarding diagnosis, study and treatment of endometriosis follow from these considerations.

Emotional stability is related to 2D:4D and social desirability in women: Possible implications on subjective well-being and psychopathology

Emotional stability-Neuroticism is a complex construct influenced by genetics and environmental factors. Women tend to exhibit higher neuroticism scores than men, which may be associated with an increased risk of suffering from some common mental conditions. Some authors have pointed out the influence of sex hormones, since they induce sexual differentiation of the brain that can lead to sex-specific behaviors. 2D:4D digit ratio is commonly used as a marker of prenatal sex hormones. In this study we analyzed whether there was an association between 2D:4D and personality measured through the BFQ in a homogeneous sample of 101 young women college students. We found a positive association between 2D:4D and emotional stability, as well as with its subdimensions emotion control and impulse control. This association could be quadratic and nonlinear. However, no association was found with the other four dimensions. We also measured anxiety, depression and global life satisfaction, variables related to neuroticism. We observed that emotional stability is positively associated to social desirability and global life satisfaction, and negatively related to anxiety and depression. On the other hand, we did not find any association between 2D:4D and anxiety, depression, and global life satisfaction. These results can be linked to other aspects such as subjective well-being and psychopathological symptoms. This study may help to better understand how these constructs are related and could lead to future projects to elucidated how these variables influence personality.

Digit ratio (2D:4D) and handedness: A meta-analysis of the available literature

The Geschwind-Behan-Galaburda and sexual differentiation models predict an association between elevated foetal androgen exposure and left-handedness whereas the callosal hypothesis predicts the opposite. We present a meta-analysis of correlations between handedness and digit ratio (2D:4D), a putative marker of prenatal testosterone. Left-handedness predicted low (male-typical) right-hand digit ratio (R2D:4D), high (female-typical) left-hand digit ratio (L2D:4D), and low R2D:4D-L2D:4D directional asymmetry (D_[R-L]). Effect sizes were extremely small and not moderated by sex or method of measuring handedness or 2D:4D. The same general pattern was observed after excluding the very large study (110,329 males, 90,412 females) of Manning and Peters ([2009]. Digit ratio (2D:4D) and hand preference for writing in the BBC Internet Study. Laterality: Asymmetries of Body, Brain and Cognition, 14(5), 528-540. doi:10.1080/13576500802637872); however, no significant effects for R2D:4D were observed once these samples were removed. The results do not confirm any theory linking prenatal androgens with handedness, so we speculate they instead reflect the mechanical action of writing causing subtle changes in the musculature and/or fat pads of the fingers. Gripping a pen/pencil might cause an increase in 2D relative to 4D (and/or decrease in 4D relative to 2D) resulting in higher ratios on the writing-hand; furthermore, this could differ between left- and right-handers due to writing in the left-to-right direction (as in English) having asymmetrical effects depending on which hand is used.

Digit ratio (2D:4D) and transgender identity: new original data and a meta-analysis

Previously reported associations between second-to-fourth digit length ratio (2D:4D), a proxy for prenatal androgen load, and transgender identity have been inconsistent. The objectives of the present study were to provide additional original data and an updated meta-analysis concerning this association. In a study of 464 participants, we compared the 2D:4D of transgender individuals with age- and sex-matched controls. Patients were recruited at a specialized psychiatrist's medical office, whereas controls were hired via flyers, advertisements, and as convenience sample. A random-effects meta-analysis of the literature (17 samples, n = 3674) also quantifies the overall magnitude of the difference in 2D:4D between transgender individuals and controls. In our study providing new original data, we found a significantly higher (i.e. feminized) left-hand 2D:4D in the male-to-female transgender (MtF) identity [mean age: 32.3 (18; 61)] than in the male control group [mean age: 34.5 (18; 65)] with a Cohen's d = 0.271. Concordantly, the meta-analytic results suggest a significant difference in 2D:4D among MtF individuals compared to male controls [g = 0.153; 95% CI (0.063; 0.243)], which was even more pronounced when individuals had been diagnosed by a clinician instead of self-identified as transgender [g = 0.193; 95% CI (0.086; 0.300)]. In both studies, no significant results were revealed for female-to-male transgender individuals [mean age: 26.1 (18; 53)] versus female controls [mean age: 27.2 (18; 55)]. This original investigation and the updated meta-analysis clarify the association between transgender identity and 2D:4D indicating the influence of prenatal androgen on the development of gender identity in subjects born as males.

Usefulness of measurement of proximal phalanx length by using ultrasonography in newborn infants

The purpose of this study was to compare digit lengths and proximal phalanx lengths in newborn infants by using ultrasonography (USG) and to examine sex differences between the ratio of the second digit (2D) and fourth digit (4D) of digit length and that of proximal phalanx length and the associations of digit length and proximal phalanx length with birth weight and birth height. Sixty newborn infants (28 males and 32 females) were recruited. Digit lengths were measured by using a transparent ruler and proximal phalanx lengths were measured by using USG. There were significant correlations between digit length and proximal phalanx length in the left and right hands. There was no significant correlation between 2D:4D ratios of digit lengths and 2D:4D ratios of proximal phalanx lengths measured by using USG. In males, birth height was significantly associated with right fourth proximal phalanx length and with left second and fourth proximal phalanx lengths. Birth weight was significantly associated with proximal phalanx length in males. Proximal phalanx length measured by using USG was significantly associated with digit length in newborn infants. Hormonal exposure before birth may be involved in the associations of proximal phalanx length with birth weight and height in males.Impact statementWhat is already known on this subject? The ratio of the second digit (2D) and fourth digit (4D) has been used postnatally to provide a retrospective indication of the foetal hormonal environment. Digit lengths have been measured by using a direct method, photocopies, digital scans and radiographs, but the results of a study on measurement of digit lengths by using ultrasonography (USG) have not been reported.What do the results of this study add? Proximal phalanx length measured by using USG was significantly associated with digit length in newborn infants. In males, birth height was significantly associated with right fourth proximal phalanx length and with left second and fourth proximal phalanx lengths. Birth weight was significantly associated with proximal phalanx length in males.What are the implications of these findings for clinical practice and/or further research? Measurement of proximal phalanx length by using USG may be useful for a study on gender differences in foetal development and the foetal hormonal environment. Hormonal exposure before birth may be involved in the associations of proximal phalanx length with birth weight and height in males.

Second-to-fourth digit ratio and facial shape in Buryats of Southern Siberia

BACKGROUND

The 2nd-to-4th digit ratio (2D:4D) is a putative predictor of a prenatal exposure to sex hormones. 2D:4D is sexually dimorphic (males < females). Studies, linking digit ratio and full facial shapes among Europeans, show that a low 2D:4D is associated with a set of male-specific facial features. Buryats - Mongolian people from Southern Siberia - demonstrate a different pattern of facial sexual dimorphism than Europeans (narrower and more vertically elongated faces in men as opposed to women).

AIM

The aim of the present study was to investigate the association between facial shape and the 2D:4D in comparison to the pattern of facial sexual dimorphism in Buryats.

SUBJECTS

Buryats: 88 men and 80 women aged 20 ± 2 years.

OUTCOME MEASURES

To assess relationship between facial shape and 2D:4D we used a geometric morphometric approach based on standardized full-face frontal photographs and direct measurements of the digit lengths among right-handed individuals.

RESULTS

The results revealed that 2D:4D was associated with facial morphology in Buryat men, and to a lesser extent in women. Narrower faces, elongated in the vertical direction, and a narrower lower facial outline, were characteristic of Buryat men with low 2D:4D ratios, which corresponded to the male-like facial shapes in Buryats.

CONCLUSIONS

In Europeans, such facial features were reported for men with a high 2D:4D, which corresponded more to female-like European facial shapes. Hence, our results show that sex-specific morphogenesis in humans is multidirectional, and that digit ratio is capable of predicting sex-specific facial traits even in populations with differing sexually-dimorphic morphology.

Digit identity matters: origin and evolution of sexual dimorphism in the digit lengths of tropidurid lizards

Sexual dimorphism in digit lengths reflects phenotypic evolution mediated by developmental steroids. Differences in the identity of the sexually-dimorphic digit may evolve if the concentrations of sex-steroid receptors in the digit are easily modified and the initial changes have low impact on fitness. Accordingly, sexual dimorphism in digit lengths might initially originate under neutral selective regimes, being subsequently co-opted by embryonic hormonal effects on sensitive traits that are more likely to be targeted by selection. Correlated variation among sexually-dimorphic traits might therefore reflect pleiotropic hormonal modulation during development. Moreover, the identity and trend of the sexually-dimorphic digit might be evolutionarily labile even among closely-related species. We evaluated this model by assessing the identity of sexually-dimorphic digits among 11 Tropiduridae lizard species and inferring evolutionary patterns of sexual dimorphism. Assuming that digit lengths can be used as a proxy for hormonal modulation of steroid-sensitive traits during development, we tested for evolutionary associations among sexual dimorphism of digit lengths, body size and other traits that may be direct targets of sexual selection in the Tropiduridae. Sexual dimorphism in digit lengths is evolutionarily labile in the Tropiduridae, and diversity, instead of conservatism, seems to rule developmental mechanisms underlying the evolution of sexual dimorphism in digit ratios.

Depression, neuroticism and 2D:4D ratio: evidence from a large, representative sample

A body of literature reports higher rates of depression and neuroticism in female samples compared to male samples. Numerous studies have investigated the role of prenatal sex hormone exposure in this sex difference, using the ratio between the second and fourth digit of the hand (“2D:4D”) as a putative marker. However, the sample sizes of those studies were mostly small and results remained inconclusive. The aim of the present study is to test the suggested associations between depression, neuroticism and the 2D:4D ratio in a large, representative sample of over 3,000 German individuals. It was hypothesized that a higher 2D:4D (supposedly representing a more “feminine” prenatal hormone exposure) would positively predict (1) one’s history of depression as well as (2) neuroticism rates and (3) acute depressive symptom scores. Controlling for biological sex, we only found suggestive evidence for linear associations with neuroticism in the case of left hand 2D:4D ratios and the mean 2D:4D of both hands. However, additional analyses indicated that these results may have been spurious due to confounding. Our findings suggest that the 2D:4D ratio is not a relevant predictor of depression, while there was mixed evidence in the case of neuroticism.

No relationship between the digit ratios (2D:4D) and salivary testosterone change: Study on men under an acute exercise

The digit ratio (2D:4D) is said to be a potential marker of exposure to prenatal sex steroids. Some studies suggest that the 2D:4D is also linked with the testosterone response to challenging situations due to organizational effect of prenatal hormonal milieu on adult endocrine functioning. However, up to date, there were only four studies (conducted on small samples) that examined the 2D:4D and the testosterone response to a challenging situation (i.e. physical exertion or aggressive context). Here, we examined the relationship between the 2D:4D and the testosterone change under an acute exercise among 97 men. We found that the digit ratios (the right 2D:4D, the left 2D:4D, and the right minus left 2D:4D) were neither predictors of pre-exercise testosterone, nor the change in testosterone level after a cycling task. Our results add a contradictory to previous studies evidence in a discussion on the links of the 2D:4D and the testosterone change.

Lower digit ratio and higher endogenous testosterone are associated with lower empathic accuracy

Empathy is a cornerstone of human sociality. It has important consequences for our interpersonal relationships and for navigating our social world more generally. Although research has identified numerous psychological factors that can influence empathy, evidence suggests that empathy may also be rooted in our biology and, in particular, the gonadal steroid hormone testosterone. To date, much of the research linking testosterone and empathy has focused on the 2D:4D ratio (i.e., the ratio of the lengths of the index and ring fingers), and the results have been mixed. These mixed results, however, may be due to reliance on self-report measures to assess empathy, which can be vulnerable to self-presentation, as well as social-cultural norms about gender/sex differences in empathy. Moreover, although some have argued that digit ratio is an indicator of prenatal androgen exposure, the evidence for this to date is weak. Here, we aimed to follow up on this prior work, using a naturalistic empathic accuracy task in which participants dynamically track, in real-time, the emotional state of targets. We show that lower digit ratio (Study 1; N = 107) and higher circulating testosterone (Study 2; N = 76) are associated with poorer empathic accuracy performance; critically, these effects hold when controlling for sex/gender. In neither study, however, did we find effects on self-reported empathy. Our results highlight the limitations of self-report measures and support the notion that endogenous testosterone levels as well as 2D:4D ratio are related to key social-cognitive competencies like empathic accuracy.

LIN28B affects gene expression at the hypothalamic-pituitary axis and serum testosterone levels

Genome-wide association studies (GWAS) have recurrently associated sequence variation nearby LIN28B with pubertal timing, growth and disease. However, the biology linking LIN28B with these traits is still poorly understood. With our study, we sought to elucidate the mechanisms behind the LIN28B associations, with a special focus on studying LIN28B function at the hypothalamic-pituitary (HP) axis that is ultimately responsible for pubertal onset. Using CRISPR-Cas9 technology, we first generated lin28b knockout (KO) zebrafish. Compared to controls, the lin28b KO fish showed both accelerated growth tempo, reduced adult size and increased expression of mitochondrial genes during larval development. Importantly, data from the knockout zebrafish models and adult humans imply that LIN28B expression has potential to affect gene expression in the HP axis. Specifically, our results suggest that LIN28B expression correlates positively with the expression of ESR1 in the hypothalamus and POMC in the pituitary. Moreover, we show how the pubertal timing advancing allele (T) for rs7759938 at the LIN28B locus associates with higher testosterone levels in the UK Biobank data. Overall, we provide novel evidence that LIN28B contributes to the regulation of sex hormone pathways, which might help explain why the gene associates with several distinct traits.

The association between 2D:4D ratio and aggression in children and adolescents: Cross-cultural and gender differences

BACKGROUND

Two recent meta-analyses have suggested the association between digit ratio (2D:4D) and aggression is weak. This conclusion has been criticised because the meta-analyses conflate forms of aggression that show strong sex differences with those that do not, and most studies have considered post-pubertal participants.

AIMS

We test the influence of 2D:4D and ethnicity in the expression of aggression in children and adolescents in four ethnic groups of European and African origin.

STUDY DESIGN

Buss and Perry aggression questionnaire. Direct measurement of the 2nd and 4th digits.

SUBJECTS

1296 children and adolescents from Tanzania and Russia from 4 ethnic groups - Datoga, Meru, Russians, Tatars.

RESULTS

There were ethnic and gender differences in ratings on aggression with boys consistently reporting more physical aggression. In all four samples right 2D:4D was significantly lower in boys, compared to girls. With regard to our total sample of boys, the right 2D:4D was significantly and negatively associated with self-ratings on physical aggression, but no association was found for left 2D:4D. No associations between 2D:4D and physical aggression were found for girls. Hostility was negatively correlated with 2D:4D for boys, and anger was positively correlated with 2D:4D in girls.

CONCLUSION

Sex differences were strongest for right 2D:4D (boys<girls), and for physical aggression (boys>girls). Right 2D:4D was negatively related to physical aggression in boys only, suggesting possible relationship to prenatal androgenization.

Large-scale GWAS reveals insights into the genetic architecture of same-sex sexual behavior

Twin and family studies have shown that same-sex sexual behavior is partly genetically influenced, but previous searches for specific genes involved have been underpowered. We performed a genome-wide association study (GWAS) on 477,522 individuals, revealing five loci significantly associated with same-sex sexual behavior. In aggregate, all tested genetic variants accounted for 8 to 25% of variation in same-sex sexual behavior, only partially overlapped between males and females, and do not allow meaningful prediction of an individual's sexual behavior. Comparing these GWAS results with those for the proportion of same-sex to total number of sexual partners among nonheterosexuals suggests that there is no single continuum from opposite-sex to same-sex sexual behavior. Overall, our findings provide insights into the genetics underlying same-sex sexual behavior and underscore the complexity of sexuality.

Genome-wide association study of knee pain identifies associations with GDF5 and COL27A1 in UK Biobank

Knee pain is one of the most common musculoskeletal complaints that brings people to medical attention. Approximately 50% of individuals over the age of 50 report an experience of knee pain within the past 12 months. We sought to identify the genetic variants associated with knee pain in 171,516 subjects from the UK Biobank cohort and seek supporting evidence in cohorts from 23andMe, the Osteoarthritis Initiative, and the Johnston County Osteoarthritis Project. We identified two loci that reached genome-wide significance in the UK Biobank: rs143384, located in GDF5 (P = 1.32 × 10-12), a gene previously implicated in osteoarthritis; and rs2808772, located near COL27A1 (P = 1.49 × 10-8). These findings were supported in cohorts with self-reported osteoarthritis/radiographic knee osteoarthritis without pain information. In this report on genome-wide association of knee pain, we identified two loci in or near GDF5 and COL27A1 that are associated with knee pain.

Revisiting the relationships of 2D:4D with androgen receptor (AR) gene and current testosterone levels: Replication study and meta-analyses

The relationships of digit ratio (2D:4D) with the length of AR (CAG)n, and testosterone levels from saliva and blood have been extensively debated over the years. This research including three studies further clarifies such controversies. To do so, we re-examined the relationships between the length of AR (CAG)n, 2D:4D, and current testosterone levels, through replication study and meta-analysis for each study. The results indicate: (a) the length of AR (CAG)n is not significantly associated with 2D:4D; (b) current testosterone levels are not significantly associated with the ratio; and (c) the length is not significantly associated with testosterone levels. Thus, AR (CAG)n and current testosterone levels are not significantly related to 2D:4D at individual level.

Digit ratios and motor and health-related fitness in pre-adolescent females

Background: Assessing different aspects of physical fitness in children whose abilities are undeveloped and their associations with second-to-fourth digit ratio (2D:4D) may better determine the potential athleticism of an individual.Aim: The purpose of the study was to examine relationships between the digit ratios and selected motor and health-related fitness parameters in a large sample of pre-adolescent females.Subjects and methods: Participants included 8-12 year old Iranian and Afghan girls. The length of the left and right second and fourth digits was measured by scanning and computer-assisted image analysis. Motor- and health-related fitness tests were evaluated.Results: No significant correlations were noted between right 2D:4D ratio and physical fitness components. Left 2D:4D and physical fitness components were not correlated, with the exception of handgrip strength (r = -0.193). However, right and left second digit lengths were negatively correlated with predicted VO_2max (p ≤ 0.01). In addition, right-left 2D:4D was significantly negatively correlated with flexibility, and significantly positively correlated with height and body fat percentage.Conclusion: In contrast to previous investigations, it seems that left 2D:4D is a predictor of strength, but not aerobic exercise. It is suggested there may be a potential relationship between prenatal androgen exposure and high flexibility, low body fat percentage and the generation of muscular strength in pre-adolescent females.

Association of CYP19A1 single-nucleotide polymorphism with digit ratio (2D:4D) in a sample of men and women from Ningxia (China)

OBJECTIVES

2D:4D is an anthropometric indicator that may reflect the level of intrauterine sexual hormone exposure before birth. The aromatase gene (CYP19A1) mainly encodes cytochrome P450 aromatase, a key enzyme that catalyzes the conversion of androgens to estrogens in vivo and affects the development of 2D:4D. Studying the association between six single-nucleotide polymorphisms (SNPs) in CYP19A1 and digit ratios in the normal population of China will provide some basis for the biological basis of digit ratio development and promote the practical application of digit ratios.

METHODS

In this study, six SNPs (rs10046, rs2414095, rs4646, rs4775936, rs749292 and rs936306) in CYP19A1 were tested in 1949 students (692 males and 1247 females) by TaqMan SNP genotyping in Ningxia, China. The digit ratios (right and left 2D:4D and right-left 2D:4D [D_r-l]) of all participants were collected using a photographic record.

RESULTS

The frequencies of the genotypes rs2414095 (P < 0.05), rs10046 (P < 0.01) and rs4775936 (P < 0.05) in the CYP19A1 gene and their allele frequencies were significantly different between the Hui and Han populations, and the frequency of the rs2414095 genotype (P < 0.05) was significantly different between males and females in Ningxia, China. There was a sex difference in right and left 2D:4D and in D_r-l. There was no significant association between the six SNPs of the CYP19A1 gene and right and left 2D:4D, although rs4775936 showed a lower 2D:4D ratio in allele T than in allele C, in both male and female subjects. For D_r-l we found that rs4775936 associated with increased D_r-l in females (t₇₈₇ = -2.441, P < 0.05).

CONCLUSIONS

We found the different frequencies of rs10046, rs2414095 and rs4775936 between Hui and Han populations in China. There was an association between rs4775936 and D_r-l. We discuss the implications of this association for links between D_r-l and rs4775936 and prenatal sex steroids and for susceptibility to breast cancer.

Digit ratio (2D:4D) in relation to substance and computer use: a meta-analysis

Human studies have reported inconsistent associations between the length ratio of the second finger to the fourth finger (2D:4D), which is a proxy for prenatal androgen load, and substance or computer use in adolescents and adults. This meta-analysis quantifies the magnitude of this relationship and investigates the roles of sex, definition of caseness, different forms of addiction, the hand measured (right hand versus left hand), and other cohort characteristics. Univariate random-effects meta-analyses were performed, and moderators were tested with Bonferroni-corrected meta-regression analyses. The study included 18 independent samples with a total of 175,955 participants (96,316 males and 79,639 females). There was a significant difference in 2D:4D between the substance and computer-using subjects and the controls for the combined sample (Hedge's g = - 0.178 [- 0.291; - 0.064]) and for males (Hedge's g = - 0.260 [- 0.399; - 0.122]), but not for females. These effects were amplified when only analyzing studies that compared dependent versus non-dependent subjects (combined sample: g = - 0.325 [- 0.492; - 0.157]; males: g = - 0.427 [- 0.564; - 0.291]), but did not reach significance in the subgroup of studies examining other parameters of substance and computer use. When analyzing different forms of substance and computer use separately, alcohol intake and computer use revealed a significant difference in the standardized mean. Again, the effects were amplified when analyzing the subgroup of males and the subgroup of studies comparing dependent versus non-dependent subjects, with effect sizes showing Hedge's g values as many as - 0.552 [- 0.785; - 0.319] (alcohol-dependent males). Thus, this meta-analysis confirms that lower 2D:4D is associated with substance and computer dependency. Further studies are encouraged to explore the link between intrauterine hormone environment and addiction risk.

Digit ratio (2D:4D) and academic success as measured by achievement in the academic degree "Habilitation"

Introduction

Prenatal androgen exposure has important organizing effects on brain development and therefore on future behavior. Previous research has shown, that the ratio between index finger (2D) and ring finger (4D) (2D:4D) could function as a marker of prenatal androgen effects, with a relatively shorter 2D indicating a higher prenatal androgen exposure. 2D:4D is associated with status-seeking and competitive behavior but also with altruism. Therefore, 2D:4D should be related to academic success.

Methods

We examined the 2D:4D of both hands, as well as the difference between both variables (Dr-l), of 209 university graduates (74 women) employed at the Medical Faculty of the Friedrich-Alexander-University Erlangen-Nürnberg, Germany, and we assessed the relationship of these variables with academic career performance. Career performance was measured by the number of publications as first or last author, and by achievement of an academic degree used in many European countries, the so-called “Habilitation”.

Results

In a within-sex analysis we found a non-monotonic association between the right hand digit ratio and the probability of having a “Habilitation” in females. Academic success, measured by the number of publications as first or last author and the probability of a "Habilitation", increases with age. In agreement with the literature, we found higher academic success in men.

Conclusion

We found a non-monotonic relationship between right hand 2D:4D and academic success in females. However, the significance of this relationship was weak.

Which Data to Meta-Analyze, and How?

Abstract. Which data to analyze, and how, are fundamental questions of all empirical research. As there are always numerous flexibilities in data-analytic decisions (a “garden of forking paths”), this poses perennial problems to all empirical research. Specification-curve analysis and multiverse analysis have recently been proposed as solutions to these issues. Building on the structural analogies between primary data analysis and meta-analysis, we transform and adapt these approaches to the meta-analytic level, in tandem with combinatorial meta-analysis. We explain the rationale of this idea, suggest descriptive and inferential statistical procedures, as well as graphical displays, provide code for meta-analytic practitioners to generate and use these, and present a fully worked real example from digit ratio (2D:4D) research, totaling 1,592 meta-analytic specifications. Specification-curve and multiverse meta-analysis holds promise to resolve conflicting meta-analyses, contested evidence, controversial empirical literatures, and polarized research, and to mitigate the associated detrimental effects of these phenomena on research progress.

Association between ESR1 polymorphisms and second to fourth digit ratio in school-aged children in the Hokkaido Study

The ratio of the lengths of the 2nd and 4th digits (2D:4D) is considered an index of prenatal exposure to androgen. Indeed, androgen receptors have been linked to digit length, but estrogen receptors are rarely investigated in this context. Thus, we investigated the association between estrogen receptor 1 (ESR1) genetic polymorphisms and 2D:4D in school-aged children. The 2D:4D ratios were determined using Vernier calipers from photocopies of palms provided by 1800 children aged 7 years who were enrolled in an ongoing prospective cohort study in Hokkaido, Japan. The children were genotyped using cord blood collected at birth for single nucleotide polymorphisms in ESR1, specifically PvuII (T > C, dbSNP: rs2234693), XbaI (A > G, dbSNP: rs9340799), and rs2077647 (A > G). The association between ESR1 polymorphisms and 2D:4D was assessed by multiple linear regression adjusted for potential cofounding factors. Boys with the GG genotype at rs9340799 had a significantly lower 2D:4D in the right hand than boys with the AA/AG genotype (-0.96% lower, 95% confidence interval: -1.68 to -0.24). However, this association was detected only in boys born to non-smoking mothers. No significant differences were found between rs9340799 polymorphisms and 2D:4D among girls. There was also no link between 2D:4D and polymorphisms at rs2234693 and rs2077647. These data suggest that rs9340799 polymorphisms in ESR1 may contribute to digit length and 2D:4D.

Associations between neurochemical receptor genes, 2D:4D, impulsivity and relationship quality

The ratio between the second and fourth digits (2D:4D) has been widely used as a proxy for fetal exposure to androgens and has been linked to a number of sociosexual traits in humans. However, the role of genes in this equation remains unknown. Here (N = 474), we test, firstly, for associations between 2D:4D and single-nucleotide polymorphisms (SNPs) in nine neurochemical receptor genes (AR, OXTR, AVPR1A, OPRM1, DRD1/2, ANKK1, 5HTR1A/2A), and secondly, whether digit ratios mediate the relationship between genetic variation and sociosexuality. We demonstrate significant associations between AR, OPRM1 and AVPR1A and 2D:4D. Moreover, mediation analysis indicates that, in women, AR and OPRM1 variation drives digit ratios, which are related positively to impulsivity and, for OPRM1, negatively to romantic relationship quality. Although these findings are subject to multiple testing issues, this study provides preliminary evidence that in women genetic factors may affect both impulsivity and perceived relationship quality through influencing factors indexed by digit ratios.

Sex Differences in Rhesus Monkeys' Digit Ratio (2D:4D Ratio) and Its Association With Maternal Social Dominance Rank

Prenatal androgen exposure (PAE) plays a pivotal role in masculinizing the developing body and brain, and extreme exposure may contribute to autism, anxiety disorder and schizophrenia. One commonly used biomarker for PAE is the pointer-to-ring-finger digit length (2D:4D) ratio. Although this biomarker is widely used in human studies, relatively few studies have investigated 2D:4D ratio in nonhuman primates, particularly rhesus macaques (Macaca mulatta), one of the most commonly used animals in biomedical research. Thus far, data suggest that sexual dimorphism in 2D:4D ratio may be in the opposite direction in some monkey species, when compared to the pattern exhibited by humans and great apes. Using a large sample size, we investigated whether rhesus monkeys' 2D:4D ratio shows the same sex-differentiated pattern present in other Old World monkey species. We also investigated whether individual differences in 2D:4D ratio are associated with the social dominance rank of subjects' mothers during pregnancy, and the social dominance rank the subjects attained as adults. Subjects were 335 rhesus monkeys between 3 years and 24 years of age (M = 6.6). Maternal dominance rank during pregnancy and subjects' adult dominance rank were categorized into tertiles (high, middle and low). Results showed that, across both hands, male rhesus monkeys exhibited higher 2D:4D ratio than females, a pattern consistent with other monkey species and a reversal from the pattern typically observed in humans and apes. This sex difference was modulated by maternal dominance rank, with female offspring of high-ranking and middle-ranking mothers exhibiting masculinized 2D:4D ratio, indicating that maternal dominance rank during pregnancy may influence levels of PAE. There was no association between subjects' 2D:4D ratio and the social dominance rank they attained as adults. These findings show a consistent sex difference in Old World monkeys' 2D:4D ratio that diverges from the pattern observed in apes and humans, and suggest maternal social dominance rank modulates PAE in rhesus monkeys.