Sex-different abnormalities in the right second to fourth digit ratio in Japanese individuals with autism spectrum disorders

Autism spectrum disorder and new perspectives on the reliability of second to fourth digit ratio

The second to fourth digit ratio (2D:4D) is according to previous studies a likely biomarker for prenatal testosterone exposure and its effect on the human brain. It was found to be linked to autism spectrum disorders (ASD). Recently, 2D:4D raised a lot of questions with regard to its stability and autism-related behaviors. Here, we present a cross-sectional study of 2D:4D in boys (N = 91, mean age 7.63) and adults (N = 36 mean age 22.8) with ASD as well as neurotypical students, 506 participants in total. Digit ratio was assessed by taking measurements from digital scans, compared between groups and correlated with the autism quotient. Significant differences were found in the digit ratio of children and adults. Both girls and boys had 2D:4D ratio lower than women and men, both on the right (p = 0.000 in females, p = 0.000 in males) and left hand (p = 0.018 in females, p = 0.011 in males). No significant differences were found in digit ratios between neurotypical subjects and those with ASD nor was there a relationship with the reported autistic traits, which leads us to question the reliability of 2D:4D and its relation to ASD.

Second-to-Fourth Digit Ratio (2D:4D) in Psychiatric Disorders: A Systematic Review of Case-control Studies

The second-to-fourth digit ratio (2D:4D) is an indirect, retrospective, non-invasive measure that correlates negatively with intrauterine exposure to testosterone. The present meta-analysis aimed to evaluate if 2D:4D differs between patients with psychiatric disorders and controls. In September 2019, we searched in Web of Knowledge, PsycINFO, Embase, and CINHAL, and retrieved 619 papers. We finally included 43 case-control studies which compared the 2D:4D ratio of patients with autism spectrum disorder (ASD) (n = 16), schizophrenia (n = 8), gender non-conformity (n = 7), addictions (n = 5), attention deficit-hyperactivity disorder (ADHD) (n = 4), mood disorders (n = 2), and intellectual disability (n = 1) to non-clinical controls. Meta-analyses showed that, overall, psychiatric patients had lower 2D:4D than healthy controls (n = 43, overall sample = 9,484, mean difference = -0.0056, 95% confidence interval from -0.0093 to -0.002, I2 = 74%), with more pronounced differences in the right hand, males, and children. Considering psychiatric disorders individually, significant differences were found in the ASD, ADHD, and addictions groups, in which 2D:4D was significantly lower than healthy controls. Conversely, the right hand of males with schizophrenia showed higher 2D:4D than healthy controls. No other significant differences were detected. Although our results need to be cautiously interpreted and find limited applications in clinical practice, they may suggest that 2D:4D is altered in some psychopathological conditions, underlining the role of prenatal exposure to sex steroids in the etiology of psychiatric disorders.

2D:4D Ratio and Autism Spectrum Disorder in Brunei Darussalam

Background

Despite the global increase in the prevalence of autism spectrum disorders (ASD), relevant research studies are lacking in Brunei Darussalam. Various studies have shown a significant association between a lowered 2D:4D ratio (ratio of second digit/index finger to the fourth digit/ring finger) and ASD, making it one of the potential phenotypic biomarkers for early detection of autism, which is important for early intervention and management.

Objective

The objective of this study is to explore the association between 2D:4D ratio and ASD in Brunei Darussalam, as a potential tool to complement early ASD diagnosis.

Methods

We conducted a case–control study comprising 28 ASD and 62 typically developing (TD) children in the case and control group, respectively (age range: 3–11 years old; median age: 6 years old). Median 2D:4D ratios were measured, compared and analysed between the two groups. Logistic regression models were used to explore potential associations between the median 2D:4D ratio and ASD in respective gender, for both left and right hands, independently.

Results

Our study shows that the median 2D:4D ratio of left hand in ASD males is significantly lower than those in TD males, after adjusting for ethnicity and age [Odds Ratio (OR) = 0.57 (95% Confidence Interval (CI): 0.31–0.96); p = 0.044]. For females, there is no association of ASD with the median left hand 2D:4D ratio [OR = 3.09 (95% CI: 0.98–19.86); p = 0.144] or the median right hand 2D:4D ratio [OR = 1.23 (95% CI: 0.42–3.88); p = 0.702]. Our study also shows a significant positive correlation and/or a reduced asymmetry between the average 2D:4D ratio of left hands and right hands in ASD males (Pearson’s correlation (r) = 0.48; 95% CI: 0.076–0.75, p = 0.023).

Conclusions

There is significant association between a lowered median 2D:4D ratio of the left hand (in males only) and ASD diagnosis. Once validated in a larger sample size, a lowered median 2D:4D ratio on the left hand may be a potential tool to complement ASD diagnosis for males in our study population. There is no association between the median 2D:4D ratio (left or right hands) and ASD in females, which could be due to the small female sample size and/or the possibility of different aetiology for ASD in females. Reduced asymmetry between the average 2D:4D ratio of left and right hands observed in ASD males only (not in ASD females) also suggests the importance of considering gender-specific biomarkers for ASD diagnosis.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10803-021-04899-9.

The second to fourth digit ratio (2D:4D): A risk factor of bladder cancer in men

BACKGROUND

Exposure to prenatal sex steroids as indicated by the ratio of the second to fourth digit length (2D:4D) has been linked to the risk of onset of cancer, while sex steroids may expand the gender disparity in bladder cancer (BC) morbidity.

AIM

To explore the association between 2D:4D ratio and BC risk.

SUBJECTS

307 bladder cancer patients and 321 cancer-free individuals.

OUTCOME MEASURES

Relationships between 2D:4D and incidence of bladder cancer.

RESULTS

For males, a lower 2D:4D ratio of both hands was obtained in the BC group, relative to the control group (left hand: 0.940 ± 0.031 vs. 0.954 ± 0.024, t = -4.72, p < 0.001, Cohen's d = 0.491 and right hand: 0.939 ± 0.031 vs. 0.952 ± 0.022, t = -4.493, p < 0.001, Cohen's d = 0.511). In females, no differences in the 2D:4D ratio were observed between the BC and control groups (p > 0.05). Correlation analysis between 2D:4D ratio and pathological index found no correlation among the BC grade or stage (p > 0.05).

CONCLUSION

Men with BC have a lower 2D:4D ratio compared with healthy men. Therefore, having a low 2D:4D ratio is a risk factor for BC in men. Prenatal exposure to sex steroids might play a role in the etiology of BC, which could partially explain the gender disparity in the prevalence of BC.

The association between second to fourth digit ratio, reproductive and general health among women: findings from an Israeli pregnancy cohort

The ratio between the length of second and fourth digits (2D:4D) is a putative biomarker for prenatal testosterone and estrogen exposure. The aim of the study was to examine the association between 2D:4D and women’s general and reproductive health. This analysis was conducted within a prospective pregnancy cohort study. The study population included 187 women. 2D:4D was measured directly in both hands using a digital caliper. Multivariable linear and logistic models were used to study the associations between digit ratio and the studied health characteristics. Mean age of the participants was 30.7 ± 4.9 years. The mean age at menarche was 12.9 ± 1.4 years. Right hand 2D:4D mean ± SD was 0.965 ± 0.03. Left hand 2D:4D mean ± SD was 0.956 ± 0.03. An association was found between right 2D:4D and age at menarche, with older age in women with 2D:4D ≥ mean versus 2D:4D < mean (13.2 ± 1.5 and 12.8 ± 1.3 respectively, b = 0.48, 95%CI:0.06–0.91) while controlling for ethnicity. Higher 2D:4D was also associated with heavier menses bleeding and dysmenorrhea. There is an association between 2D:4D and sub optimal reproductive characteristics, including later age at menarche, heavier menses bleeding and dysmenorrhea. These findings support the association between the intrauterine period and reproductive characteristics. Further studies are required to support our findings.

Lower Digit Ratio (2D:4D) Indicative of Excess Prenatal Androgen Is Associated With Increased Sociability and Greater Social Capital

Positive social interactions are crucial for human well-being. Elevated prenatal exposure to testosterone as indicated by a low second-to-fourth finger length ratio (2D:4D) relates to more aggressive/hostile behavior in men of low 2D:4D, especially in challenging situations. How much people enjoy interacting with others is determined by the personality trait sociability. Given its role in approach and avoidance behavior, sociability might also be influenced by prenatal sex hormones, but studies are inconclusive so far. Here, we investigated the association between 2D:4D and the personality trait sociability complemented by personal social capital and personal social network size, in a population-based cohort of 4998 men. Lower 2D:4D correlated significantly with higher trait sociability, bigger personal social capital, and larger personal social network size. These effects were consistent across both hands separately and their mean value. Furthermore, both factors of sociability (1) liking party and company of friends and (2) isolation intolerance, correlated significantly with the prenatal testosterone marker. The exploratory analysis revealed no link between 2D:4D and responses to the personality trait aggression items or items of anti-social-personality disorder. Our data suggest that prenatal androgen exposure organizes the brain with lasting effects on social behavior.

Does testosterone impair men's cognitive empathy? Evidence from two large-scale randomized controlled trials

The capacity to infer others' mental states (known as 'mind reading' and 'cognitive empathy') is essential for social interactions across species, and its impairment characterizes psychopathological conditions such as autism spectrum disorder and schizophrenia. Previous studies reported that testosterone administration impaired cognitive empathy in healthy humans, and that a putative biomarker of prenatal testosterone exposure (finger digit ratios) moderated the effect. However, empirical support for the relationship has relied on small sample studies with mixed evidence. We investigate the reliability and generalizability of the relationship in two large-scale double-blind placebo-controlled experiments in young men (n = 243 and n = 400), using two different testosterone administration protocols. We find no evidence that cognitive empathy is impaired by testosterone administration or associated with digit ratios. With an unprecedented combined sample size, these results counter current theories and previous high-profile reports, and demonstrate that previous investigations of this topic have been statistically underpowered.

2D:4D ratios as an indicator of intrauterine androgen exposure in children who stutter

AIM

We aimed to explore whether there is a relationship between stuttering and digit ratio (2D:4D), which is thought to be a marker of prenatal testosterone exposure.

METHODS

We evaluated a total of 90 children who stutter (CWS; n = 40 mild-to-moderate and n = 50 severe stutters) and 40 healthy peers (CWNS) as controls. We used the Clinical Global Impression-Severity (CGIS) scale to measure the severity of stuttering. We measured the lengths of index finger (2D) and ring finger (4D) of both hands directly and divided to calculate 2D:4D ratio. The difference between the right and the left hand 2D:4D ratio (D_R-L) was also calculated.

RESULT

Significant difference was found in right 2D:4D and the mean D_R-L between the CWS and CWNS groups. Right 2D:4D was significantly lower in stuttering boys than in control boys, and in stuttering girls than control girls. Also, D_R-L was significantly lower in stuttering boys than control boys. In ANOVA, there were significant differences between the mild-to-moderate, severe stuttering and control groups in terms of right 2D:4D and D_R-L. Right hand 2D:4D and D_R-L decreased from controls to severe stutterers.

CONCLUSION

Our results suggest that lower right 2D:4D and D_R-L were related to the presence and severity of stuttering in children, i.e. CWS had lower 2D:4D and D_R-L than CWNS. Further large-scale prospective studies are needed to clarify the reliability of 2D:4D ratio as an indicator of fetal sex hormone exposure level and its relation with the presence and severity of stuttering in children.

Mindfulness-based Stress Reduction in Pregnancy: an App-Based Programme to Improve the Health of Mothers and Children (MINDFUL/PMI Study)

Unfavourable intrauterine environmental factors increase the risk of delivery complications as well as postpartum developmental and behavioural problems in children and adolescents with ongoing effects into older age. Biomarker studies show that maternal stress and the use of alcohol and tobacco during pregnancy are associated with a higher intrauterine testosterone exposure of the child. The antenatal testosterone load, in turn, is a risk factor for lasting adverse health effects which extend into adulthood. A 15-week, mindfulness-oriented, app-based programme for the reduction of stress as well as for the reduction of alcohol and tobacco use in pregnant women is established. In the monocentre, prospective, controlled, and investigator-blinded MINDFUL/PMI (Maternal Health and Infant Development in the Follow-up after Pregnancy and a Mindfulness Intervention) study, pregnant women carry out the programme. Its effect on antenatal testosterone exposure of the child is examined by assessing the index/ring finger length ratio and other biomarkers in the 1-year-old children. In addition, the programmeʼs effects on self-regulation, the developmental status and the mental health of the children at the age of one year will be investigated. Additional aspects of the course of the pregnancy and delivery represent exploratory study objectives. This longitudinal study project is intended to improve the understanding of the impact of intrauterine environmental factors on early childhood development and health. Maternal stress as well as alcohol and tobacco use during pregnancy are modifiable factors and represent potential preventive targets.

Associations Between the 2nd to 4th Digit Ratio and Autism Spectrum Disorder in Population-Based Samples of Boys and Girls: Findings from the Study to Explore Early Development

The ratio of the index (2nd) finger to ring (4th) finger lengths (2D:4D) is a proxy for fetal testosterone and estradiol. Studies suggesting 2D:4D is inversely associated with autism spectrum disorder (ASD) in males were limited by lack of confounder and subgroup assessments. Studies of females are sparse. We examined associations between ASD and 2D:4D among children in the Study to Explore Early Development; we considered case subgroups and numerous potential demographic and maternal-perinatal health confounders. We observed a modest inverse association between ASD and right-hand 2D:4D in males; subgroup analyses indicated associations were limited to ASD cases with birth defects/genetic syndromes or dysmorphic features. We observed a positive association between ASD and left-hand 2D:4D in females, overall and within most case subgroups.

The androgen model of suicide completion

Suicide is a devastating public health issue that imposes severe psychological, social, and economic burdens not only for the individuals but also for their relatives, friends, clinicians, and the general public. Among the different suicidal behaviors, suicide completion is the worst and the most relevant outcome. The knowledge of biological etiopathological mechanisms involved in suicide completion is limited. Hitherto, no objective markers, either alone or in combination, can reliably predict who will complete a suicide. However, such parameters are strongly needed to establish and optimize prediction and prevention. We introduce here a novel ideation-to-completion framework in suicide research and discuss the problems of studies aiming at identifying and validating clinically useful markers. The male gender is a specific risk factor for suicide, which suggests that androgen effects are implicated in the transition from suicidal ideation to suicide completion. We present multiple lines of direct and indirect evidence showing that both an increased prenatal androgen load (with subsequent permanent neuroadaptations) and increased adult androgen activity are involved in suicide completion. We also review data arguing that modifiable maternal behavioral traits during pregnancy contribute to the offspring's prenatal androgen load and increase the risk for suicide completion later in life. We conclude that in utero androgen exposure and adult androgen levels facilitate suicide completion in an synergistic manner. The androgen model of suicide completion provides the basis for the development of novel predictive and preventive strategies in the future.

Cross-national gender variations of digit ratio (2D:4D) correlate with life expectancy, suicide rate, and other causes of death

The second-to-fourth finger length ratio (2D:4D) is an indication of prenatal sex hormone exposure, and has sex-specifically been associated with several lethal illnesses including ischemic heart disease, diverse cancers, and suicide. Our primary aim was to verify that 2D:4D sex-specifically relates to life expectancy and suicide numbers on a national level (23 countries). We also used a hypothesis-free approach to investigate associations with other causes of death [p value adjustment for multiple hypothesis testing using the false discovery rate procedure (FDR)]. All parameters were normalized to the national mean (of males and females) and analyzed across nations. Normalized male 2D:4D correlated positively with normalized male life expectancy (at birth, r = 0.46, p = 0.029; at the age of 60, r = 0.44, p = 0.038) and negatively with normalized male suicide rates (r = − 0.49, p = 0.017). In the exploratory analyses, the normalized male 2D:4D values were negatively associated with the normalized male deaths rates from communicable, maternal, perinatal, and nutritional conditions [r = − 0.65, p(FDR) = 0.011], respiratory infections [r = − 0.69, p(FDR) = 0.008], asthma [r = − 0.65, p(FDR) = 0.011], neurological conditions [r = − 0.56, p(FDR) = 0.046], and Alzheimer’s disease and other dementias [r = − 0.59, p(FDR) = 0.036]. The normalized female parameters showed the same cross-national correlations. In line with the previous individual level findings, the results suggest that prenatal sex hormone effects are sex-specifically involved in suicide and neurological conditions. Moreover, we provide novel national level evidence that prenatal sex hormone priming may sex-specifically influence life expectancy and death risk from respiratory diseases.