Digit ratios and relation to myocardial infarction in Greek men and women

Is digit ratio (2D:4D) a biomarker for lactate? Evidence from a cardiopulmonary test on professional male footballers

BACKGROUND

Lactate accumulation is associated with vigorous exercise, cardiovascular disease and a number of cancers. Digit ratio (2D:4D) has also been linked to oxygen metabolism, myocardial infarction and various cancers. Such similarities suggest the possibility that 2D:4D is a biomarker of lactate. Here, we consider the relationship between 2D:4D and lactate during an incremental cardiopulmonary exercise test.

METHOD

The participants were male professional football players. The treadmill test began at a speed of 8 km/h when the first lactate measurement was taken. The speed was increased by 2 km/h every 3.15 min, with measurements at 10, 12, 14 and 16 km/h.

RESULTS

There were 72 Caucasian and 7 Black participants, results are reported for the most numerous group. Lactate levels increased with running speed and were not correlated with age, body size or body composition. Median splits of digit ratios (right, left and right-left 2D:4D [Dr-l]) were calculated. In comparison to the Low ratio group, the High ratio group showed higher lactate levels across speeds. Effect sizes varied from very large to huge (right 2D:4D), large (left 2D:4D) and medium (Dr-l). At the individual level, positive correlations between digit ratios and lactate at the five different speeds varied from large (right 2D:4D), medium (left 2D:4D) and small (Dr-l).

CONCLUSION

There were large positive associations between right 2D:4D and lactate at all running speeds. We discuss our findings in relation to oxygen metabolism and suggest that 2D:4D may be a biomarker for lactate in the wider context of the latter's importance in health and disease.

Sexual Dimorphism and Sex-2D : 4D Interactions on Fasting Lipid Variables in an Adult Ghanaian Population

Prenatal hormone exposure has been suggested as a correlate of adult circulating estrogen and testosterone. If this observation is true, then prenatal hormone exposure may have an association with lipid homeostasis in adulthood. The study sought to investigate sexual dimorphism and the interactions between the putative marker of prenatal hormone exposure (2D : 4D) and sex on adult fasting plasma lipid variables. The study was cross-sectional from June to December 2021 at the University for Development Studies. The participants were between 18 and 30 years of age and consisted of 206 healthy persons (female = 93, male = 113). The right hand (2D : 4DR), the left hand (2D : 4DL), and the right-left 2D : 4D difference (Dr-l) were measured using computer-assisted analysis. Fasting venous blood samples were collected and analyzed for lipid variables including total cholesterol (TCHOL) and high-density lipoprotein cholesterol (HDL-C). There were no significant differences in the 2D : 4D ratio and lipid variables between males and females. However, after adjusting for age and BMI, the 2D : 4DR (P = 0.014) and the 2D : 4DL (P = 0.007) increased with increasing fasting plasma HDL-C on average. Moreover, there were significant interactions between sex and the 2D : 4DR (P = 0.002) and also, the 2D : 4DL (P = 0.005) on fasting plasma HDL-C. The relationship between HDL-C and the 2D : 4D ratio was positive in females but negative in males. The 2D : 4DR accounted for about 54.9% and 46.0% while the 2D : 4DL accounted for about 48.2% and 14.0% of the variabilities in fasting plasma HDL-C in females and males, respectively. Prenatal hormone exposure may partly account for the sexual dimorphism in adult lipid homeostasis.

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.

Prenatal oestrogen-testosterone balance as a risk factor of migraine in adults

BACKGROUND

Migraine is a common neurological disease with extremely debilitating, but fully reversible symptoms. Women suffer from migraine more often than men. It was assumed that fluctuation of oestrogen level during menstrual cycle is one of many factors responsible for more frequent migraine attacks. The second-to-fourth digit ratio (2D:4D) is considered as an indicator of prenatal sex steroids. Balance of prenatal androgens (testosterone) and oestrogen has been studied in numerous diseases that are affected by hormones. However, the relationship between migraine and the sex steroids balance in prenatal development is still unexplained. The aim of this paper is to provide an evidence of relationship between prenatal oestrogen and testosterone exposure following 2D:4D digit ratio, and migraine prevalence in adults.

METHODS

We examined a group of 151 adults (33 males, 118 females) with migraine and a control group of 111 adults (45 males, 66 females). 2D:4D digit ratio of both hands was measured using sliding Vernier calliper.

RESULTS

Significant differences were found in the right hand. Female migraineurs had lower value of 2D:4D ratio than the control group and the right 2D:4D was lower than left 2D:4D (Δ2D:4D), suggesting prenatal testosterone dominance. The opposite relationship was observed in males. Male migraineurs had higher value of 2D:4D ratio and Δ2D:4D was greater than the control group, suggesting prenatal oestrogen dominance.

CONCLUSIONS

Our results suggest that depending on sex, different proportion of prenatal sex steroids might be a risk factor of migraine in adults. Women with migraine were presumably exposed in prenatal life to higher testosterone levels relative to oestrogen, while men with migraine were probably exposed in prenatal life to higher levels of oestrogen relative to testosterone.

Parental income inequality and children's digit ratio (2D:4D): a 'Trivers-Willard' effect on prenatal androgenization?

Income inequality is associated positively with disease prevalence and mortality. Digit ratio (2D:4D) - a negative proxy for prenatal testosterone and a positive correlate of prenatal oestrogen - is related to several diseases. This study examined the association of income inequality (operationalized as relative parental income) and children's 2D:4D. Participants self-measured finger lengths (2D=index finger, and 4D=ring finger) in a large online survey conducted in July 2005 (the BBC Internet Study) and reported their parents' income. Children of parents of above-average income had low 2D:4D (high prenatal testosterone, low prenatal oestrogen) while the children of parents of below-average income had high 2D:4D (low prenatal testosterone, high prenatal oestrogen). The effects were significant in the total sample, present among Whites (the largest group in the sample), in the two largest national samples (UK and USA) and were greater for males than females. The findings suggest a Trivers-Willard effect, such that high-income women may prenatally masculinize their sons at the expense of the fitness of their daughters. Women with low income may prenatally feminize their daughters at the fitness expense of their sons. The effect could, in part, explain associations between low income, high 2D:4D (low prenatal testosterone) and some major causes of mortality such as cardiovascular disease.

Data regarding 2D:4D and other digit ratios in Greek population

Second-to-fourth digit ratio (2D:4D) is a sexually dimorphic biometric marker, which is influenced by prenatal estrogen levels and reflects to the hormonal profile of each individual. Exposure to environmental estrogens was common in the past. Their endocrine-disrupting action, combined with their long half-time, may have a feminizing effect and an impact on health. A stratified sample of 160 Greek people was selected by random procedures and fingers' length was measured by means of an electronic caliper. Based on preliminary statistical analysis, middle aged persons, corresponding to birth in the period 1947-1972, were found to differ significantly from the rest and the original sample was subsequently divided into three age subgroups (≤37, 38-63 and ≥64 years old). 2D:4D ratio was found significantly higher in Greek people aged from 38 to 63 years old, although sexual dimorphism remained unaffected. The other digit ratios followed the same pattern, with people aged less than 38 years to share equivalent ratios with people aged more than 63 years.

Association between the 2d:4d and cardiovascular risk factors: Body mass index, blood pressure and body fat

OBJECTIVES

To examine the relationship between the cardiovascular risk factors such as obesity as measured by Body mass index (BMI), body fat and blood pressure with the second to fourth digit ratio (2d:4d); a prenatal testosterone exposure marker.

METHODS

The 2d:4d for both hands were measured for the Indian male subjects' (n = 1217). Subject's anthropometric parameters such as height, weight, skinfold thicknesses at various regions and blood pressure measurements were collected in a cross-sectional study with a convenient sampling approach. The association between digit ratio and the other variables were examined using analysis of variance, Pearson's correlation test and linear regression methods.

RESULTS

The study included 1193 subjects and all were males aged 19.69 ± 5.38 years (range 13 to 40 years). The subjects' body mass index (BMI) was 19.45 ± 3.82 and right and left hand 2d:4d were 0.958 ± 0.054, and 0.958 ± 0.061 respectively. The systolic blood pressure (SBP) and BMI significantly differed between the higher and lower half of right 2d:4d. The left hand 2d:4d was significantly correlated with SBP (r = 0.075, p = 0.028) and significantly differed between different hypertensive groups (p < 0.003, F = 3.552, df = 5).

CONCLUSION

The study observed an association between 2d:4d with hypertension and BMI among young Indian population, emphasizing the effect of prenatal testosterone on late life cardiovascular risk factor.

Digit ratio (2D:4D) is not related to cardiovascular diseases or their risk factors in menopausal women

OBJECTIVES

Digit ratio (2D:4D) is widely used as a biomarker of prenatal hormonal environment linked to the growing number of adult health and disease-related characteristics. It has been suggested that 2D:4D is a good predictor of cardiovascular diseases (CVD) risk among men, but results in women are still inconclusive. Here we test the relationship between 2D:4D and the incidence of cardiovascular diseases (CVD), and their risk factors in Polish, rural women.

METHODS

The participants were 410 women age 50 and older. Structured questionnaire was used to gather personal and medical data, including the history of CVD diagnosed by a medical doctor. Anthropometric measurements of body height, weight, and finger lengths were performed. Right-hand and left-hand 2D:4D, mean 2D:4D, D_l-r , and BMI were calculated afterward. For a subgroup of participants (n = 329) fasting blood sample was collected (in order to assess the lipid profile and glucose levels) and blood pressure was measured. Age, education level and BMI were included as potential covariates.

RESULTS

No statistically significant association was observed between 2D:4D markers and the incidence of CVD (eg, heart attack, stroke) or CVD risk factors (dyslipidaemia, dysglycaemia or hypertension), when controlled for age, education and BMI.

CONCLUSIONS

The results of our study add to the growing number of studies investigating the sex-difference of the association between 2D:4D and cardiac health. We conclude that from a public health perspective 2D:4D may not be a valuable biomarker of elevated risk of CVDs in women.

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.

Digit ratio (2D:4D) and testosterone supplementation

BACKGROUND

Testosterone (T) is taken or prescribed to enhance appearance, increase athletic performance and libido and to treat hypogonadism. Digit ratio (2D:4D) is thought to be a negative correlate of prenatal T. Here we consider the relationship between 2D:4D and T supplementation.

AIMS

Our sample was taken from the BBC internet study. Respondents were asked (y/n) if they were taking; (i) T, (ii) hormone replacement therapy with T (HRTwT). We removed extreme 2D:4D values and age and considered the most numerous ethnic group (i.e. "Whites"). Analyses were performed with a two-factor (sex*T) analysis of variance with covariate age and dependent variables 2D:4D or right-left 2D:4D (Dr-l).

RESULTS

Out of 197,589 respondents, 793 (598 males) reported taking T. There was a significant main effect for right 2D:4D such that T supplementing males had higher 2D:4D than those who did not. The sex*T interaction was significant, but the effect reversed in females. There were 22,576 (661 males) participants who reported taking HRTwT. We found a significant main effect for right 2D:4D, males taking HRTwT had higher 2D:4D than those who did not. This was reversed in females. The sex*HRTwT interaction was significant, a high Dr-l was also found in males reporting HRTwT.

CONCLUSION

Males who reported taking T or HRTwT had high right 2D:4D and/or Dr-l. The situation with females may be the reverse of that found in males but effect sizes are less. The health implications of an association between high (feminized) 2D:4D and T supplementation in males are discussed.

Finger length ratio in longevity populations

OBJECTIVES

The purpose of this study was to compare the prevalence of finger length ratio between three longevity populations (Abkhazians, Azerbaijanis, and Georgians) and one nonlongevity population (Russians), as well as between a longevity and nonlongevity sample within one ethnic group (Abkhazians).

METHODS

In a cross-sectional observational study, we compared the prevalence of finger length ratio in longevity vs nonlongevity samples.

RESULTS

A negative relationship was observed between longevity index and prevalence of type 1 (feminine type) ratio. In longevity samples, the prevalence of type 1 ratio was lower and the prevalence of type 3 (masculine type) ratio was higher than in the nonlongevity sample of Russians. This difference was statistically significant (P < .001) in both males and females. A similar difference between longevity and nonlongevity samples was exhibited in the Abkhazian samples. In males and females, a significantly higher prevalence of type 1 and lower type 3 finger ratios (P < .001) were shown in the nonlongevity samples.

CONCLUSIONS

Finger length ratio pattern in longevity populations differs from that of nonlongevity populations. In longevity samples, the prevalence of type 1 ratio was lower and the prevalence of type 3 ratio was higher vs the nonlongevity sample. A similar type of difference was seen in the longevity and nonlongevity samples belonging to one ethnic group, the Abkhazians. Previous studies found that the type 1 finger length ratio was related to important morbidities that have a potential for shortening the life span. This can be one of the most plausible explanations for our findings.

Second-to-fourth digit ratio and seborrheic dermatitis in males: a cross-sectional study

BACKGROUND

Seborrheic dermatitis is a common disease characterized by the erythematous plaques with oily-yellow desquamation. Increased sebaceous gland activity by androgenic hormones has played a role in the etiology of the disease. The second-to-fourth digit (2D:4D) ratio is thought to be a marker of prenatal androgen exposure.

OBJECTIVES

To investigate the association between 2D:4D ratios and seborrheic dermatitis in a male population.

METHODS

Healthy male controls and patients with seborrheic dermatitis were included in this study. One hundred seborrheic dermatitis patients and 120 healthy controls, aged 17-59, were enrolled. A digital Vernier caliper was used to measure the finger lengths. Seborrheic dermatitis severity was assessed using the Seborrheic Dermatitis Area and Severity Index (SDASI).

RESULTS

The 2D:4D ratios of the patients (x = 0.977) were significantly lower than those of the controls (x = 1.050) for right hands (t = 6.948; p = 0.000; > 0.05). No similar relationship was found between the 2D:4D ratio for left hands (t = 0.901; p = 0.368; > 0.05). Seborrheic dermatitis severity was negatively correlated with 2D:4D ratios of right hands (r = -0.391; p = 0.000-0.05).

STUDY LIMITATIONS

One of the main limitations of this study was the small sample, which got a head of us from acquiring certain findings about the 2D:4D ratio and seborrheic dermatitis. The other limitation is that the patient selection did not reflect the general population, as a single clinic was studied.

CONCLUSION

To the authors' knowledge, this is the first study examining the relationship between 2D:4D ratios and seborrheic dermatitis. The result of this study may indicate a line of investigation and can support the theory of prenatal androgen exposure.

Depressed female cynomolgus monkeys (Macaca fascicularis) display a higher second-to-fourth (2D:4D) digit ratio

This research aimed to provide evidence of a relationship between digit ratio and depression status in the cynomolgus monkey (Macaca fascicularis). In stable cynomolgus monkey social groups, we selected 15 depressed monkeys based on depressive-like behavioral criteria and 16 normal control monkeys. All animals were video recorded for two weeks, with the duration and frequency of the core depressive behaviors and 58 other behaviors in 12 behavioral categories then evaluated via behavioral analysis. Finger lengths from the right and left forelimb hands of both groups were measured by X-ray imaging. Finger length and digit ratio comparisons between the two groups were conducted using Student’s t-test. In terms of the duration of each behavior, significant differences emerged in “Huddling” and five other behavioral categories, including Ingestive, Amicable, Parental, Locomotive, and Resting. In addition to the above five behavioral categories, we found that depressed monkeys spent less time in parental and rubbing back and forth behaviors than the control group. Furthermore, the 4th fingers were significantly longer in the left and right hands in the control group relative to the depressed monkeys. The second-to-fourth (2D:4D) digit ratio in the left and right forelimb hands was significantly lower in the control group than that in the depressed group. Our findings revealed significant differences in finger lengths and digit ratios between depressed monkeys and healthy controls, which concords with our view that relatively high fetal testosterone exposure may be a protective factor against developing depressive symptoms (or that low fetal testosterone exposure is a risk factor).

Can the Second to Fourth Digit Ratio (2D : 4D) Be a Marker to Determine Ankylosing Spondylitis Disease Activity?

Objective

The length ratio of the index finger (2D) to the ring finger (4D) (2D : 4D ratio) is considered a biomarker of prenatal sex hormone exposure. The 2D : 4D ratio is influenced by prenatal androgen and estrogen levels. Because ankylosing spondylitis (AS) influences men more frequently and severely than women, androgens are proposed to be related to AS pathogenesis. Estrogens have immune-modulating effects and reduce AS disease activity. The aim of this study was to assess the relationship between 2D : 4D ratio and AS disease activity.

Material and Methods

In this study, 167 (43 female) patients diagnosed with AS were studied. The lengths of the second and fourth fingers were measured using a digital caliper. The 2D : 4D ratio was found by dividing the length of the second finger by the length of the fourth finger. AS disease activity was assessed with the Turkish version of the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI). AS functional status was assessed with Bath Ankylosing Spondylitis Functional Index (BASFI). L-Schober, tragus to wall distance, finger to floor distance, and chest expansion were used to evaluate mobility.

Results

In female patients, the right hand 2D : 4D ratios were higher than those in male patients. Biologic drug use was more frequent in males. The BASDAI scores were higher in female patients than in male patients. There were significant negative correlations between right and left hand 2D : 4D ratio and BASFI and BASDAI in female patients. There was no significant correlation between the 2D : 4D ratio and BASFI or BASDAI in male patients. We found a positive correlation between L-Schober and right hand 2D : 4D and a negative correlation between the left hand 2D : 4D ratio and finger to floor distance in female patients with AS.

Conclusion

The 2D : 4D ratio of the right and left hand was low in female patients with high BASFI and BASDAI and low spinal mobility (L-Schober) was also linked to low female 2D : 4D. The lack of strong associations between 2D : 4D and AS in male patients may have resulted from their higher use of biologics.

Associations between digit ratio (2D4D), mood, and autonomic stress response in healthy men

The ratio between the length of the second (index) and the fourth (ring) finger (2D4D) is a putative biomarker of prenatal testosterone (T) exposure, with higher exposure leading to a smaller ratio. 2D4D has further been linked to mental and somatic disorders. Healthy male Swiss recruits (N = 245; M_age = 20.30 years) underwent a psychosocial stress test. Mood and salivary alpha-amylase (sAA) were assessed before and after the stress test, while heart rate (HR) and heart rate variability (HRV) were measured continuously. Additionally, 2D4D (right: R2D4D; left: L2D4D) was determined and divided into quartile groups. Correlation analysis showed no associations between R/L2D4D and outcome measures. Comparing calculated quartiles for R2D4D, subjects in the lowest R2D4D quartile expressed trendwise (p < 0.10) lower positive and higher negative affect, significantly elevated sAA activity (p < 0.05), but no HR and HRV differences at baseline as compared to subjects in the upper three quartiles. With regard to acute stress, subjects in the lowest as compared to subjects in the upper three R2D4D quartiles showed a higher increase of negative affect and a stronger cardiac response (p < 0.05), but no alterations in positive affect and sAA activity. Young healthy men in the lowest R2D4D quartile revealed a more negative affect and increased physiological activity at baseline and in response to acute stress. An exposure to high levels of prenatal T might constitute a risk factor potentially increasing vulnerability to stress-related disorders in men.

2D:4D Ratio Differs in Ischemic Stroke: A Single Center Experience

Background

The index to ring finger length (2D:4D) ratio is a proxy biomarker for prenatal exposure of sex hormones. Sex hormones are associated with the pathogenesis of ischemic stroke. The purpose of the study was to demonstrate the association between 2D:4D and ischemic stroke.

Methodology

This study retrospectively reviewed the data of 100 patients with first ever ischemic stroke between September, 2016 and June, 2017. The lengths of index finger and ring finger of both hands were measured using electronic calipers and calculated for 2D:4D ratios. Receive operating characteristic (ROC) mode was used to detect predicting performance of 2D:4D ratios for ischemic stroke.

Results

2D:4D ratios in ischemic stroke patients were higher than controls in both hands (P < 0.05), except right 2D:4D ratio in females. The ROC analyses showed that the area under the curve (AUC) were 0.635 (95%CI: 0.527-0.743) for left 2D:4D ratio, and 0.647 for right (95%CI: 0.539-0.755) (P < 0.05). The AUC of left and right 2D:4D ratio in male were 0.667 (95%CI: 0.514-0.820) and 0.670 (95%CI: 0.519-0.822) (P < 0.05). In female, no significance were found in ROC analysis. And there were no correlation between 2D:4D value and stroke severity (P > 0.05).

Conclusions

The current study indicated that the diagnostic value of 2D:4D ratio was limited in ischemic stroke. Further research is required to explore the role of it in screening ischemic stroke.

Digit ratio (2D:4D) and coronary artery disease in north Chinese women

BACKGROUND

Digit ratio (2D:4D) is fixed in utero and affected by fetal sex steroids. It has been proposed as a putative biomarker of certain hormone- related adult life traits and diseases. Several evidence suggest that 2D:4D ratio may correlate with cardiovascular disease risk (e.g., coronary artery disease).

AIMS

To investigate whether there is a possible relationship between digit ratio (especially 2D:4D ratio) and coronary artery disease (CAD), and age at CAD in north Chinese women.

METHODS

Photographs of the two hands of 303 females (controls: 194; patients: 109) were collected. Left hand, right hand and right minus left hand (Dr-l) digit ratio were analyzed and compared.

RESULTS

The mean values of digit ratio in patients with CAD were lower than controls for each hand. Significant differences of 2D:4D (left and right hand: P<0.01), 2D:5D (left hand: P<0.01; right hand: P<0.05) and 3D:4D (left hand: P<0.01) were found between two groups. There were no associations between 2D:4D ratio and age at CAD on both hands.

CONCLUSION

Decreased digit ratio (especially 2D:4D ratio) may suggest a higher prenatal testosterone (lower prenatal oestrogen) exposure in north Chinese women with coronary artery disease.

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.

Fight Bite Injuries: Aggressive Tendencies Associated with Smaller Second to Fourth Digit Ratio

BACKGROUND

Fight bite injuries are typically sustained by young, combative males and are the direct consequence of an aggressive act. Second to fourth digit ratios (2D:4D) are dependent on prenatal androgen exposure and lower ratios have been shown to be linked to various psychological and physical traits, including aggression. The aim of this study was to examine the 2D:4D ratios in a cohort of patients with fight bite injuries and compare these to an age and gender-matched control group.

METHODS

The 2D:4D ratios were calculated using plain films of the hand from 133 patients (122 males, 11 females) with fight bite injuries. A further 133 radiographs were obtained from patients that did not have fight bite injuries and digit ratios were calculated in the same fashion. Statistical analysis was then carried out to compare the 2D:4D ratios between the different groups.

RESULTS

The 2D:4D ratios for male fight bite patients was significantly smaller than the male control group (p < 0.05). No significant difference was observed between the female fight bite patients and the female control group (p > 0.05).

CONCLUSIONS

Fight bite injuries are usually sustained as a result of aggression. 2D:4D ratios are reflect intrauterine androgen exposure and low ratios have been linked to aggressive tendencies. We have demonstrated that male patients who sustained fight bite injuries have a lower 2D:4D ratio then the general population, thereby suggesting that exposure to prenatal androgens can lead to aggressive tendencies in adulthood. This suggests that lower ratios may predict a predisposition to acts of aggression, and as such result in an increased likelihood of sustaining an injury such as a fight bite.

Low second to fourth digit ratio in Dupuytren disease

The ratio of the lengths of the second and fourth digits (2D:4D) has been described as reflecting endogenous prenatal androgen exposure. In general, 2D:4D is lower in men than in women and has potential as a biomarker or predictor for various diseases, athletic ability, and academic performance. Dupuytren disease has digital flexion contractures and is known to predominate in men, but the pathogenesis of the disease remains unclear. To clarify the relationships between Dupuytren disease and endogenous androgens, we performed a retrospective analysis of hand radiographs to investigate 2D:4D in Dupuytren disease. The study included male patients with Dupuytren disease (n = 22) and a control group (n = 18) of male patients with carpal tunnel syndrome. Only unaffected hands, without contractures or osteoarthritis, were evaluated for the purpose of radiographic assessment. The lengths of the phalanx and metacarpal bones in the second and fourth digits were measured by 2 independent observers who each performed 2 sets of measurements separated by a minimum 1-week interval. The 2D:4D was calculated separately for the phalanges and metacarpals, and a combined (phalanx + metacarpal) 2D:4D was also calculated. The reliability of the observer measurements was established using the intraclass correlation coefficient, and both the intra- and interobserver reliability showed excellent agreement. We found that compared with control group, the Dupuytren disease group had significantly lower phalanx and combined 2D:4D. These findings suggest that endogenous prenatal androgens could contribute to the development of Dupuytren disease, leading to its characteristic clinical presentation predominantly in men and affecting the ulnar rays.

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.

The correlation of right 2D:4D finger length ratio to the low-grade inflammation marker IL-6 in children. The Healthy Growth Study

BACKGROUND

Second to fourth digit ratio (2D:4D) is associated with cardiometabolic risk in adults.

AIM

To examine the association of right 2D:4D with cardiovascular disease risk factors in children.

STUDY DESIGN

Cross-sectional study.

SUBJECTS

A sample of 301 children (53.5% girls) aged 9-13 in Greece and their parents. Children who were sick during the previous week of examination (n=44) were excluded from the analyses.

OUTCOME MEASURES

Socio-demographic (gestational age, birth weight, age, gender, maternal education level), anthropometric (body weight and height, finger length), clinical (pubertal stage, sickness during the previous week of the examination), blood [serum high sensitivity C-reactive protein (CRP), serum high sensitivity interleukin-6 (IL-6), serum leptin], lifestyle (dietary intake, maternal smoking during pregnancy) and physical fitness (handgrip strength) data were collected. CRP, IL-6 and leptin were measured with ELISA, using standard equipment and procedures, in accordance with manufacturers' instructions.

RESULTS

Full data were available for 257 children (52.1% girls). The rank values of right 2D:4D and IL-6 were included in the analyses. Right 2D:4D was correlated only with IL-6 at a bivariate level (r=0.216, p=0.012) in girls. At a linear multivariate level, this association remained significant, even after adjusting for several potential confounders such as age, Tanner stage, maternal education level, body mass index, maternal smoking during pregnancy, duration of pregnancy, protein-, carbohydrate-, fat-intake and physical fitness (β±SE=0.220±0.066, p=0.001).

CONCLUSIONS

Right 2D:4D was found to be associated with IL-6 in girls. Right 2D:4D may be a valuable, simple screening tool of low-grade inflammation in children.

Estimation of sex from index and ring finger in a North Indian population

Estimation of sex is an important parameter in the examination of unknown dismembered and commingled remains. The present study explores the possibility of estimation of sex from length of index and ring finger and the index and ring finger ratio in 140 individuals (70 boys and 70 girls) from North India. Index finger length (IFL) and ring finger length (RFL) of the participants were measured following standard procedures and landmarks. Sex differentiation in the present study was based on sectioning point analysis. The 'sectioning point' for the IFL, RFL and the index and the ring finger ratio was estimated from the average of the mean of male and female values. Binary logistic regression (BLR) analysis was employed to derive a predicting equation for estimation of sex. The results of the present study indicate that significant sex differences exist in the IFL and RFL and index and ring finger ratio. Among finger lengths, RFL is a better predictor of sex than IFL. It is further concluded that the index and ring finger length is of limited utility in estimation of sex in forensic casework and should be employed only in cases when no other means of sexing are available. The study suggests that the index and ring finger ratio should not be employed in estimation of sex in forensic casework due to considerable overlap in male and female values.

Fundamental ratios and logarithmic periodicity in human limb bones

Fundamental mathematical relationships are widespread in biology yet there is little information on this topic with regard to human limb bone lengths and none related to human limb bone volumes. Forty-six sets of ipsilateral upper and lower limb long bones and third digit short bones were imaged by computed tomography. Maximum bone lengths were measured manually and individual bone volumes calculated from computed tomography images using a stereologic method. Length ratios of femur : tibia and humerus : ulna were remarkably similar (1.21 and 1.22, respectively) and varied little (<7%) between individuals. The volume ratio of femur : tibia was approximately half that of humerus : ulna (1.58 and 3.28, respectively; P < 0.0001). Lower limb bone volume ratios varied much more than upper limb ratios. The relationship between bone length and volume was found to be well described by power laws, with R(2) values ranging from 0.983 to 0.995. The most striking finding was a logarithmic periodicity in bone length moving from distal to proximal up the limb (upper limb λ = 0.72, lower limb λ = 0.93). These novel data suggest that human limb bone lengths and volumes follow fundamental and highly conserved mathematical relationships, which may contribute to our understanding of normal and disordered growth, stature estimation, and biomechanics.

The ratio of second to fourth digit length (2D:4D) and coronary artery disease in a Han Chinese population

BACKGROUND

The association between index finger to ring finger length ratio (2D:4D) and cardiac disorders has been reported, however it has not been discussed in terms of coronary artery disease (CAD). We investigated whether 2D:4D could be used as a marker for predisposition to CAD as assessed by coronary angiography in Chinese men and women.

METHODS

This study included 1764 persons divided into 4 groups, 441 cases with CAD and 441 persons without CAD as control in each sex of the same age. Finger lengths were measured twice for both hands using electronic calipers. Student t test was used to detect the difference of 2D:4D among groups. The receiver operator characteristic curves (ROCs) were used to detect the diagnostic effect of 2D:4D for CAD.

RESULTS

There were no significant differences in age among the four groups. A significant difference of 2D:4D ratios between right and left hand were observed only in men in both control and CAD groups. On the right hand in the control group and on both hands in the CAD group, the 2D:4D ratios were higher in women than in men (all, P < 0.001). In men with CAD, mean 2D:4D was higher than mean 2D:4D in control men (right hand 0.962±0.042:0.927±0.038; left hand 0.950±0.044:0.934±0.048; both hands, P < 0.001), but this was not observed in women. No relationship was found between 2D:4D and age (all, P >0.05). The area under the curve of right hand 2D:4D in male was 0.72 (95% CI 0.683-0.753, p<0.001), while it was 0.602 (95% CI 0.565-0.639, p<0.001) in left hand.

CONCLUSIONS

The present study showed an association between high 2D:4D ratio and CAD in both hands in men. There were no significant differences in mean 2D:4D between women with CAD and controls.