Precise tactile localization on the human fingernail.

Fingernails are specialized features of the primate hand, which are believed to contribute to manual dexterity. The sensorimotor functions of fingernails, however, remain poorly understood. This study investigates the ability of humans to precisely localize touches applied to the fingernail plate. Nine different locations on the fingernail were touched and participants judged the location by clicking a mouse cursor on a photograph of their finger. Performance in this condition was compared with stimuli applied to the skin of the fingertip. The results showed that participants are able to localize touch on the fingernails at substantially higher than chance levels. Moreover, the precision of this ability is not appreciably lower than that of the fingertips. These results show that the fingernail is a highly sensitive sensory organ, which is capable of providing rich spatial information about tactile stimuli.

What is new in flexor tendon pulleys and the gaps between them in triphalangeal fingers of the hand?

The flexor tendon pulleys in the fingers of the hand are fibrous structures of variable size, shape, and thickness that cover the synovial sheath of these tendons. Despite their clinical relevance, their arrangement and configuration in each of the triphalangeal fingers have been little studied and with small sample sizes. 192 triphalangeal fingers belonging to 48 fresh body donors' hands were dissected. Multivariate analysis was carried out. Twenty-five cases (52%) were left hands, and 26 of the 48 hands belonged to female donors (54.2%). The results were analyzed by fingers for each of the 5 annular pulleys, the 3 cruciform pulleys and the gaps between them. In addition, the most and least frequent configurations of the pulleys in each of the fingers were studied, observing that the classic pattern with all the pulleys appeared only in 3 fingers (1.56%), while the most frequent pattern was A1-A2-C1-A3-A4, which was seen in 35 fingers (18.22%). CONCLUSIONS: The flexor pulleys in the triphalangeal fingers of the hand have shown enormous variability in arrangement and shape, and also rarely appear all in the same finger. This peculiar anatomical arrangement can help the different professionals who perform their clinical work in this region.

The Role of Placental DNA Methylation at Reproduction-Related Genes in Associations between Prenatal Bisphenol Analogues Exposure and the Digit Ratio in Children at Age 4: A Birth Cohort Study.

Placental DNA methylation (DNAm) may be a potential mechanism underlying the effects of prenatal bisphenol analogues (BPs) exposure on reproductive health. Based on the Shanghai-Minhang Birth Cohort Study (S-MBCS), this study investigated associations of placental DNAm at reproduction-related genes with prenatal BPs exposure and children's digit ratios at age 4 using multiple linear regression models, and mediation analysis was further used to examine the mediating role of placental DNAm in the associations between prenatal BPs exposure and digit ratios among 345 mother-child pairs. Prenatal exposure to bisphenol A (BPA) was associated with hypermethylation at Protocadherin 8 (PCDH8), RBMX Like 2 (RBMXL2), and Sperm Acrosome Associated 1 (SPACA1), while bisphenol F (BPF) exposure was associated with higher methylation levels of Fibroblast Growth Factor 13 (FGF13). Consistent patterns were found in associations between higher DNAm at the 4 genes and increased digit ratios. Further mediation analysis showed that about 15% of the effect of BPF exposure on increased digit ratios was mediated by placental FGF13 methylation. In conclusion, the altered placental DNAm status might be a mediator underlying the feminizing effect of prenatal BPs exposure.

The associations between digit ratio (2D:4D and right - left 2D:4D), maximal oxygen consumption and ventilatory thresholds in professional male football players.

INTRODUCTION: Digit ratio (2D:4D: the relative length of the 2nd and 4th digit) is thought to be a negative correlate of prenatal testosterone. The 2D:4D is related to oxygen metabolism, but the precise nature of this relationship is unclear. The purpose of the present study was to consider associations between digit ratios (right 2D:4D, left 2D:4D, right-left 2D:4D [Dr-l]) and VO2max and ventilatory thresholds (VT1 and VT2). METHODS: One hundred and thirty-three Caucasian (n = 133) professional football players competing in Cyprus participated in the study. Players underwent anthropometric measurements, and digit lengths were measured from hand scans. They also completed an incremental cardiopulmonary test to exhaustion on a treadmill. RESULTS: There were negative correlations between digit ratios and VO2max (right 2D:4D, r = -.65; left 2D:4D r = -.37, both p < .0001; Dr-l r = -.30, p = .0005). There were no relationships between digit ratios and VT1. For VT2, there were negative relationships with digit ratios (right 2D:4D, r = -.43, p < .0001; left 2D:4D, r = -.21 and Dr-l, r = -.21, both p = .02). Digit ratios are negatively related to VO2max with large (right 2D:4D) and medium (left 2D:4D, Dr-l) effect sizes. For VT2, there were also negative correlations, which were medium (right 2D:4D) and small (left 2D:4D, Dr-l). CONCLUSION: Our findings may help clarify the relationships between digit ratios and high-intensity actions for extended periods, which are dependent on efficient oxygen metabolism.

Unveiling intra-person fingerprint similarity via deep contrastive learning.

Fingerprint biometrics are integral to digital authentication and forensic science. However, they are based on the unproven assumption that no two fingerprints, even from different fingers of the same person, are alike. This renders them useless in scenarios where the presented fingerprints are from different fingers than those on record. Contrary to this prevailing assumption, we show above 99.99% confidence that fingerprints from different fingers of the same person share very strong similarities. Using deep twin neural networks to extract fingerprint representation vectors, we find that these similarities hold across all pairs of fingers within the same person, even when controlling for spurious factors like sensor modality. We also find evidence that ridge orientation, especially near the fingerprint center, explains a substantial part of this similarity, whereas minutiae used in traditional methods are almost nonpredictive. Our experiments suggest that, in some situations, this relationship can increase forensic investigation efficiency by almost two orders of magnitude.

The association between 2D:4D digit ratio and sex-typed play in children with and without siblings.

The 2D:4D digit ratio is commonly used as a surrogate possibly reflecting prenatal testosterone levels. Indirect evidence comes from studies investigating the association between 2D:4D and human characteristics that likely relate to prenatal testosterone. In children, sex-typed play reveals large sex differences early in development and an influence of prenatal testosterone is likely. Findings on the association between 2D:4D and children's sex-typed play are heterogeneous and other influences on the development of sex-typed play have been suggested, most of all social influences like siblings, their sex and birth order. The current study examined the association between right and left 2D:4D, a proposed surrogate for prenatal testosterone exposure, which was assessed in right and left hands of N = 505 6-month-old children, and sex-typed play behavior, which was evaluated 3.5 years later using the Pre-School Activities Inventory (PSAI), and the influence of siblings. To capture differential effects of siblings' sex and birth order, dummy-coded variables were used reflecting having no siblings as well as older or younger sisters or brothers. Multiple regression models were used to investigate the association between PSAI scores and sex, right and left 2D:4D, being a singleton as well as having an older or younger sister or brother. It was shown that sex and having an older brother were significant predictors for sex-typed play. Effects were further disentangled by conducting separate regression analyses in boys and girls. In boys, a significant association between PSAI scores and having an older brother was revealed, in girls, no significant associations were found. Results are discussed highlighting the non-significant association between 2D:4D and children's sex-typed play, which weakens the applicability of 2D:4D as a surrogate reflecting influences of prenatal T. Further, the importance of social factors like siblings on children's sex-typed play is discussed.

Maximum trunk tip force assessment related to trunk position and prehensile 'fingers' implication in African savannah elephants.

African elephants have a wide range of abilities using their trunk. As a muscular hydrostat, and thanks to the two finger-like processes at its tip, this proboscis can both precisely grasp and exert considerable force by wrapping. Yet few studies have attempted to quantify its distal grasping force. Thus, using a device equipped with force sensors and an automatic reward system, the trunk tip pinch force has been quantified in five captive female African savanna elephants. Results showed that the maximum pinch force of the trunk was 86.4 N, which may suggest that this part of the trunk is mainly dedicated to precision grasping. We also highlighted for the first time a difference in force between the two fingers of the trunk, with the dorsal finger predominantly stronger than the ventral finger. Finally, we showed that the position of the trunk, particularly the torsion, influences its force and distribution between the two trunk fingers. All these results are discussed in the light of the trunk's anatomy, and open up new avenues for evolutionary reflection and soft robot grippers.

Second to fourth digit ratio (2D:4D) as the 'anatomical marker' and reproductive 'hormonal fingerprint' in the occurrence dental plaque accumulation.

OBJECTIVES: Digit ratio (2D:4D), as endocrine fingerprint, can indicate prenatal androgen exposure. It serves as an anatomical marker for various systemic diseases and a few studies relating it to oral health. The present study aims to evaluate the association between digit ratio and susceptibility to dental plaque formation. METHODS: The study was conducted on young adults aged between 18 and 25 years. Digit ratio and reproductive hormones were measured; dental plaque score and gingival index (GI) were recorded. Data were analysed using the MedCalc. v.20. RESULTS: Male and female participants were categorized into two groups based on their digit ratios being either above or below the calculated average (0.99 for females, 0.98 for males). Those with a digit ratio below the average had a significantly higher mean dental plaque score (p < 0.0001) than those with ratios at or above the average. However, there was no significant difference in the GI between the two groups. Reproductive hormone profiles varied significantly between the higher and lower digit ratio groups for both sexes. CONCLUSIONS: Digit ratio may find potential to be used as an anatomical marker to identify the susceptibility to dental plaque build-up.

Investigating the effects of prenatal testosterone exposure (via 2D:4D) and socio-relational factors on 3-6-year-old preschoolers' prosocial choices.

BACKGROUND AND AIMS: Prosocial behavior such as helping and sharing develops early in childhood. Yet very few studies have investigated physiological and relational factors shaping prosociality among children. Here, we systematically examined the role of prenatal androgen exposure alongside prestige, dominance, and friendship in 3-6-year-old preschoolers' prosocial sharing with familiar peers. METHODS: We tested a sample of 65 children, predominately of European descent. We used a cost-free direct-interaction prosocial choice task to assess children's prosocial tendencies. Second-to-fourth digit ratio (2D:4D) was used as a retrospective biomarker for prenatal androgen exposure. Prestige was measured through behavioral observations of interaction partners and visual regard, dominance through teacher questionnaires, and friendship via peer preference assessments. RESULTS: We found that children acted prosocially when tested with a familiar peer. Children with lower 2D:4D (higher prenatal androgen exposure) behaved more prosocially. Further, there were marginal associations between the donors' prosocial tendencies and their visual regard as a proxy of their prestige (positive effect) and their teacher-rated dominance relative to the recipient (negative effect). Neither age, sex, nor friendship influenced prosocial choices. CONCLUSIONS: Prenatal androgen exposure, approximated via 2D:4D, was associated with prosocial behavior. In contrast to previous research in older children, higher exposure was related to stronger prosocial tendencies, which corresponds to earlier findings on fairness in adults. Our findings point towards a potential role of sex steroids in the early development of children's social behavior, but they have to be interpreted with caution due to the small sample size of the current study. Nevertheless, they underscore the importance of integrating biological and psychological perspectives, while also highlighting the significance of studying the development of prosocial behavior within peer groups.

Early developmental masculinization among boys: More prenatal testosterone action (assessed via 2D:4D) renders their faces perceived as masculine but not pretty or cute.

The 'organizational-activational hypothesis' posits that the fetal environment has a lasting impact on offspring physical, cognitive, and behavioral phenotype. An established biomarker for human prenatal testosterone exposure is the second-to-fourth digit ratio (2D:4D). While related facial characteristics and their social perceptions have been investigated in young adults, studies focusing on younger or older age groups are scarce. Standardized facial photographs of 17 Austrian boys aged 4 to 11 years were each rated by 162 adults in Austria (78 female, 84 male) for masculinity, dominance, physical strength, maturity, independence, cuteness, and prettiness. Following high interrater agreement (Cronbach's alphas >0.96), average ratings per face were subjected to a principal component analysis. The first principal component (52 % var. expl.) correlated positively with the boys' age (r = 0.685), whereas the second principal component (37 % var. expl.) reflected organizational effects of prenatal androgen exposure (i.e. androgenization), as shown by a negative correlation with the boys' 2D:4D (r = -0.487). Geometric morphometrics was employed to extract the facial shapes corresponding to these two principal components. Overall, adults consistently attributed masculinity in line with prenatal testosterone exposure, whereby masculinity was assessed as neither pretty nor cute. In contrast to findings within adults, boys' face ratings of dominance and physical strength did not correspond with their masculinity assessments, but rather with the social attributions reflecting age-related developmental progress (maturity and independence). This adds an ontogenetic layer of complexity. Prenatal testosterone exposure influences the development of boys' facial features, which in turn even shape social stereotypes in adults.

Evaluation of digit ratio (2D:4D) in breast cancer patients.

Breast cancer is a hormone-dependent cancer. Hormonal exposure begins in the intrauterine period and continues in later years of life. 2D:4D ratio is accepted as an indicator of this exposure. The aim of this study was to investigate whether there is a difference in 2D:4D ratio between pathological subgroups of breast cancer and healthy control group. In this study, 204 participants, 154 breast cancer patients and 50 healthy control volunteers with similar age distribution, were included. Both hands of all participants were scanned using a digital scanner. The second and fourth finger lengths were measured using a digital measuring ruler with an accuracy of 0.05 mm. The 2D:4D ratio was calculated as the length of the second finger divided by the length of the fourth finger. A total of 204 patients (55 triple negative, 52 luminal B, 33 luminal A, 14 HER2-overexpessing and 50 healthy control volunteers) were subjected to finger scanning. There was no statistically significant difference in mean age between the groups. The right hand 2D:4D ratio was significantly lower in the Luminal A group compared to the other groups (p < 0.048). Although prenatal hormonal exposure is accepted as a risk factor for breast cancer, no study has evaluated patients in pathological subgroups. The 2D:4D ratio may be associated with breast cancer especially in the luminal A group in which hormone receptors are strongly positive and which has a better prognosis compared to the other groups.

First trimester maternal sex steroids and the digit ratios of mothers and children.

BACKGROUND: It is thought that digit ratios (2D:4D) are a correlate of 1st trimester maternal and foetal sex steroids. Here we consider the relationship of 2D:4D to the former. METHOD: Digit lengths were directly measured with a calliper at infant age 13 months. Measures of T and E were obtained from mother's blood at 6-8 weeks, 10-11 weeks and 1st trimester means were calculated. RESULTS: There were 69 mother-infant pairs (33 boys). Sex differences in 2D:4D (boysboys) were found. For mothers of girls: there were negative relationships between 2D:4D and T at 6-8 weeks, 10-11 weeks and 1st trimester means. For infants: girls showed more correlations between 2D:4D and hormones than boys. For boys, there was one positive association between 2D:4D and E and two positive associations for E/T. For girls, 2D:4D was negatively related to T (four correlations) and positively related to E/T (four correlations). Considering associations in the total sample and controlling for sex, at 6-8 weeks right and left 2D:4D were positively related to E. At 10-11 weeks, right and left 2D:4D were negatively related to T. For 1st trimester means, 2D:4D's were positively related to E (right and left) and negatively related to T (right). CONCLUSION: Infant 2D:4D was correlated with first trimester maternal sex steroids, particularly at 10-11 weeks. The correlations were negative for T, and positive for E and E/T with weaker effects for male infants. The latter pattern may arise because in boys T produced by foetal testes masks the effect of maternal T.

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.

Associations between 2D:4D from direct and radiographic measurements with handgrip strength in young adult Tuvans.

BACKGROUND: Digit ratio (2D:4D) - the relative lengths of the index and ring finger - is sexually dimorphic (male < female), possibly because of the sex-differentiated impact of prenatal androgenization on fetal development in the 1st trimester. The sex difference remains stable with age and has been reported in children, adolescents, and adults from industrialized and non-industrialized societies. Handgrip strength (HGS) also is sexually dimorphic (males > females) and correlates negatively with 2D:4D. AIMS: To examine in a sample of young adult Tuvans from Siberia (Russian Federation): i) the association between 2D:4D measured directly from the palms with 2D:4D measured from radiographic images of the same individuals and ii) the associations between 2D:4D and HGS in Tuvan men and women. STUDY DESIGN AND SUBJECTS: The study was cross-sectional. Participants were Tuvans (n = 185; 80 men; mean age = 21.02 years). 2D:4D was measured with a caliper from the ventral surface of the palm (both hands) and from radiographic images (left hand). HGS of both hands was measured with a digital hand dynamometer. Body height and weight were measured with an anthropometer and a body composition scale. RESULTS: 2D:4D ratios and anthropometric measures (including HGS) were sexually dimorphic. Men had lower 2D:4D and higher HGS than women. Direct measures of 2D:4D correlated positively with 2D:4D measured from radiographs. Body mass index (BMI) was a significant predictor of HGS for both sexes. Male right 2D:4D and female right and left 2D:4D correlated negatively with HGS after controlling for the influence of BMI. There were no associations with radiographic measurements of 2D:4D. CONCLUSION: Our findings provide evidence of sexual dimorphism in 2D:4D among young adult Tuvans. Together with previous research on Tuvan children and adolescents, these findings provide clear evidence of 2D:4D sexual dimorphism in pre- and postpubertal Tuvans. The small negative association between 2D:4D and HGS corresponds to similar reports across populations, suggesting that 2D:4D is a weak correlate of muscular fitness.

Ontogeny and sexual dimorphism in the human hands through a 2D geometric morphometrics approach.

OBJECTIVES: This study aims to conduct a thorough characterization of hand morphology. Employing a 2D geometric morphometric approach, we scrutinize individual fingers and the palm, delineating the ontogenetic trajectories for each biological sex and investigating the alterations that take place at various stages of human development. MATERIALS AND METHODS: A set of thirty-two 2D anatomical landmarks were assessed in a sex-balanced sample of human hands (F = 275, M = 250 males), spanning all stages of human development. Following Procrustes registration, the data on size and shape for individual fingers and the palm were examined for each biological sex and age group. Regression analysis was utilized to quantify ontogenetic trajectories for each biological sex. RESULTS: The findings suggest a gradual escalation in sexual dimorphism throughout human development, with statistically noteworthy distinctions becoming apparent in size starting at the age of 3, and in shape from the age of 7 onwards. Additionally, our analyses uncover a distinctive sigmoid pattern between sexes, indicating that biological male hands exhibit a sturdier build compared to biological female hands from early childhood onward. CONCLUSIONS: In conclusion, this study enriches our insights into sexual dimorphism in human hands, stressing the importance of considering both size and shape across different ontogenetic stages. These findings not only expand our understanding of human biological variation but also lay the foundation for future interdisciplinary research in diverse scientific domains.

Association of second and fourth digit (2D:4D) ratios with metabolic syndrome and cardiovascular disease risk.

BACKGROUND: The study aimed to investigate the association of second and fourth-digit (2D:4D) ratios with metabolic syndrome (MS) and cardiovascular disease risk (CVR). METHOD: This case-control study was conducted between February and March 2024 with 200 participants (100 patients +100 controls). Biochemical parameters (glucose, total cholesterol, HDL, LDL, triglycerides, haemogram, HbA1C) were recorded. All participants were evaluated in terms of MS diagnostic criteria. CVR was calculated with the ESC CVD Risk Calculator. Second-digit and fourth-digit measurements were performed and the 2D:4D ratio of both hands and the difference between 2D:4D of both hands (Dr-l) were obtained. The relationship between 2D:4D and MS, CVR, and gender was evaluated. p < .05 was considered statistically significant. RESULTS: Forty-one percent of the study participants were male. The right-hand 2D:4D (R2D:4D) ratio was 1.009 ± 0.04 and the left-hand 2D:4D (L2D:4D) ratio was 0.991 ± 0.04 (p < .001). R2D:4D ratio was 1.010 ± 0.04 in women and 0.985 ± 0.03 in men (p = .019). R2D:4D (p < .001), Dr-l (p = .001), and CVR (p < .001) were significantly higher in men with MS (+) compared to MS (-). CONCLUSION: In our study, the R2D:4D ratio was found to be associated with MS and CVR in men. Low intrauterine androgen exposure may affect the development of MS, but this effect is more prominent in males.

An unusual configuration of two anomalies in the extensor digitorum profundus complex in a human.

The extensor digitorum profundus complex underwent degeneration of the ulnar segments during primate adaptation and evolution. This process resulted in the preservation of only the extensor pollicis longus and extensor indicis in some apes, including humans. Consequently, anatomical variations within the digitorum profundus complex in modern humans have been well-documented, with detailed reports on their frequency and patterns in previous studies. Here, we report an unusual arrangement involving two anomalies in the extensor digitorum profundus complex, identified in a 66-year-old Japanese male cadaver. In this cadaver, two accessory muscles differentiated from both the extensor pollicis longus and extensor indicis. Notably, the latter muscle featured a tendon bifurcating towards both the thumb and index fingers, referred to as the extensor pollicis et indicis communis. Under the extensor retinaculum, the tendon of the accessory extensor pollicis longus passed through an independent compartment, whereas that of the extensor pollicis et indicis communis traversed a compartment shared by the extensor indicis and the extensor digitorum communis. Both muscles were innervated by the posterior interosseous nerve. Previous studies have reported that the accessory slip of the extensor pollicis longus and extensor pollicis et indicis communis appear at frequencies of 0.6% and 0.4-1.4%, respectively. However, to the best of our knowledge, a configuration in which both appear simultaneously has not been reported. The data from this case could provide essential insights into the variations in the extensor digitorum profundus complex in humans and non-human primates.

Understanding Covid-19: Digit ratios and duration of oxygen therapy in hospitalized Covid-19 patients.

BACKGROUND: Covid-19 severity shows a sex difference (males>females) and progressive hypoxia among the most seriously affected. Digit ratios are sexually dimorphic and may be negatively-related to prenatal (2nd-to-4th digits' ratio; 2D:4D) and pubertal (3rd-to-5th digits' ratio; 3D:5D) testosterone. Oxygen therapy is important in Covid-19 treatment and low 2D:4D is linked to efficient oxygen metabolism. We consider relationships between digit ratios and duration of oxygen treatment in hospitalized Covid-19 patients. METHODS: Digit lengths were measured from photographs of the patient's hands. Age, Sex, BMI, vaccination status and number of days of O2 treatment, were recorded. RESULTS: There were 100 (58 women) patients. Sex differences (males

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

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

2D/4D Finger Length Ratio in the Screening of Developmental Dysplasia of the Hip.

OBJECTIVE: To investigate whether there is a relationship between the 2nd finger and 4th finger length measurement ratios and developmental dysplasia of the Hip (DDH). STUDY DESIGN: Cross-sectional observational study. Place and Duration of the Study: Department of Orthopaedics and Traumatology, Meram Faculty of Medicine Hospital, Konya, Turkiye, from January 2020 to May 2023. METHODOLOGY: Infants were screened for DDH with Graff method for the ultrasounds of both hips. Lengths of the 2nd and 4th fingers of both hands were measured and recorded. Patients with additional risk factors for developmental dysplasia of the hip (breech birth, family history, oligohydramnios, swaddling) were excluded. RESULTS: Two hundred and fifty-six babies were screened including 55.1% (n = 141) girls and 44.9% (n = 115) boys. Their mean age was 2.51 ± 0.80 months. The average lengths were 31.73 ± 3.05 mm, for the left 2nd finger and 34.26 ± 3.48 mm for the left 4th finger. In the hip USG measurements, the mean alpha angles were 62.91 ± 3.12° for the right hip and, 63.20 ± 3.55° for the left hip. Eighteen (7%) of babies who underwent hip ultrasound (USG) had unilateral or bilateral DDH. Among these cases, 2.7% (n = 7) had right, 2.3% (n = 6) had left, and 2% (n = 5) had bilateral DDH. There was no statistically significant correlation between the ratios of right 2/4 finger lengths and the right alpha angle (rs = 0.051; p = 0.421). There was a statistically positive and statistically significant correlation between the ratios of left 2/4 finger lengths and the left alpha angle (rs = 0.154; p = 0.013). CONCLUSION: Only the left-hand finger ratio among the parameters in the model had a statistically significant effect on DDH. Therefore, the left hand 2D/4D finger length may be of value in screening for DDH. KEY WORDS: Developmental dysplasia of the hip, Second to fourth finger digit ratio, Ring finger, Digit ratios.