Embryological development and prevalence of digital flexion creases

Is prenatal testosterone-estrogen balance related to critical shoulder angle?

BACKGROUND

The 2D:4D ratio (an indicator of prenatal testosterone-estrogen balance) is the ratio of the second finger length to the fourth finger length. We hypothesized that low 2D:4D values indicating high prenatal testosterone exposure may be associated with increased critical shoulder angle (CSA).

AIMS

The aim of this study was to evaluate the relationship between CSA and 2D:4D ratio.

METHODS

Meeting the study criteria, 252 patients were included in the study. We measured CSA on true anterior-posterior radiographs, glenoid version(GV) and glenoid inclination(GI) on MRI images and the lengths of the second and fourth fingers on both hands of the patients. Additionally, we compared 2D:4D ratios and CSA, GV, GI measurements.

RESULTS

We found a significant negative correlation between CSA and the 2D:4D ratio in both hands (p < 0.001). Patients with CSA > 35° had a significantly lower 2D:4D ratio than patients with CSA < 35° (p < 0.001). When the patients were grouped according to CSA35°, the cut-off value for the left-hand 2D:4D ratio was 0.96, which showed 84.8 % sensitivity and 83.3 % specificity(AUC:0.911). Patients were compared in terms of CSA by categorizing as 2D:4D > 1 and 2D:4D < 1. Accordingly, the CSA value was significantly lower in patients with 2D:4D > 1. In the classification made according to this length classification of the left hand, the cut-off value was 30.25°. This value showed 92.2 % sensitivity and 85 % specificity(AUC:0.956).

CONCLUSION

The 2D:4D ratio is related to CSA. A low 2D:4D ratio(<0.96), indicating high intrauterine testosterone exposure, is associated with CSA > 35°, while a high 2D:4D ratio (>1), indicating low intrauterine testosterone exposure, is associated with a low CSA(<30.25°).

Is the ratio of the index to ring finger length, a potential marker for prenatal testosterone-estrogen balance, related to posterior tibial slope?

BACKGROUND

The 2D:4D ratio, an indicator of prenatal testosterone-estrogen balance, is the index finger (second finger) size's ratio to the ring finger (fourth finger) size. Asymmetric growth in the proximal tibial growth plate is considered to cause the increased posterior tibial slope (PTS) formation. Factors determining the amount of this asymmetry still need clarification. This study aims to evaluate the relationship between the 2D:4D ratio, which indicates the prenatal testosterone-estrogen balance, and the PTS.

METHOD

Meeting the study criteria, 267 patients were included in the study. We measured the medial PTS (MPTS) and lateral PTS (LPTS) on MRI images and the lengths of the second and fourth fingers on both hands of the patients. Additionally, we compared 2D:4D ratios and MPTS and LPTS measurements.

RESULTS

We found a significant negative correlation between MPTS and the 2D:4D ratio, as well as between LPTS and the 2D:4D ratio in both hands (MPTS left vs. right hand: P < 0.001, r = -0.627 vs. P < 0.001, r = -0.498) (LPTS left vs. right hand: P < 0.001, r = 0.589 vs. P < 0.001, r = 0.404). Separately among males and females, there was a significant negative correlation between MPTS and the 2D:4D ratio, as well as between LPTS and the 2D:4D ratio in both hands (for males: MPTS left vs. right hand: P < 0.001, r = -0.607 vs. P < 0.001, r = -0.540)(for males: LPTS left vs.right hand: P < 0.001, r = 0.451 vs. P < 0.001, r = 0.406) (for females:MPTS left vs. right hand: P < 0.001, r = -0.638 vs. P < 0.001, r = -0.446) (for females:LPTS left vs.right hand: P < 0.001, r = 0.618 vs. P < 0.001, r = 0.403).

CONCLUSIONS

The 2D:4D ratio, an indicator of intrauterine testosterone-estrogen balance, is related to PTS. The effect of testosterone on the growth plate of the proximal tibia may be one of the factors determining the PTS value.

LEVEL OF EVIDENCE

III retrospective comparative study.

Self-Efficacy and the Digit Ratio in a Group of Sports University Students

Self-efficacy is one's awareness of being able to cope optimally with different situations. Perceived self-efficacy is a belief that closely involves emotional and personological functioning. In fact, when one perceives oneself as capable, the likelihood of success increases significantly. The aim of this research was to verify a possible correlation between self-efficacy and the Digit Ratio (2D:4D), referred to as prenatal androgen levels, and whether these correlate with some psychological variables, considering possible gender differences. This study involved 56 sports university students, whose 2D:4D ratio was calculated. Moreover, self-assessment questionnaires: the Self-efficacy Scale (SES), the Big Five Questionnaire-2 (BFQ-2), the Profile of Mood State (POMS), the State-Trait Anxiety Inventory Form Y (STAI-Y) and the Emotional Regulation Questionnaire (ERQ) were administered. The data show that the perceived levels of self-efficacy seem to be influenced by an innate predisposition linked to prenatal androgen values to which the subjects were exposed during uterine life (2D:4D). This negative correlation indicates that the higher the value of the digit ratio, the more likely it is that the level of perceived self-efficacy will be lower. Finally, the degree of perceived self-efficacy also seems to depend on the levels of subjective anxiety, understood both as a personological disposition and a contingent condition, and the latter also seems to be influenced by prenatal androgen levels, particularly in women.

Digit ratio (2D:4D) and its relationship to foetal and maternal sex steroids: A mini-review

The challenges of terrestrial existence may mean that the early development of tetrapod limb traits is linked to the development of the urogenital system and sex steroids. One such limb trait is the sex-dependent ratio of the lengths of the 2nd and 4th digits (2D:4D). Direct evidence for the association between early sex steroids and offspring 2D:4D can be obtained by manipulating foetal sex hormones. However, this is not ethically permissible in humans. It is widely accepted that 2D:4D is a biomarker for early foetal sex hormones in tetrapods but the link in humans remains controversial. Here we review the evidence that (i) manipulation of sex steroids in early development leads to sex-dependent changes in 2D:4D throughout the tetrapods, and (ii) maternal sex steroids cross the placenta and thus are associated with offspring 2D:4D in both non-human and human animals. We suggest a research focus on associations between human maternal sex steroids and offspring 2D:4D to clarify the link between 2D:4D and early sex steroids. A protocol is proposed to examine the correlation between 1st-trimester maternal sex steroids and offspring 2D:4D. Such an association may explain the existence and medium effect size of the human sex difference in 2D:4D.

The developmental basis of fingerprint pattern formation and variation

Fingerprints are complex and individually unique patterns in the skin. Established prenatally, the molecular and cellular mechanisms that guide fingerprint ridge formation and their intricate arrangements are unknown. Here we show that fingerprint ridges are epithelial structures that undergo a truncated hair follicle developmental program and fail to recruit a mesenchymal condensate. Their spatial pattern is established by a Turing reaction-diffusion system, based on signaling between EDAR, WNT, and antagonistic BMP pathways. These signals resolve epithelial growth into bands of focalized proliferation under a precociously differentiated suprabasal layer. Ridge formation occurs as a set of waves spreading from variable initiation sites defined by the local signaling environments and anatomical intricacies of the digit, with the propagation and meeting of these waves determining the type of pattern that forms. Relying on a dynamic patterning system triggered at spatially distinct sites generates the characteristic types and unending variation of human fingerprint patterns.

Cognitive Performances: The Role of Digit Ratio (D2:D4) With a Protective Factor for Anxiety

This study aimed to identify a possible correlation between the D2:D4 ratio and state and/or trait anxiety in adult healthy subjects and, if so, whether it exists any difference between men and women. In addition, we also wanted to observe whether there is a relationship between participants' age and state and/or trait anxiety. The research involved 125 subjects of both sexes, who were calculated the D2:D4 ratio and were administered the self-assessment questionnaire State-Trait Anxiety Inventory (STAI-Y). Results show that there are positive significant correlations between the D2:D4 ratio and score at state anxiety and trait anxiety, in the total sample. However, if men are examined separately from women, it can be observed that only men have a statistically significant relationship between D2:D4 ratios and state anxiety and trait anxiety. Moreover, about possible relations between the age of participants and state and trait anxiety, a significant negative relationship was observed, without differences between men and women. However, only subjects with a D2:D4 ratio ≥ 1, without differences between men and women, showed a statistically significant negative linear correlation between their age and their state and trait anxiety. The present data allow us to conclude that a low D2:D4 ratio (<1) represents a protective factor against anxiety in both men and women and that this protection seems likely to act throughout life.

Radiographic digit ratios (2D:4D) of Afro-Caribbean children: Comparisons with published data from white children

BACKGROUND

Digit ratio (2D:4D) from soft-tissue measurements of fingers from children and adults from Black and White ethnic groups show sex differences (males<females) and group differences (Black< White). However, less is known about such differences in radiographic 2D:4D.

AIM

To consider sex and ethnic differences in radiographic 2D:4D of children of Afro-Caribbean descent and to compare these means with "standards" from White children.

SUBJECTS AND METHODS

A cross-sectional design with samples from Afro-Caribbean children aged 6 to 11 years compared to published radiographic measurements for White children in the Fels Longitudinal Study.

RESULTS

Radiographic 2D:4D showed ethnic differences such that Afro-Caribbeans<Whites. There was an age-stable right-side sex difference (boys<girls) in the 2D:4D of the distal phalanx and the distal soft-tissue tip in the Afro-Caribbean children but not in the proximal- and middle-phalanges or the composite length of the phalanges. Sex differences in 2D:4D (boys<girls) were present in the White children in the middle and proximal phalanges and composite phalange length but not in the distal phalanx.

CONCLUSION

In Afro-Caribbean children, mean radiographic 2D:4D was lower than that of White children and sexual dimorphism of 2D:4D (boys<girls) was confined to the distal phalanx and fingertip soft-tissue. In contrast in White children, there were no sex differences in the distal phalanx but there were in the middle-, proximal and composite phalanges (boys<girls). We discuss whether these differences in 2D:4D are widespread among Blacks and Whites and the implications for the interpretation of radiographic 2D:4D and morphological soft-tissue 2D:4D across macro-ethnic groups.

Risk-taking behavior, the second-to-fourth digit ratio and psychological features in a sample of cavers

Background

The risk-taking behavior is largely modulated by the subject's history, its lifestyles, by the characteristics of the situations with which it is compared, and also by the effects of prenatal androgens. Thus, the personality of the single person is a significant predictor of such way of acting.

Methods

The present study aimed to explore the relationship between Digit Ratio Measurement (2D:4D) and personality factors capable to be good predictors for choosing highly risky activities, such as caving. Furthermore, our purpose was to investigate whether 2D:4D ratio is related to cavers' affective states and to assess the personological and emotional features of 34 healthy cavers, aged between 24 and 71 years (M = 39.70, SD = 9.81).

Results

Data analysis showed several significant correlations between 2D:4D and Deliberate Risk Taking (RTI) and Precautionary Behavior (RTI), confirming that 2D:4D is a reliable index able to predict risk-taking behaviors. Furthermore, data analysis showed that Conscientiousness and its sub-dimension Scrupulousness (BFQ-2) are recurrent among significant correlations; in particular, the latter reports negative correlations with many factors of POMS. Moreover, all participants seemed to have a good attitude to collaboration, in terms of goal-direct strategy, and an adequate management of negative affective states, useful to maintaining a good level of stress within the group. Finally, the BFQ-2 factor Openness to culture seemed to be a predominant feature in the cavers, and this feature could be considered as predictive in the choice of an activity, such as caving, which requires curiosity, perseverance and a great planning of cave exploration.

The permanence of friction ridge skin and persistence of friction ridge skin and impressions: A comprehensive review and new results

This study addresses the permanence and persistence of friction ridges and the persistence of impressions made from these friction ridges over months and years. Permanence is the unchanging presence and appearance of friction ridge arrangements and their attributes between recurring observations of the skin. Permanence was evaluated from direct photographs of fingers collected over a period of 30-45 days (covering one or more skin regeneration cycles) as well as after 8 or more years had elapsed. Persistence embodies the operational concept of whether or not a pair of images displays sufficient similarity upon which to base an informed decision that they were made by the same finger, while acknowledging certain dissimilarities or distortions due to friction ridge physiology, image capture, matrix, substrate, and applied pressure. Persistence applies to both friction ridge skin and impressions made from these friction ridges. Permanence and persistence of skin were assessed from direct photographs of fingers taken two months apart and from finger photographs separated by an interval of at least 8 years. Permanence and persistence were also assessed from impressions taken over 4 months, as well as those separated by 8-53 years. Variability due to capture method was assessed by using four image capture methods over a four month period: direct photography of fingers, impressions captured by ink, holographic imaging, and live scan. Qualified latent fingerprint examiners assessed all changes observed over time, as well as any limitations imposed by capture method. The practice of comparison and identification of fingerprint impressions was upheld, as was the prevailing use of the word persistence to describe stability of friction ridges. All photographs and impressions of the same finger were identifiable as originating from the same source. Within all the periods of observation, level 1 detail was permanent and persistent. Persistence, but not permanence, was supported for level 2 detail. Notably, the small changes observed were only in appearance; there were no changes in the presence of new, or absence of existing, minutiae. Level 3 details of ridge edge shape and pore presence were neither permanent nor persistent. Ridge width was permanent and persistent. Incipient ridges were neither permanent nor persistent.

Digit ratio, personality and emotions in skydivers

The aim of the present study was investigate if there is an association between second-to-fourth digit length (2D:4D) ratio and personality factors capable of serving as predictors of individual choice towards high-risk activities in a group of experts skydivers; Furthermore, their skills in regulating anxiety and emotions were assessed. The 2D:4D ratio of the right hand of 41 expert skydivers was measured and each of them completed four questionnaires: Big Five Questionnaire-2 (BFQ-2), Profile of Mood States (POMS), State-Trait Anxiety Inventory Form Y (STAI-Y) and Risk-Taking Inventory. Lower 2D:4D ratios did not appear associated with a greater propensity for taking risks but rather with a lower aptitude to assume precautions in unsafe conditions. In fact, the only sub-dimensions of personality, analyzed by the BFQ-2, correlated with the 2D:4D ratio were conscientiousness and agreeableness. Furthermore, prior to launch, the skydiver's level of stress, measured by the POMS, or state anxiety, measured by the STAI-Y, was not significantly correlated with 2D:4D ratio; whereas there was significant positive correlation between 2D:4D values and trait anxiety. Data analysis further revealed that social desirability correlated negatively with state anxiety and total mood disturbance index, and positively with emotion control. The present results suggest that lower 2D:4D ratio may represent a significant predictor of less attentive precautionary behavior when risk-taking.

The second-to-fourth digit ratio correlates with aggressive behavior in professional soccer players

The aim of this study was to test the hypothesis that high levels of testosterone during prenatal life, testified by a low second-to-fourth digit ratio (2D:4D), as well as in adulthood affect the aggressive behavior of professional soccer players. Using 18 male professional players from a first level Italian Soccer Team we calculated: i) the 2D:4D ratio of the right hand, ii) the number of yellow and red cards per game, iii) the mean salivary testosterone concentration (Sal/T) and iv) the handling of aggressive impulses as assessed by the Picture Frustration test (PFT). Soccer players with a lower 2D:4D ratio had a higher number of fouls per game. A significant negative correlation was observed between Sal/T and 2D:4D ratio, as well as between 2D:4D ratio and the aggressiveness of players. By contrast, a significant positive correlation of Sal/T and fouls/game score and PFT was detected. No significant correlation was detected between 2D:4D or Sal/T and the playing position of players. Results of this study revealed that in professional soccer players, aggressive behavior, with the consequent increased risk of fouls during the game, is more likely to occur in individuals with high testosterone levels, not only in adulthood, but also during their intrauterine life.

Genetic association suggests that SMOC1 mediates between prenatal sex hormones and digit ratio

Men and women differ statistically in the relative lengths of their index and ring fingers; and the ratio of these lengths has been used as a biomarker for prenatal testosterone. The ratio has been correlated with a wide range of traits and conditions including prostate cancer, obesity, autism, ADHD, and sexual orientation. In a genome-wide association study of 979 healthy adults, we find that digit ratio is strongly associated with variation upstream of SMOC1 (rs4902759: P = 1.41 × 10(-8)) and a meta-analysis of this and an independent study shows a probability of P = 1.5 × 10(-11). The protein encoded by SMOC1 has recently been shown to play a critical role in limb development; its expression in prostate tissue is dependent on sex hormones, and it has been implicated in the sexually dimorphic development of the gonads. We put forward the hypothesis that SMOC1 provides a link between prenatal hormone exposure and digit ratio.

Segmental 2:4 digit ratio. Unilateral, bilateral and hand-type differences in men

Most studies of the 2:4 digit ratio (DR) of the human hand have analyzed its possibilities for use as an indicator of the functional, psychological, and, with rare exception, morphological features of the body. Each of the functional flexor segments (each phalanx) contributes to the common variability of the total digital length. The aim of this study was to determine patterns in the relationships between each segmental digit ratio (SDR) and the overall 2:4 DR. We studied the variability of the SDRs in comparison with the general 2:4 DR of 202 young males aged 16-21 years. The length of the functional segments of the digits was measured between the flexor skin furrows on the palmar surface. The change in the SDR means that values can be ranked as follows: proximal SDR (SDR-P)>DR>distal SDR (SDR-D)>medial SDR (SDR-M). Bilateral differences are inherent in the segmental SDR-P. Most quantitative regularities inherent in the total 2:4 DR are also intrinsic to the 2:4 DR of the distal segment of the digit; in particular, this phenomenon is displayed in hands of the ulnar (male) type. Overall, the values of the distal rather than the other functional flexor segments of the second and fourth digits are similar in magnitude to the general 2:4 DR. At the same time, the greatest correlation and hence, the largest contribution to the total variability in the general DR is from the variability of the SDR-P values. Our data demonstrate the importance of various digit segment sizes in determining their overall length and the derivative ratios.

Second-to-fourth digit ratio predicts success among high-frequency financial traders

Prenatal androgens have important organizing effects on brain development and future behavior. The second-to-fourth digit length ratio (2D:4D) has been proposed as a marker of these prenatal androgen effects, a relatively longer fourth finger indicating higher prenatal androgen exposure. 2D:4D has been shown to predict success in highly competitive sports. Yet, little is known about the effects of prenatal androgens on an economically influential class of competitive risk taking-trading in the financial world. Here, we report the findings of a study conducted in the City of London in which we sampled 2D:4D from a group of male traders engaged in what is variously called "noise" or "high-frequency" trading. We found that 2D:4D predicted the traders' long-term profitability as well as the number of years they remained in the business. 2D:4D also predicted the sensitivity of their profitability to increases both in circulating testosterone and in market volatility. Our results suggest that prenatal androgens increase risk preferences and promote more rapid visuomotor scanning and physical reflexes. The success and longevity of traders exposed to high levels of prenatal androgens further suggests that financial markets may select for biological traits rather than rational expectations.

Defining the basic aesthetics of the hand

BACKGROUND

Hand aesthetics have been poorly described because function is the main reason why patients consult a surgeon about their hands. Ideal proportions are based on normal anatomy, which is a prerequisite for aesthetics.

METHODS

A literature review was performed.

RESULTS

Anatomically correct proportions are, besides adequate soft tissue, the most important aspects of hands considered to be beautiful. The golden proportion may be used to identify suboptimal areas. Extrinsic and intrinsic aging must be distinguished, and therapy should be determined accordingly.

CONCLUSION

Hand aesthetics are based on normal anatomy. Knowing this is essential for every surgeon treating hand patients.

Comparative investigations of human and rat dermatoglyphics: palmar, plantar and digital pads and flexion creases

The morphological features of the palmar, plantar and digital areas of the rat were studied and compared to the corresponding human traits. The location and the timing of appearance of the volar pads and flexion creases of human and rat fetuses were investigated to determine the feasibility of using rats as an experimental model for studying the factors influencing early development of the dermatoglyphics in humans. Comparisons between analogous developmental stages of human and rat fetuses demonstrate striking similarities in overall fetal development. However, marked differences between human and rat fetuses were found in the timing of developmental milestones and in some morphological features. Provided that these differences are taken into consideration, rats can serve as a useful experimental model in studies of the utility of the epidermal ridge configurations and flexion creases in medical disorders.

Pathogenesis of retinoic acid-induced abnormal pad patterns on mouse volar skin

BACKGROUND

Abnormal dermatoglyphs on human volar skin have been reported in many syndromes, but little is known about the pathogenesis. Patterns of pads on rodent limb volar skin are homologous to human dermatoglyphs.

METHODS

In previous studies, we showed that transplacental exposure to teratogens induced abnormal pads in mouse fetuses. Moreover, teratogens caused abnormal pad patterns at levels below those that caused skeletal malformations. In this study, we examined morphology and cytokinetics in developing abnormal pads. Pregnant mice were treated with all-trans-retinoic acid at 20 mg/kg orally at embryonal day (E) 12.5 (vaginal plug = E0). The hindlimbs of the embryos were harvested and observed under a light microscope and by scanning electron microscopy. Cell proliferation and cell death were estimated by 5-bromo-2'-deoxyuridine (BrdU) labeling, Nile blue A vital staining, and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL).

RESULTS

Retinoic acid induced aplasia of the fibular tarsal pad and supernumerary interdigital pads on hindlimbs. Cell proliferation was observed in the area of developing pad, but cell death was very rarely seen in either normal or abnormal pads.

CONCLUSIONS

Retinoic acid disturbed pad patterning as a whole rather than individual pad formation.

Pads and flexion creases on the plantar surface of hammertoe mutant mouse (Hm)

The purpose of the present work was to determine the effects of the hereditary malformation of Hammertoe mutant mice (gene symbol Hm) on the surrounding morphological structures and, specifically, on the volar pads, i.e., the sites of the epidermal ridge patterns (dermatoglyphics). The hindlimbs of the wild-type (+/+) Hammertoe mice show no anomalies and their major pad and flexion crease configurations correspond to those of normal mice. The heterozygous (Hm/+) and homozygous (Hm/Hm) mice display a fusion of the interdigital tissues involving all digits with the exception of digit I. In Hm/Hm mice, this webbing extends to the distal phalanx and the markedly flexed digits form a shape resembling a hammer. In Hm/+ mice, the interdigital webbing does not extend as far and the digits show moderate flexion compared to those of Hm/Hm mice. Both Hm/Hm and Hm/+ have a rudimentary extra digit in the postaxial area of the hindlimbs. The ventral volar skin of the flexed digits is incompletely developed. The more posterior digits show the more severe camptodactyly. These aberrant configurations are related to the abnormal occurrence of the programmed cell death (PCD) in the interdigital zones II-IV and the proximal part of the postaxial margin during hindlimb development. They are limited to the pads on the plantar surface of the postaxial area; the preaxial area is not affected. As a result of a severe camptodactyly of digit V, its volar skin is shifted into the distal portion of the hypothenar area. This shifting affects the number, size, and location of the pads, especially of the hypothenar pad, resulting in varying pad configurations, such as a displacement of the distal and proximal components of the hypothenar pad, or a fusion of the two components of the hypothenar pad, leading to a reduced final pad number. These pad modifications are induced by the postaxial plantar surface shifting proximally and are not affected by the presence of an extra rudimentary digit. The pad modifications in Hammertoe mice with webbed digits and postaxial polydactyly resemble closely those of the previously studied mice with genetic preaxial polydactyly.

Palmar and plantar pads and flexion creases of genetic polydactyly mice (Pdn)

Attempts to gain a better understanding of the relationship between the epidermal ridge patterns (dermatoglyphics) and flexion creases on the volar aspects of human hands and feet and specific medical disorders led to a search for a suitable animal model, allowing studies of the fetal development of the pertinent structures. A common experimental animal, the rat (Rattus norvegicus), was found to be an excellent candidate, owing to the strong resemblance of the volar pads and flexion creases on its palmar and plantar surfaces to those of human subjects. A hereditary preaxial polydactyly mouse (Pdn) provides an opportunity to study the effects of this malformation on the surrounding morphological structures and, specifically, on the volar pads, i.e., the sites over which the dermatoglyphic patterns develop. The hands and feet of the wild-type (+/+) mice show no anomalies, and their major pad and flexion crease configurations correspond to those of normal rats. The heterozygous (Pdn/+) mice, in spite of having a thumb/big toe with a duplicated distal phalanx on their hands/feet, did not display any alterations in palmar/plantar pads. The homozygous (Pdn/Pdn) mice have a protrusion in the thenar area and one to three supernumerary digits on the preaxial portion of both the hands and feet. The effect of these anomalies was found to be limited to the pad and flexion crease configurations in the preaxial areas; the postaxial sites were not affected. The original number of pads on the thenar/first interdigital areas of Pdn/Pdn mice was apparently identical to that of the +/+ and Pdn/+mice. The preaxial protrusion, however, affected the number, size, and location of the pads observed in the newborn mice, resulting in varying pad configurations, such as fused and scattered pads or a pad cluster formed by gathering the neighboring pads. These pad modifications were induced by the preaxial plantar/palmar protrusion only and were not affected by the presence of supernumerary preaxial digits. In view of the similarities in the morphology and fetal development of human and mouse distal limbs, the present study is relevant to human subjects, particularly to the understanding of the significance of dermatoglyphic variations in individuals with specific medical disorders. Future studies of naturally occurring or experimentally induced limb malformations in mice or rats should provide valuable insights into the development of human hands and feet and into factors contributing to their congenital anomalies.

Fetal and postnatal development of palmar, plantar, and digital pads, and flexion creases of the rat (Rattus norvegicus)

Fetal development of the hands and feet of rats was investigated to determine the feasibility of using rats as an experimental model for studying the factors influencing early development of the hands and feet, and especially the dermatoglyphics in humans. Eighty rats fetuses of 14-21 days gestational age and 80 newborn rats of 0-7 days of age were used to study the morphological features of the palmar, plantar, and digital areas and to determine the timing of appearance and the location of the volar pads and flexion creases. Comparisons between analoguous developmental stages of rat and human fetuses demonstrate striking similarities in overall fetal development. Marked differences, however, were found between rat and human fetuses in the timing of developmental milestones and in some morphological features. The results indicate that rats can serve as a useful experimental model in studies of the utility of the epidermal ridge configurations and flexion creases in medical disorders, provided that the differences in the timing of development are taken into consideration.

Dermatoglyphics on volar skin of mice: the normal pattern

BACKGROUND

Mouse volar skin has many protrusions, both large and small. They can be observed more clearly after removal of the epidermis, as they are chiefly constructed of dermal structures. They form "dermatoglyphs." This report describes the normal pattern of these protrusions to establish a normal standard for detection of abnormalities.

METHODS

Limbs of young and adult mice were fixed in 10% formalin and treated with 5% KOH to remove the epidermis layer. They were observed under a dissecting microscope after toluidine blue staining, or by scanning electron microscopy. Several limbs were used for light microscopic observation.

RESULTS

Four types of protrusions are observed. 1) Digital pads: single large pads on each digital tip. They locate over the distal phalanx. 2) Interdigital pads and carpal (tarsal) pads (or thenar and hypothenar pads): large pads similar to digital pads. There are five on the palm and six on the sole. 3) Caterpillar pads: elongated thin protrusions on the ventral side of the digits. They form stripes transverse to the axis of the digits. 4) Cobblestone pads: many small protrusions between the interdigital and carpal (tarsal) pads. "Caterpillar pads" and "cobblestone pads" are reported here for the first time. Each pad contains sweat glands and has sweat duct openings and dermal ridges on its top.

CONCLUSIONS

A detailed description of the normal pattern is indispensable for identification of abnormal patterns. The present description, therefore, can be used as a normal standard when genetically or environmentally induced anomalies are assessed.