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| REVIEW ARTICLE |
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| Year : 2018 | Volume
: 10
| Issue : 5 | Page : 220-223 |
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Hormonal fingerprints: A potential screening tool
Rakhi Issrani1, Abdalwhab MA Alzwiri1, Namdeo Prabhu2, Ahmed Shawkat Hashem1
1 Department of Preventive Dentistry, College of Dentistry, Jouf University, Sakaka, Kingdom of Saudi Arabia
2 Department of Oral and Maxillofacial Surgery and Diagnostic Sciences, College of Dentistry, Jouf University, Sakaka, Kingdom of Saudi Arabia
| Date of Web Publication | 24-Oct-2018 |
Correspondence Address:
Dr. Rakhi Issrani
Department of Preventive Dentistry, College of Dentistry, Jouf University, Sakaka
Kingdom of Saudi Arabia
 Source of Support: None, Conflict of Interest: None  | Check |
DOI: 10.4103/jioh.jioh_151_18
The ratio between second and fourth digit lengths (2D:4D ratio) is termed as hormonal fingerprint. This ratio is sexually dimorphic and can be measured by various methods using digital vernier calipers, radiographs, photographs, photocopies, and scanners. In the medical scenario, 2D:4D ratio is used as a biological marker for predicting and diagnosis of many metabolic disorders mainly coronary heart disease and autism, whereas, in dentistry, this method is still in blooming stage. This article highlights the role of hormonal fingerprints as potential biomarkers in early diagnosis, prognosis, and early lifestyle interventions for many dental diseases.
Keywords: Biomarker, caries risk, hormonal fingerprints, malocclusion, second-to-fourth digit ratio
How to cite this article:
Issrani R, Alzwiri A, Prabhu N, Hashem AS. Hormonal fingerprints: A potential screening tool. J Int Oral Health 2018;10:220-3 |
| Introduction | |  |
Currently, the so-called hormonal fingerprint also called second-to-fourth digit ratio (2D:4D ratio) has received a lot of research attention. It refers to the relative length of the fourth digit compared to the second digit and is reported to be a stable, reproducible, and consistent feature for an individual.[1],[2] Although there are other digit ratios (3D:5D) that can be used for assessing sexual dimorphism and relationship to various human phenotypic traits, 2D:4D ratio has been shown to be more sensitive.[3] Being identified as a new risk marker in the medical field, 2D:4D digit ratio has been used to envisage many medical diseases at a very early stage of life, thus unfastening this field for the early prediction of diseases pertaining to many other disciplines.
Establishment and sexual dimorphism of digit ratio
Research confirms that the 2D:4D ratio is sexually differentiated in humans – males tend to have lower 2D:4D than females. The reason documented for this sexual dimorphism is that men tend to have greater relative length of the ring finger when compared with their index finger. The primary mechanism explaining this sexual difference is that the development of digits and gonads take place by the common genes Homeobox A and D. The steadiness of this digit ratio throughout the life is due to the timing of gene regulation which is constant. The other recommended mechanism is that finger ratio, being a function of androgen sensitivity rather than androgen concentration, is affected by exposure to androgens, and thus this digit ratio can be regarded as an easy measure for prenatal androgen exposure. These dissimilarities in the digit ratios are established by the 13th or 14th week of intrauterine life (second trimester) and exhibit substantial constancy over the lifetime.[1] This digit ratio also varies among different ethnic groups, and surprisingly, this variation is far larger than the difference between the sexes. This was shown in the study done by Manning et al., where in addition to the significant sexual dimorphism in 2D:4D, the mean ratios also varied between the English, Scottish, Uygur, Han and Jamaican children.[3]
[Table 1] depicts the correlation between the 2D:4D ratio and various traits in humans.[3] | Table 1: Correlation between the digit ratios and various traits in humans
Click here to view |
| Methods of Measurement | | |
The following methods are commonly implemented for measuring 2D:4D ratio:[3]
Digital vernier calipers
The index and ring fingers are determined from the fingertip to the midpoint of the base of the crease, on the ventral surface of the hand, using digital vernier calipers. Further, the digit ratio is obtained by dividing these values and calculating the mean of the multiple measurements for both hands and divided for the calculation of 2D:4D ratio of both the hands separately.
Radiographs
Radiographs can also be used for the measurement; however, it always has an ethical consideration to radiation exposure.
Digital photographs
Digital photographs may also be used with the hand held in supine position and fingers extended. Later, the length of the fingers can be measured directly or by using image editing software.
Photocopies
The photocopies of hands can also be used to measure the digit ratios, but this method tends to give lower values for digit ratios as compared to the values obtained from direct measurements.
Digital scanners
The above-mentioned methods are reported to be less accurate and precise. Digital scanners were therefore introduced to overcome these limitations. Flat-bed scanners are suitable in terms of precision, expediency, and expenses. The individual is instructed to place both the hands on the scanner with all the fingers extended and visible. For more accuracy, a small inscription is drawn on the bottom creases of the index and ring finger. The contrast, brightness, and size can be adjusted with the help of imaging editing software, mainly Adobe Photoshop.
Implications in dentistry
In the past 5 years, many papers have documented the relations between 2D:4D and human traits and behaviors. Dental studies pertaining to the effect of hormonal fingerprint on oral health are very sparse.
A study was conducted by Verma et al.[2] to determine the correlation between caries risk and 2D:4D ratio. Two hundred and fifty children with age ranging from 6 to 16 years were selected and PROP (6-n-propylthiouracil) sensitivity test was carried out by placing a strip on the dorsal surface of their tongue. The hormonal fingerprint was made by measuring the length ratio of the index and ring finger with the help of digital vernier caliper. There was a positive correlation between low 2D:4D ratio, i.e., high prenatal androgen levels and high caries index. It was concluded that the hormones have an impact on taste perception and dietary preferences, which in turn influence their caries index.
A study was conducted by Premkumar and Gurumurthy[4] to compare 2D:4D ratio with patients having orthognathic, retrognathic, and prognathic mandibles. A total of 320 individuals were included in the study, of which 60 individuals had retrognathic mandible, 55 had prognathic mandible, and 205 had normal mandible. 2D:4D ratio was determined with the help of vernier calipers. Low 2D:4D ratio was seen in prognathic mandible cases. These findings suggested that testosterone plays an important role in mandibular growth. Hence, it was concluded that hormonal fingerprint, being an invasive and reproducible procedure, can be used for early detection of mandibular prognathism and also as a diagnostic tool in correlating mandibular growth with casual relations between hormones and craniofacial development. This relationship between hormones (especially testosterone) and bone growth can be substantiated by the fact that hormones serve as general epigenetic factors contributing to craniofacial growth and development.
Hopp et al.,[5] conducted the study to assess the correlations between 2D:4D and success in practical and theoretical examinations in the dental school curriculum of a Brazilian university. A total of 80 individuals (40 males) had their right-hand palm photographed by a digital camera attached to a standardizing device and Adobe Photoshop was used to measure the index and ring fingers. Theoretical and practical grades were significantly negatively correlated to digit ratio in males (P = 0.02 and 0.004, respectively), but not in females (P = 0.89 and 0.77, respectively). This finding supports a link between high prenatal testosterone and intelligence in males.
Another study was conducted by Priyanka et al.,[1] to depict the role of hormonal fingerprints in the early detection of malocclusion, caries, and the influence of Basal Metabolic Index (BMI) on malocclusion and caries. Overall, 300 children from both sexes between the age group of 10 and 15 years were selected. Measurement of digits was made using the digital vernier caliper. Among the study population, majority of the participants were having 2D:4D ratio <1. The rate of occurrence of malocclusion increased with increase in the value of 2D:4D ratio, whereas higher BMI values were associated with normal occlusal conditions and lower 2D:4D ratio. High caries incidence was reported in children with malocclusion. Hence, this study concluded that hormonal fingerprints could be used as an early predictor of the occurrence of malocclusion and BMI which in turn influences the caries index.
A study was conducted by Lakshmi et al.[6] to evaluate the association between genetic taste sensitivity, dietary preferences, and salivary flow rate in 6- to 14-year-old children for identification of individuals at higher risk of developing dental caries. Propylthiouracil sensitivity test was carried out to classify the individuals as tasters or nontasters and for dietary preferences the individuals were categorized as sweet likers and dislikers. The salivary flow rate was estimated by collecting unstimulated saliva by spitting method. A positive relation between low digit ratio (2D:4D ratio), nontasters, sweet likers, and high caries index among the participants was found.
Future research should particularly target three issues. First, it is of utmost importance to bear in mind that hormonal prints can be affected by a number of factors, as most of the dental diseases are multifactorial in origin, each one having profound affects; hence, we urge that comprehensive studies need to be undertaken in the near future to encompass all these factors. Second, it is essential to understand that ethnicity of the individuals and geographical location on individuals have rather significant consequences on hormonal prints and hence necessitate exploration which are necessary to confirm the role of ethnicity and location on an individual with the dental disease. Third, future research concerning the association between different dental diseases and the 2D:4D digit ratio should include a broader age range with larger sample size.
[Table 2] shows the summary of the studies conducted to evaluate the association between 2D:4D ratio with various parameters. | Table 2: Summary of the studies conducted to evaluate the association between second-to-fourth digit ratio with various parameters
Click here to view |
| Conclusion | | |
The 2D:4D ratios provide an inside into the prenatal life of an infant which gives information about the behavior, probability of disease occurrence, intelligence, and reproductive abilities. 2D:4D ratio is predictive of many diseases and may be used in diagnosis, prognosis, and early lifestyle interventions which may delay the onset of disease or facilitate its early detection. Despite its history, hormonal fingerprinting is still a new and developing science and much remains to be discovered. Time and the continued efforts of dedicated researchers will eventually lift hormonal fingerprinting out of its fairground environment and enable it to be regarded as a valuable tool for doctors, psychologists, and other medical professionals since these digit ratios have continued to show promise as biomarkers of health and diseases.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
| References | | |
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[Table 1], [Table 2]
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