High 3D:5D ratio: A possible correlate of externalizing and internalizing problems: An exploratory study

Abstract

-Background and Objectives:The second to fourth (2D:4D) digit ratio is a sexually dimorphic trait which has been studied to examine the association between fetal hormones and a variety of behaviors. Lower 2D:4D ratios, suggestive of exposure to higher levels of prenatal testosterone, have been associated with male-linked disorders, while higher 2D:4D ratios, suggestive of exposure to weaker prenatal androgen action, have been associated with female-linked disorders. Past research has concentrated on the 2D:4D ratio, whereas the relationship between other ratios, such as the 3D:5D ratio, and psychopathology has not much been studied before. Therefore, the aim of this study was to assess the correlation between the 2D:4D and 3D:5D ratio, and internalizing as well as externalizing symptoms, in a large non-clinical sample (143 boys, 150 girls) of white Caucasian children aged 7 to 13 years.Methods: Externalizing and internalizing symptoms were assessed with the Child Behavior Checklist (CBCL).Results: The 3D:5D ratio in boys and in girls was positively associated with scores on Externalizing Problems. Further, in girls only, the 3D:5D ratio was positively correlated to scores on Internalizing Problems.Conclusions: The 3D:5D ratio can be considered a correlate of externalizing and internalizing problems in children from the general population. In humans, the critical period in prenatal life for sexual differentiation starts around the 7 th -8 th week after conception 1 . Until this moment the genitalia are undifferentiated and the level of testosterone determines whether the fetus then starts to develop into male or female. Prenatal hormones that influence the sexual differentiation also have an effect on sexual differences in behavior.Fetal hormones and its effects on behavior can be studied in a variety of ways. Direct measurements such as hormone levels being extracted from the umbilical cord at birth or assessing hormonal levels of the fetus or the mother during pregnancy suffer from disadvantages due to their invasive nature, selection biases, and ethical considerations. Researchers interested in the effect of prenatal hormones on the behavior of children or adults, therefore often rely on indirect measures. Cohen-Bendahan and colleagues 2 described three indirect methods of examining the behavioral effects of prenatal exposure to sex hormones: otoaucoustic emissions, finger length ratio, and dermatoglyphics. In this paper, we will focus on finger length ratios.Since 1875 3 , it is known that the length of the index finger, compared to the length of the ring finger, the 2D:4D ratio, is a sexually dimorphic trait, not only in humans 4 but also in bonobos 5 . Lower ratios are more common in men and ratios closer to one are more characteristic of women 6,7 . The relative length of fingers is fixed for life within the first three months of pregnancy 6,8 . Finger length ratio is considered as a marker of the amount of testosterone the fetus was exposed to in the womb. A higher level of prenatal testosterone ...

Investigating the reliability and sex differences of digit lengths, ratios, and hand measures in infants

“…play behavior in children 67 – 69 , as well as with several developmental disorders 70 – 72 , psychiatric disorders 73 or even various types of cancer 74 – 79 . Similar results have been already reported for alternative digit ratios that could be linked to coronary heart diseases 80 , attention deficit hyperactivity disorder 81 , and externalizing and internalizing behaviors in children 82 . Although the underlying mechanisms, factors, and complex relations are not yet fully clarified, a valid and reliable measurement of hand and digit measures would be especially valuable in younger cohorts.…”

Finger ridge‐counts correlate with the second to fourth digit ratio (2d:4d)

“…The correlation of digits 2 and 4 with 2d:4d is perhaps the most intuitive, but other correlations involved different digit combinations and asymmetry. The ratio of digit 3 to 5 lengths is also dimorphic and may correlate with behavioral phenotypes (de Bruin et al, 2011). The exact mechanism by which hormones influence ridge‐counts remains far from clear.…”