The relationship between the biomarker ratio D2:D4 and the psycho-pedagogical diagnosis of ADHD. Data from a study

The digital ratio D2:D4 (length of the index finger between the length of the ring finger) is a biomarker that reports the presence of high levels of testosterone during the prenatal period. A differential digital pattern (D2 < D4) has been found in several disorders (ASD or Klinefelter's syndrome) although data for Attention Deficit Hyperactivity Disorder (ADHD) are not conclusive (Stevenson et al., 2007; Wang et al., 2017). The aim of this paper was to determine whether digital ratio can be used as an indicator in the psychoeducational diagnosis of ADHD. A sample of 82 students of both sexes aged between 6 and 16 years (M = 11.77, SD = 2.97) from the Andalusian Community was taken. Among the members of the sample there were no differences in terms of sex, age, or cognitive level. The sample was divided into two groups, the group with a psycho-pedagogical diagnosis of ADHD and the control or undiagnosed group. The group with ADHD consisted of 42 subjects and the control group consisted of 46 subjects. All sessions were conducted individually for each of the subjects and their families following these guidelines: the session began with the parent signing a consent form that allowed the therapist to proceed with the intervention. After that, the TONI-2 non-verbal intelligence test was given to the child by the therapist in a quiet room. At the same time, the parents responded to the Conners Scale questions on behaviour at home to verify the existence or not of behavioural symptoms compatible with the presence of ADHD. For parents of children with ADHD diagnosis, an interview was conducted to learn about the course of the disease to have a general profile of the patient and his or her disorder. Finally, the participants' right hand was scanned at the same school with an HP DeskJet 2630 scanner printer. Using the scanner and the Adobe Photoshop (R) tool, the length of the index and ring fingers was measured [(from proximal line of the finger to the end of the distal phalanx of the index (D2) and ring (D4) fingers]. The digital measurements from the scanned images were taken by the two researchers who signed the work, and there was more than 90 % agreement on the measurements. The results show a lower digital index in participants in the ADHD group (.945) versus the control group (.995), these differences being significant (p = 0.000), regardless of gender. In addition, the presence of certain behaviours in the home environment (measured with the Conners Scale) correlates positively with a low value of the digital index (r = .47; p = .001) and with the psycho-pedagogical diagnosis of ADHD. Significant differences have been shown in this study. Subjects with a psychopedagogical diagnosis of ADHD have been exposed to higher levels of testosterone during pregnancy since they present a lower D2:D4 ratio compared to the participants in the control group (without a diagnosis of ADHD), in line with the work of Martel et al. (2008) and Wang et al. (2017). In addition, this study has found that the group with psychopedagogical diagnosis of ADHD has a shorter index finger than the ring finger in both boys and girls, while for the control group the digital pattern is reversed or there is no difference between the two fingers. Therefore, we consider that the digital ratio biomarker (D2:D4) may be an additional useful criterion for the psychopedagogical diagnosis of ADHD or at least as a screening method.