The developmental origins of autism spectrum disorder: The 2D:4D digit ratio as biomarker

Introduction: Autism spectrum disorder (ASD) is identified as a sexually dimorphic disorder, meaning that it may be influenced by fetal levels of testosterone and estrogen [1]. As described by several studies, levels of prenatal sex hormones can be related to the digit ratio of the index (2D) and ring (4D) finger [2]. It has been known that males tend to have longer fourth digits relative to second digits than females, indicating higher levels of fetal testosterone in comparison to estrogen in males [2]. As the development of the central nervous system (CNS) is also influenced by prenatal sex hormones, it has been suggested that the 2D:4D digit ratio may be a biomarker for the risk of developing CNS diseases such as autism. One study found that N= 72 children diagnosed with autism had lower 2D:4D digit ratios when compared to age-matched healthy controls [3], and a 2012 meta-analysis confirmed that adults with autism tend to have a lower 2D:4D digit ratio [4]. However, recent studies could not replicate these findings [5]. Aim(s) of the study: To determine the usefulness of the 2D:4D digit ratio as biomarker for autism spectrum disorder. Methods: Participants were recruited among students from Utrecht University. For both hands, digit lengths of the second (2D, index finger) and fourth (4D, ring finger) finger were measured using digital Vernier calipers recording to 0.01 mm. In addition to demographics, the Autism Spectrum Quotient (AQ) questionnaire was completed. The AQ is divided into four subscales, each assessing a different aspect of ASD. The subscales comprise 'social insights and behavior', 'difficulties with change', 'communication', 'phantasy and imagination', and 'detail orientation'. Using correlational analyses, the relationship between the 2D:4D digit ratio and the overall AQ scores and those of its subscales was computed. Results of participants with dove-type personality (2D:4D >1.00) were compared to those with a hawk-type personality (2D:4