title: The second to fourth digit ratio (2D:4D) in Saudi boys with autism: A potential screening tool.
abstract: BACKGROUND
  Autism is a neurodevelopment disorder with a strikingly higher prevalence in boys than girls. There are many theories regarding this gender bias, and prenatal exposure to high levels of fetal testosterone (FT) may be a predisposing factor. The second to fourth digit ratio (2D:4D) is the only indirect measure that reflects this association postnatally. Thus, this study measured the lengths of the index finger (2D) and the ring finger (4D) and calculated the 2D:4D ratio. Subsequently, this ratio was used to indirectly determine the potential prenatal exposure to high levels of FT in autistic children.
  
  
  METHODS
  This case-control study was conducted with 60 male children with 31 individuals having classic-onset autism and 29 individuals serving as age-matched, healthy controls. The lengths of both the index (2D) and the ring (4D) fingers of the right hand of both autism and control groups were obtained using a scanner and the 2D:4D ratio was calculated.
  
  
  RESULTS
  The 2D:4D ratio in the current study was significantly lower in boys with autism compared to the controls (p ≤ 0.001).
  
  
  CONCLUSIONS
  This study demonstrates a significantly lower 2D:4D ratio in Saudi boys with autism, which indirectly suggests that these boys were exposed to high levels of prenatal FT. Accordingly, prenatal exposure to high levels of FT is a risk factor for the development of autism, and the postnatal measurement of the 2D:4D ratio could be a potential screening tool.
authors.affiliation: Department of Physiology, College of Medicine, Riyadh, Saudi Arabia; Autism Research and Treatment Center, AL-Amodi Autism Research Chair, College of Medicine, Riyadh, Saudi Arabia. Electronic address: D_fl329@hotmail.com.
authors.forename: Felwah S
authors.initials: FS
authors.lastname: Al-Zaid
authors.affiliation: Department of Physiology, College of Medicine, Riyadh, Saudi Arabia.
authors.forename: AbdelFattah A
authors.initials: AA
authors.lastname: Alhader
authors.affiliation: Department of Physiology, College of Medicine, Riyadh, Saudi Arabia; Autism Research and Treatment Center, AL-Amodi Autism Research Chair, College of Medicine, Riyadh, Saudi Arabia.
authors.forename: Laila Y
authors.initials: LY
authors.lastname: Al-Ayadhi
mesh_terms: D000886:Anthropometry; D001321:Autistic Disorder / Q000175:diagnosis*; D016022:Case-Control Studies; D002648:Child; D002675:Child, Preschool; D005385:Fingers; D006801:Humans; D008297:Male; D012529:Saudi Arabia; D012727:Sex Characteristics
keywords: Autism; Digit ratio; Fetal testosterone