Second to fourth digit (2D:4D) ratios have been previously measured as an indicator of prenatal testosterone levels. It is believed that a lower ratio (a longer fourth finger to second finger) is indicative of higher prenatal exposure to testosterone.
Objectives:
The objective in the current study was to compare 2D:4D ratios between boys with an Autism Spectrum Disorder (ASD) and typically developing (TD) boys to ascertain if ASD is related to higher exposure to prenatal testosterone. Associations between 2D:4D ratio and autism severity were also explored.
Methods:
Participants comprised of 65 boys (4-16 years of age) with an ASD and 30 TD boys, along with their parents. Diagnosis of ASD was confirmed by administration of the Autism Diagnostic Observation Schedule (ADOS). Measurements of the second and fourth fingers were obtained by measuring from the metacarpophalangeal joint to the finger-tip to establish 2D:4D ratios of participants and their parents.
Results:
The 2D:4D ratio was significantly lower in boys with ASD compared to TD boys. Significantly lower ratios were also found in the mothers of children with ASD compared to the mothers of TD boys. Although a similar pattern of lower 2D:4D ratio was observed in fathers of boys with ASD, the group differences were not significant.
In addition, boys who met the ASD cut-off scores on the ADOS had significantly lower 2D:4D ratios than boys who met the AD criteria. Likewise, the mothers and fathers of boys with ASD had lower 2D:4D ratios than mothers and fathers of boys with AD; however, these latter parental differences were not significant.
Some relationships were found between 2D:4D ratio and autism severity.
Conclusions:
Consistent with previous research, the data indicated a lower 2D:4D ratio amongst boys with an ASD, implying higher prenatal testosterone levels, compared to TD boys. Genetic factors may also be involved given the similar patterns found in the mothers and fathers of children with an ASD. A lower ratio amongst boys with ASD compared to those with AD implicates other factors may be involved in the relationship between 2D:4D ratio and autism severity. The implications of these findings will be discussed.
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