A Critical Review of the Research on the Extreme Male Brain Theory and Digit Ratio (2D:4D)

@article{Teatero2013ACR,
  title={A Critical Review of the Research on the Extreme Male Brain Theory and Digit Ratio (2D:4D)},
  author={Missy L. Teatero and Charles Netley},
  journal={Journal of Autism and Developmental Disorders},
  year={2013},
  volume={43},
  pages={2664-2676}
}
Boys are more likely than girls to be diagnosed with an autism spectrum disorder (ASD). The extreme male brain (EMB) theory of ASD suggests that fetal testosterone (FT) exposure may underlie sex differences in autistic traits. A link between the organizational effects of FT on the brain and ASD is often drawn based on research using digit ratio (2D:4D), a putative biomarker, without a full survey of the findings. This paper critically and quantitatively reviews the research on the relationship… 
Testing the Extreme Male Brain Theory of Autism Spectrum Disorder in a Familial Design
TLDR
The findings emphasize the role of familially based elevated pre‐ and postnatal testosterone levels in the liability for ASD, but challenge the use of 2D:4D ratio as a proxy of prenatal testosterone exposure solely.
Associations Between the 2nd to 4th Digit Ratio and Autism Spectrum Disorder in Population-Based Samples of Boys and Girls: Findings from the Study to Explore Early Development
TLDR
A positive association between ASD and left-hand 2D:4D in females, overall and within most case subgroups is observed and subgroup analyses indicated associations were limited to ASD cases with birth defects/genetic syndromes or dysmorphic features.
Sex-different abnormalities in the right second to fourth digit ratio in Japanese individuals with autism spectrum disorders
TLDR
The present findings suggest that high prenatal testosterone could be a risk factor both for Japanese men and women with ASDs, elucidating one potential etiology of ASDs in women.
Digit ratio and autism spectrum disorders in the Avon Longitudinal Study of Parents and Children: a birth cohort study
TLDR
There was no strong evidence of an association between 2D:4D and ASD diagnosis or traits, although the CIs were wide and these results are not consistent with the extreme male brain theory.
2D:4D Ratio in Neurodevelopmental Disorders: A Twin Study
TLDR
Investigating the association between the ratio and NDDs in twins can provide insight into genetic and/or environmental factors driving the ratio.
The 2D : 4D Digit Ratio as a Biomarker for Autism Spectrum Disorder
TLDR
Gender specific associations between the 2D : 4D digit ratio and specific autism traits were observed, which were stronger in men than in women.
Autism spectrum disorder beyond the extreme male brain
Autism spectrum disorder (ASD) is an umbrella-term for neurodevelopmental conditions characterized by both impairments in communication and social interaction and unusually restricted and repetitive
Social communication and emotion difficulties and second to fourth digit ratio in a large community-based sample
TLDR
A novel association between an extreme measure of 2D:4D in males suggests threshold effects and warrants replication, and an association was found between measures of social communication and emotion recognition, and the lowest 10 % of second to fourth digit ratio ratios.
Associations Between the 2D:4D Proxy Biomarker for Prenatal Hormone Exposures and Symptoms of Developmental Language Disorder.
  • S. Redmond, A. Ash
  • Psychology
    Journal of speech, language, and hearing research : JSLHR
  • 2017
TLDR
Prenatal hormone exposures may play a role in the etiology of some language symptoms and Modest associations were found between 2D:4D digit ratios and some Clinical Evaluation of Language Fundamentals-Fourth Edition subtests.
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