2D:4D Ratio in Neurodevelopmental Disorders: A Twin Study.
Lynnea Myers, Annelies Van't Westeinde, Ralf Kuja-Halkola and 2 others
PMID 29704141WHAT IT FOUND
Finger length ratios showed no link to autism, but males with ADHD had lower ratios.
Female autism traits correlated with higher ratios, opposite to predictions. Results vary by sex and analysis method, offering no clear clinical guidance.
Key findings
01The study found no association between the 2D:4D finger ratio and a diagnosis of autism spectrum disorder (ASD).
02A lower 2D:4D ratio was associated with an ADHD diagnosis in males, but not in females.
03In females, a higher 2D:4D ratio was associated with increased autistic traits, which contradicted the researchers' prediction.
STILL TO COME
How it was doneWhat they found
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What it does not show
The study found no link between the finger ratio and autism, which contradicts the 'extreme male brain' theory. The finding that higher finger ratios in females linked to more autistic traits was unexpected and the authors state it must be interpreted with caution. The sample was limited to twins from a specific region in Sweden, so results may not apply to other populations. The number of participants in specific diagnosis groups was small, which may have made it hard to detect other connections.
Declared interests
The study was funded by numerous organizations including Horizon 2020, Vetenskapsrådet, and the Autism and Asperger Society Stockholm. No specific conflicts of interest were declared by the authors.
The easy way to misread this
Do not use the 2D:4D finger ratio to screen for autism or ADHD in clinical practice. The study failed to find a link for autism, and the findings for ADHD and traits were inconsistent between sexes and analysis methods, meaning this physical measure is not a reliable diagnostic tool.