2D:4D Ratio in Neurodevelopmental Disorders: A Twin Study.

Area of Science:

• Developmental Psychology
• Behavioral Genetics
• Neurodevelopmental Disorders

Background:

• The second to fourth digit (2D:4D) ratio is a proposed biomarker for prenatal androgen exposure.
• Limited research exists on the 2D:4D ratio's association with neurodevelopmental disorders (NDDs) beyond autism spectrum disorder (ASD).
• Twin studies offer a unique approach to disentangle genetic and environmental influences on the 2D:4D ratio and NDDs.

Purpose of the Study:

• To investigate the association between the 2D:4D digit ratio and various NDDs in a twin sample.
• To explore the relationship between the 2D:4D ratio, autistic traits, zygosity, and sex.
• To examine potential genetic and environmental factors influencing the 2D:4D ratio in the context of NDDs.

Main Methods:

• Collected hand images from 238 twins (70 monozygotic, 49 dizygotic) with NDDs or typical development.
• Calculated the 2D:4D ratio from hand images.
• Analyzed associations between the 2D:4D ratio and DSM-5 defined categorical NDDs, autistic traits, zygosity, and sex.

Main Results:

• Small associations were found for males between the 2D:4D ratio and diagnoses of any NDD and attention-deficit/hyperactivity disorder (ADHD).
• Males, on average, exhibited lower 2D:4D ratios compared to females.
• No significant associations were reported for autistic traits or zygosity.

Conclusions:

• The 2D:4D ratio may have a modest association with certain NDDs, particularly in males.
• Sex differences in the 2D:4D ratio are evident in this NDD twin cohort.
• Further research incorporating physical anomalies may offer deeper etiological insights into NDDs.