Handedness and 23 Early Life Characteristics in 37,495 Dutch Twins.

Area of Science:

• Developmental Psychology
• Behavioral Genetics
• Human Biology

Background:

• Previous research in singletons suggests links between early-life factors and handedness.
• Replication of these associations in twin studies is inconsistent.
• Understanding handedness determinants is crucial for developmental research.

Purpose of the Study:

• To examine associations between 23 early-life characteristics and handedness in a large twin cohort.
• To test replication of known singleton-based handedness associations in twins.
• To investigate twin-specific factors (zygosity, chorionicity, birth order) related to handedness.

Main Methods:

• Analysis of 37,495 five-year-old twins.
• Assessment of handedness using three definitions: left-handedness (LH), mixed-handedness (MH), and non-right-handedness (NRH).
• Statistical examination of 23 early-life characteristics, including sex, birth weight, gestational age, season of birth, breastfeeding, and twin-specific variables.

Main Results:

• Non-right-handedness (NRH) prevalence was higher in twins (16.19%) and their parents (15.09%) compared to singleton adults (7.23%).
• Replicated associations in twins included LH/NRH with parental LH, male sex and lower gestational age with NRH, and LH with not being breastfed.
• Mixed-handedness (MH) was linked to neurodevelopmental delays and externalizing problems; other previously reported associations did not replicate, and no twin-specific factors were significant.

Conclusions:

• Handedness development in twins shows some replicated associations with early-life factors but also unique patterns.
• The study underscores the importance of using multiple handedness definitions for comprehensive analysis.
• Findings suggest a limited number of consistently replicated associations across different study populations and methodologies.