Handedness in twins: meta-analyses.

Area of Science:

• Human Genetics
• Developmental Neuroscience
• Behavioral Genetics

Background:

• Atypical handedness (left-, mixed-, or non-right-) is more prevalent in twins than singletons.
• Higher rates of handedness concordance are observed in monozygotic (identical) compared to dizygotic (fraternal) twins.
• Genetic factors are suggested to play a role in handedness determination.

Purpose of the Study:

• To conduct a comprehensive meta-analysis on handedness prevalence and concordance in twins.
• To compare handedness rates between twins and singletons.
• To investigate differences in handedness prevalence and concordance between monozygotic and dizygotic twins.

Main Methods:

• Systematic review of 59 studies.
• Three random-effects meta-analyses on twin-singleton and monozygotic-dizygotic twin comparisons.
• Analysis of handedness concordance rates in twin pairs.
• Testing for effects of moderating variables like sex, age, and assessment methods.

Main Results:

• Twins exhibit higher prevalence of left- and non-right-handedness compared to singletons (ORs 1.40 and 1.36, respectively).
• Prevalence of atypical handedness among twins has decreased in more recent studies (post-1975).
• Handedness concordance is elevated in monozygotic compared to dizygotic twins (OR 1.11), but prevalence rates do not differ significantly between twin types.

Conclusions:

• The apparent higher prevalence of atypical handedness in twins may be influenced by secular trends and unmeasured covariates, questioning a direct relationship with twinning itself.
• Genetic factors significantly contribute to handedness concordance in twins.
• Further research controlling for covariates is needed to definitively establish the relationship between twinning and handedness.