Twins, birth weight, cognition, and handedness

Segal, Nancy L.

doi:10.1073/pnas.1213701109

Cited by 3 publications

(3 citation statements)

References 6 publications

(5 reference statements)

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“…First, the twins included in Segal [ 65 ] and Gopalakrishman [ 66 ] seemed to overlap with the twins investigated by Sicotte et al [ 10 ], so we could not include those new studies.…”

Section: Methodsmentioning

confidence: 99%

Handedness in twins: meta-analyses

et al. 2022

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Background In the general population, 10.6% of people favor their left hand over the right for motor tasks. Previous research suggests higher prevalence of atypical (left-, mixed-, or non-right-) handedness in (i) twins compared to singletons, and in (ii) monozygotic compared to dizygotic twins. Moreover, (iii) studies have shown a higher rate of handedness concordance in monozygotic compared to dizygotic twins, in line with genetic factors playing a role for handedness. Methods By means of a systematic review, we identified 59 studies from previous literature and performed three sets of random effects meta-analyses on (i) twin-to-singleton Odds Ratios (21 studies, n = 189,422 individuals) and (ii) monozygotic-to-dizygotic twin Odds Ratios (48 studies, n = 63,295 individuals), both times for prevalence of left-, mixed-, and non-right-handedness. For monozygotic and dizygotic twin pairs we compared (iii) handedness concordance Odds Ratios (44 studies, n = 36,217 twin pairs). We also tested for potential effects of moderating variables, such as sex, age, the method used to assess handedness, and the twins’ zygosity. Results We found (i) evidence for higher prevalence of left- (Odds Ratio = 1.40, 95% Confidence Interval = [1.26, 1.57]) and non-right- (Odds Ratio = 1.36, 95% Confidence Interval = [1.22, 1.52]), but not mixed-handedness (Odds Ratio = 1.08, 95% Confidence Interval = [0.52, 2.27]) among twins compared to singletons. We further showed a decrease in Odds Ratios in more recent studies (post-1975: Odds Ratio = 1.30, 95% Confidence Interval = [1.17, 1.45]) compared to earlier studies (pre-1975: Odds Ratio = 1.90, 95% Confidence Interval = [1.59–2.27]). While there was (ii) no difference between monozygotic and dizygotic twins regarding prevalence of left- (Odds Ratio = 0.98, 95% Confidence Interval = [0.89, 1.07]), mixed- (Odds Ratio = 0.96, 95% Confidence Interval = [0.46, 1.99]), or non-right-handedness (Odds Ratio = 1.01, 95% Confidence Interval = [0.91, 1.12]), we found that (iii) handedness concordance was elevated among monozygotic compared to dizygotic twin pairs (Odds Ratio = 1.11, 95% Confidence Interval = [1.06, 1.18]). By means of moderator analyses, we did not find evidence for effects of potentially confounding variables. Conclusion We provide the largest and most comprehensive meta-analysis on handedness in twins. Although a raw, unadjusted analysis found a higher prevalence of left- and non-right-, but not mixed-handedness among twins compared to singletons, left-handedness was substantially more prevalent in earlier than in more recent studies. The single large, recent study which included birth weight, Apgar score and gestational age as covariates found no twin-singleton difference in handedness rate, but these covariates could not be included in the present meta-analysis. Together, the secular shift and the influence of covariates probably make it unsafe to conclude that twinning has a genuine relationship to handedness.

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“…First, the twins included in Segal [ 65 ] and Gopalakrishman [ 66 ] seemed to overlap with the twins investigated by Sicotte et al [ 10 ], so we could not include those new studies.…”

Section: Methodsmentioning

confidence: 99%

Handedness in twins: meta-analyses

et al. 2022

View full text Add to dashboard Cite

show abstract

“…First, the twins included in Segal (2012) and Gopalakrishman (2012) seemed to overlap with the twins investigated by Sicotte et al (1999), so we could not include those new studies.…”

Section: Overlapping Datasetsmentioning

confidence: 99%

Handedness in Twins: Meta-Analyses

Ls¹,

Schmitz²,

Παπαδάτου-Παστού³

et al. 2021

Preprint

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Background: In the general population, 10.6 % of people favor their left hand over the right for motor tasks. Previous research suggests higher prevalence of atypical (left-, mixed-, or non-right-) handedness in (i) twins compared to singletons, and in (ii) monozygotic compared to dizygotic twins. Moreover, (iii) studies have shown a higher rate of handedness concordance in monozygotic compared to dizygotic twins, in line with genetic factors playing a role for handedness.Methods: We identified 59 studies from previous literature and performed three sets of random effects meta-analyses on (i) twin-to-singleton Odds Ratios (21 studies, n = 189,422 individuals), (ii) monozygotic-to-dizygotic twin Odds Ratios (48 studies, n = 63,295 individuals), and (iii) concordance Odds Ratios (44 studies, n = 36,217 twin pairs). We also tested for potential effects of moderating variables such as sex, age, the method used to assess handedness and the twins’ zygosity.Results: We found (i) evidence for higher prevalence of left- (Odds Ratio = 1.40) and non-right- (Odds Ratio = 1.36), but not mixed-handedness (Odds Ratio = 1.08) among twins compared to singletons. We further showed a reduction of difference over time, which suggests that higher levels of left-handedness observed in twins are linked to a higher frequency of birth complications which might have dropped nowadays in their overall prevalence because of better healthcare. While there was (ii) no difference between monozygotic and dizygotic twins regarding prevalence of left- (Odds Ratio = 0.98), mixed- (Odds Ratio = 0.96), or non-right-handedness (Odds Ratio = 1.01), we found that (iii) handedness concordance was elevated among monozygotic compared to dizygotic twin pairs (Odds Ratio = 1.11). Moderator analyses showed our results to be robust against potentially confounding variables.Conclusion: We provide the largest and most comprehensive meta-analysis on handedness in twins. Results suggest that the previously reported effect that twins are more likely to be left-handed than singletons is robust. Furthermore, we also provide robust evidence that monozygotic twins are more likely to be concordant for handedness than dizygotic twins. In line with recent genome-wide association studies, this finding supports a partially genetic determination of handedness.

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“…We are grateful for Professor Segal's interesting letter (1), prompting us to delve deeper into a question that was nested within, but not directly addressed by our recent article (2): Are relationships between birth weight (BW) and intelligence quotient (IQ) variation within twin pairs modulated by patterns of handedness discordance? In a sample of 67 monozygotic (MZ) twin pairs (of which ∼40% pairs were discordant for handedness), Professor Segal had found that lower IQ most often segregated with lower BW in handedness-discordant twin pairs when the left-handed member had the lower BW (3).…”

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confidence: 99%

Reply to Segal: Are relationships between birth weight and intelligence quotient variation within twin pairs modulated by patterns of handedness discordance?

Raznahan

Greenstein

Lee

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

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We are grateful for Professor Segal's interesting letter (1), prompting us to delve deeper into a question that was nested within, but not directly addressed by our recent article (2): Are relationships between birth weight (BW) and intelligence quotient (IQ) variation within twin pairs modulated by patterns of handedness discordance? In a sample of 67 monozygotic (MZ) twin pairs (of which ∼40% pairs were discordant for handedness), Professor Segal had found that lower IQ most often segregated with lower BW in handedness-discordant twin pairs when the left-handed member had the lower BW (3). This finding was argued to support two theoretical accounts for reported associations between twinning and left-handedness: the accompaniment of left-handedness by BW reduction relative to the right-handed cotwin [discordant left lighter (HDll)] indexing consequences of prenatal compromise, and left-handedness without BW reduction relative to the cotwin [discordant left heavier (HDlh)] potentially indexing the alternative mechanism of "delayed zygotic splitting and disrupted asymmetry determination" in twins.In our sample, there was a statistically nonsignificant trend toward elevated rates of left-handedness in twins relative to singletons [14.5% twins (12.5% MZ, 17.5% DZ), 11% singletons]. Mimicking Professor Segal's analytic approach (3) in our sample of 17 handedness-discordant (6 HDll, 11 HDlh) and 65 right-right handedness concordant (HC) MZ twin pairs, we found that (i) cosegregation of lower BW and lower IQ status within twin pairs was not significantly different across HDll, HDlh, and HC groups (lower IQ consistently accompanied lower BW in ∼67% of pairs), but (ii) mean twin pair IQ, lighter twin IQ, and heavier twin IQ were (albeit nonsignificantly) lower in HDll than HDlh groups [e.g., mean pair IQ (SD): 109 (11.9) vs. 113 (14.4)], with HC twins intermediate [110 (11.5)].Although our data are inconsistent with the hypothesis that patterns of hand-discordance modify the relationship between BW and IQ discordance in twins, they are consistent with the proposal that HDll pairings could denote the presence of greater prenatal compromise than HDlh pairings. Intrigued by the converse speculation-that HDlh pairings denote disrupted asymmetry determination-we used in vivo structural neuroimaging data to explicitly test whether within-pair discordance for cerebral asymmetry is greater in HDlh than in HDll pairs. In one structural brain MRI scan for each member of the 17 HD MZ pairs in our sample, we derived measures of local surface area (SA) at ∼40,000 points (vertices) in each cerebral hemisphere as previously described (2). We then quantified pair-wise SA asymmetry concordance by correlating intervertex differences in SA asymmetry [(Left − Right)/(Left + Right) × 0.5] within each twin pair. Mean SA asymmetry concordance estimates for HDlh and HDll groups were low (0.06 vs. 0.1) and statistically indistinguishable from each other (P = 0.1).Thus, our follow-up analyses suggest that patterns of handedness discordance do no...

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Twins, birth weight, cognition, and handedness

Cited by 3 publications

References 6 publications

Handedness in twins: meta-analyses

Handedness in twins: meta-analyses

Handedness in Twins: Meta-Analyses

Reply to Segal: Are relationships between birth weight and intelligence quotient variation within twin pairs modulated by patterns of handedness discordance?

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