Handedness in twins: A critical review

McManus, I. C.

doi:10.1016/0028-3932(80)90130-x

Cited by 76 publications

(41 citation statements)

References 23 publications

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“…It is also possible that other factors, such as twin-twin transfusion syndrome (which occurs more commonly in MZ MC than MZ DC twins) may be responsible for some of the previous findings of increased discordance in some MZ twin samples (Hay & Howie, 1980). Reviews of the literature examining handedness in twins by McManus (1980) and Sicotte, Woods and Mazziotta (1999) found no support for the theory of mirror imaging. Similarly, studies that have examined the relationship between handedness and chorionicity have found no difference in hand preference (Derom et al, 1996), or hand skill (Carlier et al, 1996), between MZ MC and MZ DC twins.…”

Section: Does the Process Of Mz Twinning Affect Handedness?mentioning

confidence: 94%

“…Mirrored features in chiral twins are restricted to those of ectodermal derivative (McManus, 1980), suggesting that the timing of lateralization, and period of plasticity in which lateralization may be altered, may be tissue specific (Levin, 1999). The hypothesis that handedness may be influenced by mirror imaging originates from the belief that handedness is causally related to cerebral lateralization of language functions (Newman, 1928).…”

Section: Does the Process Of Mz Twinning Affect Handedness?mentioning

confidence: 99%

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Special Twin Environments, Genetic Influences and their Effects on the Handedness of Twins and their Siblings

et al. 2003

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It has been suggested that twinning may influence handedness through the effects of birth order, intra-uterine crowding and mirror imaging. The influence of these effects on handedness (for writing and throwing) was examined in 3657 Monozygotic (MZ) and 3762 Dizygotic (DZ) twin pairs (born 1893-1992). Maximum likelihood analyses revealed no effects of birth order on the incidence of left-handedness. Twins were no more likely to be left-handed than their singleton siblings (n = 1757), and there were no differences between the DZ co-twin and siblingtwin covariances, suggesting that neither intra-uterine crowding nor the experience of being a twin affects handedness. There was no evidence of mirror imaging; the co-twin correlations of monochorionic and dichorionic MZ twins did not differ. Univariate genetic analyses revealed common environmental factors to be the most parsimonious explanation of familial aggregation for the writing-hand measure, while additive genetic influences provided a better interpretation of the throwing hand data.

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Section: Does the Process Of Mz Twinning Affect Handedness?mentioning

confidence: 94%

Section: Does the Process Of Mz Twinning Affect Handedness?mentioning

confidence: 99%

Special Twin Environments, Genetic Influences and their Effects on the Handedness of Twins and their Siblings

et al. 2003

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“…Twinnrp2.doc 08/07/08 8 percent for left-handed writing). It had been suggested earlier that twins are more often left-handed, but the evidence was controversial and rejected [21]. There is now strong evidence for this difference [16,25,26].…”

Section: Outline Of the Right Shift Theorymentioning

confidence: 98%

Cerebral asymmetry in twins: predictions of the right shift theory

Annett

2003

Neuropsychologia

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A study of the heritability of lobar brain volumes in twins has introduced a new approach to questions about the genetics of cerebral asymmetry. In addition to the classic comparison between monozygotic (MZ) and dizygotic (DZ) twins, a contrast was made between pairs of two right-handers (RR pairs) and pairs including one or more non-right-hander (non-RR pairs), in the light of the right shift (RS) theory of handedness. This paper explains the predictions of the RS model for pair concordance for genotype, cerebral asymmetry and handedness in healthy MZ and DZ twins. It shows how predictions for cerebral asymmetry vary between RR and non-RR pairs over a range of incidences of left-handedness. Although MZ twins are always concordant for genotype and DZ twins may be discordant, differences for handedness and cerebral asymmetry are expected to be small, consistent with the scarcity of significant effects in the literature. Marked differences between RR and non-RR pairs are predicted at all levels of incidence, the differences slightly larger in MZ than DZ pairs.Keywords: Twin concordance, cerebral dominance, handedness, genetics.Twinnrp2.doc 08/07/08 3Findings for monozygotic (MZ) and dizygotic (DZ) twins have an important role in the evaluation of genetic theories because for most purposes MZ twins can be taken to be identical genetically, whereas DZ twins share fifty percent of their genes, on average. MZ twin pairs often differ for handedness, and this occurs with about the same frequency as in DZ pairs. These observations rule out mirror-imaging as the main cause of discordance for handedness in MZ twins. They also rule out direct genetic determination of right-and left-handedness. It has been widely believed that discordance for handedness in MZ pairs, and the similarity of levels of discordance between MZ and DZ pairs, contra-indicate any genetic influence on handedness.However, recent theories include chance postulates that allow MZ twins to differ for laterality, even in the presence of a genetic influence. Geschwind, Miller, DeCarli and Carmelli [17] have investigated the heritability of lobar brain volumes in twins in the light of such models. Some of the cerebral asymmetries that were present in the brains of twins from pairs of two right-handers (RR pairs) were greatly diminished in the brains of twins from pairs that included one or two left-handers (non-RR pairs). In the latter, the reduction was evident for both right-handers and left-handers. This supports the theory that the key genetic contrast is between people who carry a typical directional bias and those who lack this bias, and then lateralise at random. for sexes combined. Sex differences and certain types of non-healthy twins will be considered in discussion. Outline of the right shift theoryThe RS theory [3] was formulated after some 10 years work on questions about hand preference, hand skill, and related abilities. The theory depended on the discovery that several puzzles about handedness, including preferences in humans versus ...

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“…Similarly, many studies have reported increased rates of left-handedness in twins as compared to singletons. However, twins and singletons are seldom assessed using the same handedness criteria, recruited in the same manner, or matched for age and sex (McManus, 1980). Several of the more recent studies have found no differences in the prevalence of left-handedness between twins and singletons (Ellis et al, 1988;Medland et al, 2003;Morley & Caffrey, 1994).…”

mentioning

confidence: 99%

“…With few exceptions, sample sizes have not been adequate to detect genetic or environmental effects that account for less than 50% of the total phenotypic variance with 80% power. While the sample size required to detect small to medium genetic effects may be beyond the resources of any one research group, such sample sizes can be reached through collaboration (Medland et al, 2003) or meta-analysis (McManus, 1980;Sicotte et al, 1999).…”

mentioning

confidence: 99%

Handedness in Twins: Joint Analysis of Data From 35 Samples

et al. 2006

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S imultaneous analysis of handedness data from 35 samples of twins (with a combined sample size of 21,127 twin pairs) found a small but significant additive genetic effect accounting for 25.47% of the variance (95% confidence interval [CI] 15.69-29.51%). No common environmental influences were detected (C = 0.00; 95% CI 0.00-7.67%), with the majority of the variance, 74.53%, explained by factors unique to the . No significant heterogeneity was observed within studies that used similar methods to assess handedness, or across studies that used different methods. At an individual level the majority of studies had insufficient power to reject a purely unique environmental model due to insufficient power to detect familial aggregation. This lack of power is seldom mentioned within studies, and has contributed to the misconception that twin studies of handedness are not informative.The etiology and neurological implications of lefthandedness have been the subject of debate for over a century. The first twin study comparing the handedness of monozygotic (MZ) and dizygotic (DZ) twins was published 81 years ago (Siemens, 1924); since this time there have been 34 published studies on 35 samples. However, there has been little consistency of results. The area has become one of the most controversial in laterality with the proposal of special twin effects, (such as differential right-shifts effects or mirror imaging effects; Annett, 2002;Newman, 1928) and questions raised regarding the suitability of the twin method for studying handedness and laterality in general (Nagylaki & Levy, 1973).Comparison of results across studies is complicated by differences in methodology. Handedness can be assessed as either hand preference or hand skill; two separate but related traits. Hand preference is typically a directional measure. In its simplest form it is assessed by asking 'are you left or right handed?', or 'which hand do you write with?' In its more complex form, hand preference is assessed by asking (or asking the participant to demonstrate) which hand is preferred for a range of items. Handedness questionnaires range in length from four (Coren, 1993) to 55 items (Healey et al., 1986), the number of response choices ranging from two to five, with the responses resulting either in a handedness score/quotient or a grouping classification. The diverse methods of assessing hand preference and the number of questionnaires available within the literature in part reflects the lack of a gold standard and conceptual differences regarding the evolution and nature of handedness.In contrast, hand skill is typically a quantitative measure of the degree of motor dominance of one hand over the over. Common tests of hand skill involve measuring the time taken to move a series of pegs on a specially designed board (Annett, 1985), or counting the number of circles that can be dotted with a pen in 20 seconds (Tapley & Bryden, 1985). Typically, the task(s) is performed with each hand and a dominance or lambda score is calculated expressing the di...

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Handedness in twins: A critical review

Cited by 76 publications

References 23 publications

Special Twin Environments, Genetic Influences and their Effects on the Handedness of Twins and their Siblings

Special Twin Environments, Genetic Influences and their Effects on the Handedness of Twins and their Siblings

Cerebral asymmetry in twins: predictions of the right shift theory

Handedness in Twins: Joint Analysis of Data From 35 Samples

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