Genetic and Environmental Influences on the Handedness and Footedness in Japanese Twin Children

Handedness in twins: meta-analyses

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.

Four meta-analyses across 164 studies on atypical footedness prevalence and its relation to handedness

Human lateral preferences, such as handedness and footedness, have interested researchers for decades due to their pronounced asymmetries at the population level. While there are good estimates on the prevalence of handedness in the population, there is no large-scale estimation on the prevalence of footedness. Furthermore, the relationship between footedness and handedness still remains elusive. Here, we conducted meta-analyses with four different classification systems for footedness on 145,135 individuals across 164 studies including new data from the ALSPAC cohort. The study aimed to determine a reliable point estimate of footedness, to study the association between footedness and handedness, and to investigate moderating factors influencing footedness. We showed that the prevalence of atypical footedness ranges between 12.10% using the most conservative criterion of left-footedness to 23.7% including all left- and mixed-footers as a single non-right category. As many as 60.1% of left-handers were left-footed whereas only 3.2% of right-handers were left-footed. Males were 4.1% more often non-right-footed compared to females. Individuals with psychiatric and neurodevelopmental disorders exhibited a higher prevalence of non-right-footedness. Furthermore, the presence of mixed-footedness was higher in children compared to adults and left-footedness was increased in athletes compared to the general population. Finally, we showed that footedness is only marginally influenced by cultural and social factors, which play a crucial role in the determination of handedness. Overall, this study provides new and useful reference data for laterality research. Furthermore, the data suggest that footedness is a valuable phenotype for the study of lateral motor biases, its underlying genetics and neurodevelopment.

Twin Database of the Secondary School Attached to the Faculty of Education of the University of Tokyo

This article profiles the historical twin databases of the secondary education school attached to the Faculty of Education at the University of Tokyo. The school was established in 1948. Every year, about 50 pairs of twins of all sex and zygosity combinations, aged 11-12 years, take an examination, and about 10-20 pairs are admitted based on the results. Three datasets exist: one for applicants (11-12 years old), one for junior and senior high school students (12-18 years old) and one for graduates (18-85 years old). Linking the records from these three databases should facilitate several important research projects, for example, life course genetic epidemiologic studies and the verification of the so-called developmental origins of health and disease hypothesis.

Foot use and hand preference during feeding in captive black-and-white snub-nosed monkeys (Rhinopithecus bieti)

Postural origin theory predicts that body postures are related to hand preference in nonhuman primates due to hemispheric specialization. Foot preference, especially in manipulating objects, is also a good predictor of hemispheric specialization in humans. We studied limb (hand and foot) preferences in 11 captive adult black-and-white snub-nosed monkeys (Rhinopithecus bieti) to see how limb preference is influenced by postures and foot manipulation. Hand preference was significantly different for this group between quadrupedal standing and clinging postures, and sitting and clinging postures, but not between bipedal standing and clinging postures. Individuals were significantly more likely to use the right hand in the clinging posture than in quadrupedal standing or sitting postures. In the sitting posture, individuals maintained their respective hand preference even when the food was on the other side of the body. There was a gender difference in the sitting posture, where females preferred their right hand but males preferred their left. Individuals who did not routinely use their feet to manipulate objects, compared to those who did, shifted to greater right hand use from the clinging posture to the bipedal posture. One male individual and his offspring were more likely to use their feet to manipulate objects than the rest of the monkeys. In the present study, we reveal the first evidence of a postural effect on hand preference in R. bieti as well as a foot preference in this species. Our results mostly agree with the postural origin theory and hemispheric specialization.

Investigação da lateralidade em recém-nascidos prematuros

O estudo objetivou investigar a existência de coordenação mão-boca e preferência manual em recém-nascidos (RNs) prematuros a partir da estimulação gustativa, comparando a lateralidade dos bebês e seus genitores. Trata-se de estudo experimental e analítico, com procedimento duplo-cego. Participaram 90 RNs prematuros de uma maternidade pública de Sergipe. O teste durou 15 minutos, dividido em 3 períodos de 5 minutos. Nos primeiros 5 minutos, linha de base inicial - LB1, nenhum estímulo foi aplicado. No segundo momento, houve estimulação gustativa com sacarose para análise (PA) a 12% ou água, em 5 doses de 0,2 mL a cada minuto; e no último período, linha de base final - LB2, houve observação do recém-nascido sem aplicação de estímulo, durante 5 minutos. Foi realizado registro da frequência e duração dos comportamentos das mãos direita (MBD) e/ou esquerda (MBE) na região oral e sucção das mãos direita (SMD) e/ou esquerda (SME) dos RNs durante os estados comportamentais (sono profundo, sono leve, sonolento, alerta, agitado/irritado e choro) apresentados por estes. Os dados foram executados no software Statistical Package for the Social Sciences. Como resultado encontrou-se correlação forte de MBD e SMD na LB2, independente do estímulo recebido, evidenciando que a estimulação aumentou a correlação dos comportamentos do lado direito do corpo. Sugere-se realização de novas pesquisas sobre lateralidade, contemplando maior número de pais sinistros na amostra.

Genetic and environmental structure of individual differences in hand, foot, and ear preferences: a twin study

Recent studies with large sample size have reported moderate heritability of hand preference. However, little is known about genetic and environmental factors for lateral preference. We examined the genetic and environmental factors for hand, foot, and ear preferences using a twin design study. A lateral preference questionnaire was administered to twin participants (N=956). Phenotypic correlation matrices of lateral preferences were computed for monozygotic and dizygotic twin pairs, and were subjected to Cholesky decomposition to compute additive genetic and unique environmental correlation matrices. Promax rotation factor analysis of each genetic and environmental correlation matrix yielded six genetic and four environmental factors. Factor-loading patterns for these factors indicated that hand and foot lateral activities were affected by different genetic factors. By contrast, each of the four environmental factors was mainly associated with hand, foot, or ear preference. These results suggest that the genetic structure for lateral preference may be more complex than the environmental structure. In particular, hand preference may be multidimensional in terms of genetic factors.

Twin database of the secondary school attached to the Faculty of Education of the University of Tokyo: lifecourse database of twins

This article profiles the historical twin databases of the secondary education school attached to the Faculty of Education at the University of Tokyo. The school was established in 1948. Every year, about 50 pairs of twins of all sex and zygosity combinations and aged 11-12 years take an examination, and about 10-20 pairs are admitted based on the results. Three data sets exist: one for applicants (11-12 years), one for junior and senior high school students (12-18 years), and one for graduates (18-79 years). Record linkage of these three databases should facilitate several important research projects; for example, the lifecourse genetic epidemiologic studies and verification of so-called developmental origin of health and disease hypothesis.

Nongenetic factors associated with human handedness and footedness in Japanese twin children

OBJECTIVE

The aim of this study is to clarify the factors related to the handedness and footedness of twins using two of the largest databases on Japanese twins available.

METHODS

The first group consisted of 1,131 twin pairs, all school children either 11 or 12 years old (S group), and the second group consisted of 951 twin pairs of different ages (1-15 years) in several maternal associations (M group). All data were gathered using a questionnaire. Factors associated with the handedness or footedness of twin individuals were analyzed by univariate and multivariate logistic analyses.

RESULTS

Multivariate logistic analysis showed that for handedness, birth year (OR=1.02) and neonatal asphyxia (OR=1.62) were selected in the S group, and sex (OR=1.34), the age of twins (OR=1.56), parity (OR=1.31), gestational age (OR=1.58), and family history (OR=1.82) were selected in the M group. for footedness, birth complications (OR=1.37) were selected in the S group, and sex (OR=1.33), the age of twins (OR=1.69), gestational age (OR=1.83), and family history (OR=2.49) were selected in the M group. Factors associated with handedness and footedness specific to twins, such as zygosity, placentation, birth order within twin pairs and the sex of the cotwin, were not found, although being a twin might have some effects.

CONCLUSION

It was concluded that factors that affect handedness or footedness in general, such as sex, birth year, age, parity, neonatal asphyxia, gestational age, birth complications, and family history, seem to have stronger effects on handedness and footedness than being a twin.

Handedness is modulated by sex and self-perception

The distribution of handedness is different for men and women. Less pronounced right- or left-handedness in men is well established and often attributed to direct effects of genetic factors. Many studies observing this sex difference assessed handedness via questionnaire. It may therefore be influenced by a sex-specific bias in self-perception. Permanent inadequate self-perceptions are key characteristics of hypochondriasis. The study therefore tested 1017 participants (614 females) on two standard questionnaires to assess handedness and hypochondriasis: the Edinburgh Inventory and the Whiteley Index. Effects of sex, hypochondriac traits and the direction of handedness (left-handers; right-handers) on the degree of handedness (DH; the strength of lateralisation) were tested with multivariate linear regression. In confirmation of previous results, the DH is lower (less pronounced) in right-handed males than right-handed females, but is similar across sexes in left-handers. Regression analyses showed that for right-handers, male sex and higher hypochondriac traits are independent predictors of lower DH. For left-handers, main effects of sex and hypochondriac traits are not significant whereas a significant interaction of these two factors indicates that in left-handed men higher hypochondriac traits are associated with a differentially stronger shift towards lower DH compared to left-handed women. In conclusion, the DH is modulated by sex-specific effects of self-perception for left-handers but not right-handers. The implications of this finding on current theories of the inheritance of handedness are discussed. The assessment of hypochondriac traits might be useful to control response bias in questionnaire-based studies of human handedness.

Twin Database of the Secondary School Attached to the Faculty of Education of the University of Tokyo

This article profiles the historical twin databases of the secondary education school attached to the Faculty of Education at the University of Tokyo. The school was established in 1948. Every year, about 50 pairs of twins of all sex and zygosity combinations and aged 11 to 12 years take an examination, and about 10 to 20 pairs are admitted based on the results. Three independent datasets exist: one for applicants (11–12 years), one for students (12–18 years), and one for graduates (18–72 years). These three historical databases and research perspectives are introduced herein.

Origins of handedness: a nationwide study of 30,161 adults

The origins of human handedness remain unknown. Genetic theories of handedness have received much attention, but some twin studies suggest modest, perhaps negligible genetic effects on handedness. A related question concerning handedness is whether twins have higher rates of left-handedness than do singletons. We studied handedness, with information on forced right-handedness, in a sample of 30,161 subjects aged 18-69 from a questionnaire survey of the older Finnish Twin Cohort. Left-handedness was found to be more common in twins (8.1%) and triplets (7.1%) than in singletons (5.8%), whereas ambidextrousness was more common in triplets (6.4%) than in twins (3.4%) and singletons (3.5%). As in many other studies, males were more likely to be left-handed. Ambidextrous subjects were more likely to become right-handed writers even if not forced to use their right hand. We fit maximum likelihood models to our twin data to estimate the contribution of additive genetic, common environment and unique environmental effects to hand preference. Results, depending on the model, indicate that unique environmental effects account for most observed variance in handedness, both in childhood (92-100%) and adulthood (74-86%). When forced right-handedness was taken into account, estimates of familial effects increased. Concordance for left-handedness in twins is rare, and accordingly, very large samples are needed to detect the familial effects. Our results show that forced-handedness can have an effect on estimates of genetic effects.