Handedness in Non-clinical Populations: Secular Trend, Relations to Schizotypy, and Heritability
Date Issued
2004
Date
2004
Author(s)
Su, Chiu-Hsia
DOI
en-US
Abstract
Part I: Handedness in Non-clinical Populations: Secular Trend and Relations to Schizotypy
Objectives: This study aimed to evaluate whether there was a secular trend in quantitatively measured handedness and the relations between handedness and schizotypal personality features among representative samples of community adults and school students in Taiwan.
Methods: A total of 175 primary school students, 1020 junior high school students, and 342 adult subjects aged 20 to 65 years were recruited in northern Taiwan during the period of 1993-1996. Subjects completed self-reported questionnaires, including the handedness questionnaire, the Schizotypal Personality Questionnaire (SPQ), and Perceptual Aberration Scale (PAS). The relations between schizotypal personality and handedness were evaluated in two approaches. In the first approach, both schizotypal personality and handedness were assumed to be continuous variables and partial Pearson product moment correlations between the two were calculated with adjustment for age and sex. In the second approach, both schizotypal personality and handedness were grouped into subjects with extreme scores and controls with nondeviant scores. Both groups were then compared for their handedness or schizotypal personality, respectively.
Results: Both females and males were found to have a trend of increasing age with a more degree toward right-handedness, and the changes became more obvious either before age 20 or after age 60 years. Schizotypal personality features and handedness were significantly associated as revealed by both the correlation analyses and case-control comparisons, especially for the PAS and Cognitive-Perceptual Dysfunction.
Conclusions: A clear secular trend of increasing left-handedness among younger generations was found. Schizotypal subjects, especially those with the positive aspect of schizotypy, would be more likely to be away from the right-handedness. The results suggest that there might be a common biological cause underlying the atypical cerebral lateralization and schizotypal personality features.
Part II: A Twin Study of Handedness among Adolescents in Taiwan
Objectives: This study aimed to evaluate the genetic and environmental contributions to quantitatively measured handedness among adolescent twins in Taiwan with the use of structural equation modeling. Furthermore, whether twining might influence handedness was assessed by comparing twins and singletons.
Methods: A total of 321 pairs of twins, 36 same-sex sib-pairs, and 1020 singleton subjects were recruited from the junior high schools in Taipei during the period of 1994 to 1998. All subjects completed the self-reported handedness questionnaire. Twins’ zygosity was determined by a combination of DNA typing and physical similarity. The Mx program was used to estimate parameters for a full model that contains effects from additive genes (A), shared environment (C), and nonshared environment (E) and a series of reduced model by treating the handedness either as a continuous or categorical variable.
Results: The twins did not have a distribution in handedness different from that of the singletons. For both the directional and the consistent handedness, the estimates from the full model ACE indicated no evidence of heritability. When the model was reduced to AE, the contribution from additive genes was estimated to be 16% (direction) and 23% (consistency) for continuous approach and 34% (direction) and 10% (consistency) for categorical approach. The corresponding estimates for the contribution from shared environment in the CE model were 15% (direction) and 20% (consistency) for continuous approach and 32% (direction) and 11% (consistency) for categorical approach. Both the AE and the CE model had an acceptable fit to the data, but the CE model tended to be more parsimonious in terms of Akaike’s information criteria.
Conclusions: Twining did not lead to an increased left-handedness in adolescent twins as compared with singletons. Handedness in adolescent twins assessed by the self-reported questionnaire is not substantially heritable. Environmental factors, especially those not shared between siblings, are the most important ones for explaining the variations in adolescent handedness.
Subjects
精神分裂病質
遺傳率
慣用手
世代趨勢
Heritability
handedness
Schizotypy
Secular Trend
Type
thesis
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