Brain size, head size, and intelligence quotient in monozygotic twins

Brain size, head size, and intelligence quotient in monozygotic twins

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Brain size, head size, and intelligence quotient in monozygotic twins M.J. Tramo, MD; W.C. Loftus, BS; T.A. Stukel, PhD; R.L. Green, MD; J.B. Weaver, PhD; and M.S. Gazzaniga, PhD Article abstract-Many studies of monozygotic (MZ) twins have revealed evidence of genetic influences on intellectual functions and their derangement in certain neurologic and psychiatric diseases afflicting the forebrain. Relatively little is known about genetic influences on the size and shape of the human forebrain and its gross morphologic subdivisions. Using MRI and quantitative image analysis techniques, we examined neuroanatomic similarities in MZ twins and their relationship to head size and intelligence quotient (IQ). ANOVA were carried out using each measure as the dependent variable and genotype, birth order, and sex, separately, as between-subject factors. Painvise correlations between mea- sures were also computed. We found significant effects of genotype but not birth order for the following neuroanatomic measures: forebrain volume (raw, p 5 0.0001; normalized by body weight, p = 0.0003); cortical surface area (raw, p = 0.002; normalized, p = 0.001); and callosal area (raw, p 5 0.0001; normalized by forebrain volume, p = 0.02). We also found significant effects of genotype but not birth order for head circumference (raw, p = 0.0002; normalized, p 5 0.0001) and full-scale I& (p = 0.001). There were no significant sex effects except for raw head circumference (p = 0.03). Significant correlations were observed among forebrain volume, cortical surface area, and callosal area and between each brain measure and head circumference. There was no significant correlation between I& and any brain measure or head circumference. These results indicate that: 1) forebrain volume, cortical surface area, and callosal area are similar in MZ twins; and 2) these brain measures are tightly correlated with one another and with head circumference but not with I& in young, healthy adults. NEUROLOGY 1998;50:1246-1252 Monozygotic (MZ) twins manifest similarities in cog- nitive skills and other behavioral characteristics that are attributable, for the most part, to the identity of their gene~.l-~ In light of current knowledge about brain-behavior relationships in humans6s7 and cellu- lar and physiologic mechanisms underlying brain de- velopment in anirnal~,~,~ one might hypothesize that MZ twins possess similarities in brain anatomy. Un- til recently, it has been difficult to test this hypothe- sis quantitatively. With the advent of in vivo brain imaging as a clinical tool over the past quarter cen- tury has been the development of computer-based image processing techniques that permit quantita- tive analyses of neuroanatomic data contemporane- ously with behavioral asse~srnent.~~-'~ In the present study, we analyzed total forebrain volume, total cere- bral cortical surface area, callosal cross-sectional area, head circumference, and full-scale intelligence quotient (IQ) in normal adult MZ twins. In addition
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This note was uploaded on 05/18/2011 for the course ANTHRO 600 taught by Professor Different during the Spring '08 term at Kansas.

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Brain size, head size, and intelligence quotient in monozygotic twins

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