title: Genetics of anisotropy asymmetry: registration and sample size effects.
abstract: Brain asymmetry has been a topic of interest for neuroscientists for many years. The advent of diffusion tensor imaging (DTI) allows researchers to extend the study of asymmetry to a microscopic scale by examining fiber integrity differences across hemispheres rather than the macroscopic differences in shape or structure volumes. Even so, the power to detect these microarchitectural differences depends on the sample size and how the brain images are registered and how many subjects are studied. We fluidly registered 4 Tesla DTI scans from 180 healthy adult twins (45 identical and fraternal pairs) to a geometrically-centered population mean template. We computed voxelwise maps of significant asymmetries (left/right hemisphere differences) for common fiber anisotropy indices (FA, GA). Quantitative genetic models revealed that 47-62% of the variance in asymmetry was due to genetic differences in the population. We studied how these heritability estimates varied with the type of registration target (T1- or T2-weighted) and with sample size. All methods consistently found that genetic factors strongly determined the lateralization of fiber anisotropy, facilitating the quest for specific genes that might influence brain asymmetry and fiber integrity.
authors.affiliation: Laboratory of Neuro Imaging, Department of Neurology, UCLA, CA, USA.
authors.forename: Neda
authors.initials: N
authors.lastname: Jahanshad
authors.forename: Agatha D
authors.initials: AD
authors.lastname: Lee
authors.forename: Natasha
authors.initials: N
authors.lastname: Leporé
authors.forename: Yi-Yu
authors.initials: YY
authors.lastname: Chou
authors.forename: Caroline C
authors.initials: CC
authors.lastname: Brun
authors.forename: Marina
authors.initials: M
authors.lastname: Barysheva
authors.forename: Arthur W
authors.initials: AW
authors.lastname: Toga
authors.forename: Katie L
authors.initials: KL
authors.lastname: McMahon
authors.forename: Greig I
authors.initials: GI
authors.lastname: de Zubicaray
authors.forename: Margaret J
authors.initials: MJ
authors.lastname: Wright
authors.forename: Paul M
authors.initials: PM
authors.lastname: Thompson
mesh_terms: D016880:Anisotropy; D001921:Brain / Q000033:anatomy & histology* / Q000502:physiology*; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000379:methods*; D010641:Phenotype; D015203:Reproducibility of Results; D018401:Sample Size; D012680:Sensitivity and Specificity; D014427:Twins / Q000235:genetics*