Review of Twin and Family Studies on Neuroanatomic Phenotypes and Typical Neurodevelopment

Abstract

This article reviews the extant twin studies employing magnetic resonance imaging data (MRI), with an emphasis on studies of populationbased samples. There have been approximately 75 twin reports using MRI, with somewhat under half focusing on typical brain structure. Of these, most are samples of adults. For large brain regions such as lobar volumes, the heritabilities of large brain volumes are consistently high, with genetic factors accounting for at least half of the phenotypic variance. The role of genetics in generating individual differences in the volumes of small brain regions is less clear, mostly due to a dearth of information, but rarely because of disagreement between studies. Multivariate analyses show strong genetic relationships between brain regions. Cortical regions involved in language, executive function, and emotional regulation appear to be more heritable than other areas. Studies of brain shape also show significant, albeit lower, genetic effects on population variance. Finally, there is evidence of significant genetically mediated relationships between intelligence and brain structure. At present, the majority of twin imaging studies are limited by sample sizes small by the standards of behavioral genetics; nevertheless the literature at present represents a pioneering effort in the pursuit of answers to many challenging neurobiological questions.

Quantifying the heritability of task-related brain activation and performance during the N-back working memory task: A twin fMRI study

“…>50%) as found here and reported previously. It is also considerably lower than that reported for lobar and overall brain volumes, and regional grey and white matter volumes, which in general have a high heritability (reviewed by Schmitt et al, 2007), as indicated here for total grey matter volume. However, our heritability estimates for task-related brain activation are comparable in magnitude to a recent study in which genetic influences accounted for 38% of the variance in activation of the dorsal anterior cingulate cortex during an interference task (Matthews et al, 2007).…”

“…Two recent twin studies using fMRI, the first focussing on sadness in a reasonably large sample (104 pairs) of 8-year-old twins (Côté et al, 2007), and the second using an interference processing task and a small sample of 20 female twin pairs (Matthews et al, 2007), suggest that there may be a modest, if any, genetic influence on neural activation, as captured by fMRI, and that the genetic contribution to individual differences in task-related brain activation may be both task specific and regionally variable. This is in contrast to twin studies using structural MRI that indicate there is a strong influence of genes on the volumes of brain structures, and on grey and white matter subvolumes; heritability of subcortical regions has been less well studied showing lower and more variable heritabilities (reviewed by Schmitt et al, 2007).…”

Hippocampal volume changes in healthy subjects at risk of unipolar depression

“…However, the latter might be partly due to reduced statistical power in the smaller subgroup of MZ twins (40 MZ vs. 72 DZ). Because heritability estimates of hippocampal volume are low to moderate (Peper et al, 2007;Schmitt et al, 2007) it is possible that the observed hippocampal volume reductions are best explained by environmental rather than genetic influences. In line with such an interpretation are findings from a recent study of 10 MZ twin pairs discordant for the risk of anxiety and depression.…”

Prefrontal and Striatal Volumes in Monozygotic Twins Concordant and Discordant for Schizophrenia

“…[31][32][33] Behavioral genetic studies have shown that the frontal lobe is under substantial genetic control in healthy humans, with heritability estimates of frontal volumes of approximately 90%. 34,35 What is less clear is the extent to which frontostriatal volume changes in schizophrenia are influenced by the genetic risk for the disorder itself. The subtle yet statistically reliable volumetric changes seen in patients with schizophrenia could reflect the impact of genetic, epigenetic, or environmental factors.…”