The heritability of volumes of brain structures and its relationship to age: A review of twin and family studies

Total brain volume (BV) and the volumes of brain substructures are influenced by genes, the magnitude of which changes with age. One approach to the examination of genetic influences on the volumes of brain structures is to determine their heritability using twin and family studies. We reviewed published cross-sectional studies which examined heritability in healthy subjects at different ages. We identified 32 studies, which examined a total of 77 brain volumetric measures. The findings of our review showed that BVs are under significant genetic influence at all ages, although different brain regions showed different heritability levels. Furthermore, the cross-sectional approach of our review found that heritability factor for the majority of BVs declined with age, such as in the total brain and cerebrum, followed by subsequent increment of environmental influences. Overall, this study identified for the first time a cross-sectional pattern for brain structures' heritability changes with age, and suggests the potential for longitudinal investigations in the future. © 2013

rec. a Mireille Armisen-Marchetti, Sapientiae facies. Études sur les images de Sénèque, Paris, Les Belles Lettres, 1989

The relative contributions of genetic and environmental factors to brain structure change throughout the lifespan. Brain structures have been reported to be highly heritable in middle-aged individuals and younger; however, the influence of genes on brain structure is less studied in older adults. We performed a magnetic resonance imaging study of 236 older twins, with a mean age of 71.4 ± 5.7 years, to examine the heritability of 53 brain global and lobar volumetric measures. Total brain volume (63%) and other volumetric measures were moderately to highly heritable in late life, and these genetic influences tended to decrease with age, suggesting a greater influence of environmental factors as age advanced. Genetic influences were higher in men and on the left hemisphere compared with the right. In multivariate models, common genetic factors were observed for global and lobar total and gray matter volumes. This study examined the genetic contribution to 53 brain global and lobar volumetric measures in older twins for the first time, and the influence of age, sex, and laterality on these genetic contributions, which are useful information for a better understanding of the process of brain aging and helping individuals to have a healthy aging. © 2014 Elsevier Inc

Alterations in resting state connectivity along the autism trait continuum: a twin study

© 2018, Springer Nature Limited. Autism spectrum disorder (ASD) has been found to be associated with alterations in resting state (RS) functional connectivity, including areas forming the default mode network (DMN) and salience network (SN). However, insufficient control for confounding genetic and environmental influences and other methodological issues limit the generalizability of previous findings. Moreover, it has been hypothesized that ASD might be marked by early hyper-connectivity followed by later hypo-connectivity. To date, only a few studies have explicitly tested age-related influences on RS connectivity alterations in ASD. Using a within-twin pair design (N=150 twins; 8–23 years), we examined altered RS connectivity between core regions of the DMN and SN in relation to autistic trait severity and age in a sample of monozygotic (MZ) and dizygotic (DZ) twins showing typical development, ASD or other neurodevelopmental conditions. Connectivity between core regions of the SN was stronger in twins with higher autistic traits compared to their co-twins. This effect was significant both in the total sample and in MZ twins alone, highlighting the effect of non-shared environmental factors on the link between SN-connectivity and autistic traits. While this link was strongest in children, we did not identify differences between age groups for the SN. In contrast, connectivity between core hubs of the DMN was negatively correlated with autistic traits in adolescents and showed a similar trend in adults but not in children. The results support hypotheses of age-dependent altered RS connectivity in ASD, making altered SN and DMN connectivity promising candidate biomarkers for ASD