Genetic and environmental influence on white matter: insight from an Italian twin population study

The heritability of white matter (WM) has been a central focus of diffusion neuroimaging and genetic research. Twin studies have reported high heritability estimates for WM integrity, primarily based on fractional anisotropy (FA). However, other diffusion tensor imaging (DTI) metrics-mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD)-remain less explored.

In the present twin study, we assessed WM heritability using FA, MD, AD, and RD metrics. Tract-Based Spatial Statistics was applied to DTI data from 81 healthy twin pairs (33 monozygotic, 48 dizygotic) recruited through the population-based Italian Twin Registry. Twin correlations and genetic and environmental variance components were estimated for each DTI index across brain regions.

Monozygotic twins exhibited higher correlations than dizygotic twins across most brain regions; however, a few regions showed an unexpected inverse pattern. Notably, while several regions demonstrated strong genetic influences, others showed no detectable genetic contribution, suggesting a substantial role for environmental factors in shaping WM characteristics in those areas.

These findings revealed regional variability in WM heritability and challenged the assumption of uniform genetic influence, highlighting the importance of considering early environmental factors and supporting the development of more nuanced models of WM development.