Brain structural differences in monozygotic twins discordant for body mass index.

Background: Substantial efforts have been made to investigate the neurobiological underpinnings of human obesity with a number of studies indicating a profound influence of increased body weight on brain structure. Although body weight is known to be highly heritable, uncertainty remains regarding the respective contribution of genetic and environmental influences.

Methods: In this study we used structural magnetic resonance imaging (MRI) data from the Human Connectome Project (HCP). Voxel-based morphometry (VBM) was applied to study BMI-associated differences in gray matter volume (GMV) within monozygotic (MZ) twin pairs discordant for BMI (ΔBMI ​> ​2.5 ​kg*m, n = 68 pairs). In addition, we investigated the relationship of ΔBMI (entire range) with GMV differences within the entire sample of MZ twin pairs (n = 153 pairs).

Results: Analyses of BMI discordant twin pairs yielded less GMV in heavier twin siblings (p < 0.05 FWE; paired t-Test) within the occipital and cerebellar cortex, the prefrontal cortex and the bilateral striatum including the nucleus accumbens. A highly converging pattern was found in regression analyses across the entire sample of MZ twin pairs, with ΔBMI being associated with less GMV in heavier MZ twins.

Conclusion: While MZ twins share the same genetic background, our findings indicate that non-genetic influences and the mere presence of a higher BMI constitute relevant factors in the context of body weight related structural brain alterations.