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.