Environmental predominance on brain structure and connectivity in language-related regions: a multimodal twin study in adolescence

Language alterations are recognized as early markers of psychopathological vulnerability, yet genetic and environmental factors underlying language-related brain regions remain unknown. We applied univariate twin analyses and risk-discordant comparisons to multimodal dataset from 31 healthy twin pairs (9-31 years) and 17 pairs discordant for psychopathological risk (10-27 years). Gray matter volume (GMV), cortical thickness (CT), and functional interactions, specifically effective connectivity (EC), were assessed in eight bilateral language-related regions, alongside linguistic, emotional-behavioural, temperamental, and personality-related phenotypes. In healthy twin pairs (27-31 pairs, depending on data completeness), genetic and environmental determinants were estimated for all phenotypes. In 17 pairs discordant for psychopathological risk, intra-pair neuroimaging differences were tested for association with psychopathological discordance and zygosity, and individual brain measures were compared across high-risk twins, their low-risk co-twins, and healthy controls. Environmental factors predominated in structural and functional brain variability, while genetic contributions were limited, region-specific. Narrative fluency and psychological traits showed stronger heritability. Findings converged on the right middle frontal gyrus, where GMV and CT alterations reflected non-shared environment and risk expression. Despite the small sample, preliminary results suggest neurobiological vulnerability in language networks arises from environmental rather than genetic factors, informing environmental susceptibility to adolescent mental illness.