Morphometric Analysis of Neocortical and Infratentorial Structures: Genetic and Environmental Insights from a Twin Neuroanatomical Study.

Background and Objective: Brain morphometry is shaped by a complex interplay of genetic and environmental factors, including physiological and neuropsychiatric conditions. These influences can vary across distinct brain regions, yet the precise contributions of genetics and environment to regional variation in healthy brains remain poorly understood. This study examines the heritability of specific brain structures to provide deeper insights into their development. Materials and Methods: We studied 118 healthy adult twins from the Hungarian Twin Registry using T1-weighted magnetic resonance imaging (T1W MRI) and the volBrain pipeline for structural measurements. Results: In all regions, monozygotic (MZ) twins showed a higher resemblance than dizygotic (DZ) twins in total brainstem and cerebellar volumes, with significant heritability (A: 90.5-92.6%) and minimal unique environmental effects (E: <1%). For supratentorial regions, regarding the total gray matter volume, all regions exhibited high heritability (A: 74.5-92.4%) and minimal environmental influence (E: <1.5%). In average cortical thickness analysis, the frontal lobe, temporal lobe, and pre-central gyrus were influenced by shared and unique environmental factors (C: 63-66.5%; E: 33.4-37%), whereas genetics were more prominent in the parietal lobe, occipital lobe, and post-central gyrus (A: 67.7-85%; E: 15-32.3%). Conclusions: Genetics strongly influence cortical gray matter volume in supratentorial regions (both total and regional), as well as the total brainstem volume and the total and cortical gray matter volumes of the cerebellum in infratentorial regions. This genetic influence extends to the average cortical thickness of the parietal lobe, post-central gyrus, and occipital lobe, while the frontal lobe, temporal lobe, and pre-central gyrus are more affected by environmental factors. These findings emphasize the importance of understanding region-specific genetic and environmental contributions to brain structure, which could guide personalized therapeutic and preventive strategies for neurological conditions.