Gyrifizierung und Hirnvolumen bei mono- und dizygoten Zwillingspaaren - Ein Vergleich

Abstract

Many studies reported that gyrification and brain volumes are strongly genetically influenced. The aim of this study is to analyze the genetic influence on gyrification in prefrontal lobe and volumes of prefrontal lobes, temporal lobes, cerebellum and total brain. Therefore MRI-scans of six healthy monozygotic (MZ) and dizygotic (DZ) pairs of twins as well as age-matched unrelated pairs were compared. The gyrification index (GI) was measured by an automated version (A-GI) through the whole prefrontal lobes and by a manual version (M-GI) in three prefrontal coronal slices. Moreover, different brain volumes (total brain volume, volumes of temporal lobes, prefrontal lobes, and cerebellum) were analyzed. Similarities between monozygotic, dizygotic and unrelated pairs of the brain morphologies were evaluated by calculating the absolute differences, Pearsons product moment correlations and intraclass correlation coefficients (ICC). The analysis revealed that the mean values of the M-GI and A-GI in the prefrontal lobes of MZ twins were not significantly more similar than the ones of DZ twins. The ICC of the M-GI and A-GI were not higher in MZ twins than in DZ twins. The comparison of the two methods of measuring gyrification demonstrated higher mean values of the A-GI compared to the M-GI. The brain volumes of MZ twins were not significantly more similar compared to the DZ twins. ICCs of brain volumes in MZ twins were not higher than those in DZ twins. The comparison of twins and unrelated pairs revealed a greater similarity concerning the measured brain volumes and a trend to more similarity concerning A-GI in twin pairs. As a result of the nonsuperior similarity of the A-GI and M-GI as well as those of the brain volumes comparing MZ to DZ twins a lower genetic influence can be assumed, which is in contrast to some previous studies. In fact, different environmental factors like intrauterine influences, learning processes throughout life and aging processes seem to have a prominent influence on human brain morphology. However, the comparison between twins and unrelated pairs implies also a genetic influence.