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Human Brain Cortex Structures Mediated by Genetic Factors

NEW YORK (GenomeWeb) – The relatively well conserved creases and crinkles of the human cortex appear to fall under the influence of genetic factors, according to a study published online today in PLOS Genetics.

Researchers from the US and Norway brought gene expression profiles for half a dozen post-mortem brain samples together with array-based genotyping data for hundreds of twin pairs and thousands more unrelated individuals for whom brain scan images were available. Their results supported the notion that the brain's cortical surface patterns are controlled by genetic factors, which might also contribute to the functional interplay between parts of the cortex.

"Despite considerable individual variability in the size and folding patterns of the cortex, the overall organizational patterns seem highly consistent," co-senior author Chi-Hua Chen, a radiology researcher at the University of California at San Diego, said in a statement. "Our study shows that genetic factors are likely to be important for laying down this basic cortical patterning. The challenge for the future work will be to identify these specific genetic variants."

For their analyses, the researchers did array-based genotyping on 2,364 unrelated individuals subject to brain imaging, assessing directly genotyped and imputed SNPs and nearly 2.5 million sites in the genome. They also considered imaging data for 466 individuals from the Vietnam Era Twin Study of Aging, representing 134 sets of identical twins and another 99 non-identical twin pairs.

Along with the imaging data, which provided a glimpse at cortical structures at a dozen brain sites, the team factored in transcriptomic data generated for post-mortem brain samples from five men and one woman assessed for the Allen Brain Atlas project. Together, the data indicated that the cortical structures and folds are mediated by genetic factors: the researchers saw distinct clusters of expressed genes that were shared across the same sites of the human cortex between individuals, along with relatively close genetic ties between cortical regions from a given lobe.

Based on these findings, the study's authors noted that genetic similarities between nearby brain regions "could mirror lineage relationships of cortical neurons generated from proximal parts of the developing cortex under common influences of genetic gradients."

The team suspects that the between-region genetic distinctions it detected may reflect functions performed in various parts of the brain's cortex, particularly since the functionally complex frontal lobe formed the most distinct gene expression cluster.

Overall, more than 71 percent of gene expression was shared across the cortical regions considered in the post-mortem samples, the researchers noted, though the frontal lobe contained the highest proportion of genes with site-specific expression.

"We found a consistent pattern of genetically-mediated relationships among cortical brain regions across different data sets and different analytical techniques," Chen and her co-authors wrote. "These cortical brain regions are genetically defined and largely correspond to known functional specialized regions."