The patterns of ridges (gyri) and grooves (sulci) differ between ancestral populations. Source: Wikimedia Commons
Researchers at the University of California, San Diego, found that genetic ancestry was correlated with the geometry of the brain’s outer surface. They could use surface patterns to estimate the proportion of various ancestries in American subjects from diverse lineages (1,2).
An individual’s ancestry can be determined using small parts of their DNA, known as single-nucleotide polymorphisms (SNPs), which match within a given population. The researchers used SNPs from reference populations from four continental regions: West Africa, North and Western Europe, East Asia, and the Native American region (2).
For the study, they recruited adolescents from the US who were older than the age of 12 and had no prior history of brain damage or disease. Twelve was the minimum age because the cortical surface has been found to change very little after this age (2).
The researchers first determined the proportion of SNPs and genetic ancestry in these individuals based upon the four reference populations. They then tested to see if differences in the patterns in the gyri and sulci of the brain corresponded with proportions of genetic ancestry, and found that patterns in the folding of the brain accounted for between 47 to 66 percent of the variation between subjects (1,2).
This data was used to create models to find patterns among the different populations and found certain trends: For example, the researchers found a more posterior and inward temporal surface among those with African ancestry, and protrusions in the occipital and frontal regions in those with European ancestry. Subjects with significant East Asian ancestry had variations in temporal-parietal areas, while those with Native American ancestry had flatter frontal and occipital surfaces. Many of these findings seemed to match with previous studies of variations in the surface of the skull (2).
The researchers also looked at other aspects of the brain, such as the aspect ratios of the cerebral cortex, the volume of subcortical structures, surface area, and cognitive abilities, but they did not find as strong of associations as they did with surface geometry (1,2). The variations in brain surface even held up after analysis among those with particularly diverse ancestries (2).
With these genetic correlations, the researchers hope to arrive at better understandings of the genetic basis behind abnormalities, and hope that accounting for these differences will help make assessing brain development and disease more personalized (1).
References:
1. University of California – San Diego. (2015, July 9). A new wrinkle: Geometry of brain’s outer surface correlates with genetic heritage: Patterns in sulci and gyri don’t predict cognitive ability, but may help diagnose disease. ScienceDaily. Retrieved July 18, 2015 from www.sciencedaily.com/releases/2015/07/150709180214.htm
2. Chun Chieh Fan, Hauke Bartsch, Andrew J. Schork, Chi-Hua Chen, Yunpeng Wang, Min-Tzu Lo, Timothy T. Brown, Joshua M. Kuperman, Donald J. Hagler, Nicholas J. Schork, Terry L. Jernigan, Anders M. Dale. Modeling the 3D Geometry of the Cortical Surface with Genetic Ancestry. Current Biology, 2015; DOI: 10.1016/j.cub.2015.06.006