Identifying genomic regions involved in brain development

A joint effort between two large international research consortia has identified genomic regions linked with changes in the size of the hippocampus, a brain structure involved in memory. These findings will help scientists understand the development of the hippocampus, which is involved in neuropsychiatric illnesses such as dementia, bipolar disorder, and Alzheimer’s disease. 

The research team, which included Daniah Trabzuni of King Faisal Specialist Hospital and Research Centre in Saudi Arabia, examined the genomes of over 30,000 individuals to find variants associated with differences in the size of the hippocampus. Their analysis revealed that these differences were linked with six regions of the genome, two of which were already known. 

The nature of the relationship between these regions and hippocampus remains unclear. “We have narrowed down the effect of these loci to the hippocampus, but now need to ask additional questions to find out their exact effect,” says Hieab Adams of the Netherlands’ Erasmus University Medical Center, one of the lead authors of the study. Researchers will need to tease apart the roles of these loci and determine whether they act as general growth factors for the hippocampus or affect specific subregions.

Most of the individuals included in the study were of European descent, making it unclear whether these findings can be generalized to other populations. “We actively looked for samples of non-European ancestry, but unfortunately there weren’t many studies with such data available,” explains Adams.

The team also found a correlation between genetic variants influencing the hippocampus and variants associated with Alzheimer’s disease, suggesting that some genes affect both the hippocampus and the disease, although the six loci identified in the study were not linked with Alzheimer’s.

“It’s important to realize that these six loci are only the tip of the iceberg, while hundreds to thousands of loci are still hidden from us. Larger studies will hopefully identify more of these variants that also are related to Alzheimer’s,” says Adams.

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