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Genetic differences among ethnically diverse individuals are largely due to structural elements called copy number variants (CNVs), according to a study published today (August 6) in Science. Compared with other genomic features, such as single nucleotide variants (SNVs), CNVs have not previously been studied in as much detail because they are more difficult to sequence. Covering 125 distinct human populations around the world, geneticist Evan Eichler at the University of Washington in Seattle and an international team of colleagues studied the genomes of 236 people-analyzing both SNVs and CNVs. "The take-home message is that we continue to find a lot more genetic variation between humans than we appreciated previously," Eichler told The Scientist.

Published today (17:00BST, 03/06/2015) in the journal Neuron, their work presents strong evidence that disruption of a delicate chemical balance in the brain is heavily implicated in the disorder. In the largest ever study of its kind, the team found that disease-linked mutations disrupt specific sets of genes contributing to excitatory and inhibitory signalling, the balance of which plays a crucial role in healthy brain development and function.