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Mapping mosaicism: Tracing subtle mutations in our brains

brain genetic mosaicism
(Erik Jacobsen, Threestory Studio. Used with permission.)

DNA sequences were once thought to be the same in every cell, but the story is now known to be more complicated than that. The brain is a case in point: Mutations can arise at different times in brain development and affect only a percentage of neurons, forming a mosaic pattern.

Now, thanks to new technology described last week in Neuron, these subtle “somatic” brain mutations can be mapped spatially across the brain and even have their ancestry traced.

Like my family, who lived in Eastern Europe, migrated to lower Manhattan and branched off to Boston, California and elsewhere, brain mutations can be followed from the original mutant cells as they divide and migrate to their various brain destinations, carrying their altered DNA with them.

“Some mutations may occur on one side of the brain and not the other,” says Christopher Walsh, MD, PhD, chief of Genetics and Genomics at Boston Children’s Hospital and co-senior author on the paper. “Some may be ‘clumped,’ affecting just one gyrus [fold] of the brain, disrupting just a little part of the cortex at a time.”

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