In Nature Genetics, researchers report a novel mechanism for the origin of brain chromosomal mosaicism and link brain mosaic chromosome 1q gain to a distinct clinical phenotype. In most people, every cell in his/her body contains the same genetic information. However, . sometimes people can have two or more genetically different sets of cells. This usually happens during fetal development and is known as mosaicism. Sometimes one of those groups of cells has genetic changes that can cause diseases or disorders. Neurologists, neurosurgeons, and genomics experts have been working together to test for mosaicism in brain tissues resected during epilepsy surgery. Research has shown that mosaicism in the brain is a significant contributor to epilepsy. In a new study, published on October 23, 2023 in Nature Genetics, researchers from Nationwide Children’s Hospital in Columbus, Ohio describe an alternate origin of brain mosaicism in some children with focal epilepsy. The article is titled “Post-Zygotic Rescue of Meiotic Errors Causes Brain Mosaicism and Focal Epilepsy.”