The brain removes many genomically abnormal neurons around birth

A Nature study used two whole-genome methods on 2,357 single neurons from postmortem human brains spanning fetal to adult life. On average, about 25.9% of prenatal cortical neurons carried widespread copy-number variation across multiple chromosomes, and this fraction fell roughly 4.5-fold after birth in both methods. Neurons with the heaviest abnormalities were mainly eliminated around the perinatal period, while smaller CNV burdens declined more slowly across life. Analysis of 44,861 nuclei also linked high CNV burden to abnormal synaptic-gene expression, suggesting that synapse formation and programmed cell death together form a genome-quality-control process in the developing human brain. Donors and postmortem samples are limited, the design cannot watch cells in one person over time, and not every variant neuron is necessarily harmful. Work now needs to test which genetic or environmental factors disrupt selection and whether this contributes to neurodevelopmental disease.