Summary:
A single-cell genomic study led by Harvard Medical School and Boston Children’s Hospital reveals that the human brain relies on a natural Darwinian quality-control process before and around birth to purge genetically flawed cells. Publishing in Nature, researchers discovered that up to 46% of prenatal neurons harbor widespread copy number variants, large duplications or deletions of DNA segments linked to autism, schizophrenia, and epilepsy. These abnormal cells fail to express essential synaptic genes, losing the competitive race to wire into functional neural circuits and dying off so that only healthy, genetically intact neurons dominate the mature brain.
Key Facts:
- Pervasive Prenatal DNA Variants: An average of 25.9% (and up to 46%) of neurons in the prenatal human cortex carry substantial copy number variants (CNVs), which plummets to an average of 6.2% following birth.
- Synaptic Selection Mechanism: Joint DNA/RNA single-cell sequencing of 44,861 individual cells revealed that neurons with high CNV burdens downregulate genes critical for creating and maintaining synapses, preventing them from competing successfully for circuit survival.
- Clinical Implications for Autism: The failure or dysregulation of this cellular pruning checkpoint could explain how genetically vulnerable neurons persist, potentially driving neurodevelopmental disorders like autism and schizophrenia or accelerating neuron loss in adult neurodegeneration.
Source: Harvard Medical School / Boston Children’s Hospital
During human fetal gestation, the cerebral cortex generates an astronomical surplus of neurons, only to eliminate a substantial fraction of them through programmed cell death shortly before and immediately after birth. While developmental neurobiologists have recognized this massive cellular winnowing for decades, the evolutionary and biological rationale for overproducing and discarding precious brain cells has remained unclear.
Now, a collaborative investigation from Harvard Medical School and Boston Children’s Hospital reveals that this massive cellular culling serves as an essential quality-control checkpoint.
Publishing October 28 in the journal Nature, the researchers discovered that the developing fetal brain is rife with somatic copy number variants (CNVs), large-scale deletions and duplications of DNA segments. Through a fierce, Darwinian competition for synaptic connectivity, the brain systematically weeds out these genetically flawed cells, ensuring that neurons with optimal genomic integrity form the foundation of our cognitive networks.
Mapping Genomic Chaos at Single-Neuron Scale
Somatic copy number variations have long been implicated in neurodevelopmental and psychiatric conditions, including autism spectrum disorder, schizophrenia, intellectual disability, and refractory epilepsy. However, assessing these structural DNA mutations across individual brain cells historically required prohibitively expensive whole-genome sequencing protocols.
To solve this technological bottleneck, the team engineered a cost-effective, low-pass single-cell sequencing strategy that captures an initial genomic snapshot of thousands of individual cells.
The investigators profiled 1,526 neurons from 16 individuals, validating their observations with high-depth sequencing of 831 neurons from 12 individuals across NIH-funded postmortem tissue repositories. Lead computational analyst Yifan Zhao, PhD, alongside co-senior author Peter Park, PhD, professor of biomedical informatics in the Blavatnik Institute at HMS, constructed specialized algorithms to map and quantify CNVs at single-cell resolution.
The data revealed an unexpected reality: an average of 25.9%, and in some prenatal specimens, up to 46%, of cortical neurons carried widespread genomic duplications or deletions.
However, this elevated mutation rate was short-lived. By the neonatal period, the proportion of CNV-carrying neurons dropped steeply to an average of just 6.2%, confirming a rapid, perinatal elimination window.
“Between 13 and 46 percent of neurons in the developing brain are riddled with copy number variants, but there seems to be a mechanism by which these abnormal neurons are eliminated around the time of birth,” said Park. “Now we can see these changes one neuron at a time, map where in the genome they occur, and compare how common they are from before birth to old age.”
Co-senior author Christopher A. Walsh, MD, PhD, Bullard Professor of Pediatrics and Neurology at Boston Children’s Hospital and an investigator of the Howard Hughes Medical Institute, drew parallels to early embryology: “We were totally unprepared for how common these were in early development. But it makes sense in the context of what we know about the formation of excess neurons and in the context of the IVF literature,” where early embryos often display aneuploid or mutated cells yet go on to develop into healthy infants.
Synaptic Competition: Survival of the Fittest Genome
To pinpoint how the brain recognizes and executes defective neurons, the researchers performed simultaneous single-cell multi-omic profiling, sequencing both the DNA and RNA across 44,861 individual cortical cells.
Transcriptomic mapping revealed the functional defect: neurons with high burdens of copy number variants suffered from widespread dysregulation of gene programs responsible for building and maintaining synapses.
In the developing nervous system, newborn neurons must compete aggressively with their neighbors to wire into active functional circuits. Neurons that successfully secure synaptic partnerships receive life-sustaining neurotrophic signals, while disconnected cells are triggered to undergo apoptosis. Because CNV-damaged neurons cannot express the proper molecular machinery to form stable synaptic bridges, they lose the competitive battle and are naturally eliminated.
“This competition for synapses has been described for years, but without the benefit of a genomic understanding,” Walsh explained. “We didn’t realize that this struggle for survival — this Darwinian competition — was nature’s quality control mechanism in the brain.”
“The brain is selecting for genomic integrity,” added co-first author Diane Shao, MD, PhD, HMS instructor of neurology at Boston Children’s Hospital. “If that quality control system can be disrupted, that could be part of what goes wrong in neurodevelopmental disorders like autism. Understanding the mechanism could eventually point us toward what to look for, and maybe what to protect.”
Somatic Mosaicism and Neurodegeneration
While the vast majority of damaged neurons are purged around birth, the study noted that a small percentage of CNV-bearing cells persist into adult life even in healthy brains. Whether this lingering mosaic diversity plays an adaptive computational role or represents an inevitable biological leakage remains an active area of study.
The research team is expanding its focus to examine whether this developmental quality-control system falters in autism, where aberrant synaptic pruning is already a documented clinical feature.
Furthermore, Walsh and colleagues are testing whether latent, genetically abnormal neurons that evade perinatal elimination become hyper-vulnerable to metabolic stress in late life, potentially driving early cell death in adult neurodegenerative illnesses such as Alzheimer’s disease.
Authorship, funding, disclosures
Additional authors of this work include Joseph Brew, Yahia Adla, Urmi Ghosh, Vinayak V. Viswanadham, Lovelace J. Luquette, Sijing Zhao, Andrea J. Kriz, Xuyu Qian, Takumi Taketomi, Shannon Coy, Sandro Santagata, Michael Miller, and Fuminori Tsuruta.
This work was supported by the National Institutes of Health (grants K08-NS128074, R01-NS032457, R01-HG012573, and R01-CA269805), the Templeton Foundation, the SMaHT consortium (UH3-NS132144), the Program in Genetics and Genomics PhD Training (grant T32GM141745), the Howard Hughes Medical Institute Jane Coffin Childs Fellowship, the HMS Program in Neuroscience Award, Ludwig Cancer Research and the Ludwig Center at Harvard, and the Brigham and Women’s Hospital President’s Scholars Award. Christopher A. Walsh is an Investigator of the Howard Hughes Medical Institute.
Park and Walsh are members of the scientific advisory board for Bioskryb Genomics, Inc. Walsh is also a member of the scientific advisory board for Mosaica Therapeutics and an advisor to Maze Therapeutics.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- Journal paper reviewed in full.
- Additional context added by our staff.
About this genetics and neurodevelopment Research:
- Media Contact: Katie Brace
- Source: Harvard
- Image Credit: Image credited to Neuroscience News
- Original Research is Open Access: Nature (Oct 28, 2026). “Perinatal elimination of genetically aberrant human cortical neurons.” Authors: Diane D. Shao, Yifan Zhao, Joseph Brew, Yahia Adla, Urmi Ghosh, Vinayak V. Viswanadham, Lovelace J. Luquette, Sijing Zhao, Andrea J. Kriz, Xuyu Qian, Takumi Taketomi, Shannon Coy, Sandro Santagata, Michael Miller, Fuminori Tsuruta, Peter J. Park & Christopher A. Walsh.
- DOI: 10.1038/s41586-026-11190-3
Abstract
Perinatal elimination of genetically aberrant human cortical neurons
Human neurons are postmitotic and long-lived, requiring precise genomic regulation. Normal neuronal function is highly dosage-sensitive, with copy number variants (CNVs) and heterozygous point mutations associated with a host of neurodevelopmental and neuropsychiatric conditions.
Here we investigated somatic CNVs arising in single neurons to understand the dynamic processes that shape the normal neuronal genetic landscape. Altogether, we sequenced 2,357 single neurons from human postmortem brain from fetal to postnatal life.
Two single-cell whole-genome sequencing approaches—Tn5-transposase-based amplification (1,526 neurons, 16 individuals) and primary template amplification (831 neurons, 12 individuals)—showed that an average of 25.9% [12.7–46%] of prenatal cortical neurons have highly aberrant genomes, that is, widespread CNVs involving multiple chromosomes.
This proportion reduced by about 4.5-fold after birth across the two single-cell whole-genome sequencing approaches (Fisher meta-analysis P = 3.5 × 10−6). Neurons with widespread CNVs were mainly eliminated perinatally, timed roughly parallel to periods of programmed cell death, whereas neurons with smaller CNV burdens declined slowly in frequency with postnatal age.
CNVs in surviving neurons were depleted for dosage-sensitive genes and genes involved in neurodevelopmental disorders (hypergeometric test P < 0.05), suggesting selective elimination of neurons with these CNVs. Analysis of 44,861 nuclei with single-nucleus assay for transposase-accessible chromatin (snATAC) and single-nucleus RNA sequencing (snRNA-seq) showed that neurons with high CNV burdens exhibited abnormal synaptic gene expression, suggesting that abnormal synaptic gene regulation contributes to neuronal elimination.
Elimination of defective neuronal genomes might represent an important developmental genome quality-control process that may be vulnerable in neurodevelopmental disease, and suggests purifying selection during human neurodevelopment.
