Summary: Although male and female brains are far more similar than different in overall structure, a high-resolution genetic study has uncovered thousands of subtle molecular distinctions. Using single-nucleus RNA sequencing (snRNA-seq) across six cortical regions, researchers mapped gene activity at cell-type resolution and identified patterns that may help explain sex differences in the prevalence and progression of several brain disorders.
The team found that sex accounts for only a small portion of total variation in brain gene expression, but over 3,000 genes show sex-biased transcription in at least one cortical region. A subset of these genes overlaps with genetic risk factors for conditions such as ADHD, schizophrenia, depression, and Alzheimer’s disease, suggesting biological mechanisms that could modify disease vulnerability between the sexes.
Key Findings
- Disease overlap: Many genes with sex-biased expression are also implicated in neuropsychiatric and neurodegenerative disorders. This overlap suggests that biological sex can act as a multiplier or buffer for genetic risk, altering susceptibility or resilience.
- Small but widespread differences: Sex explains a very small fraction of total brain variation. Differences are subtle, distributed across many genes and cell types, and are not concentrated in a single dramatic change.
- Biology and experience: The authors acknowledge the difficulty of separating innate biological effects from life-long socialization and experience, which can also shape gene activity through epigenetic mechanisms.
- High-resolution, cell-type view: By applying snRNA-seq, the study revealed sex-biased expression in specific cell types—such as neurons, oligodendrocytes, and astrocytes—that bulk-tissue analyses or standard imaging cannot resolve.
Source: AAAS
Overview: A new single-cell analysis across multiple human cortical regions shows subtle but consistent differences in gene expression between males and females. These differences are small in magnitude yet broad in scope, and their patterns overlap with genes linked to disorders that display sex differences in frequency or course.
Biological sex, typically defined by XX chromosomes for females and XY for males, is associated with measurable differences in the risk, prevalence, and progression of many psychiatric and neurological disorders. While social and environmental factors clearly contribute, the consistent cross-cultural patterns and predictable developmental timing point to underlying sex-related molecular differences in the brain.
To examine this, Alex DeCasien and colleagues performed highly resolved transcriptomic profiling using snRNA-seq on postmortem cortical tissue from 30 adults (15 female and 15 male). They sampled six cortical regions—some previously linked to sex-biased anatomy and others not—to compare molecular signatures against known anatomical variation.
Their analysis showed that sex accounts for only a minor share of overall gene expression variation. Still, over 3,000 genes displayed sex-biased expression in at least one region, and 133 genes showed consistent sex differences across multiple regions and cell types. Although sex chromosomes produced some of the strongest differences, most sex-related variation occurred in autosomal genes and appeared largely regulated by sex steroid hormones.
Importantly, many of the sex-biased genes overlap with variants associated with ADHD, schizophrenia, depression, and Alzheimer’s disease. This intersection suggests molecular pathways through which sex can influence disease risk, protection, or progression.
The study authors and commentators emphasize that social influences may reinforce or shape these patterns. To disentangle biological from experiential effects, future work will need to determine when these sex differences first appear—ideally examining prenatal and early postnatal brain tissue to test whether patterns exist before substantial social exposure.
Key Questions Answered:
A: No. Overall brain structure and the bulk of gene expression are highly similar. The study reports modest, cell-type–specific differences in gene activity—more akin to tuning differences in the same basic machinery rather than entirely different architectures.
A: Some genes tied to these disorders also show sex-biased expression. If protective or risk-associated genes are naturally more or less active in one sex, that could shift population-level vulnerability or resilience against specific conditions.
A: Yes. Lifelong experiences and environmental exposures can alter gene expression through epigenetic mechanisms. Definitive separation of biological from social causes will require studies that sample brains before extensive socialization, such as prenatal or newborn tissue.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- The journal paper was reviewed in full for accuracy.
- Additional context and clarifications were added by editorial staff.
About this genetics and neuroscience research news
Author: Science Press Package Team
Source: AAAS
Contact: Science Press Package Team – AAAS
Image: Image credit: Neuroscience News
Original Research: Closed access. “Sex effects on gene expression across the human cerebral cortex at cell type resolution” by Alex R. DeCasien et al., published in Science. DOI: 10.1126/science.aea9063
Abstract
Sex effects on gene expression across the human cerebral cortex at cell type resolution
INTRODUCTION
Sex differences in brain-related health outcomes may stem from differences in gene expression shaped by both sex chromosome complement and circulating hormones. Understanding these molecular differences is key to explaining sex-biased patterns in neurological and psychiatric disease.
RATIONALE
Most prior work relied on bulk tissue or single-region analyses. This study presents a large single-nucleus transcriptomic dataset from 169 samples taken from 15 females (ages 26–71) and 15 males (ages 27–78) across six cortical regions chosen for known or suspected sex-biased anatomy, enabling a refined map of sex-related transcriptional patterns at cell-type resolution.
RESULT
Sex effects on expression are organized by cortical region, cell type, and gene. Pronounced differences were found in the fusiform cortex and across oligodendrocytes, astrocytes, and excitatory neurons. Over 3,000 genes showed sex-biased expression, with 133 genes (including 119 autosomal) exhibiting consistent differences across multiple region-by-cell-type combinations. Sex chromosome genes produced the strongest signals, but many autosomal genes also showed sex-biased patterns regulated by sex steroids and X-linked transcription factors. The study identified 13 core autosomal signatures linked to cortical architecture, cellular processes, hormone regulation, and sex-specific genetic risk for neuropsychiatric and neurodegenerative diseases.
CONCLUSION
This work significantly expands the resolution and scope of knowledge about sex differences in the adult human brain and provides an open data resource for future research. Follow-up studies are needed to determine when these differences emerge during development and whether they generalize across diverse populations.