Summary: Although male and female brains are far more alike than different in structure, a high-resolution genetic analysis 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 small but widespread sex-related differences in transcription.
The study shows that sex accounts for only a small portion of overall brain variation, yet more than 3,000 genes display sex-biased expression 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, offering biological insight into why some brain disorders affect the sexes differently.
Key Findings
- Disease overlap: Many genes that show sex-biased expression also appear in genetic studies of neuropsychiatric and neurodegenerative disorders, suggesting that biological sex can amplify or buffer genetic risk.
- Small but widespread differences: Sex explains a very small fraction of the total variation in gene expression. Differences are generally subtle, distributed across many genes, cell types, and cortical regions, rather than concentrated in a few large effects.
- Biology and experience: The researchers note that sex-related transcriptional differences could arise from biological factors and also be shaped or reinforced by lifelong social and environmental influences.
- Cell-type specificity: Single-nucleus RNA sequencing enabled detection of cell-type–specific differences (for example, neurons versus glial cells) that are invisible in bulk tissue assays or standard brain imaging.
Source: AAAS
Overview
Men and women, defined here by typical XY and XX chromosome complements, differ in the risk, prevalence, and progression of many psychiatric and neurological conditions. While cultural and environmental factors contribute to these differences, their persistence across populations and developmental timing implies that sex-dependent patterns of gene expression in the brain may play an important role.
To test this idea, Alex DeCasien and colleagues performed a high-resolution transcriptomic survey using snRNA-seq on postmortem cortical tissue from 30 adults (15 male, 15 female). They sampled six cortical regions chosen to include areas previously associated with sex-biased structural differences as well as regions not known to differ by sex. This design allowed a direct comparison between molecular and anatomical variation.
The authors found that biological sex accounts for only a small portion of overall expression variation. Still, analysis revealed over 3,000 distinct genes with sex-biased expression in at least one region, and 133 genes with consistent sex differences across multiple regions and cell types. Although the most pronounced differences involved sex chromosome genes, the majority of sex-related transcriptional variation occurred in autosomal genes and appeared to be influenced largely by sex steroid hormones.
Importantly, many sex-biased genes overlap known genetic risk loci for disorders such as ADHD, schizophrenia, depression, and Alzheimer’s disease. This overlap suggests possible molecular pathways through which sex may modulate vulnerability or resilience to specific brain disorders.
The authors and accompanying commentators emphasize that social and experiential factors can alter gene expression via epigenetic mechanisms. Distinguishing lifelong environmental effects from intrinsic biological differences will require additional work, including studies that examine gene expression patterns before substantial postnatal social influence.
Key Questions Answered:
A: No. The findings reinforce that male and female brains are fundamentally similar. The differences lie mainly in the level of activity of particular genes rather than in wholesale structural differences—comparable to two very similar machines tuned for slightly different performance characteristics.
A: Genes implicated in these disorders often show sex-biased expression. If protective genes are more active in one sex, that sex may exhibit greater resilience; conversely, higher expression of risk-related genes could increase vulnerability.
A: Yes. The researchers acknowledge that experience and environment can modify gene expression. To conclude that differences are biologically innate, comparable sex-biased patterns would need to be shown in very early development, before social influences accumulate.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- The underlying journal paper was reviewed in full.
- Additional context was added by the editorial staff.
About this genetics and neuroscience research news
Author: Science Press Package Team
Source: AAAS
Contact: Science Press Package Team – AAAS
Image: The image is credited to Neuroscience News
Original Research: Closed access. “Sex effects on gene expression across the human cerebral cortex at cell type resolution” by Alex R. DeCasien, Pavan Auluck, Siyuan Liu, Ningping Feng, Abdel G. Elkahloun, Qing Xu, Stefano Marenco, Mark R. Cookson, and Armin Raznahan. Published in Science. DOI: 10.1126/science.aea9063
Abstract
Sex effects on gene expression across the human cerebral cortex at cell type resolution
INTRODUCTION
Differences in brain-related health outcomes between sexes may arise from distinct patterns of gene expression. These patterns are likely shaped both by sex chromosome complement and by circulating hormone levels.
RATIONALE
Most prior studies of molecular sex differences in the brain have used bulk tissue or focused on single regions. This work presents a large-scale single-cell transcriptomic analysis of adult human cortex using 169 samples from 30 donors (15 female, ages 26–71; 15 male, ages 27–78) across six cortical regions selected for their relevance to sex-biased anatomical measures.
RESULTS
Sex effects on gene expression show patterned variation across regions, cell types, and genes. The strongest effects were observed in multiple cell types in the fusiform cortex, in oligodendrocytes, astrocytes, and excitatory neurons across regions, and among a subset of sex chromosome and autosomal genes. Over 3,000 genes exhibited sex-biased expression, with 133 genes (119 autosomal) showing consistent differences across region × cell-type combinations. Sex chromosome genes produced the largest differences, driven by conserved X–Y gametologs, cell type–specific biases, and escape from X-inactivation. Autosomal sex effects organized into 13 core expression signatures shaped by regional cortical features, cellular compartments, regulation by sex steroids and X-linked transcription factors, and links to sex-biased genetic risk for neuropsychiatric and neurodegenerative diseases.
CONCLUSION
This study advances the resolution and scope of knowledge about sex differences in the human brain and makes a new data resource available for future work. Additional research is needed to determine when these sex differences first emerge during development and whether they generalize across populations.