Gene Activity in Human Cortex Shows Striking Sex Differences

Why It Matters

The discovery reframes how biological sex influences brain biology, offering molecular explanations for gender disparities in neurodegenerative and neurodevelopmental diseases and opening new avenues for precision therapies.

Key Takeaways

• Over 3,000 cortical genes differ between XX and XY brains
• 133 genes show consistent sex bias across six cortical regions
• Most sex‑biased genes are autosomal, not linked to chromosome dosage
• Female‑biased genes enriched for multiple sclerosis risk loci
• Sex explains 0.3% expression variance yet drives disease prevalence gaps

Pulse Analysis

The prevailing view in neuroscience has long linked sex differences to subcortical structures rich in hormone receptors, leaving the cerebral cortex largely unexamined. A recent single‑cell transcriptomics analysis of post‑mortem cortex from 30 adults overturns that assumption, revealing more than 3,000 genes with sex‑biased expression and a core set of 133 genes consistently divergent across six regions. Notably, 119 of these are autosomal, indicating that chromosome dosage alone cannot explain the molecular disparity. This cortical map reshapes our understanding of how biological sex imprints the brain at the cellular level.

The sex‑biased gene signatures intersect with disease risk pathways, offering a molecular foothold for the pronounced gender gaps seen in conditions such as autism and multiple sclerosis. Female‑biased genes are enriched for loci identified in genome‑wide studies of multiple sclerosis, while male‑biased expression peaks in the fusiform gyrus, a region implicated in facial‑recognition deficits in autism. Although sex accounts for only about 0.3 percent of overall transcriptional variance, its influence can magnify at the population level, shaping prevalence and severity patterns across neurodegenerative and neurodevelopmental disorders.

Researchers plan to probe these findings with brain organoids derived from individuals carrying atypical sex chromosome complements, such as Klinefelter (XXY) or trisomy X, to tease apart chromosome, hormone, and environmental contributions. Mapping circulating hormone levels to cortical gene expression across the lifespan could further untangle sex from gender effects. As the field moves beyond using sex as a proxy variable, the new cortical atlas provides a roadmap for targeted therapeutics and precision medicine, potentially allowing interventions that address the underlying molecular drivers of sex‑biased brain disease.