Scientists have uncovered extensive differences in gene expression between male and female brain cells in a landmark study published in Science and reported by Nature, shedding new light on long-debated questions about why brain disease risks differ between sexes. By analysing more than one million brain cells across multiple brain regions, researchers identified a complex but consistent pattern of molecular variation linked to biological sex.
The study found more than 100 genes that showed stable differences in activity between male and female brains across several regions of the cortex. Although these differences were described as subtle, researchers argue they may help explain why certain neurological and psychiatric disorders show sex-based patterns. Schizophrenia, attention deficit hyperactivity disorder and Parkinson’s disease are more commonly diagnosed in biological males, while Alzheimer’s disease and mood disorders such as depression and anxiety occur more frequently in females. For decades, scientists have sought a biological explanation for these patterns, but the underlying mechanisms have remained elusive.
To investigate, researchers examined approximately 680,000 excitatory neurons, 290,000 inhibitory neurons and 270,000 supporting glial and other cells taken from 30 human brain tissue samples. Across more than 4,300 genes analysed, sex accounted for less than 1 per cent of variation in gene expression. This reinforces a key conclusion highlighted in Nature’s coverage of the study: most variation in the human brain occurs between individuals rather than between sexes. However, the team also identified 3,382 genes showing sex-biased expression in at least one brain region, along with a core set of 133 genes that consistently differed across all regions and cell types studied.
Researchers described these 133 genes as a potential “molecular anchor point” for understanding how sex influences brain biology. Most of these genes are not located on sex chromosomes, but many respond to sex hormones such as oestrogen and testosterone. This suggests that differences in gene activity are not simply determined by XX or XY chromosomes, but are shaped by a broader biological system involving hormonal signalling and gene regulation.
The study also raises the possibility that environmental and social factors may contribute to the observed differences. Because many of the genes are sensitive to hormonal environments, their expression could be influenced by stress, health status, and life experiences. Scientists involved in the research emphasised that sex and gender are deeply interconnected in humans, making it difficult to separate purely biological effects from environmental influences that accumulate over a lifetime.
Experts quoted in Nature caution that the findings should not be interpreted as evidence of fundamentally different male and female brains. Instead, the brain is highly plastic, continuously shaped by development, experience and environment. Even where statistically significant differences exist, they are small and do not translate into simple functional differences between sexes. The study therefore highlights subtle regulatory patterns rather than rigid biological distinctions.
A key limitation of the research is that it provides only a snapshot of gene activity at a single point in time. Gene expression can change in response to ageing, disease, and environmental exposure, meaning that the observed differences may reflect dynamic processes rather than fixed biological states. Researchers also note that distinguishing between sex-based biology and gendered environmental influences remains one of the most difficult challenges in neuroscience.
Despite these uncertainties, the findings are seen as an important step toward understanding how molecular variation in the brain may contribute to disease vulnerability. Some of the identified genes are involved in neural development and immune system regulation, both of which have been implicated in disorders such as Alzheimer’s disease. This raises the possibility that even small differences in gene expression could influence how the brain responds to ageing, stress or pathology.
The research also reflects a broader shift in neuroscience toward single-cell analysis techniques, which allow scientists to examine gene activity at unprecedented resolution. Rather than averaging signals across entire tissue samples, researchers can now map differences at the level of individual cells, revealing patterns that were previously hidden.
However, scientists stress that these insights are not yet sufficient for clinical application. The relationship between gene expression differences and actual disease outcomes remains indirect, and further studies across larger and more diverse populations will be required to confirm and extend the findings reported in Nature.
The study contributes to a growing understanding that brain biology cannot be reduced to simple binary categories. Instead, sex-related differences in gene activity appear to form part of a much larger and more complex system shaped by genetics, hormones and environment. Researchers say the challenge now is to translate these molecular insights into a deeper understanding of brain disease risk, with the long-term goal of developing more precise and equitable treatments for neurological and psychiatric conditions.