What if you could look inside every major organ of the human body and see how genes behave, how they turn on, how much they’re used, and how that activity changes depending on your DNA? That’s exactly what the Genotype-Tissue Expression (GTEx) Consortium set out to do. Led by researchers from institutions including the Broad Institute of MIT and Harvard, the GTEx project represents one of the most ambitious efforts to date to map how genetic variation affects gene activity in different tissues.

Genes carry the instructions for making proteins, the building blocks of life. But not all genes are equally active in every part of the body. For example, the same gene might be highly active in the pancreas but barely used in the brain. The GTEx team wanted to understand what controls these differences, and how they’re influenced by inherited genetic differences between people.

To do this, researchers collected tissue samples from nearly 1,000 deceased donors and performed RNA sequencing to measure gene expression in 49 different tissue types, including the heart, liver, lungs, skin, and various brain regions. RNA sequencing provides a snapshot of which genes are being actively transcribed into messenger RNA (mRNA), a key step in making proteins, and how much they are being used.

They then searched for expression quantitative trait loci (eQTLs), genetic variants that are associated with changes in gene expression levels. These variants act like dimmer switches, turning gene activity up or down depending on the DNA sequence. By identifying these switches in a tissue-specific way, the researchers created a detailed atlas of genetic regulation across the human body.

Why does this matter? Understanding how gene expression varies by tissue can help explain why certain diseases affect specific organs. For instance, a genetic variant linked to heart disease might only influence a gene’s activity in heart tissue, not in blood or skin. This insight is vital for pinpointing disease mechanisms and developing targeted therapies.

The GTEx atlas also provides a roadmap for interpreting results from genome-wide association studies (GWAS), which identify genetic variants associated with diseases but often don’t tell us how those variants work. By linking variants to gene activity, GTEx helps fill in those missing connections.

In addition to supporting disease research, the GTEx dataset is a goldmine for exploring fundamental biology—such as how gene expression differs between men and women, how aging affects gene activity, and how various tissues respond to stress or injury.

With all the data publicly available, GTEx has become a foundational resource in the field of functional genomics, enabling discoveries across neuroscience, immunology, cardiology, and beyond. It reminds us that while all cells share the same DNA, the way that DNA is used can vary profoundly depending on where it’s located in the body.