Some of Your Proteins Are Not the Ones Your Genes Ordered

A team at the Weizmann Institute of Science has counted the protein variants that sit in healthy human tissue alongside the standard version of the same protein: 13,910 of them across 29 tissues, covering 7,215 different single-amino-acid swaps. The work was published in Nature on September 14, 2026.

Methods to find such variants, count them and work out what they do have been lacking, the authors write. Their survey sets out to measure them across normal tissue.

They come from two directions. Some are written into a person's DNA: inherited differences, or mutations picked up during life. The rest are mistakes: the cell misreads a gene while assembling the protein and inserts the wrong amino acid. For both kinds, how abundant a variant is tracks how common the matching gene variant is in the human population.

Hundreds of the non-genetic versions showed up consistently in more than one healthy person, or landed on parts of a protein already recorded as functional. In laboratory-grown cancer cells starved of amino acids, specific substitution patterns recurred. The authors propose that these non-genetic variants make up a new class of functional variation, and that they open a route into protein sequences the genetic code cannot reach on its own.

The paper also reports experimental confirmation of non-genetic substitution on selected purified proteins. Nature posted the peer-reviewed accepted version and says the final edited version will replace it.