Synesthesia's Molecular Roots Traced Back to Rare DNA Mutations

For people with auditory-visual synesthesia, striking a piano key may ignite visions of turquoise geometric patterns or a twanging guitar string could create the sensation of billowing orange foam. Many aspects of life may feel like a sober LSD trip for people who experience this neurological phenomenon, and in a study published Monday in the Proceedings of the National Academy of Sciences, scientists came one step closer to characterizing exactly who these people are.

In a statement released Monday, scientists from the Max Planck Institute for Psycholinguists and the University of Cambridge report a discovery that they hope will eventually “explain the biology of synaesthesia.”

Previous brain-imaging studies have demonstrated that the visual areas of synesthetes’ brains are more active and that synesthetes have altered cortical wiring at the embryo stage, but until now scientists haven’t been able to trace the phenomenon back to its molecular roots. In the new paper, they show that auditory-visual synesthetes — one of at least 60 known sense variants — carry variants of genes related to the development of neural connections and cell migrations. Characterizing these genes, the authors write, is the first step in understanding how a person’s genes influences these extrasensory associations.

Synesthesia is known to run in families, so the scientists examined DNA samples belonging to several generations of three families with multiple cases of auditory-visual synesthesia. Using genomic sequencing, the scientists searched the DNA for changes that altered the way genes code for proteins. There were consistent variations on genes associated with cell migration and axogenesis, the process that enables brain cells to wire up to their correct partners — a consistent theme across all three families. Six genes were altered within these synesthetes: COL4A1, ITGA2, MYO10, ROBO3, SLC9A6, and SLIT2.

“These results are consistent with the neuroimaging-based hypothesis about the role of hyperconnectivity in the etiology of synesthesia and offer a potential entry point into the neurobiology that organizes our sensory experiences,” the scientists write.

Now that these genes have been identified, the scientists hope to better understand how and when they turn on during development and affect the way the brain is wired. Of course, there’s still a huge amount to learn when it comes to understanding how people can experience something as spectacular as the blending of color and sound. That’s why the team behind this study has put out the call for other synesthetes — especially families of them — to come and participate in future studies. The scientists have also created this short quiz that people can use to test for the ability: If you pass, you join the just one percent of folks who pulsate with the involuntary cross-activation of their senses.

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