A mutation in the MC1R gene is responsible for red hair and a heightened sensitivity to pain.

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Genetics and Pain

It's something of a scary thought, but medical science is not totally sure exactly how anesthesia works. But the University of Louisville study has pulled back the curtain a bit on the mysterious inner workings of the higher brain. If redheads need more anesthesia than non-redheads, it probably has something to do with their genetic makeup. Luckily, geneticists have already figured out which gene is causing the anomaly.

The melanocortin-1 receptor (MC1R) gene is responsible for the production of pigments in the body. Redheads' bodies produce the red pigment pheomelanin in increased amounts, and underproduce the dark pigment eumelanin. It's because of the levels of these pigments that redheads have red hair and their skin doesn't tan well.

Beyond this, scientists can only speculate why the gene may have an effect on pain. One explanation could be that the MC1R gene is also involved in hormones that stimulate pain receptors in the brain. The same mutation that inhibits the production of one pigment and increases another could also overproduce a pain-related hormone, making redheads more sensitive to pain.

Another explanation suggests that the pigments themselves cause an increase in pain sensitivity. With the MC1R gene not functioning properly, the melanin doesn't have a receptor site to bind with. The pigments may seek other, similar receptors to bind to, such as the brain's pain receptors. The poor fit between the pain receptor and the pigment could overstimulate the brain's pain response, accounting for the increased need for anesthesia.

Researchers also found a link between this gene and increased sensitivity to pain in studies of mice. Lab mice with a mutated MC1R gene -- and a lighter fur color -- require more anesthesia to prevent pain than mice with a properly functioning MC1R gene.

So while geneticists are confident that the MC1R gene is directly related to pain, it's the space in between point A and point B that requires filling in. The University of Louisville study provided the first demonstrable link between a phenotype (a visible genetic trait) and anesthesia. Since anesthesia's effects on the brain aren't fully understood, studying the role genes play in these higher functions could answer questions about which regions of the brain are responsible for these functions.

It's also good news for another branch of medicine -- pharmacogenetics. This relatively recently created field studies how humans react differently to drugs, based on differences in their genes. Rather than simply using more general anesthesia to knock out a redhead -- and increase the risk of overdose -- future pharmacogenetic research may yield a totally separate anesthesia, one that's designed specifically for redheads.

For more information on redheads, genetics, anesthesia and related topics, read the next page.