In 2007, dermatologist Peter Itin was contacted by a Swiss woman with an unusual quandry: She was having trouble entering the U.S. because she had no fingerprints. Regulations require all non-residents to be fingerprinted when they enter the country, and the authorities were baffled when the woman said that she simply hadn't been born with any.

When Itin looked into the case, he found that eight other members of the woman's extended family also had been born printless. Ultimately, working with Israeli dermatologist Eli Sprecher and other colleagues, Itin tracked down three other unrelated families that included people with adermatoglyphia, which they dubbed "immigration delay disease," and successfully located the single gene mutation responsible in 2011.

"It's an exceedingly rare condition," says Sprecher, who's one of just a handful of doctors worldwide to have dealt with the disease firsthand. "Generally, from the movies, we only hear of criminals who try to get their fingerprints removed, and no one's heard of this disease, so I think that's why border control authorities have found it so troubling."

The finger pads of people with adermatoglyphia are entirely flat—they have none of the arching or looping ridges that characterize the fingerprints of virtually all humans. Otherwise, though, people with the condition are entirely healthy, minus a slightly reduced number of sweat glands. There are other genetic disorders (including NFJS and dermatopathia pigmentosa reticularis) that lead to missing fingerprints, but they also cause much more severe health impacts, such as thin, brittle hair and teeth.

For Sprecher and Itin, the fact that an entirely-healthy person could be somehow born without fingerprints presented a puzzle. After finding the three other groups of related people with the same condition, they suspected that it had a genetic cause.

When they sequenced the DNA of 16 members of the woman's family (nine with adermatoglyphia, and seven without), their hunch proved correct. Those in the former group all had a mutation in a region of DNA that codes for a protein called SMARCAD1, while the latter group had a normal form of the gene. The shorter, mutated version of the gene, they found, interferes with the way RNA is spliced together—a crucial step in the process of using a gene to produce a protein—which prevents the protein from forming correctly.

It's still unclear how exactly this protein is involved in fingerprint development, a process that happens in the womb. The researchers suspect it might play a role in helping a fetus' skin cells fold over one another, producing a fingerprint's ridges, but further work is needed to test the idea. That's because, even though they're something we see everyday, scientists in general have conducted extremely little research into how fingerprints normally form.

Adermatoglyphia, though, is providing an unexpected window into the process. "This condition actually helped us get insights into the mechanisms that regulate the formation of fingerprints. If it weren't for this disease, we'd never know that this gene had anything to do with it," Sprecher says. "Sometimes, through the study of an extraordinary disorder, you gain insight into the ordinary aspects of our biology."