Urge to groom is partly genetic makeup, study says

Discovery offers hope in compulsive disorders

January 03, 2002|By Michael Stroh | Michael Stroh,SUN STAFF

Fussy about your face? Got a teen who lives to preen?

It might not be just vanity or hormones at work. Grooming behavior, a new study shows, might be partly in the genes.

Researchers at the University of Utah School of Medicine have pinpointed a gene that, when disabled, causes mice to obsessively lick and nibble their fur until they grow bald and sore-scarred.

The finding "is spectacular if it's true," says Ann Graybiel, a neuroanatomist at the Massachusetts Institute of Technology who studies habit formation in the brain.

In addition to providing new biological insight into why we groom, a behavior practiced by creatures ranging from worms to man, the discovery of a grooming gene could also lead to better treatment of obsessive compulsive diseases.

For example, people with obsessive compulsive disorder, a condition affecting roughly 3 percent of the U.S. population, often exhibit excessive grooming, scrubbing their hands for hours on end, sometimes until they bleed.

People with a closely related disorder, tricotillomania, meanwhile, pluck out their eyebrows, eyelashes and hair until there's nothing left.

"It had been thought there was a genetic component to these conditions, but nobody has made a connection to a particular gene," says Mario Capecchi, the University of Utah geneticist who conducted the new study.

The discovery, published yesterday in the journal Neuron, came as a surprise to Capecchi and co-author Joy Greer, a graduate student in his lab. The duo had been studying a family of genes called Hox that were known to play a key role in embryo development. Specifically, the genes help direct the construction of a creature's arms, heart and other organs.

When researchers created a litter of mice that lacked the gene Hoxb8, they found the animals developed just fine. But after three weeks, the researchers began to notice bald spots and open sores when they checked on the animals in the morning

By videotaping the cage around the clock, researchers discovered why: The mutant mice were primping themselves raw, spending twice as long licking and biting themselves as healthy mice. The scientists found tufts of hair in their teeth and stomach.

Everything else about the mice looked normal-even the way in which they groomed themselves. "They just overdo it," Capecchi says.

Grooming, scientists know, plays a number of important roles. By preening, animals rid themselves of parasites and germs, staving off disease. It's also an important part of courtship - as anyone who has seen a teen monopolize the bathroom before a hot date can attest.

"Grooming is a very elemental, probably innate, behavior," says Graybiel. "It's something that we and all other animals do."

To ensure that the mice's obsessive grooming was not the result of itchiness or some other neurological problem, Capecchi and his partner placed normal rats in the cage with the mutants. To their surprise, the genetically altered rats began tearing out their cagemates' fur, too.

Scientists caution that it remains to be seen whether the Hoxb8 gene plays a similar role in humans. Even if it does, the gene likely works in concert with others and the environment, says Capecchi.

He and colleagues next plan to study whether the gene is hardwired from birth in mice or whether it can be reprogrammed later in life, a finding that might open the door to the possibility of drug therapy.

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