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Black Cats Provide Lucky Break to Disease Research

By Maggie Fox, Health and Science Correspondent

WASHINGTON (Reuters) - Black cats, once considered unlucky, may have provided a lucky break to disease researchers, according to a report published on Monday.

Different genetic mutations give black coats to different species of cats. Some of the mutations are in genes that, in humans, are linked with diseases such as AIDS, a team at the National Cancer Institute and the University of Maryland found.

Dr. Stephen O'Brien, Eduardo Eizirik and colleagues were wondering what made cats black -- not out of idle curiosity, but because such genes often confer protection against disease. Otherwise, animals with unusual coloring would go extinct.

"In understanding how wild species like cats evolve genetic resistance to disease, we might discover new natural genetic resistance that might help in human disease," O'Brien said in a telephone interview.

Black cats might be better able to hunt at night, he noted, "but there is another fascinating aspect which I noticed because I work with the Cancer Institute."

For instance, his team found that a gene called MC1R makes jaguars black when mutated. Humans also have an MC1R gene that, when mutated, gives some people red hair.

It is in a family of genes called 7-transmembrane receptors. A receptor acts as a doorway into cells and is often used by bacteria and viruses to infect cells.

"HIV enters cells through a 7-transmembrane receptor called CCR5," O'Brien said. "So perhaps the selective pressure that allowed these mutations to survive in cats may not be to camouflage... Perhaps the mutations cause resistance of the cats to bugs."

The team's next step is to look for whatever possible advantages the mutations may offer. Making the cats black may just be a side effect, O'Brien said.

He said that 99.99 percent of all mammal species that ever lived have gone extinct. "The ones we have now are the survivors," he added.

The research started because the team wondered why there are black jaguars, leopards and house cats, but no black tigers or lions, O'Brien said.

A domestic cat has about 10 genes for coat colors and coat appearance, resulting in the 40-odd breeds of cat, he said.

The black mutation is very common, so O'Brien and his team wondered whether it dated back to the earliest ancestor of all cats or arose separately among the species.

Writing in the journal Current Biology, they said they found that the black domestic cat, the jaguar and the small South American jaguarundi each derive their coloring from a different type of mutation.

This casts a new light on animals that at one point were even tortured by people who saw them as agents of the devil.

"We have had black cats and they have been mythical all along," O'Brien said, "but now they been demystified."