Even the cutest cats can prove a nightmare for allergy sufferers.Getty

This week witnessed an event that will have some animal lovers cheering: the arrival on the market of long-promised 'allergy-free' pet cats. But you might be surprised at how low-tech these cute kitties are — especially considering the almost US$4,000 price tag.

The cats are being sold by Allerca, a company based in San Diego, California. It is currently taking orders for deliveries next year.

Founder Simon Brodie says he started by trying to genetically engineer a low-allergy cat, but during the early testing stages the team accidentally stumbled on animals that seemed to be naturally sniffle-free.

"Maybe you could say we got lucky," he says, with the "totally naturally occurring cat."

That has allowed the company to be first on the scene in what is predicted to be a very lucrative market, overtaking companies attempting to create hypoallergenic cats by transgenic methods.

Allerca has not yet published any data on its cats, although Brodie says that the company intends to do so.

Hush hush

Allerca initially planned to use the gene-silencing technique called RNA interference to quieten the gene that encodes Feld1, the protein that affects allergy sufferers. For those whose antibodies overreact to this protein, symptoms can include swelling, breathing problems, hives and even anaphylactic shock.

But when testing the genetic diagnostic tools that would be used to detect which cats had had the correct gene silenced, the team found three cats that make a slightly different version of the protein, one that does not harm allergy sufferers. Brodie describes it as a 50,000 to 1 shot.

To test the cats, the group looked in detail at a second-generation descendant of this stock: a feline named Joshua.

Sheldon Spector, a clinical allergy expert at the University of California, Los Angeles, recruited ten allergic volunteers, blindfolded them, and exposed them to Joshua, a regular cat named Tiki, or a furry dummy cat. Subsequent diaries of their symptoms suggest that Joshua was more allergy-friendly than Tiki.

The data have not been published in a journal. Spector says that Allerca paid his expenses for the research.

Cat fight

The work has prompted strong scepticism from a rival company. "I don't think you can have a non-GM hypoallergenic cat," argues David Avner, founder of Felix Pets in Denver, Colorado, which is attempting to use genetic modification (GM) to create low-allergy pets.

Avner says that Allerca should publish data showing whether or not proteins from the cats' skin and hair bind to human antibodies in the test tube, a process that underpins the allergic reaction.

More will be needed if Allerca is to silence its critics, Spector admits. "There are lots of things I think they should do," he told news@nature.com. "I keep telling them, do this and do this." There are limitations, he says, with the data he has collected so far.

Brodie counters that there's no substitute for real-life experience, and that trials with human volunteers have been successful. "It's all well and good to do these things in the test tube, but we want to make it as real-life as possible," he says. "We don't have the data yet, but we do know the animals work."

Brodie stands by his product, which includes a fully vaccinated kitten and a complementary test for existing allergens in your home. "If these scientists are sceptical, and if they happen to be allergic themselves, I would say 'come and hold one of our cats'," he says.

Advance orders now stretch into 2008, Brodie says, with some customers offering to pay $6,000 to shorten the wait.

Visit our petssurprisingly.html">newsblog to read and post comments about this story.  

Allerca, San Diego