The famous two-faced cat, Frank and Louie

The famous two-faced cat, Frank and Louie (sometimes called Frankenlouie), passed away this week at the ripe old age of 15.

For instance, Janus cats may have too much of the sonic hedgehog (SHH) protein, which plays a role in forming an animal's face during development. In some experiments, chick embryos expsoed to an excess of SHH were born with two beaks and eyes spaced far apart.

Frank and Louie was a ragdoll cat, and while cats—both purebred and otherwise—can fall prey to a number of genetic problems, Lyons doesn't think breeding plays a role in the occurrence of Janus cats, since the condition is so rare.

Lucky Feline

Though it may have two faces, a Janus cat almost certainly shares one brain, Lyons said. 

"I would suspect there would be brain-function abnormalities."

Lyons says the fact that other organs like the esophagus weren't doubled up likely saved Frank and Louie's life and allowed it to survive.

"In this particular case, one [side] didn't have a lower jaw or esophagus. If you had both sides of the face eating, I don't know what kind of complications that would cause. Initially the complications are going to be with the ability to eat and breathe properly."

Two-faced animals aren't limited to cats, either, she added.

: 'Frankenlouie', the world's oldest Janus cat - a feline with two faces- died at the age of 15 on Thursday December 4, 2014

Compassionate Owner

Although Janus cats often die young, when left to their own devices cat mothers will often abandon, kill, or even eat a kitten with such severe deformities.

Frank and Louie's owner Marty Stevens has said in previous interviewsthat she took the cat home so that it wouldn't be euthanized, something Lyons applauds. 

"It's very nice that there are individuals in our society that have this type of compassion," said Lyons.

"Like taking care of a handicapped child, they've taken care of a [special-needs] cat for 15 years."

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