Frank and Louie's two-faced appearance is caused by a protein called… (Steven Senne / Associated…)
By now most of you probably have seen pictures of Frank and Louie, who, at age 12, is the oldest-living two-faced cat. They (he?) have two mouths, although only one is used for eating, and one brain. Although Frank and Louie have three eyes, only two are operational, and they seem to work just fine.
The disorder is called diprosopus, or craniofacial duplication, a rare condition that causes duplication of the face and sometimes the cerebral frontal lobes. Felines with this condition are often called Janus cats after the Roman god who had two faces.
Frank and Louie's long life has been attributed to the care and love from his (their?) owner, who so far has only been identified as a woman named Marty who reportedly lives in Massachusetts and saved the cat from being euthanized when he was brought into the veterinary medicine school where she worked.
Most cats with the condition don't live long due to related health issues, but Frank and Louie have beaten the odds and now have a place in the 2012 Guinness World Records book.
Diprosopus occurs in humans as well as animals; the most notable recent case occurred in India in 2008. A baby girl named Lali Singh was born with two complete faces -- doubles of everything, with one body -- and she was something of a media sensation in her small village. Sadly, two months after her birth she died of a heart attack. Most babies with the disorder are stillborn.
The condition is thought to be caused by a protein with the unusual name sonic hedgehog homolog, which has a corresponding gene. Sonic hedgehog proteins are responsible for signalling cells about proper formation of limbs and organs during embryonic development; the one that causes diprosopus is said to be linked with brain and face patterning.
Having too little of the protein can cause cyclopia, which produces only one eye socket and gives the appearance of a cyclops.
We applaud Marty for taking such good care of of Frank and Louie and wish all of them many more happy birthdays to come.