The second most popular story on Stuff yesterday featured a kitten in Perth that was born with two faces:
Coco appears to be healthy, only has one brain, can only eat through one mouth but meow’s through both simultaneously. I’ll be interested to find out if the kitten can see through four eyes, which is not impossible. Mammalian brains are surprisingly good at re-wiring themselves to accomodate extra sense organs.
Some of the overseas media are reporting that the kitten is a kind of cojoined twin – they are almost certainly wrong. Coco will have a condition called Diprosopus, a congenital disease caused by mutation or malfunction of the genes that control embryonic development.
One of the mysteries of molecular biology in the mid-20th century was to discover how genes ‘built’ a body from a tiny cluster of identical cells. How does your liver ‘know’ that its supposed to be a liver and not a brain? The answer is that the cells respond to signaling proteins that have a different concentration in different parts of the embryo.
By analogy, its a bit like making a cake, but by putting different levels of flour, eggs, sugar and baking soda in different parts of the cake dish you end up with part cake, part souffle, part omelette and part quiche. What’s incredible is that this process works perfectly a large percentage of the time.
Sadly in Coco’s case the malfunctioning gene also controls the development of the brain, so the kitten might not be long for this world. The kitten may also have problems eating and breathing at the same time. Humans born with two faces rarely survive live birth and those that do die within days.
The gene that causes diprosopus is called ‘sonic hedgehog homolog’, because molecular biologists have an odd idea of humour. Genetic therapists hate the name, because they don’t relish telling parents that they might have to terminate a pregnancy because the embryo has a mutation in the ‘sonic hedgehog’ gene.