Janus meets Sonic the Hedgehog

Frank and Louie... has two mouths, two noses and three eyes. He turned 12 years old this month, setting the record for "longest surviving Janus cat," according to Guinness World Records. Frank and Louie has a case of craniofacial duplication, an extremely rare congenital condition... Frank and Louie was born on September 8, 1999 and was adopted by a woman who lives near Worcester, Massachusetts. Picture: REUTERS/David Niles

This was one of the Telegraph "pictures of the day."  The last time I posted a report about this anomaly was almost three years ago; this time I decided to read more about the biology involved.  These excerpts from the Wikipedia entry on diprosopus (literally "two" + "face"):

Although classically considered conjoined twinning (which it resembles), this anomaly is not normally due to the fusion or incomplete separation of two embryos. It is the result of a protein called sonic hedgehog homolog (SHH)...

Among other things, the SHH protein governs the width of facial features. In excess it leads to widening of facial features and to duplication of facial structures. The greater the widening, the more of the structures are duplicated, often in a mirror image form...

Most human infants with diprosopus are stillborn. Known instances of humans with diprosopus surviving for longer than minutes to hours past birth are very rare; only a few are recorded...

And a final tidbit for the "grammar Nazis."  Note this cat is named "Frank and Louie," so a grammatically correct sentence actually begins "Frank and Louie was born..."