Flippin' your fins you don't get too far, Legs are required for jumpin' dancin'...

For Valentine’s Day, I went with a friend to see Disney on Ice. It was magical. Obviously all of the princesses were there including Ariel (the little mermaid for you morons that don’t know who that is). In honor of Ariel, I am going to post about real mermaids today. OK, really they are just humans born with a birth defect that makes them look like mermaids.

Sirenomelia (mermaid syndrome) is a super rare (1 in 100,000 live births) congenital birth defect where the newborn’s legs are fused together, appearing to look like a mermaid’s tail. Sirenomelia is not a genetic disorder and occurs randomly. A mom can have tons of healthy children, then a child with this disorder and go on to have more normal babies. The exact cause is not certain, but there are two main theories.

The first is the theory of caudal regression syndrome. Under this explanation, sirenomelia is caused by the failure of the cells within the caudal mesodermal axis. This includes a failure of both axial and intermediate mesodermal cells… just kidding (that was a line from a paper I wrote in an embryology class about sirenomelia). Basically this theory just says there are problems with the developing baby’s cells and therefore the cells end up developing improperly.

A second possible cause of sirenomelia is the vascular steal theory. Babies born with sirenomelia are usually from pregnancies associated with the presence of only a single umbilical artery (there should be two). This one umbilical artery is believed to “steal” blood supply (and thus oxygen supply) away from the developing embryo, mainly the lower (caudal) portion. Not enough oxygen means poor development.

Those born with sirenomelia suffer from a lot of other complications besides just fused legs. Most are born with messed up bone structures (lubrosacral and pelvic bone abnormalities), kidney development failure (bilateral renal agenesis), a malformed rectum (anorectal atresia) and malformed or completely absent boy/girl parts (agenesis of the external genitalia). These are serious complications and often lead to death within 2 days of birth. Depending on the severity of the condition and availability of health care, surgery may be an option to survive sirenomelia. There are only four known cases of children with sirenomelia living into childhood.