Mermaid syndrome is also known as Sirenomelia, which is derived from the Greek and Roman term "siren" (singing creatures that lured sailors to their death). It a congenital deformity characterized by the lower limbs fused together. It may also result in additional malformations such as, "absent external genitalia, imperforate anus, lumbosacral vertebral and pelvic abnormalities and renal agenesis" (http://www.afrjpaedsurg.org/ ). It is found in 1.05 out of 100,000 births and can be diagnosis in the first trimester "by noting the short crown - rump length on ultrasonography" (http://www.afrjpaedsurg.org/ ). There is a strong correlation between mermaid syndrome and diabetic mothers.

According to the European Journal of Radiology, mermaid syndrome dates far back and is probably what inspired siren and mermaid myths, so it is unclear who first "found" mermaid syndrome (it's not a condition that was discovered). For more information about the etiology, check out http://www.journals.elsevierhealth.com/periodicals/eurr/article/PIIS0720048X05004183/abstract ).