been found to cause or be associated with sirenomelia. The srn (siren) gene is observed to cause hindlimb fusion in homozygous mice. Mice with knockouts or mutations in both tsg1 and bmp7 will also have hindlimb fusion. Diagnosis Though obvious at birth, sirenomelia can be diagnosed as early as 14 weeks gestation on prenatal ultrasound. When there is low amniotic fluid around the fetus (oligohydramnios), the diagnosis is more difficult. Prognosis Sirenomelia is usually fatal. Many pregnancies with a sirenomelic fetus spontaneously miscarry. One-third to one-half of infants are stillborn, with all but a few dying in the neonatal period. In cases of monoamniotic twins where one is affected, the twin with sirenomelia is protected from Potter sequence (particularly pulmonary hypoplasia and abnormal facies) by the normal twin's production of amniotic fluid. Epidemiology This condition is found in approximately one out of every 100,000 live births; studies produce rates from 1 in 68,741 to 1 in 97,807. It is 100 to 150 times more likely in identical (monozygotic) twins than in singletons or fraternal twins. Sirenomelia is not associated with any ethnic background, but fetuses with sirenomelia are more likely to be male. Etymology The word sirenomelia derives from the ancient Greek word seirēn, referring to the mythological Sirens, who were sometimes depicted as mermaids, and melos, meaning "limb". History Sirenomelia was first reported in 1542. In 1927, Otto Kampmeier discovered the association between sirenomelia and single umbilical artery. Notable individuals Only a few individuals who had some functioning kidney tissues have survived the neonatal period. Tiffany Yorks Tiffany Yorks of Clearwater, Florida (May 7, 1988 – February 24, 2016) underwent successful surgery in order to separate her legs before she was a year old. She was the longest-surviving sirenomelia patient to date. She had mobility issues due to her fragile leg bones and compensated by using crutches or a wheelchair. She died on February 24, 2016, at the age of 27. Shiloh Pepin Shiloh Jade Pepin (August 4, 1999 – October 23, 2009) was born in Kennebunkport, Maine, United States with her lower extremities fused, no bladder, no uterus, no rectum, only 6 inches of large intestine, no vagina, only one quarter of a kidney and one ovary. Her parents initially anticipated she could expect only a few months of life. At age 4 months, her natural kidney failed, and she began dialysis. A kidney transplant at age 2