thumb|upright|Sirenomelia
Sirenomelia, also called mermaid syndrome, is a rare congenital deformity in which the legs are fused together, giving the appearance of a mermaid's tail, hence the nickname.
Classification
[[File:Sirenomelia.svg|left|thumb|Classification of sirenomelia by the presence or absence of bones within the lower limb.<br>
I) all bones of thigh and lower leg present<br>
II) fused fibula<br>
III) fibula absent<br>
IV) partially fused femur, fused fibula<br>
V) partially fused femur<br>
VI) fused femur, fused tibia<br>
VII) fused femur, tibia absent]]Sirenomelia is classified by the skeletal structure of the lower limb, ranging from class I, where all bones are present and only the soft tissues are fused, to class VII where the only bone present is a fused femur.
Presentation
Sirenomelia is mainly characterized by the fusion of both legs with rotation of the fibula. It may include the absence of the lower spine, as well as abnormalities of the pelvis and renal organs. It was previously thought to be a severe form of sacral agensis/caudal regression syndrome, but more recent research confirms that these two conditions are not related. In general, the more severe cases of limb fusion correlate with more severe dysplasia in the pelvis. Rather than the two iliac arteries present in fetuses with complete renal agenesis, fetuses with sirenomelia display no branching of the abdominal aorta, which is always absent.
Associated defects recorded in cases of sirenomelia include neural tube defects (rachischisis, anencephaly, and spina bifida), holoprosencephaly, hypoplastic left heart syndrome, other heart defects, esophageal atresia, omphalocele, intestinal malrotation, persistent cloaca, and other limb defects (most commonly absence of the radius). although a few sources question this association. Prenatal cocaine exposure has also been suggested as an association with sirenomelia. 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. It is 100 to 150 times more likely in identical (monozygotic) twins than in singletons or fraternal twins. 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, 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 the age of four months, her natural kidney failed, and she began dialysis. A kidney transplant at age two lasted a number of years, and in 2007, a second kidney transplant was successful. She attended Consolidated Elementary School. She remained hopeful about her condition, joked often, and lived her life happily, despite her challenges, as seen in the TLC documentary Extraordinary People: Mermaid Girl. Shiloh and her family were debating surgery because of the risks involved, even though it would improve her quality of life. Many people who have sirenomelia undergo surgery at a young age, but Shiloh was already eight years old at the time and had not undergone surgery. Shiloh was the only one of three survivors of sirenomelia without surgery for separation of the conjoined legs. She died of pneumonia on October 23, 2009, at Maine Medical Center in Portland, Maine, at the age of ten; having appeared on The Oprah Winfrey Show on September 22, 2009. Shiloh gained a following of admirers after documenting her condition on television and the internet.
Milagros Cerrón
Milagros Cerrón Arauco (April 27, 2004 – October 24, 2019) was born in Huancayo, Peru. Although most of Milagros' internal organs, including her heart and lungs, were in perfect condition, she was born with serious internal defects, including a deformed left kidney and a very small right one located very low in her body. In addition, her digestive, urinary tracts and genitals shared a single tube.
This birth defect occurs during the gastrulation week (week 3) of embryonic development. Gastrulation establishes the three germ layers: ectoderm, mesoderm and endoderm. It seems that complications such as defects in the urogenital system as mentioned above can be possibly due to malformations in the intermediate mesoderm.
A four-hour operation to insert silicone bags between her legs to stretch the skin was successfully completed on February 8, 2005. A successful operation to separate her legs to just above the knee took place May 31, 2005, in a "Solidarity Hospital" in the district of Surquillo in Lima. The procedure, however, was so intensive that she became traumatized to the degree of losing her ability to form proper speech patterns, leaving her nearly mute. It is not known if this was a physiological or psychological condition. However, at Milagros' second birthday, her mother reported that she knew more than 50 words. A second operation to complete the separation up to the groin took place on September 7, 2006.
Her doctor Luis Rubio said he was pleased with the progress Milagros had made, but cautioned that she still needed 10 to 15 years of rehabilitation and more operations before she could lead a normal life, particularly reconstructive surgery to rebuild her rudimentary anus, urethra and genitalia.
Milagros' parents are from a poor village in Peru's Andes Mountains; the Solidarity Hospital had given a job to her father Ricardo Cerrón so that the family could remain in Lima, while the City of Lima pledged to pay for many of the operations.
She died on October 24, 2019, at the age of 15.