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What

Sirenomelia syndrome describes a congenital birth defect in which infants are born with a single lower extremity or with their legs fused together, giving the appearance of a mermaid. It frequently includes malformations of the urogenital and gastrointestinal tracts, and is associated with a wide range of other anomalies across many organ systems.

Who

This defect affects about 1 in every 60,000-100,000 live births, and is 100 times more likely to occur in identical twins than in singletons or fraternal twins. It is also 3 times more likely to occur in males than females. About 300 cases have been reported thus far, but the majority of patients die within days after birth. Only 2 patients with the condition have survived into childhood and are alive today—one in the United States, and the other in Peru.

Signs and Symptoms

The most obvious sign of sirenomelia syndrome is the presence of a single lower limb; this may refer to single or fused femurs (thigh bones) as well as the presence or absence of either or both feet. If there are feet and knees present, they are rotated such that the back of the knee and foot is facing forward. In addition to this malformation, patients with sirenomelia syndrome also have a single umbilical artery (normally there are 2) and either missing or abnormally developed kidneys that may lead to another condition in utero called oligohydramnios, in which there is too little amniotic fluid in the sack. Oligohydramnios can interfere with the development of the lungs and cause a flattened facial appearance from compression against the mother’s abdomen. Along with the kidney malformations, patients also frequently have other urogenital abnormalities, such as absent bladder or simplified/missing external genitals. Likewise, the anus is often imperforate, or unopened. In some cases, fetuses may also have defects of the vertebral column, abdominal wall, or chest. Apart from the single lower limb, single umbilical artery, and kidney abnormalities, however, all of these other clinical findings vary highly between cases.

Possible Causes

Sirenomelia syndrome is a condition present in affected children at birth. It is not believed to be hereditary, but rather due to some teratogenic, or birth defect-causing, agent that has yet to be implicated. There has also been some association of in vitro fertilization (IVF) with increased risk for sirenomelia syndrome, but most cases are not associated with IVF. Whatever the underlying cause, on a physiological level, the features of sirenomelia syndrome are due to the failure of an abnormal umbilical artery to supply blood to the lower part of the body during development in utero. As a result, the kidneys and lower extremities do not form properly.

Diagnosis

At birth, sirenomelia syndrome is diagnosed based on the clinical presence of signs described above. Prenatally, the diagnosis is best made using ultrasound to examine the blood vessels in the umbilical cord. The appearance of these blood vessel anomalies in color-flow imaging, in combination with ultrasound detection of kidney malformations and a single lower extremity, allows for a fairly accurate prenatal diagnosis. ultrasound images may be difficult to obtain though, due to the sirenomelia-associated decrease in amniotic fluid, which prevents a clear view of the fetus. Sirenomelia syndrome may not be detected by amniocentesis, chromosome analysis, or DNA analysis.

Treatment

Thus far, only 2 patients with sirenomelia syndrome have been successfully treated for survival past infancy. The older of these patients was the first to ever undergo surgery for separation of her legs and feet, beginning when she was just 25 days old. Under the care of orthopedic and plastic reconstructive surgeons, she has since regained use of her legs and is now able to walk. Likewise, the second surviving patient with sirenomelia syndrome was operated on to separate her legs; in the future, she will also undergo genital reconstruction surgery for her malformed anus, urethra, and genitals. The decision to operate on patients with sirenomelia syndrome rests on the extent of the abnormalities, especially with regard to the kidneys.

Prognosis

The prognosis for babies born with sirenomelia syndrome is very poor, with almost all patients dying within a day or two after birth from kidney complications. For that reason, termination of pregnancy is a common option in prenatally diagnosed cases. In the exceptional cases of sirenomelia syndrome without kidney malformations, however, surgery allows for a much better prognosis—the 2 surviving patients offer hope that a once-lethal condition may potentially be treatable. Parents with one child with sirenomelia usually do not have any other children with the disorder.

Connect with other parents

In the spirit of community and support, Madisons Foundation offers the unique service of connecting parents of children with rare diseases. If you would like to be connected to other parents of children with this disease, please fill out this brief form.

Weblinks

Genetic Alliance: Advocacy, Education &Empowerment
General resources, glossary, and tools for understanding genetic disease.

Shriners Hospitals for Children: Patient Success Stories
Article on only surviving American patient with sirenomelia syndrome. Contains information on Shriners Hospital, which was responsible for patient’s treatment.

Google Search for Sirenomelia Syndrome

References and Sources

Silva SR and Jeanty P (1999). Sirenomelia. www.thefetus.net/page.php?id=440. Dordoni D and Freeman PC (1991). Sirenomelia sequence. www.thefetus.net/page.php?id=441. Patel S and Suchet I (2004). The role of color and power Doppler ultrasound in the prenatal diagnosis of sirenomelia, ultrasound Obstet Gynecol, 24:6, p 684-91.