National Center for Advancing and Translational Sciences Genetic and Rare Diseases Information Center, a program of the National Center for Advancing and Translational Sciences

Sirenomelia


Other Names:
Mermaid malformation; Fused legs and feet; Sirenomelus; Mermaid malformation; Fused legs and feet; Sirenomelus; Sirenomelia sequence; Mermaid syndrome See More
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Sirenomelia is a birth defect in which affected infants are born with a single lower extremity or with two legs that are fused together. The symptoms and physical findings associated with the condition vary greatly among affected individuals and may include malformations of the spine and skeletal system (commonly with vertebrae either absent or defective); absent or underdeveloped internal and external sex organs, rectum, kidneys and/or bladder; closed rectal opening (imperforate anus); and other abnormalities of the lower gastrointestinal tract. The exact cause is unknown, but it is believed to result from irregularities in early development of the blood circulating system within the embryo. Surgery has been successful in separating joined legs. Other treatment is symptomatic and supportive.[1]
Last updated: 3/24/2016

This table lists symptoms that people with this disease may have. For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed. This information comes from a database called the Human Phenotype Ontology (HPO) . The HPO collects information on symptoms that have been described in medical resources. The HPO is updated regularly. Use the HPO ID to access more in-depth information about a symptom.

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Medical Terms Other Names
Learn More:
HPO ID
80%-99% of people have these symptoms
Absence of the sacrum 0010305
Ambiguous genitalia
Ambiguous external genitalia
Ambiguous external genitalia at birth
Intersex genitalia
[ more ] 		0000062
Anal atresia
Absent anus
0002023
Renal hypoplasia/aplasia
Absent/small kidney
Absent/underdeveloped kidney
[ more ] 		0008678
Sirenomelia 0010497
30%-79% of people have these symptoms
Abnormality of the cardiovascular system
Cardiovascular abnormality
0001626
Aplasia/Hypoplasia of the radius 0006501
Spina bifida 0002414
Tracheoesophageal fistula 0002575
Percent of people who have these symptoms is not available through HPO
Anterior sacral meningocele 0007293
Autosomal dominant inheritance 0000006
Back pain 0003418
Constipation 0002019
Dermoid cyst 0025247
Headache
Headaches
0002315
Hemisacrum 0009790
Meningitis 0001287
Meningocele 0002435
Neurogenic bladder
Lack of bladder control due to nervous system injury
0000011
Rectal abscess 0005224
Sacral lipoma 0012033
Urinary retention 0000016
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Last updated: 7/1/2020
The exact cause of sirenomelia is unknown. Researchers believe that both environmental and genetic factors may play a role (multifactorial). Some cases are thought to result from irregularities in early development of the circulatory system, as some individuals with sirenomelia have a single large artery branching off of the aorta (instead of the usual two). Abnormalities in this blood delivery system decreases blood flow to the lower areas of the embryo, interfering with development.[1] Some of the risk factors that have been identified in this condition include maternal diabetes, teratogens, genetic factors and maternal age younger than 20 years.[2] 
Last updated: 3/24/2016

If you need medical advice, you can look for doctors or other healthcare professionals who have experience with this disease. You may find these specialists through advocacy organizations, clinical trials, or articles published in medical journals. You may also want to contact a university or tertiary medical center in your area, because these centers tend to see more complex cases and have the latest technology and treatments.

If you can’t find a specialist in your local area, try contacting national or international specialists. They may be able to refer you to someone they know through conferences or research efforts. Some specialists may be willing to consult with you or your local doctors over the phone or by email if you can't travel to them for care.

You can find more tips in our guide, How to Find a Disease Specialist. We also encourage you to explore the rest of this page to find resources that can help you find specialists.

Healthcare Resources

These resources provide more information about this condition or associated symptoms. The in-depth resources contain medical and scientific language that may be hard to understand. You may want to review these resources with a medical professional.

Where to Start

  • The National Organization for Rare Disorders (NORD) has a report for patients and families about this condition. NORD is a patient advocacy organization for individuals with rare diseases and the organizations that serve them.

In-Depth Information

  • The Monarch Initiative brings together data about this condition from humans and other species to help physicians and biomedical researchers. Monarch’s tools are designed to make it easier to compare the signs and symptoms (phenotypes) of different diseases and discover common features. This initiative is a collaboration between several academic institutions across the world and is funded by the National Institutes of Health. Visit the website to explore the biology of this condition.
  • Online Mendelian Inheritance in Man (OMIM) is a catalog of human genes and genetic disorders. Each entry has a summary of related medical articles. It is meant for health care professionals and researchers. OMIM is maintained by Johns Hopkins University School of Medicine. 
  • Orphanet is a European reference portal for information on rare diseases and orphan drugs. Access to this database is free of charge.
  • PubMed is a searchable database of medical literature and lists journal articles that discuss Sirenomelia. Click on the link to view a sample search on this topic.

Questions sent to GARD may be posted here if the information could be helpful to others. We remove all identifying information when posting a question to protect your privacy. If you do not want your question posted, please let us know.

  1. Crawford SE. Sirenomelia. NORD. 2012; http://rarediseases.org/rare-diseases/sirenomelia/.
  2. Sirenomelia. Orphanet. July 2015; http://www.orpha.net/consor/cgi-bin/OC_Exp.php?lng=en&Expert=3169.