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$Unique_ID{BRK04223}
$Pretitle{}
$Title{Sirenomelia Sequence}
$Subject{Sirenomelia Sequence Mermaid Syndrome Sirenomelus Caudal Regression
Syndrome Caudal Dysplasia Sequence }
$Volume{}
$Log{}
Copyright (C) 1990 National Organization for Rare Disorders, Inc.
777:
Sirenomelia Sequence
** IMPORTANT **
It is possible that the main title of the article (Sirenomelia Sequence)
is not the name you expected. Please check the SYNONYM listing to find the
alternate names and disorder subdivisions covered by this article.
Synonyms
Mermaid Syndrome
Sirenomelus
Information on the following diseases can be found in the Related
Disorders section of this report:
Caudal Regression Syndrome (Caudal Dysplasia Sequence)
General Discussion
** REMINDER **
The information contained in the Rare Disease Database is provided for
educational purposes only. It should not be used for diagnostic or treatment
purposes. If you wish to obtain more information about this disorder, please
contact your personal physician and/or the agencies listed in the "Resources"
section of this report.
Sirenomelia Sequence is a birth disorder in which a child is born with a
single lower extremity or with two legs that are fused together. However,
due to the wide range of possible physical deformities that can occur, no two
cases of Sirenomelia Sequence are ever exactly the same.
Symptoms
Sirenomelia Sequence is characterized by irregular development of the lower
limbs. The deformity appears at birth (congenital) usually as a single lower
extremity or as two legs that are joined together. Accompanying
malformations of the spine and skeletal system, with vertebrae either absent
or defective commonly occur. The internal and external sex organs, rectum,
kidneys and/or bladder may also be missing or underdeveloped. The rectal
opening (anus) may be completely closed (imperforate), and other
abnormalities of the lower gastrointestinal tract are often present.
Causes
The cause of Sirenomelia Sequence is unknown. It is believed to result from
irregularities in early development of the blood circulating system (vascular
system) within the embryo. Individuals with Sirenomelia Sequence have been
found to have a single large artery arising from high in the abdominal cavity
without the usual two umbilical arteries which normally branch out of the
lower part of the aorta and carry blood to the tail (caudal) end of the
embryo. The single artery present (called a "steal" vessel since it
essentially steals blood from the lower portion of the embryo) diverts the
flow of blood which normally circulates from the aorta (vitelline artery)
through the umbilical arteries to lower points of the embryo, throughout the
yolk sac and on to the placenta. Instead, the steal vessel redirects the
blood flow to the placenta without ever reaching the tail (caudal) end of the
embryo. As a result of this rerouted blood flow, the steal vessel also
diverts nutrients away from the blood-deprived portion of the embryo.
Arteries in this caudal area are underdeveloped and tissues dependent upon
them for nutrient supply fail to develop, are malformed, or arrest their
growth in some incomplete stage. In individuals with Sirenomelia, the lower
limb bud of the embryo fails to divide into two legs.
Affected Population
Sirenomelia Sequence occurs once in every 60,000 to 100,000 births.
Related Disorders
Symptoms of the following disorder can be similar to those of Sirenomelia
Sequence. Comparisons may be useful for a differential diagnosis:
Caudal Regression Syndrome, also called Caudal Dysplasia Sequence, is
characterized by abnormal development of the tail (caudal or distal) end
region of the embryo. Abnormalities associated with Caudal Regression
Syndrome may include incomplete development of the vertebrae, flattening of
the buttocks, disruption of the distal spinal cord resulting in neurological
impairment and an inability to control urination and bowel movement
(incontinence). There may be extreme lack of growth in the caudal region.
Less common abnormalities may include absence of kidneys, cleft lip, cleft
palate, microcephaly and closed (imperforate) anus.
Therapies: Standard
Sirenomelia Sequence can be detected in a fetus during the second trimester
of pregnancy by ultrasound. Recently, surgery has been successful in
separating joined legs. In preparation for surgery, balloon-like tissue
expanders are inserted under the skin. When they are filled with a salt
solution over a period of time, the balloons expand making the skin stretch
and grow. The excess skin is then used to cover the legs once they are
separated.
Other treatment is symptomatic and supportive. Prognosis depends on the
extent of involvement of the gastrointestinal system, vertebrae and other
structural deformities.
Therapies: Investigational
This disease entry is based upon medical information available through April
1990. Since NORD's resources are limited, it is not possible to keep every
entry in the Rare Disease Database completely current and accurate. Please
check with the agencies listed in the Resources section for the most current
information about this disorder.
Resources
For more information on Sirenomelia Sequence, please contact:
National Organization for Rare Disorders (NORD)
P.O. Box 8923
New Fairfield, CT 06812-1783
(203) 746-6518
NIH/National Institute of Child Health and Human Development
9000 Rockville Pike
Bethesda, MD 20892
(301) 496-5133
For information on genetics and genetic counseling referrals, please
contact:
March of Dimes Birth Defects Foundation
1275 Mamaroneck Avenue
White Plains, NY 10605
(914) 428-7100
Alliance of Genetic Support Groups
35 Wisconsin Circle, Suite 440
Chevy Chase, MD 20815
(800) 336-GENE
(301) 652-5553
References
SMITH'S RECOGNIZABLE PATTERNS OF HUMAN MALFORMATION, 4th ed.: Kenneth Lyons
Jones, M.D.; W.B. Saunders Company, 1988. Pp. 574-575.
PRENATAL DIAGNOSIS OF SIRENOMELIA. M. Sitori et al.; J ULTRASOUND MED
(February, 1989: issue 8 (2)). Pp. 83-88.
SIRENOMELIA. ANGIOGRAPHIC DEMONSTRATION OF VASCULAR ANOMALIES. G.
Malinger et al.; ARCH PATHOL LAB MED (July, 1982; issue 106 (7)). Pp. 347-
348.
VASCULAR STEAL: THE PATHOGENETIC MECHANISM PRODUCING SIRENOMELIA AND
ASSOCIATED DEFECTS OF THE VISCERA AND SOFT TISSUES. R.E. Stevenson et al.;
PEDIATRICS (September, 1986: issue 78 (3)). Pp.451-457.