Trisomy 18 Syndrome

National Organization for Rare Disorders, Inc.

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It is possible that the main title of the report Trisomy 18 Syndrome is not the name you expected.

Disorder Subdivisions

  • None

General Discussion

Trisomy 18 syndrome is a rare chromosomal disorder in which all or a critical region of chromosome 18 appears three times (trisomy) rather than twice in cells of the body. In some cases, the chromosomal abnormality may be present in only a percentage of cells, whereas other cells contain the normal chromosomal pair (mosaicism).

Depending on the specific location of the duplicated (trisomic) portion of chromosome 18--as well as the percentage of cells containing the abnormality--symptoms and findings may be extremely variable from case to case. However, in many affected infants, such abnormalities may include growth deficiency, feeding and breathing difficulties, developmental delays, mental retardation, and, in affected males, undescended testes (cryptorchidism). Individuals with trisomy 18 syndrome may also have distinctive malformations of the head and facial (craniofacial) area, such as a prominent back portion of the head; low-set, malformed ears; an abnormally small jaw (micrognathia); a small mouth with an unusually narrow roof (palate); and an upturned nose. Affected infants may also have narrow eyelid folds (palpebral fissures), widely spaced eyes (ocular hypertelorism), and drooping of the upper eyelids (ptosis). Malformations of the hands and feet are also often present, including overlapped, flexed fingers; webbing of the second and third toes; and a deformity in which the heels are turned inward and the soles are flexed (clubfeet [talipes equinovarus]). Infants with trisomy 18 syndrome may also have a small pelvis with limited movements of the hips, a short breastbone (sternum), kidney malformations, and structural heart (cardiac) defects at birth (congenital). Such cardiac defects may include an abnormal opening in the partition dividing the lower chambers of the heart (ventricular septal defect) or persistence of the fetal opening between the two major arteries (aorta, pulmonary artery) emerging from the heart (patent ductus arteriosus). Congenital heart defects and respiratory difficulties may lead to potentially life-threatening complications during infancy or childhood.

Supporting Organizations

Birth Defect Research for Children, Inc.

976 Lake Baldwin Lane
Orlando, FL 32814
Tel: (407)895-0802

Genetic and Rare Diseases (GARD) Information Center

PO Box 8126
Gaithersburg, MD 20898-8126
Tel: (301)251-4925
Fax: (301)251-4911
Tel: (888)205-2311

Let Them Hear Foundation

1900 University Avenue, Suite 101
East Palo Alto, CA 94303
Tel: (650)462-3174
Fax: (650)462-3144

National Consortium on Deaf-Blindness

The Teaching Research Institute
345 N. Monmouth Avenue
Monmouth, OR 97361
Tel: (800)438-9376
Fax: (503)838-8150
Tel: (800)438-9376

Perkins School for the Blind

175 North Beacon Street
Watertown, MA 2472
Tel: (617)924-3434
Fax: (617)926-2027

Support Organization for Trisomy 13/18 and Related Disorders, UK

c/o Christine Rose
48 Froggatts Ride
West Midlands, B76 2TQ SOFT
United Kingdom
Tel: 1213513122

Support Organization for Trisomy 18, 13, and Related Disorders

2982 S. Union Street
Rochester, NY 14624-1926
Fax: (585)594-1957
Tel: (800)716-7638

The Arc

1825 K Street NW, Suite 1200
Washington, DC 20006
Tel: (202)534-3700
Fax: (202)534-3731
Tel: (800)433-5255

UNIQUE - Rare Chromosome Disorder Support Group

G1 The Stables
Station Road West
Oxted, RH8 9EE
United Kingdom
Tel: 0044 (0)1883 723356

For a Complete Report

This is an abstract of a report from the National Organization for Rare Disorders (NORD). For a full-text version of this report, go to and click on Rare Disease Database under "Rare Disease Information".

The information provided in this report is not intended for diagnostic purposes. It is provided for informational purposes only.

It is possible that the title of this topic is not the name you selected. Please check the Synonyms listing to find the alternate name(s) and Disorder Subdivision(s) covered by this report.

This disease entry is based upon medical information available through the date at the end of the topic. 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.

Last Updated:  5/22/2008
Copyright  2004 National Organization for Rare Disorders, Inc.