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

Trisomy 18


Other Names:
Chromosome 18 trisomy; 18 trisomy; Edwards syndrome; Chromosome 18 trisomy; 18 trisomy; Edwards syndrome; Trisomy 16-18 (formerly); Trisomy E (formerly) See More
Categories:
Trisomy 18 is a chromosome disorder characterized by having 3 copies of chromosome 18 instead of the usual 2 copies. Signs and symptoms include severe intellectual disability; low birth weight; a small, abnormally shaped head; a small jaw and mouth; clenched fists with overlapping fingers; congenital heart defects; and various abnormalities of other organs. Trisomy 18 is a life-threatening condition; many affected people die before birth or within the first month of life. Some children have survived to their teenage years, but with serious medical and developmental problems. Most cases are not inherited and occur sporadically (by chance).[1][2]
Last updated: 7/7/2015

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
Atrial septal defect
An opening in the wall separating the top two chambers of the heart
Hole in heart wall separating two upper heart chambers
[ more ] 		0001631
Broad forehead
Increased width of the forehead
Wide forehead
[ more ] 		0000337
Cachexia
Wasting syndrome
0004326
Camptodactyly of finger
Permanent flexion of the finger
0100490
Cognitive impairment
Abnormality of cognition
Cognitive abnormality
Cognitive defects
Cognitive deficits
Intellectual impairment
Mental impairment
[ more ] 		0100543
Cryptorchidism
Undescended testes
Undescended testis
[ more ] 		0000028
Deviation of finger
Atypical position of finger
Finger pointing in a different direction than usual
[ more ] 		0004097
Dolichocephaly
Long, narrow head
Tall and narrow skull
[ more ] 		0000268
Global developmental delay 0001263
High forehead 0000348
Hypertelorism
Wide-set eyes
Widely spaced eyes
[ more ] 		0000316
Hypertonia 0001276
Intrauterine growth retardation
Prenatal growth deficiency
Prenatal growth retardation
[ more ] 		0001511
Low-set, posteriorly rotated ears 0000368
Microretrognathia
Small retruded chin
0000308
Muscular hypotonia
Low or weak muscle tone
0001252
Narrow face
Decreased breadth of face
Decreased width of face
[ more ] 		0000275
Narrow mouth
Small mouth
0000160
Narrow palate
Narrow roof of mouth
0000189
Narrow pelvis bone 0003275
Omphalocele 0001539
Pointed helix
Spock's ear
0100810
Prominent occiput
Prominent back of the skull
Prominent posterior skull
[ more ] 		0000269
Short nose
Decreased length of nose
Shortened nose
[ more ] 		0003196
Short stature
Decreased body height
Small stature
[ more ] 		0004322
Triangular face
Face with broad temples and narrow chin
Triangular facial shape
[ more ] 		0000325
Underdeveloped supraorbital ridges
Flattened bony protrusion above eyes
0009891
Ventricular septal defect
Hole in heart wall separating two lower heart chambers
0001629
30%-79% of people have these symptoms
Abnormal morphology of female internal genitalia 0000008
Abnormal toenail morphology
Abnormality of the toenail
Abnormality of the toenails
[ more ] 		0008388
Abnormality of the fontanelles or cranial sutures 0000235
Abnormality of the hip bone
Abnormality of the hips
0003272
Anal atresia
Absent anus
0002023
Bilateral single transverse palmar creases 0007598
Blepharophimosis
Narrow opening between the eyelids
0000581
Choanal atresia
Blockage of the rear opening of the nasal cavity
Obstruction of the rear opening of the nasal cavity
[ more ] 		0000453
Cleft palate
Cleft roof of mouth
0000175
Congenital diaphragmatic hernia 0000776
Delayed skeletal maturation
Delayed bone maturation
Delayed skeletal development
[ more ] 		0002750
Epicanthus
Eye folds
Prominent eye folds
[ more ] 		0000286
Esophageal atresia
Birth defect in which part of esophagus did not develop
0002032
Hydronephrosis 0000126
Microcephaly
Abnormally small skull
Decreased circumference of cranium
Decreased size of skull
Reduced head circumference
Small head circumference
[ more ] 		0000252
Non-midline cleft lip 0100335
Oligohydramnios
Low levels of amniotic fluid
0001562
Webbed neck
Neck webbing
0000465
5%-29% of people have these symptoms
Abnormality of retinal pigmentation 0007703
Abnormality of the lower limb
Lower limb deformities
0002814
Abnormality of the ribs
Rib abnormalities
0000772
Anencephaly 0002323
Aplasia/Hypoplasia of the corpus callosum 0007370
Arnold-Chiari malformation 0002308
Cataract
Clouding of the lens of the eye
Cloudy lens
[ more ] 		0000518
Cyclopia
Cyclops eye
Single central eye
[ more ] 		0009914
Glaucoma 0000501
Holoprosencephaly 0001360
Iris coloboma
Cat eye
0000612
Microcornea
Cornea of eye less than 10mm in diameter
0000482
Microphthalmia
Abnormally small eyeball
0000568
Postaxial hand polydactyly
Extra little finger
Extra pinkie finger
Extra pinky finger
[ more ] 		0001162
Spina bifida 0002414
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Last updated: 7/1/2020
In most cases, trisomy 18 is caused by having 3 copies of chromosome 18 in each cell in the body, instead of the usual 2 copies. The extra genetic material from the 3rd copy of the chromosome disrupts development, causing the characteristic signs and symptoms of the condition.

About 5% of people with trisomy 18 have 'mosaic trisomy 18' (when there is an extra copy of the chromosome in only some of the body's cells). The severity of mosaic trisomy 18 depends on the number and locations of cells with the extra copy.

Very rarely, an extra piece of chromosome 18 is attached to another chromosome; this is called translocation trisomy 18, or partial trisomy 18. If only part of the long (q) arm of chromosome 18 is present in 3 copies, the features may be less severe than in people with full trisomy 18.[1]
Last updated: 1/30/2012
Most cases of trisomy 18 are not inherited and occur randomly due to errors in the formation of eggs or sperm. If an egg or sperm gains an extra copy of chromosome 18 during cell division and contributes to a pregnancy, the embryo will have an extra chromosome 18 (trisomy) in each cell of the body.

Mosaic trisomy 18 (when some body cells have trisomy 18 and some have a normal chromosome make-up), is also typically not inherited. Mosaic trisomy 18 is also due to an error in cell division, but the error occurs early in embryonic development. About 5% of affected people have a mosaic form of trisomy 18.

Partial trisomy 18 (when only part of chromosome 18 is present in 3 copies) can be inherited. An unaffected parent can carry a rearrangement of genetic material between chromosome 18 and another chromosome. This rearrangement is called a balanced translocation because there is no extra or missing genetic material. However, a person with a balanced translocation has an increased risk with each pregnancy to have a child with trisomy 18.[1]
Last updated: 7/7/2015

Research helps us better understand diseases and can lead to advances in diagnosis and treatment. This section provides resources to help you learn about medical research and ways to get involved.

Clinical Research Resources

  • ClinicalTrials.gov lists trials that are related to Trisomy 18. Click on the link to go to ClinicalTrials.gov to read descriptions of these studies.

    Please note: Studies listed on the ClinicalTrials.gov website are listed for informational purposes only; being listed does not reflect an endorsement by GARD or the NIH. We strongly recommend that you talk with a trusted healthcare provider before choosing to participate in any clinical study.

Patient Registry

  • A registry supports research by collecting of information about patients that share something in common, such as being diagnosed with Trisomy 18. The type of data collected can vary from registry to registry and is based on the goals and purpose of that registry. Some registries collect contact information while others collect more detailed medical information. Learn more about registries.

    Registries for Trisomy 18:
    Chromosome 18 Registry & Research Society
     
  • The Tracking Rare Incidence Syndromes (TRIS) project seeks to increase the knowledge base on rare incidence trisomy conditions, and to make this information available to families and interested educational, medical and therapeutic professionals.

    TRIS Project
    Deborah A. Bruns, Ph.D., Principal Investigator
    Counseling, Quantitative Methods, and Special Education
    Wham Building, Room 223 MC 4618
    Carbondale, IL 62901
    Phone: 618-453-2311
    E-mail: tris@siu.edu

Support and advocacy groups can help you connect with other patients and families, and they can provide valuable services. Many develop patient-centered information and are the driving force behind research for better treatments and possible cures. They can direct you to research, resources, and services. Many organizations also have experts who serve as medical advisors or provide lists of doctors/clinics. Visit the group’s website or contact them to learn about the services they offer. Inclusion on this list is not an endorsement by GARD.

Organizations Supporting this Disease

Living with a genetic or rare disease can impact the daily lives of patients and families. These resources can help families navigate various aspects of living with a rare disease.

Financial 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

  • Genetics Home Reference (GHR) contains information on Trisomy 18. This website is maintained by the National Library of Medicine.
  • MedlinePlus was designed by the National Library of Medicine to help you research your health questions, and it provides more information about this topic.
  • 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

  • Medscape Reference provides information on this topic. You may need to register to view the medical textbook, but registration is free.
  • The Merck Manual for health care professionals provides information on Trisomy 18.
  • 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.
  • 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 Trisomy 18. 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. Submit a new question

  • My son and his wife were told the baby she carries has Edwards syndrome. Does this mean if she gets pregnant again, any future child will have this condition as well? Will she be able to have a normal child? See answer

  • I lost a baby to Edwards syndrome. Are my surviving children at risk for any problems as a result? See answer


  1. Trisomy 18. Genetics Home Reference. March, 2013; http://ghr.nlm.nih.gov/condition/trisomy-18. Accessed 8/23/2015.
  2. Haldeman-Englert C. Trisomy 18. MedlinePlus. August 2011; http://www.nlm.nih.gov/medlineplus/ency/article/001661.htm. Accessed 1/17/2012.
  3. Trisomy 18. Genetics Home Reference (GHR). January 2009; http://ghr.nlm.nih.gov/condition/trisomy-18. Accessed 1/17/2012.