June 23, 2008
Trisomy 18, is the second most common trisomy syndrome. It occurs in 1/3000 to 1/8000 births. The condition presents with numerous
developmental disorders and malformations.
The median life span of children with ED is about 2 weeks, and only
5%-10% will survive their first year. (1)
Girls are three times more
likely to have Trrisomy 18 then boys.
See our page: Edwards Syndrome
What is Trisomy 18? What causes it? Trisomy 18 occurs when a baby has three chromosomes in the eighteenth position instead of the normal two. It is also called Edwards syndrome (or Edward's syndrome), and is the second most common trisomy, after Trisomy 21 (Down syndrome). It occurs in about 1:5000 to 1:8000 births.
The other type of trisomy is Trisomy 13 (Patau's Syndrome), which occurs less frequently than Edwards Syndrome. These three trisomies: 21, 18, and 13, are the only full trisomies that have ever led to a live birth. Most trisomies (about 95%) are full trisomies. That is, the extra chromosome occurs in every cell in the baby's body. This type of trisomy is not hereditary, and it is by far the most common type. In most literature, and on this website, Trisomy 18 means full Trisomy 18.
There are also partial and mosaic trisomies. Mosaic trisomies occur when the extra chromosome is present in some (not all) of the cells, and partial trisomies occur when only part of an extra chromosome is present. Some partial trisomies are translocations, usually caused by a parent's translocation, which may be hereditary. For more information, see Translocations from the The Centre for Genetics Education.
Unlike Down syndrome, Edwards Syndrome is usually fatal, with most of the babies dying before birth and those who do make it to birth typically living only a few days. However, a small number of babies (<10%) live at least one year (ref 1). To learn about Trisomy 18, we met with physicians, specialists, and genetic counselors and we searched the Internet and read as much as we could.
What we learned was that for Trisomy 18 babies, it is as if they don't quite get finished developing. For example, their brains are not properly developed; certain neurons don't make it all the way to the outside of the brain but remain in little clusters throughout the brain. This means that they will frequently have problems doing basic, instinctive, functions like sucking, swallowing, and breathing. And it is impossible to know the extent of these problems until the baby is born.
Some other typical problems are holes in the heart that don't close, openings in the back (spina bifida) and stomach (omphalocele), and organs that are not properly formed. Additionally, Trisomy 18 babies are usually small, as if they stopped developing and growing about the 7th month in utero.
One other key thing we learned was that Trisomy 18 babies have a susceptibility that healthy babies don't. That is, they succumb to things that would not be fatal to a healthy baby. Therefore, the approach of fixing the individual problems is rarely successful with babies with Trisomy 18. After learning these things, we explained Trisomy 18 very simply to others in A Letter to Our Friends that we gave them at our daughter's memorial service.
Types of Trisomy 18:
This list may not be inclusive:
Diagnosis is made through a variety of exams, and tests. A physical exam can show an unsually large uterus or a higher then normal amount of amniotic fluid. It can also show fingerprint patterns, and a short breast bone. Upon birth, a small placenta may be noticed.
Other disgnostic signs include:
Signs of congenital heart disease, such as Atrial septal defect (ASD), Patent ductus arteriosus (PDA), Ventricular septal defect (VSD) may also be present.
There may also be kidney difficulties including: Horseshoe kidney, , Polycystic kidney
As one might imagine, treatment courses are planned on a
case=by-case basis and will depend upon the number and severity of comorbidities.
Even possible treatment can be a controversial subject and heroic measures to try to prolong life for infantsborn with complete trisomy 18 are generally not recommended, by some.
Treatment may be done surgically for abnormalities of his or her body such as heart, kidney, or genital malformations. Infections should also be treated accordingly since there is a higher risk for middle ear infection, pulmonary infection, and urinary tract infection. Some children may benefit from psychological counseling as well as academic support to avoid depression, social isolation and difficulties at school. On the milder end of the mosaic spectrum, a minimally affected child will be treated the same way one would treat a normal child. It is important to raise a special child in an encouraging and supportive environment. (2)
Alternative namesEdwards syndrome
DefinitionTrisomy 18 is a syndrome associated with the presence of a third (extra) number 18 chromosome.
Causes, incidence, and risk factorsTrisomy 18 is a relatively common syndrome affecting approximately 1 out of 3,000 live births and affecting girls more than three times as often as boys. Multiple abnormalities are associated with the presence of an extra number 18 chromosome. Many of these abnormalities are not compatible with more than a few months of life. Few infants survive beyond the first year.
Expectations (prognosis)The abnormalities of trisomy 18 are generally not compatible with more than a few months of life. Fifty percent of the affected infants do not survive beyond the first week of life. More than 10 children have survived to teenage years, but usually with marked handicaps.
ComplicationsComplications depend on the specific abnormalities that affect the infant.
Calling your health care providerCall your health care provider and genetic counselor if you have had a child with Trisomy 18 and you plan to have another child.
PreventionPrenatal diagnosis of trisomy 18 is possible with an amniocentesis and chromosome studies on amniotic cells. Parents who have a child with translocational trisomy 18 should have chromosome studies, because they are at increased risk for another child with trisomy 18.
Update Date: 8/19/2003
Updated by: Douglas R. Stewart, M.D., Division of Medical Genetics, Hospital of the University of Pennsylvania, Philadelphia, PA. Review provided by VeriMed Healthcare Network.
What is Trisomy 18?
Trisomy 18 is a rare chromosome abnormality, affecting about one in every 3,000 to 4,000 babies, which involves severe mental retardation as well as physical birth defects. Most babies with this condition do not live longer than a few days, weeks, or months; about 70% of fetuses conceived with Trisomy 18 die before birth. Those who do survive are usually small for their age and have a poor suck and weak cry. They have feeding problems, since it is difficult for them to coordinate breathing, sucking, and swallowing. Only about 10% are alive at the time of their first birthday, although some children do live for years. Children with Trisomy 18 who survive past infancy usually do not walk, but some have learned a few words or signs to use in communicating. Some children with Trisomy 18 smile responsively and interact with family members.
In addition to mental retardation, babies with Trisomy 18 have various birth defects. The most common of these are heart defects, a cleft lip (when the upper lip does not form properly), and kidney problems. The babies are often born with their fists clenched; this is due to abnormalities in the nervous system which prevent the hand muscles from receiving proper instructions to move normally.
The problems with Trisomy 18 are caused by an extra chromosome -- specifically a third copy of chromosome number 18. Chromosomes, which normally come in pairs – one in each pair from the mother and one from the father -- are the packages of genetic material which give the baby the instructions for growth and development. The extra genetic material that a baby with Trisomy 18 receives interferes with these instructions and causes abnormalities in many organs of the body. The extra copy of chromosome 18 was present in either the sperm or the egg which went to form the baby, and this mistake occurred either prior to or just at conception. Many parents wonder why Trisomy 18 occurred, but we know of nothing that either parent could have done that would have caused or prevented this from happening.
It is very unusual for a family to have a second child with Trisomy 18. If you were under 30 years old when pregnant with your baby with Trisomy 18, then there is approximately a 1% chance for another baby to have Trisomy 18. If you were over 30, then your risk is not increased; it is simply the same as that of any other woman your age. Prenatal diagnosis is an option for you in a future pregnancy, even though the risk of recurrence is low.
Occasionally Trisomy 18 is present in only some of the baby’s cells; this is known as mosaic Trisomy 18; in these cases the outlook is often better than for those babies with full Trisomy 18.
Trisomy 18 can be diagnosed prenatally through CVS or amniocentesis ; it is also one of the conditions screened for in the XAFP program. Sometimes ultrasound findings provide the first indication that the baby has a problem.
In other cases a baby with Trisomy 18 may be diagnosed shortly after birth. If facial features, a heart defect, or other problems raise the possibility of Trisomy 18, a blood chromosome study will be done to confirm the diagnosis. If a baby is born with Trisomy 18, decisions about care and interventions (such as heart surgery) will have to be made and should be discussed with your baby’s doctor.
If you have just learned during your pregnancy that your baby has Trisomy 18 and are trying to decide whether or not to continue your pregnancy, you will probably not find many sources of information on this condition. There is an organization called SOFT (Support Organization for Trisomy 18, 13, and Related Disorders) which is a group composed of parents who have children with Trisomy 18 and other related conditions, as well as professionals who have an interest in caring for children with those conditions. These parents are strong advocates for their children and emphasize the positive aspects involved in raising a child with Trisomy 18. Parents who continue a pregnancy with a baby with Trisomy 18 or who have a baby born unexpectedly with this condition have found this group to be a great support. Their website can be found at http://www.trisomy.org.
*Link no longer available
Abstracts and Studies:
, Manchester, UK, Siddharth.Banka@manchester.ac.uk.
Mosaic trisomy 18 has a wide phenotypic spectrum ranging from near normal to early death. We report two cases that add to our knowledge of the disease.
Patient 1 was a girl with a tracheoesophageal fistula, horse-shoe kidneys and a ventricular septal defect. Karyotyping of her lymphocytes showed complete trisomy 18. Due to her milder phenotypes, skin fibroblasts were karyotyped. Patient 2 was a boy with biventricular hypertrophic cardiomyopathy, patent ductus arteriosus, ventricular and atrial septal defects and significant feeding problems.
Karyotyping of the skin and lymphocytes in patients 1 and 2 respectively revealed trisomy 18 mosaicism. Both children had only mild learning problems and were generally healthy with satisfactory growth. Patient 1 illustrates the possibility of significant discrepancy between the levels of trisomic cells in skin fibroblasts and lymphocytes leading to misdiagnosis. This finding has significant implications in medical management and counselling. Hypertrophic cardiomyopathy in patient 2 is recognized as a novel finding for this condition.
There is the possibility of good outcome for patients with mosaic trisomy 18, even in the presence of multiple congenital anomalies.
Support Groups and Resoures:
4301 Connecticut Ave. N.W. Suite 404
Washington, D.C. 20008-2369
2982 S Union St
Rochester, NY 14624
Trisomy 18 & 13 - Lucile Packard Children's Hospital
Trisomy 18 - eMedicine
Trisomy 18 - MedGen Genetics
Trisomy 18 - Genetics Home Reference
Codes and Classifications:
Q91 Edwards' syndrome and Patau's syndrome
|Q91.0||Trisomy 18, meiotic nondisjunction|
|Q91.1||Trisomy 18, mosaicism (mitotic nondisjunction)|
|Q91.2||Trisomy 18, translocation|
|Q91.3||Edwards' syndrome, unspecified|
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