Genetic: Edwards Syndrome
Genetic: Edwards Syndrome
Edwards syndrome is a genetic disorder caused by the presence of an extra copy of chromosome 18 or by a portion of chromosome 18 trans-located (attached) to another chromosome plus two copies of chromo-some 18. It is the second most common genetic disorder caused by a trisomy, the most common being Down syndrome, or trisomy 21. Edwards syndrome was first identified in 1960 by a British geneticist,
John H. Edwards (1928–2007), who analyzed blood samples taken from a severely malformed baby who died in a British children's hospital.
Edwards syndrome is a condition in which babies who survive until birth have a low birth weight; small and abnormally shaped heads; small jaws and mouth; and clenched fists with overlapping fingers. They also suffer from mental retardation, heart defects, kidney disorders, and other organ abnormalities affecting most systems of the body. Most children with Edwards syndrome die within a few days of birth.
Edwards syndrome occurs once in every 6,000 to 8,000 live births in the United States. About 95 percent of children conceived with the syndrome, however, die before birth. Between 5 and 10 percent of children born with trisomy 18 live beyond twelve months.
About 80 percent of children born with Edwards syndrome are female; it is thought that being male increases the risk of dying from
the disorder before birth. The risk of having a child with the disorder increases with the mother's age.
Edwards syndrome is equally common in all races and ethnic groups.
Almost all cases—92 percent—of Edwards syndrome involve genetic errors that occur during the formation of germ cells (eggs and sperm) or during cell division shortly after the egg is fertilized by the sperm. The most common form of Edwards syndrome occurs when an egg or sperm carrying two copies of chromosome 18 is involved in conception. The reason for the extra copy in the abnormal germ cell is a genetic error called nondisjunction. During the normal process of germ cell formation, the paired chromosomes in the cell divide so that each daughter cell has only one member of the pair. In nondisjunction, one daughter cell gets both members of the chromosome pair and the other cell has none. If a germ cell carrying two copies of chromosome 18 is fertilized by a normal germ cell from the other parent, the child will have three copies of chromosome 18. This genetic error is called a full trisomy 18.
A few cases (about 2 percent) of Edwards syndrome develop when a part of chromosome 18 becomes attached to another chromosome either before or at the moment of conception. This type of genetic error is called a translocation. The child will be born with two copies of chromosome 18 plus some extra genetic material from chromosome 18 attached to another chromosome. A child with this type of genetic error is said to have partial trisomy 18.
A heartbreaking aspect of prenatal testing is that some parents are told that their child has Edwards syndrome or another condition that will lead to the baby's death shortly after birth. Parents who choose not to end the pregnancy when they receive this diagnosis can now turn to hospice programs that will support them and help them make plans for the birth and other medical decisions. Although hospices for dying adults and school-age children have existed in the United States since the 1970s, until the early 1990s there were few hospice programs available for babies with fatal conditions.
Since the 1990s at least 40 U.S. hospitals have started perinatal hospice programs, which help families make decisions about the birth, to take birthing classes apart from families expecting healthy babies, to prepare religious and other rituals for the child's birth, and to stay with the baby during its short life. If the child lives beyond the first few days, the parents are given advice on caring for the child at home. Families who have used perinatal hospice programs are very positive about the programs, according to one group of researchers. Parents report being more emotionally and spiritually prepared for their infant's death; experiencing less intense despair and sadness; and feeling a sense of peace.
About 5 percent of cases of Edwards syndrome occur in children who have some body cells with the extra copy of chromosome 18 and some body cells without the extra copy. This condition is called mosaic
trisomy 18. It is thought to result from random errors in cell division during the early stages of fetal development. Children with mosaic trisomy 18 are less severely affected than those with full trisomy 18 and have a longer survival period.
The symptoms of Edwards syndrome include a high mortality rate even before birth. Most embryos with full trisomy 18 die during pregnancy or are expelled from the mother's womb in what is called a spontaneous abortion or miscarriage. Those who survive until birth usually live only a few days; most die from breathing problems, heart or kidney defects, generalized infection, or feeding difficulties. Although some children with mosaic trisomy 18 do not have all the physical features that characterize the syndrome, the following are considered typical:
- Mental retardation and delayed movement (100 percent of infants)
- Poor muscle tone, seizures, and breathing difficulties
- Abnormally small head, abnormally small eyes, flattened nose, small jaw, pointed ears, cleft lip, and cleft palate
- Severely retarded growth with clenched hands, missing bone in forearm, rocker-bottom feet
- Heart abnormalities (90 percent of infants), underdeveloped lungs, incomplete esophagus, double spleens, missing appendix, and missing gallbladder
- Underdeveloped sex organs in both boys and girls
- Underdeveloped thyroid and thymus glands
Diagnosis of Edwards syndrome is usually made on the basis of the child's appearance at birth. It can be diagnosed before birth on the basis of ultrasound studies during the first three months of pregnancy; a sample of the mother's blood plasma; or by genetic analysis of cells taken from the baby's blood or the amniotic fluid that surrounds the baby inside the womb.
In some cases the diagnosis is suspected before birth on the basis of certain characteristics of the pregnancy. These include a smaller than average placenta (the organ that attaches the baby to the wall of the mother's uterus), a low level of fetal activity, irregular heartbeat, and slowed fetal growth.
There is no treatment for Edwards syndrome itself. Infants who survive the first two days often require intensive treatment for infections, breathing difficulties, and problems with feeding. Surgery to correct heart defects is rarely performed because of the baby's short life expectancy.
The prognosis of Edwards syndrome is extremely poor. Newborns have a 40 percent chance of living a full month; infants have a 5 percent chance of surviving a full year; children have a 1 percent chance of surviving to age ten years. The very small number of children with Edwards syndrome who live as long as ten years suffers from severe mental retardation, digestive problems, and difficulty in walking.
Since Edwards syndrome is thought to be caused by a spontaneous genetic mutation rather than an inherited genetic defect, there is no way to prevent it. Pregnant women over thirty-five should have tests during the first trimester (three-month period) of pregnancy to screen for the syndrome. These tests may involve ultrasound studies, which can detect abnormalities in the baby's heart or facial development, followed by a photographic analysis of cells taken from the fluid that surrounds the baby in the womb. This analysis, or karyotype, is needed to distinguish Edwards syndrome from other genetic disorders that can cause heart defects and facial abnormalities. Doctors recommend that the parents of a child with Edwards syndrome should consult a genetic counselor for advice about future pregnancies.
It is possible that the increasing numbers of women having children in their thirties or forties will lead to an increase in the number of children born with Edwards syndrome. Many women whose fetuses are diagnosed with the syndrome choose to end their pregnancies before childbirth. A newer option is the perinatal hospice (see sidebar), a special type of hospital program where parents who know that their baby has a fatal condition can choose to have the baby and remain with it during the baby's few days of life.
In addition to perinatal hospice programs, there are also online support groups for parents of children with Edwards syndrome and other rare genetic disorders.
SEE ALSO Down syndrome; Patau syndrome
WORDS TO KNOW
Germ cell : A cell involved in reproduction. In humans the germ cells are the sperm (male) and egg (female). Unlike other cells in the body, germ cells contain only half the standard number of chromosomes.
Hospice : A facility or program for meeting the spiritual as well as the physical needs of people who are terminally ill.
Karyotype : A photomicrograph of the chromosomes in a single human cell. Making a karyo-type is one way to test for genetic disorders.
Mosaicism : A condition in which a person has some body cells containing an abnormal number of chromosomes and other cells containing the normal number. Mosaicism results from random errors during the process of cell division that follows conception.
Nondisjunction : A genetic error in which one or more pairs of chromosomes fail to separate during the formation of germ cells, with the result that both chromosomes are carried to one daughter cell and none to the other. If an egg or sperm with a paired set of chromosomes is involved in the conception of a child, the child will have three chromosomes in its genetic makeup, two from one parent and one from the other.
Perinatal : Related to the period around the time of a baby's birth.
Rocker-bottom feet : Abnormally long and slender feet with pointed heels turned outward like the bottom rails of a rocker.
Translocation : A genetic error in which a part of one chromosome becomes attached to another chromosome during cell division.
Trisomy : A type of genetic disorder in which a cell contains three copies of a particular chromosome instead of the normal two.
Barnes, Ann M., and John C. Carey. Care of the Infant and Child with Trisomy 18 or 13: Medical Problems, Reported Treatments and Milestones. La Fox, IL: SOFT Distribution Center, 1996.
Kuebelbeck, Amy. Waiting with Gabriel: A Story of Cherishing a Baby's Brief Life. Chicago: Loyola Press, 2003.
Banerjee, Neela. “A Place to Turn When a Newborn Is Fated to Die.” New York Times, March 13, 2007. Available online at http://www.embracingourdying.com/articles/fatednewborn.html (accessed May 1, 2008).
“Obituary: Professor John Edwards.” The Times (UK), January 17, 2008. Available online at http://www.timesonline.co.uk/tol/comment/obituaries/article3203473.ece (accessed May 1, 2008). This is an article about the pioneering doctor who identified the cause of Edwards syndrome.
Genetics Home Reference. Trisomy 18. Available online at http://ghr.nlm.nih.gov/condition=trisomy18 (updated July 2006; accessed May 1, 2008).
Support Organization for Trisomy 18, 13, and Related Disorders (SOFT). Trisomy 18 Facts. Available online at http://www.trisomy.org/trisomy18.php (cited May 1, 2008; accessed September 30, 2008).
Trisomy 18 Foundation. What Is Trisomy 18? Available online at http://www.trisomy18.org/site/PageServer?pagename=parents_whatisT18 (cited May 1, 2008; accessed September 30, 2008).
Wilsford, Mindy. A Trisomy 18 Journey. Available online at http://www.geocities.com/wilsfordmindy/ (updated May 2006; accessed May 1, 2008). This is a Web site created by the family of a child who died from Edwards syndrome in 2002. It contains information about the syndrome as well as materials related to grief and support resources.