Edwards syndrome

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Trisomy 18
Classification and external resources
Chromosome 18
ICD-10 Q91.0-Q91.3
ICD-9 758.2
DiseasesDB 13378
eMedicine ped/652 

Trisomy 18 or Edwards Syndrome (named after John H. Edwards, who first described the syndrome in 1960) is a genetic disorder. It is the most common autosomal trisomy after Down Syndrome that carries to term.

It is caused by the presence of three — instead of two — copies of chromosome 18 in a fetus or infant's cells.

The additional chromosome usually occurs before conception. A healthy egg or sperm cell contains individual chromosomes - one to contribute to each of the 23 pairs of chromosomes needed to form a normal cell with 46 chromosomes. Numerical errors arise at either of the two meiotic divisions and cause the failure of segregation of a chromosome into the daughter cells (non-disjunction). This results in an extra chromosome making the haploid number 24 rather than 23. Fertilization of these eggs or sperm that contain an extra chromosome results in trisomy, or three copies of a chromosome rather than two.

Contents

[edit] Prognosis

The survival rate of Edwards Syndrome is very low. About half die in utero. Of liveborn infants, only 50% live to 2 months, and only 5–10% will survive their first year of life. Major causes of death include apnea and heart abnormalities. It is impossible to predict the exact prognosis of an Edwards Syndrome child during pregnancy or the neonatal period. Because major medical interventions are routinely withheld from these children, it is difficult to determine what the survival rate or prognosis would be with aggressive medical treatment.

[edit] Incidence/prevalence

The rate of occurrence for Edwards Syndrome is approximately one in 3,000 (for conception) and approximately one in 6,000 (for live births), as 50% of those diagnosed prenatally with the condition will not survive the prenatal period. Although women in their 20s and 30s may conceive Edwards Syndrome babies, there is an increased risk of conceiving a child with Edwards Syndrome as a woman's age increases, with the average age for this disorder being 32½.[1]

[edit] Variations

A small percentage of cases occur when only some of the body's cells have an extra copy of chromosome 18, resulting in a mixed population of cells with a differing number of chromosomes. Such cases are sometimes called mosaic Edwards syndrome. Very rarely, a piece of chromosome 18 becomes attached to another chromosome (translocated) before or after conception. Affected people have two copies of chromosome 18, plus extra material from chromosome 18 attached to another chromosome. With a translocation, the person has a partial trisomy for chromosome 18 and the abnormalities are often less than for the typical Edwards syndrome.

[edit] Features and characteristics

Symptoms and findings may be extremely variable from case to case. However, in many affected infants, the following may be found:

[edit] References

  1. ^ Prevalence and Incidence of Edwards Syndrome. Diseases Center-Edwards Syndrome. Adviware Pty Ltd. (2008-02-04). Retrieved on 2008-02-17. “mean maternal age for this disorder is 32½”
  • Stenson, Carol M. (1999). Trisomy 18: A Guidebook for Families. University of Nebraska Medical Center. ISBN 1-889843-29-6.
  • Barnes, Ann M. (2000). Care of the infant and child with trisomy 18 or 13: medical problems, reported treatments and milestones. University of Nebraska Medical Center. ISBN 1-889843-58-X.


v • d • e
Pathology: chromosome abnormalities (Q90-Q99, 758)
Autosomal trisomies
Autosomal monosomies/deletions
X/Y linked
Translocations
Other