Everything about Edward Syndrome totally explained
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.
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's difficult to determine what the survival rate or prognosis would be with aggressive medical treatment.
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 won't survive the prenatal period. Although women in their 20s and 30s may conceive Edwards Syndrome babies, there's 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.
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.
Features and characteristics
Symptoms and findings may be extremely variable from case to case. However, in many affected infants, the following may be found:
Further Information
Get more info on 'Edward Syndrome'.
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