Alternate name: Trisomy 18
Characteristics/ Phenotype
Trisomy 18, also known as
Edward’s syndrome, is a condition which is caused by an error in cell
division, known as meiotic disjunction. The child develops three copies of chromosome 18 in each cell of
their body, instead of the usual two. Babies with Edward's syndrome will grow
slowly in the womb and will have a low birthweight after birth. It may lead to
severe intellectual and physical defects.
Doctors
may suspect that a baby has Edward's syndrome just by their characteristic
features, although the disease must be confirmed with genetic tests. Mosaic trisomy 18
may be very severe or hardly noticeable, depending upon the number of cells that
have the extra chromosome. In rare cases, there is no extra chromosome present;
rather, a portion of the long arm of chromosome 18 becomes attached to another
chromosome during the formation of egg and sperm cells or very early in
development of the embryo. In this case, the individual has two copies of
chromosome 18 plus the additional material from chromosome 18 that is attached
to another chromosome. This is known as translocation, and the extra genetic
material causes the developmental abnormalities in the same way as the presence
of an entire extra chromosome.
The
features of Edward’s syndrome are as follows:
Physically,
signs of Edward’s syndrome include a small, abnormally shaped head(known as
microcephaly), sometimes a strawberry shaped-head, a small jaw (known as
micrognatia) and mouth, long fingers that overlap, with short fingernails and
clenched fists, low-set ears and smooth rounded base feet. These patients also have
medical problems from mild to worst; some gets heart and kidney problems, feeding
problems in infancy, leading to poor growth, breathing problems, hernias in the
wall of their tummy, part of the intestinal tract
is outside the stomach (known as omphalocele),the esophagus doesn’t connect to the stomach (esophageal artesia),
bone abnormalities, such as a curved spine is also common.
Unfortunately,
most babies with Edward's syndrome are miscarried or stillborn.
A third of
babies born alive will die within a month of birth because of life-threatening
medical problems.
Only 5-10%
of babies with full Edward's syndrome survives beyond one year, and will live
with severe disabilities. Survival to adulthood is extremely rare in trisomy
18. However, a few reports have described individuals who survived to the teen
or early adult years.
Frequency
Trisomy 18 occurs in about 1 in 5,000-6,000 live-born
infants. Although women of all ages can have a child with trisomy 18, the
chance of having a child with this condition increases as a woman gets older. Up to 95% of fetuses with trisomy 18 die in the
prenatal period (prior to delivery). Girls are affected more commonly than
boys.
Diagnosis
(47, XY, +18) or (47, XX,
+18)
Can be diagnosed through:
Karyotyping,
Prenatal testing for trisomy 18, Screening tests such as
measurement of alpha fetoprotein (AFP) levels (sometimes referred to as a triple screen), Ultrasound, Analysis of fetal chromosomal material obtained
during amniocentesis or chorionic villus sampling.
Cause/s
Trisomy 18 is not an inherited condition; it
occurs as the result of random events during egg and sperm formation. The type of error that
occurs is known as nondisjunction,
and this leads to an egg or sperm cell with an abnormal number of chromosomes.
Treatments/ Recommendations
There is no cure for
Edward's syndrome and the symptoms can be very difficult to manage. You are
likely to need help from a wide range of different health professionals.
Your child may benefit
from physiotherapy and occupational therapy, if limb abnormalities affect their
movements. They may need to be fed through a feeding tube.
If infections arise,
it may be treated. Transfusions may be made for low blood cell counts, and medications such as
diuretics and/or digoxin to
manage heart
failure.
As a parent carer, it's
important that you look after your own health and wellbeing first before you
commit to nurse your baby.
Measures
that can be done includes nutritional support to your child and
sincere love and care.
References
Genetic and Rare Diseases Information Center (GARD). "Trisomy 18." NIH Office of Rare Diseases Research. <http://rarediseases.info.nih.gov/GARD/Disease.aspx?PageID=4&DiseaseID=6321>.
Genetics Home Reference. "Trisomy 18." U.S. National Library of Medicine. 30 Jan. 2012. <http://ghr.nlm.nih.gov/condition/trisomy-18>.
"What Is Trisomy 18?" Trisomy 18 Foundation. 2010. <http://www.trisomy18.org/site/PageServer?pagename=whatisT18_whatis>.
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