DOWN'S SYNDROME - a patient's guide
Dr Rodney Marks - Family Doctor
What is Down's Syndrome?
Human cells consist of 46 chromosomes which contain the genetic
material which makes us all unique, e.g. have blue eyes, brown hair
etc. These 46 chromosomes are made up of 23 pairs. The most common
abnormality of chromosomes is a condition called Trisomy 21 or Down's
Syndrome. Discovered by John Down in the late 19th century.
Trisomy 21 is when the cells have 22 normal pairs of chromosomes
but 3 chromosomes of the number 21. This form of DS is the most
common, but a small percentage of DS individuals have some normal
cells between and are called mosaic.
Physical characteristics of DS:
*Note: All these characteristics do not appear in all DS
individuals.
- Facial: flat face, upward and slanted eyes, epicanthic folds
(skin folds at the eyes), speckled irises (part of the eye) called
Brushfield spots. High arched palate.
- Hands: Simian crease (continuous line in the palm of the
hand), short broad hands, underdevelopment of middle portion of
the 5th finger resulting in the finger bending towards the outside
of the hand.
- Cardiac malformations - discussed later in this article.
- Pelvis: Abnormal shape of the pelvis - flattened.
- Intestine: underdevelopment.
- Short stature with height and skull circumference less than
the normal populations.
Mentally: The intellectual handicap of DS individuals varies, with
the mosaic types having the highest IQs.
Incidence of DS:
The incidence of DS in the population is very linked to maternal
age as is shown in the table below:
|
Maternal Age (years)
|
Incidence of DS per live births:
|
|
20
|
1 in 1,667
|
|
30
|
1 in 952
|
|
35
|
1 in 385
|
|
40
|
1 in 106
|
|
45
|
1 in 30
|
Screening for DS:
A variety of tests can be carried out on pregnant women to
determine the presence of DS:
- Amniocentesis consists of sampling of some of the amniotic
fluid which surrounds the fetus.
- Chorionic villus sampling (CVS) consists of sampling the
placenta which is sampled through the cervix.
- Maternal blood tests for maternal serum alpha-fetoprotein and
unconjugated oestriol are low when the fetus has DS. Human
chorionic gonadotrophin (HCG) which is an indicator for pregnancy,
is excessively raised in the presence of DS.
- Ultrasound study of the fetus's nuchal (neck skin) fold
thickness and long-bone length.
Numerous criteria are considered in deciding which test(s) are
appropriate to screen for DS.
Problems developing in DS individuals:
- Thyroid disease.
- Cardiac (heart) defects.
- Respiratory problems.
- Macroglossia (large tongue).
- Leukemia.
- Alzheimer's disease.
- Atlanto-axial instability.
1. Thyroid disease:
The thyroid gland is in the front of the neck and controls the
general metabolism of the body. In DS thyroid dysfunction can be
clinically more difficult to diagnose.
Hypothyroidism (underactive thyroid) can present with slow speech,
thick tongue, slow thinking, fatigue, constipation, dry skin, poor
concentration. All these features can be found in DS individuals with
normal thyroid functions.
2. Cardiac defects:
The normal heart is divided into 4 chambers. 2 atria on top and 2
ventricles below. The left and right sides of the heart are separated
by a septum (wall) and valves separate the upper and lower
chambers.
The common cardiac defects in DS are: openings between the 2
atria, openings between the 2 ventricles, openings where all 4
chambers meet, persistent patent ductus arteriosus which is part of
the circulation in a fetus which should disappear at birth.
3. Respiratory problems:
DS individuals, particularly under the age of 5 years, are prone
to respiratory disease. Their lack of muscle tone, poor cough reflex
and reduced immunity make them more prone to these infections and
prolong recovery time once infected. Common causes for
hospitalisation are due to pneumonia, bronchiolitis, croup and
asthma.
4. Macroglossia:
Macroglossia is a large tongue. Macroglossia can interfere with
breathing and cause difficulty swallowing. Also, it can be
cosmetically unacceptable and the young DS individual can often be
seen with their tongue protruding. Surgery is available for this
condition.
5. Leukemia (cancer of the blood cells):
Two common types of leukemia that occur in DS are : Acute
lymphocytic leukemia and Acute megakaryoblastic leukemia.
6. Alzheimer's disease:
Alzheimer's disease is a condition resulting in general
disintegration of intellectual abilities. It has been found that DS
individuals are more prone to Alzheimer's disease and at a younger
age than the rest of the population.
7. Atlantoaxial instability:
The neck bones are called the cervical spine and the first 2
bones, or vertebrae, are called the Atlas and the Axis. DS
individuals are susceptible to instability of these 2 vertebrae,
called atlantoaxial instability. Spinal cord compression may be a
consequence of atlantoaxial instability.
Screening tests for individuals with DS:
- Thyroid testing. Due to the problems with abnormal thyroid
detection as mentioned above, regular testing should be carried
out. At 6 months of age, again at 12 months and then annually. A
simple blood test is required.
- X-ray of neck: Physical activities, e.g. contact sport, could
affect these vertebrae. X-rays should be obtained at 5-8 yrs of
age, 10-12 yrs and at 18 yrs.
Future of DS individuals:
Today people with DS live at home with their families and seldom
in institutions. They are active participants in the educational,
vocational, social and recreational activities of the community. They
are integrated into the regular educational system and take part in
sports, camping, music, art programmes and all the other activities
of their communities. In addition they are socialising with people
with and without disabilities. As adults they are obtaining
employment and living in group homes and other independent housing
arrangements.
General comments:
This article gives only a basic overview of Down Syndrome. Should
you have concerns about your pregnancy contact your general
practitioner to discuss the screening tests appropriate for you.
If you have a child with DS take your child to your GP early on
when they get an infection as the DS individual can have a
respiratory infection for some time before they present with a
serious cough. Also, ongoing ear infections can reduce their hearing
and prevent intellectual development.
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