Down’s include translocation of chromosome 21, where a

Down’s Syndrome cannot
be described as a single list that affects all individuals in the same uniform
way. Many experience a range of physical and mental symptoms and difficulties
related to the condition, the best way to describe this sliding scale of differing symptoms associated with Down’s
Syndrome is a ‘spectrum disorder’. The
explanation for this variety in range and severity is involved in the specific
genetic mutation of the individual. Figures show that 94% of those reported
with Down’s syndrome have a full trisomy of chromosome 21, meaning that all
cells present in their body- old and new- have an extra copy of chromosome 21. Other
genetic mutations responsible for Down’s Syndrome include translocation of
chromosome 21, where a portion of chromosome 21 becomes attached to chromosome
14 causing an imbalance in the individual’s
chromosomes. Or mosaic Down’s syndrome, where a fraction of cells are affected
due to errors in later development leading to trisomic cells and otherwise
normal cells throughout the body.1

Regarding that the
differences in genetic mutation are the most prominent cause of the condition,
it does not fully account for the reports of distinct uniqueness among
symptoms. Referencing the figure stated above, if the individual’s genetics were the sole cause of the variation
then  94% of Down’s Syndrome sufferers
should experience comparable symptoms due to the comparable disposition of the genetic
mutation. This unpredictable nature means that two individuals who suffer from the same or similar genetic
mutation could present with vastly different physical and/or mental effects.

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Physical
Aspects

The severity and impact
that physical features have will vary between individuals as a result of their
unique genetic makeup and environment they live in. However medical conditions
that are associated with Down’s Syndrome can have a greater impact, depending
on the severity and management of the independent condition.

Most people with Down’s
Syndrome exhibit 3 similar craniofacial features. Brachycephaly- a smaller head
that is partly flattened at the back, which occurs due to the front skull bone
and side skull bones join together before full development. Severe cases can
increase the risk of problems such as vision or hearing loss and seizures,
treatment at a young age can reduce any risks.2 The eyes often
have upslanting palpebral fissures (an upward slanting of the eyes) and also
have epicanthic folds (an extra skin fold of the inner eyelid).3
Other notable craniofacial features among individuals with Down’s Syndrome is a
low nasal bridge. This means that the bony area at the top of the nose does not
protrude as what is considered normal giving the face a somewhat flat
appearance. Individuals ears may be smaller than typical with the upper portion
folding outwards however these have no
risk to health the health of the child.

A majority of infants show signs
of hypotonia (low muscle tone), their muscles will appear weak and as a result, they will look floppy. The effects of
this hypotonia are not limited to one muscle group, all muscles throughout the
body will be affected to some degree. Consequently,
this decrease in total muscle tone will have implications on the baby’s ability
to feed, roll over, sit-up, stand and eventually talk. Hypotonia will improve with
age however it cannot be cured. There is an increased risk of orthopaedic
problems although management through physical therapy can help reduce any
complications. 3

Some children and
adults with Down’s syndrome can suffer from neck problems due to what is known
as an atlantoaxial subluxation (AAI). It occurs
where the first cervical vertebra meets
the second i.e. the atlantoaxial joint. Problems caused include neck pain and limited
mobility, head tilt or incoordination and difficulty walking. Symptoms result
from increased mobility of the joint causing vertebrae to slip severely enough
to directly damage the spinal cord. Seldom these problems will progress leading
to paralysis.4  Treatment is
only needed if signs of spinal cord compression appear.5

Due to anatomical
differences in people with Down’s Syndrome,
there is a higher risk of the individual suffering from Obstructive Sleep
Apnoea (OSA). OSA is described as sleep abnormalities that are caused
by a complete or incomplete upper airway obstruction during sleep. This results
in a reduction in inhaled air entering lungs with high levels of carbon dioxide
in the blood. There are various reasons for OSA occurrence,
however, the tongue in particular
can cause problems in those with Down’s syndrome, as they already have enlarged
tongues. The obstruction is caused by the tongue falling back towards the
throat and decreasing airflow in and out. Other anatomical variances from
normal eg. hypotonia can contribute to OSA.6

Individuals with Down’s Syndrome will
have physical features of their extremities that are associated with the
condition. Individuals tend to have a wider palm than commonly seen and a single
palmar crease (used to be called a simian crease). The palmer crease is one of the
commonly used markers for Down’s Syndrome. Some will present with a single
palmar crease while others will have what is considered is normal palmar
creases. Also, individuals may have
shorter fingers/thumbs and can have trouble isolating finger actions, while
this has no serious impact on their
health it can cause problems with fine motor skills and manual dexterity.7
Some individuals may have a large gap between their first and second toe
(sandal gap) but it has no effect on their physical health.8

 

Mental
Aspects

A common way to distinguish
the severity of the mental symptoms of the condition are the terms mild,
moderate and severe when describing a specific aspect.9 For
example, some may present with severe learning disabilities affecting their
daily life whereas others may present with mild learning disabilities that have
little to no effect on their day to day life.

Although individuals
with Down’s Syndrome have no restriction on how well they can interact with
others, speaking clearly may arise as a problem when they develop as children,
that is that speech may be difficult to comprehend. For a child with Down’s Syndrome, their speech development will be
hindered several things. Phonological difficulties and articulation disorders
are thought to be the main cause of delayed speech development.10
Also, hearing difficulties can cause problems when processing auditory
information. Anatomical and physiological differences will also contribute to
delayed speech development, for example as described above the hypotonia, a
smaller oral cavity or respiratory problems will also impact the developmental
rate of speech development. Speech development can follow normal development or
an atypical pattern. All children, with or without Down’s Syndrome speech
development takes time and will vary for each. It is important to remember that
each child is an individual with unique factors impacting on their speech
development.11

An IQ scale is used as
a measure of a person’s intelligence. For neurotypical’s, IQ scores
anywhere between 70 and 130 are considered normal. A mild intellectual
disability is classified with IQ scores between 55 and 70. Scores of 40 to 55
are determined as a moderately intellectual disability. In general individuals
with Down’s syndrome score anywhere within 40 to 70. Often it is said that individuals
with Down’s syndrome are unable to learn or have a predetermined limit on their
ability to learn.3
Despite average lower IQ scores, through early intervention, good education and
encouragement people with Down’s syndrome have no restriction on their learning
capacity although their rate of learning may be slightly lower.

The physical impact
that any physical or mental symptoms have on the individual will depend on the
severity of the problem and can be easily treated in some cases. However these
symptoms can also have a negative effect on the mental health of the
individual, therefore children and adults with Down’s Syndrome are at a higher
risk of developing mental health problems. Mental health difficulties are comprised of a vast list of disorders, for
example; anxiety, obsessive-compulsive
behaviours, hyperactive-type behaviours, sleep difficulties, depression and
regression ( a decline in cognitive and social skills).12 Treatment
of mental issues begins by ruling out physical causes or a significant life
change eg. bereavement that could trigger the change in their behaviour pattern
and following through with therapies to overcome the problem.

As discussed above Down’s
Syndrome is caused by full or partial trisomy of chromosome 21. Research has
shown that the prevalence of  Alzheimer’s
disease among those with Down’s Syndrome is linked to this trisomy of
chromosome 21. Alzheimer’s disease is a form of dementia caused by progressive
destruction of brain cells and neural
pathways which affects memory, judgment making, communication and motor skills. 13
Three copies of a gene that encodes the amyloid precursor protein (APP), that
is one of the main causes in the change in brain chemistry associated with
Alzheimer’s, is present on chromosome 21.14 It is thought that the
interaction between APP production and the extra copies of chromosome 21
increases the risk of early onset
Alzheimer’s. Several other genes on chromosome 21 have been discovered that are
involved in the ageing process that will
also contribute to the onset of
Alzheimer’s. Studies suggest that approximately 30% of people with Down’s syndrome are affected by Alzheimer’s in their
50s, increasing to 50% of 60 year olds.13

Challenging behaviour,
along with other contextual behavioural patterns have been indicated to be more
common among younger children with Down’s Syndrome compared to that of
neurotypical developing children. Challenging
behaviour includes attention or hyperactivity problems, social
withdrawal, noncompliance, and compulsions. Additionally, anxiety and
depression symptoms can increase with age which can impact on behaviour. These
negative behavioural types can be especially problematic for family members,
caregivers and professionals involved in their care.15 Also
personal behavioural skills relating to lifestyle choices can be poor in those
with Down’s Syndrome. Commonly these include impulsive behaviour, poor
judgement and a short attention span.3

 

Genetic Screening for Down’s
Syndrome

Genetic screening tests determine whether an individual
has a mutation in their DNA that could cause a medical genetic disorder. The
tests are able to diagnose a genetic condition, establish the chances of the
individual developing a genetic disorder and determine if the individual
carries a mutation which could be passed on to any children they have. High
risk groups for genetic disorders are offered routine screening tests or you
will need referral from your GP.16

Pre-pregnancy
screening involves looking at family and medical history of both the mother and
the father and creating pedigree charts to determine inheritance patterns.
However this method of screening cannot be certain of the outcome of the
pregnancy, it is only an indicator of the risk. Currently there are several
available tests that test for Down’s Syndrome during pregnancy, which are
offered to high risk groups including those with a family history of Down’s
Syndrome and/or mothers over 35 years of age and fathers over 40 years of age.17
Although these tests are available there is no obligation to have them,
due to the increased risk of miscarriage many women choose not to undergo the
tests.

At
weeks 10 to 14 there is a combined test that asses that chance the baby having Down’s
Syndrome (trisomy 21) and the chance of other conditions caused by trisomy 13
or 18. This test involves an ultrasound and a blood test. There is a blood test
available form weeks 14 to 20 called the quadruple test that is specific to Down’s
Syndrome.18 These blood tests measure 4 hormones: afp, Hcg, uE3
and inhibin, which is combined with the mothers age to estimate the risk. If these
tests show a high risk (results higher than 1 in 150) then you will be referred
on for diagnostic tests.19 A nuchal translucency (NT) scan may be
performed in weeks 11 to 14 measures the amount of fluid under the skin at the
back of baby’s neck via unltrasound, although all babies have fluid present an
increased amount is linked to Down’s Syndrome.20

3 prenatal
diagnostic tests are available to women. Between weeks 11 to 14 chronic villus
sampling (CVS) is offered if previous tests have indicated a high chance of
genetic disorders. A small sample of cells will be removed from the placenta
using one of 2 methods: transabdominal or transcervical.21
Amniocentesis again is only offered to those with a higher chance of genetic
disorders and is performed in weeks 15 to 20 of the pregnancy. A fluid sample
from within the amniotic sac which contains foetal cells is removed via a long
thin needle being passed through the abdominal wall into the amniotic sac.22
Cordocentesis is a diagnostic test that is only performed if CVS and
amniocentesis have been inconclusive. It is performed later in the pregnancy
during weeks 18 to 24, were a needle is inserted directly into the umbilical
cord and a foetal blood sample is taken.23 All are done with the
use of an ultrasound to reduce the risk of complications. Results can be
discussed with your genetic counsellor. After birth the doctor will do a
physical exam of the baby to check for any physical symptoms and order a blood
test to determine the karyotype (number and visual appearance of chromosomes)
of the baby, this will confirm or negate a diagnosis of Down’s Syndrome.

 

Genetic Counselling for
Down’s Syndrome

Prospective or new
parents may be appointed a genetic counsellor to help them understand the
genetic disorder, in this case Down’s Syndrome, that their child has an
increased risk of being diagnosed with. They are professionals who have
completed an accredited course in medical genetics and counselling skills.
Working closely along with the family, they will talk through any risks that
may be present, explain inheritance patterns, clarify any medical science
involved that is unclear and outline screening options specific to Down’s
Syndrome. They understand that one choice may be the best for one family but
not for another; they will never pressure you to make decisions only provide
you all the information you need to make an informed choice.24

Family and medical
history from both parents will be evaluated by the genetic counsellor, this
involves information relating to your immediate family and your relatives.
Information needed will include things such as family members with genetic
disorders, miscarriages in the family, results of previous prenatal tests and
outcomes of past pregnancies along with any medications taken before or after
the pregnancy. 24  

 The counsellor will isolate any potentially
problematic areas within the family/medical evaluation and discuss any risks
presented by them and determine the possibility of your child having Down’s
Syndrome. When the chance of genetic disorders have been estimated, general
risks that could be faced during your pregnancy and risks specific to your
situation and the genetic disorder will be explained. The counsellor will do
this by checking the parental genetic information and using family and medical histories.25

If it has been
determined from genetic and family history data that there is a risk of your
child having Down’s Syndrome the counsellor will refer you on to have screening
tests for that specific disorder. All options will be talked through with the
counsellor and any tests that have been decided upon the counsellor will then
refer you to the correct services and help you make appointments. Results from
the tests will also be sent to your counsellor, this allows them to evaluate
them and gives you an opportunity to ask questions about any concerns. Some
pre-conception options for those with an increased risk include: having a
child, IVF treatment where the eggs are tested before implantation, using low
risk donor egg or sperm and adoption. After conception there are also options
if you have received a high severity diagnosis; preparing for the child,
surgery to minimise severity (only a few defects can be treated this way) or
termination of the pregnancy. 24  

Postnatal, the genetic
counsellor will still work with your family helping you to fully understand the
genetic disorder and all the challenges that may be faced due to it. They are
able to refer you to specialists for further help and again can help to arrange
appointments. For example children with Down’s Syndrome often have heart
conditions, the counsellor will be able to refer you to a cardiologist who will
be able to discuss possible treatment options. The genetic counsellor will also
be able to refer you to support services and groups for both you and your baby
when they are older. 24  

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