Week 3
Down Syndrome
1. Describe the clinical features of Down Syndrome
• In regards to the clinical features of down syndrome, one must look at both physical
and cognitive characteristics.
Common Physical features
Microgenia
Abnormally small chin
Mongoloid fold
Fold of the upper eyelid on the inner corner of the eye
Shortened limbs
Shortened hands, feet and long bones (arms and legs), neck
Clindoactyly
Curvature of the 5th fingers (little fingers) and toes towards
the others
Hypotonia
Low muscle tone
Protruding tongue
Due to small oral cavity
Brushfield spots
White spots on the iris
Single palmar creases
A single transverse palmar crease instead of the usual two
Other
Small teeth, flattened face/nose, excessive space between
large toe and second toe, flexible ligaments
• It is also common for Down Syndrome patients to suffer abnormalities to other bodily
systems and organs.
 Congenital heart disease is the most concerning problem with Down syndrome
patients with many developing sever cardiovascular problems in later life (most
commonly a ventricular septal defect).
 Also get GI tract abnormalities, respiratory and endocrine issues.
Cognitive Characteristics
 Most patients with Down Syndrome have a decreased intellectual capability,
with the severity of this trait varying on a case by case basis (can range
anywhere from IQ 30 – IQ 70).
Note: Individuals with mosaic Down Syndrome have IQ of 10 – 30 points higher.
 Also a delay in motor skills and speech.
 Nevertheless, patients with Down Syndrome are described as happy,
affectionate, caring and playful people
2. Outline the epidemiology of Down Syndrome in the Australian population and in
population subgroups.
• Down syndrome is the most common chromosomal condition affecting newborn
babies.
• It is due to trisomy 21, which can manifest in a variety of different ways.
• It has been shown that the chance of a woman having a Down Syndrome child
increases with age (see diagram below from NSW centre for genetic education)
• It was difficult to find the prevalence of Down syndrome in population subgroups in
Australia. Nevertheless, I found a table in a paper from the American Journal of
Epidemiology describing the prevalence of Down Syndrome in California between
differing ethnic groups. (see diagram on next page)
• Although from a different country, it clearly shows that the Asian population has the
highest risk of having Down Syndrome children whilst the African American population
have the lowest risk.
Note: The open squares are observed live births while the coloured squares are adjusted
total live births.
3. Discuss the causes of Down Syndrome and how these affect the likelihood of
recurrence within families.
• There are three genetic variations that can cause Down Syndrome.
1.
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Trisomy 21
Seen in 95% of all cases of Downs Syndrome
The extra copy of chromosome 21 is apparent in cells of the baby
It is caused by meiotic nondisjunction
2. Mosaic Down Syndrome
 Extremely rare and occurs in about 1% of all cases
 Some of the cells in the baby have 47 chromosomes (trisomy 21) whilst others
have the usual 46.
 The number of cells which contain the extra chromosome 21, and in which
tissues or organs they occur, effects the severity and characteristics of condition
 It is caused by abnormal cell division shortly after fertilization
3.
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Translocation Down Syndrome
Seen in 4% of all cases
Extra copy of chromosome 21 is attached (translocated) to another chromosome
It is an inherited form of the condition and carriers have a 2-3% chance of
having a down syndrome child.
o Robertsonian Translocation most common form of Translocation Down
Syndrome.
 Usually when 21 chromosome attaches to 14 – called a fourteen,
twenty one translocation, written t(14:21)
 Down Syndrome will occur when there are two chromosome 21,
one 14, and one t(14:21)
 From PBL it was worked out that if female has Robertsonian
Translocation and mates with normal father, there are 6 possible
outcomes: 3/6 chance death (due to monosomy and one due to
trisomy 14), 1/6 chance completely normal, 1/6 down syndrome,
1/6 normal phenotype but abnormal genotype.
4. Describe the effects of Down Syndrome at personal and societal level, identifying
community support services available.
• Down Syndrome affects, but does not determine, development and achievement in a
person.
• People with Down Syndrome demonstrate a wide range of capabilities.
• People with Down Syndrome usually live with family or paid staff who assist them in
their daily lives
• These days Down Syndrome people can:
 Attend childcare settings, pre-schools, primary and high schools alongside other
children of their age.
 Adults with Down Syndrome attend post-school training, participate in the
workforce and are valued members of the community.
 An increasing number are achieving independent living, with some level of
support, within the community.
• A GP plays a vital role in monitoring the health and well being of both Down Syndrome
patients and their family. Vigilance is required with regard to a change in behaviour or
function that may indicate physical disease, sensory deterioration, medication side
effects or mental health disorder.
• Also, Down Syndrome NSW is an independent charity established in 1980, and run by
families. It is funded by private and public donations, and NSW health. They provide
many services for people with Down Syndrome, their families, and others working with
people with Down Syndrome.