Down's syndrome

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=== Trisomy 21  ===
 
=== Trisomy 21  ===
  
Before or at conception, a pair on chromosome 21 in spem or egg cells fail to seperate properly - nondisjunction, which results in an embryo with three copies of chromosome 21 instead of the usual two. Most cases of Down's syndrome are a result of a random chromosomal defect during the formation of reproductive cells, especially egg cells. An error during gamete cell division, non-disjunction, results in the cell with an abnormal number of chromosomes. As the embryo develops, the extra chromosome is replicated in every cell of the body. This is the most common form, and accounts for about 95% of cases. 
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An error during gamete formation results in a failure of the chromosomal pair on chromosome 21 to separately properly, which results in an embryo with three copies of chromosome 21. This is known as non-disjunction. Most cases of Down's syndrome are a result of a random chromosomal defect during the formation of reproductive cells, especially egg cells. An error during gamete cell division, non-disjunction, results in the cell with an abnormal number of chromosomes. As the embryo develops, the extra chromosome is replicated in every cell of the body. This is the most common form, and accounts for about 95% of cases.   
  
 
=== Mosaic trisomy 21  ===
 
=== Mosaic trisomy 21  ===
  
This is the least common form and accounts for about 1% of cases. 
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Mosaic refers to mixed or a pattern. Like trisomy 21, this isn't inherited; instead it is caused by random events that occur during cell division in early foetal development. This is the least common form and accounts for about 1% of cases.   
  
 
=== Translocation trisomy 21  ===
 
=== Translocation trisomy 21  ===
  
Chromosome 21 becomes attached to another chromosome during gametic cells formation or during early foetal development. No genetic material is gained or lost during balanced translocation. 
+
Part of chromosome 21 is in the cell, which becomes attached to another chromosome during gametic cells formation or during early foetal development. This is transferred to other cells as it divides. In some cases, parents unaffected by Down's syndrome may have translocation trisomy 21, which can be inherited by their offspring. 
  
== '''Causes'''<br> ==
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== '''Causes'''<br> ==
To date, the cause of the extra of partial chromosome is still unknown, Maternal age is a contributory factor towards a higher risk of a baby having Down's syndrome with trisomy 21 or mosaicism. There is no conclusive scientific research to suggest that [[javascript:void(0);/*1448929934861*/|environmental]] factors or parental activities before or during preganancy are the causes.&nbsp;
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 +
To date, the cause of the extra of partial chromosome is still unknown, Increasing maternal age (especially pregnant women aged 35 or over) is a contributory factor towards a higher risk of a baby having Down's syndrome with trisomy 21 or mosaicism. There is no conclusive scientific research to suggest that [[Javascript:void(0);/*1448929934861*/|environmental]] factors or parental activities before or during preganancy are the causes.&nbsp;  
  
 
== '''Symptoms'''  ==
 
== '''Symptoms'''  ==
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=== Physical  ===
 
=== Physical  ===
  
*Flattened face and nose
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*Flattened face and nose  
*Short neck with excess skin at the back
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*Short neck with excess skin at the back  
*Small hands and feet
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*Small hands and feet  
*Upward slanting eyes with a skin fold from upper eyelid that covers inner corner of the eye
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*Upward slanting eyes with a skin fold from upper eyelid that covers inner corner of the eye  
*Brushfield spots: white spots on coloured part of the eye&nbsp;
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*Brushfield spots: white spots on coloured part of the eye&nbsp;  
*Abnormally shaped ears
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*Abnormally shaped ears  
*Poor muscle tone (hypotonia)
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*Poor muscle tone (hypotonia)  
 
*[[Heart disease|Heart disease]]  
 
*[[Heart disease|Heart disease]]  
 
*Congenital heart defects  
 
*Congenital heart defects  
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*Delayed develop
 
*Delayed develop
  
== '''Diagnosis'''  ==
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== '''Screening and diagnosis'''  ==
 +
 
 +
Before a clinical diagnosis is made, prenatal screening tests are carried out to predict the probability of the foetus having Down's syndrome. Conversely, diagnostic tests are more accurate in determining whether or not the foetus will have Down's syndrome.&nbsp;<br>
 +
 
 +
'''Screening'''
 +
<br>
 +
 
 +
'''Prenatal diagnosis'''
  
Prenatal
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Chorionic villus sampling - obtain sample of material from the placenta and test for chromosal abnormalities.&nbsp;
  
Chorionic villus sampling
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<span style="font-size: 13.28px; line-height: 19.92px;">Amniocentisis - examines amniotic fluid (fluid sac surrounding the baby), and test it for protein levels</span><br>
  
<span style="font-size: 13.28px; line-height: 19.92px;">Amniocentisis</span>  
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<span style="font-size: 13.28px; line-height: 19.92px;">Percutaneous umbilical blood sampling &nbsp;- examines blood from the umbilical cord</span>
  
At birth  
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'''Diagnosis at birth'''
  
 
Non-invasive prenatal testing  
 
Non-invasive prenatal testing  
  
Karyotope analysis of newborn&nbsp;
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Karyotope analysis of newborn - obtain a blood sample from newborn and observe the cells.&nbsp;
  
 
== '''Treatment&nbsp;'''  ==
 
== '''Treatment&nbsp;'''  ==

Revision as of 18:15, 1 December 2015

Down's syndome is disorder caused by having an extra chromosome on chromosome 21 (referred to as trisomy 21), giving a total of 47 chromosomes instead of the normal 46 in humans.This extra chromosome copy disrupts the normal course of brain and body development, thus affecting both physical development and intellectual ability. Although individuals with Down's syndrome behave and look similar, their intellectual capability varies from mild to moderately low. As sufferers age (often about the age of 50), they may often experience a progressive decline in cognitive function, which can result in an increased risk of Alzheimer's, a neurodegenerative disease that causes dementia: a gradual loss of memory, motor skills, and judgement. 

Contents

Types

There are three main types of Down's syndrome:

Trisomy 21

An error during gamete formation results in a failure of the chromosomal pair on chromosome 21 to separately properly, which results in an embryo with three copies of chromosome 21. This is known as non-disjunction. Most cases of Down's syndrome are a result of a random chromosomal defect during the formation of reproductive cells, especially egg cells. An error during gamete cell division, non-disjunction, results in the cell with an abnormal number of chromosomes. As the embryo develops, the extra chromosome is replicated in every cell of the body. This is the most common form, and accounts for about 95% of cases. 

Mosaic trisomy 21

Mosaic refers to mixed or a pattern. Like trisomy 21, this isn't inherited; instead it is caused by random events that occur during cell division in early foetal development. This is the least common form and accounts for about 1% of cases. 

Translocation trisomy 21

Part of chromosome 21 is in the cell, which becomes attached to another chromosome during gametic cells formation or during early foetal development. This is transferred to other cells as it divides. In some cases, parents unaffected by Down's syndrome may have translocation trisomy 21, which can be inherited by their offspring. 

Causes

To date, the cause of the extra of partial chromosome is still unknown, Increasing maternal age (especially pregnant women aged 35 or over) is a contributory factor towards a higher risk of a baby having Down's syndrome with trisomy 21 or mosaicism. There is no conclusive scientific research to suggest that environmental factors or parental activities before or during preganancy are the causes. 

Symptoms

Physical

Young children are more susceptible to developmental delay. This may be a consequence of poor muscle tone, which impacts the ability to stand, balance, and sit normally, so they may reach these milestones slower than other children,

Intelletual and behavioural

Screening and diagnosis

Before a clinical diagnosis is made, prenatal screening tests are carried out to predict the probability of the foetus having Down's syndrome. Conversely, diagnostic tests are more accurate in determining whether or not the foetus will have Down's syndrome. 

Screening

Prenatal diagnosis

Chorionic villus sampling - obtain sample of material from the placenta and test for chromosal abnormalities. 

Amniocentisis - examines amniotic fluid (fluid sac surrounding the baby), and test it for protein levels

Percutaneous umbilical blood sampling  - examines blood from the umbilical cord

Diagnosis at birth

Non-invasive prenatal testing

Karyotope analysis of newborn - obtain a blood sample from newborn and observe the cells. 

Treatment 

Related conditions and disorders

References


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