Uploaded by x-aimee-kate-x on Jan 31, 2005
Downs Syndrome- A Chromosome Abnormality
In humans the Chromosome compliment is 46, however in a person with the disease called Downs Syndrome, an extra chromosome is formed to give 47. Usually in Downs Syndrome there is an extra copy of chromosome 21. Also called Trisomy 21, this is the most common variant of Downs. The effects of this extra chromosome are that this person will have a learning disability. The average life expectancy for a sufferer of Downs Syndrome without further complications is between 40-55 years. The older a female is the more likely she is to give birth to a child with Downs Syndrome. The chart below shows the age at which a mother is more likely to give birth to a child with this disease.
Down Syndrome Birth Rate Probability
Age of mother Probability of Giving birth to a child with Downs
25 1 in 1400
30 1 in 800
35 1 in 380
38 1 in 190
40 1 in 110
45 1 in 30
Apart from Trisomy 21 there are two other types of Downs Syndrome. The second form is called Translocation and it occurs in about 3% or 4% of Downs cases. In this form an extra part of chromosome 21 attaches to another chromosome. In half of Downs cases with Translocation one of the parents’ carries an extra 21’st chromosome in a balanced or hidden form.
In the third form, Mosaic, the individual with Downs has an extra 21’st chromosome in only some of the cells. This however is extremely rare and only affects about 2% of all Downs cases.
In a person with Downs Syndrome there are some distinguishing characteristics. Low muscle tone, or hypotnia, means that the muscle appears to be relaxed or floppy. This will affect movement of the body. Skin is one of the most sensitive areas of an individual with Downs Syndrome. The skin is fair and is prone to irritation or cracking. Their hair is usually very short an fine as well as sparse.
During childhood, Downs sufferers usually have speech impediments or language problems of some kind. There may also be intellectual delays. This is why it is important for the child to have speech therapists and attend early intervention, beginning early in life.