Down syndrome (trisomy 21) Custom Search Down syndrome is the most common chromosomal abnormality in human beings. It is due to abnormal number of chromosomes in the cells. Normal cells in human beings have 23 pairs (total of forty six) of chromosomes except the gemetocytes (ovum and sperm) which have 23 chromosomes each. In Down’s syndrome the cells will have an extra chromosome. The chromosomes are numbered from 1 to 23. Cells in Down’s syndrome have an extra 21st chromosome. That is why it is also called trisomy 21 (tri meaning 3) Please click on the graphic to enlarge. Note three chromosomes for 21 instead of the normal two.
The exact cause for this is not known. Advanced age of parents is a well known risk factor. Clinical features: Children with Down’s syndrome have some unique physical characteristics. The eyes slant down towards the nose (mongoloid slant). The occiput (back of head) is flat . They usually have a single horizontal crease across the palms. It is called Simian crease. It should however be noted that simian crease may be found in otherwise normal children also. The fingers of hands are shorter than normal. Hypotonia (decreased muscle tone) is another common feature. Many children with Down’s syndrome have congenital heart disease. Mental retardation is invariably present but its severity may vary. Complications: Children with Down’s syndrome are at increased risk of developing leukemia (blood cancer). Those surviving beyond the age of 35 years are prone to develop Alzheimer's disease. There is no cure for Down’s syndrome. Management consists of assessment of the level of intelligence and rehabilitation. Congenital heart disease may require surgery. Regular follow up is needed to detect leukemia in the early stage. Custom Search
Page last reviewed on 2nd January 2011
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