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Down Syndrome is also known as Trisomy 21.
It is a genetic disorder caused when abnormal cell division results in an extra full or partial copy of chromosome 21.
This extra genetic material causes the developmental changes and physical features of Down syndrome.
Down syndrome varies in severity among individuals, causing lifelong intellectual disability and development delays.
It’s the most common genetic chromosomal disorder and cause of learning disabilities in children. It also commonly causes other medical abnormalities, including heart and gastrointestinal disorders.
Symptoms: Each person with Down syndrome is an individual – intellectual and developmental problems may be mild, moderate or severe, Some people are healthy while others have significant health problems such as serious heart defects.
Children and adults with Down syndrome have distinct facial features. Though not all people with Down syndrome have the same features, some of the more common features include:
1. Flattened face
2. Small head
3. Short neck
4. Protruding tongue
5. Upward slanting eye lids
6. Unusually shaped or small ears
7. Poor muscle tone
8. Broad, short hands with a single crease in the palm
9. Relatively short fingers and small hands and feet
10. Excessive flexibility
11. Short height
Infants with Down syndrome may have an average size, but typically they grow slowly and remain shorter than other children the same age.
Most children with Down syndrome have mild to moderate cognitive impairment. Language is delayed, and both short and long-term is affected.
Causes: Human cells normally contain 23 pairs of chromosomes. One chromosome in each pair comes from the father, the other from the mother.
Down syndrome results when abnormal cell division involving chromosome 21 occurs. These cell divisions abnormalities result in an extra partial or full chromosome 21. This extra genetic material is responsible for the characteristic features and developmental problems of Down syndrome. Anyone of three genetic variations can cause Down syndrome.
Trisomy 21- About 95% of the time, Down syndrome is caused by trisomy 21- the person has three copies of chromosome 21, instead of the usual two copies, in all cells. This is caused by abnormal cell division during the development of the sperm cell or egg cell.
Mosaic Down Syndrome- In this rare form of Down syndrome, a person has only some cells with an extra copy of chromosome 21. This mosaic of normal and abnormal cells is caused by abnormal cell division after fertilization.
Translocation Down Syndrome- Down syndrome can also occur when a portion of chromosome 21 becomes attached (translocated) onto another chromosome before or at conception. These children have the usual two copies of chromosome 21., but they have additional genetic material from chromosome 21 attached to another chromosome.
Is it inherited?
Most of the time, Down syndrome is not inherited. It is caused by mistake in cell division during early development of the fetus.
Translocation Down syndrome can be passed from parent to child. However, only about 3 – 4% of children with Down syndrome have translocation and only some of them inherited it from one of the parents.
When balanced translocations are inherited, the mother or father has some rearranged genetic material from chromosome 21 on another chromosome, but no extra genetic material. This means he or she has no signs or symptoms of Down syndrome, but can pass an unbalanced translocation onto children, causing a Down syndrome in the children.
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