How Is Down Syndrome Inherited?

Types of Down Syndrome

There are different types of Down syndrome depending on the way the cell divide itself. Here is more about it:

  • Trisomy 21: A baby develops Down syndrome when there is an error in the process of cell division (nondisjunction). Also called Trisomy 21, the type refers to a condition in which there is an embryo that contains three copies of chromosome 21. Under normal circumstances, there should be only two. This happens when a pair of 21st chromosomes does not separate at conception. With the development of the embryo, there will be an extra chromosome in every cell of the body. This is called trisomy 21 and accounts for 95% of all Down syndrome cases.
  • Mosaicism: A baby gets this type of Down syndrome when there is a mixture of two types of cells. It means some of the cells will have 46 chromosomes, while others may have 47 chromosomes with an extra chromosome 21. This type of Down syndrome accounts for only 1% of all cases and is quite rare. People with this type of genetic disorder will have fewer characteristics of Down syndrome as compared to those who have Trisomy 21.
  • Translocation: It accounts for 4% cases of Down syndrome in which the total number of chromosomes in cells stays normal (46) but there is an additional copy of chromosome 21 attached to another chromosome. This could be a full or partial copy of chromosome 21 and usually attaches itself to chromosome 14. In this type, some characteristics of Down syndrome will be quite visible.

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