A quick science lesson for today. There are 3 different types of Down syndrome.
- Trisomy 21. 95% of all cases involve a pair of 21st chromosomes (from either the mother or father) that fail to separate before fertilization, passing along both copies instead of the typical one. This is called Trisomy 21. This is the type of Down syndrome that Gigi has.
- Mosaicism occurs when nondisjunction (when chromosomes fail to separate properly) of chromosome 21 takes place in one of the initial cell divisions after fertilization. As a result, roughly half of the cells in the body contain 3 copies of the 21st chromosome, while the rest of the cells are typical. Mosaicism accounts for about 1% of all cases of Down syndrome (least common).
- Translocation accounts for about 4% of all cases of Down syndrome. This occurs when an additional full or partial copy of chromosome 21 breaks off during cell division and attaches to another chromosome. While the total number of chromosomes remains 46, the presence of an additional full or partial chromosome 21 causes the characteristics of Down syndrome. In very rare instances, Translocation can be an inherited occurrence. This occurs when a parent carries a partial 21 chromosome that gets passed.