Essay: Categories of Down syndrome
Trisomy 21: Trisomy 21 is a major type of Down syndrome, since it accounts to 95% of patients diagnosed with Down syndrome. The simple description for Trisomy 21 is (47, XX, +21) and is caused by a meiotic nondisjunction event. Trisomy 21 results from failure of 21st chromosome pair to split to fuse with other chromosome from opposite sex.
Translocation: This kind of the Down syndrome occurs in about 3% to 4 % among patients diagnosed with Down syndrome. Has a simple formula of (45, XX, t (21q; 21q)) that validates its name to some times isochromosome. In this case, an extra part of the 21st chromosome gets stuck onto another chromosome resulting to hidden of a chromosome form.
Mosaicism: In this kind of Down syndrome, the person has an extra 21st chromosome in only some of the cells but not all of them. It is on the minimal level as only 1 to 2% amongst the patients diagnosed with Down syndrome.