what causes trisomy to occur?
Trisomy 18, also known as Edwards syndrome, is the second most common trisomy behind trisomy 21 (Down syndrome). It occurs in 1 in 5,000 live births and it is caused by the presence of an extra chromosome 18 and similar to Down syndrome. It is seen more commonly with increasing maternal age.
In most individuals with Trisomy 13 Syndrome, duplication of chromosome 13 is caused by spontaneous (de novo) errors during the division of reproductive cells in one of the parents (e.g., nondisjunction during meiosis).