What causes 47, XYY syndrome ?
What causes 47, XYY syndrome? 47,XYY syndrome is caused by the presence of an extra copy of the Y chromosome in each of a male's cells. This is typically due to a random event during the formation of a sperm cell in the father, usually before conception (fertilization of the egg). In this case, the father's two Y chromosomes do not separate when sperm cells are being made. If two Y chromosomes are present in a sperm that fertilizes an egg (with an X chromosome), the resulting embryo will be a male with an extra Y chromosome. It is also possible that a similar random event could occur very early in an embryo's development. It is not fully understood why an extra copy of the Y chromosome leads to an increased risk for the features associated with 47, XYY syndrome in some males. Importantly, there is nothing either parent can do (or not do) to cause or prevent 47, XYY syndrome.