The term new (or de novo) mutation is used to describe a genetic trait that is present in a child but not in either of its parents. Up until now, new mutations have been thought to occur during the production of either the mother's egg or father's sperm cells, prior to fertilization. Depending upon when in the production process the mutation takes place, other sperm and egg cells might also carry the mutation, meaning there is a chance that future children will also be affected. This may be either directly (whereby the child shows the trait/condition) or as carrier (the child doesn't show the trait him/herself but has the ability to pass the genetic defect to his/her offspring). Understandably, this can cause a lot of concern when planning a family.

When looking at genetic conditions, it is very useful to study identical twins, as they start life with exactly the same genetic make-up. If one identical twin develops a genetic condition but the other doesn't, it can provide clues about the origin of the genetic mutation.

Researchers at the Austin Health and Epilepsy Research Centre, University of Melbourne have recently shown that a rare form of genetic epilepsy, known as Dravet syndrome, can be caused by a genetic mutation in the embryo shortly after fertilization, and is not necessarily passed down from the parents. Although the study was very limited (it specifically looked at people with an identical twin who had a diagnosis of Dravet syndrome), Lead Investigator, Professor Sam Berkovic, is excited about the findings and their possible implications for other genetic conditions:

"While this study focused on an uncommon form of epilepsy, this finding may have implications for those with other forms of genetic epilepsy, and in fact other types of genetic disease."

A lot more investigation is needed, but if these theories are confirmed, a test could potentially be developed in the future, specifically for the siblings of people with genetic epilepsy (or other genetic conditions), confirming whether or not the mutation originated in the egg/sperm cells of the parents. If this were shown not to be the case, the siblings could be reassured that they would not pass the condition to their own children. This would remove a lot of distress and enable people to make better informed decisions about their future and the potential risks to their offspring.

Read more here