BRCA-1 Odds

We have the BRCA-1 mutation on my dad's side of the family. Three geneticists claim that the odds of inheriting the mutation are 50/50 with no exception. 6 out of 6 of his kids have the mutation. While statistics can jive with these results, it really is quite unlikely. So, something else is going on beyond the 50/50 odds. Can someone explain? Is "overexression" the right term here? If so (or not), how does that work?

[Jordanna Joaquina, MS, CGC]

Although it may appear that the odds are greater than 50% given the amount of family members with the mutation, it's still 50/50 as the geneticists explained.

Not to minimize the significance of a BRCA mutation, but one way to explain it is like tossing a coin. Each time you flip a coin there is a 50% chance to get heads and a 50% chance to get tails. Each flip is an independent event and the coin is unaware of the last result or the next result. Each pregnancy is an independent event with a 50% chance of inheriting the gene copy with the mutation and a 50% chance of inheriting the normal gene copy - that is as long as only one parent has a mutation and not both parents. Although it is very unfortunate, this is how 6 children can each have had inherited the same mutation from a parent.

As you are probably aware, having a BRCA mutation does not cause cancer but does increase the lifetime risk to develop certain types of cancer. We recommend that your family meet with genetics and oncology to discuss appropriate, routine cancer screening and surveillance (if not already doing so). We hope your family is getting the support it needs and wish you the best.