Can the mutation happen anytime in life or is it from birth only? I have a son with LDS2 and a healthy older daughter. My son is de novo so they had parental testing, I guess
Year, so, mutations can be passed from parent to child by virtue of that change being in the cells that are making the egg cell or the sperm cell that are giving rise to that child that's what we call an inherited mutation. Mutation can occur during the formation of the egg cell or the sperm cell that go into the conception of a child so the parent doesn't have the change in any cell of their body but it was that one egg cell or one's one sperm cell that developed the change and then gave rise to a child with new Loeys-Dietz syndrome for that family.
Very, very, very, very rarely someone with a genetic condition has a change that occurred later in development typically not after they were born but when they were still forming in their mother's uterus but you know somewhere later on in the developmental process so they may only have the mutation in their blood and their skin where they may only have the mutation in their cardiovascular system but not in their skeleton that's something that's called a somatic mutation. It's exceedingly rare and unlikely to explain the situation that you're describing in your family. It's, if I understand your family correctly your affected child likely has a new change that was caused by a mutation or a DNA change in the egg cell or sperm cell that went into their conception and your other child, you know, did not develop that same change.
You know, a good question, a good follow-on question is if I have a child with a new mutation that's causing a new case of Loeys-Dietz syndrome in my family is there any risk that I'm going to have another child affected with Loeys-Dietz syndrome with the same mutation?
The answer is yes because occasionally a woman has the mutation in a population of cells just in their ovary or a man has the mutation just in a small population of cells in his testes so they don't have Loeys-Dietz syndrome themselves but there is a higher than zero risk that they will have another child with that same mutation because another egg cell or another sperm cell would be made that has that change that's something that's called germline mosaicism. It has been described for Loeys-Dietz syndrome but also rather uncommon.
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