Can a woman have one daughter with fragile X syndrome, and one daughter without?

Question

hi,

I have two daughters...

Can one daughter have fragile x syndrome, and one daughter does not carry it fully?

Both daughters coming from the same mom and dad biologically?

Thanks

Answer 1

Of course you can. Just as with any other genetic issue, not ALL your children will have it!

Answer 2

yes, it's possible

Answer 3

Yes - and it doesn't matter if they have the same mother and father.  If they had different fathers and you were the carrier they could both have it, both not have it, one have a full-mutation, one be a carrier.

When a woman is a carrier she has two X chromosome and with each child she will only pass on one of the two. Typically one has normal CGG repeats (doesn't carry the FX mutation) and one has the abnormal CGG repeats.  With each pregnancy, (if the mom is the carrier) a female has a 50/50 chance of passing it on.  In my family my mother was a carrier, my older sister had a full-mutation (over 200 CGG repeats - we never new), I had a pre-mutation was a carrier 125 CGG repeats and my younger sister was passed on the X chromosome with the normal CGG repeats - doesn't carry the FX mutation.

If the father is the carrier he will pass the mutation on to all of his daughters (keep in mind a male only has one X chromosome).  Typically, the CGG repeats don't expand so all of his daughters will be carriers.

What you need to understand about Fragile X and girls from what existing research has told us is that 1/3 of the girls may have no symptoms, 1/3 of the girls will have learning disabilities and 1/3 of the girls may be as severely affected as their male counterparts.

Another thing is, although it is not common sometimes females who carry the pre-mutation are affected.

The only way you will know for sure is if you test both daughters.

I have girls who carry the full-mutation and they are not affected, attend regular school - have no IEPs or 504s, are honor roll students.

Answer 4

Why not? Isn't it a mutation?

Answer 5

Fragile X is carried on the X chromosome.  If neither you or your husband have symptoms, then you are probably the carrier.  You have two X chromosomes.  One has the gene for fragile X, the other does not.  Each of your children will inherit one X from you.  It is then a 50-50 chance for each child to get the X with the fragile X gene.  Unless a female inherits two copies (one from mom and one from dad which is very rare), she will only be a carrier of the syndrome.  Some carriers exhibit symptoms while others do not.  In your situation, you daughters could both have fragile X, but only one exhibits symptoms, or one could have fragile X and one could not.  The only way to know for sure is to have a genetic test.

Answer 6

Yes. My family is in the same situation. My daughter (adopted) biological mother just recently tested + for Fragile X. So now my next step is to call the genetics clinic for an appointment. My daughter's only official diagnosis yet is Global Developmental Delay with Moderate Mental Retardation. From researching Fragile X, it fits my baby girl to a T. She has a younger sister who has been adopted by a friend of mine, and she has delays, but not nearly as significant. She has already been to genetics and has the Fragile X gene, but not any significant number of repetitions. They attribute her delays in speech and motor skills to an abnormality in her tongue and her petit mal seizures. I think my daughter will likely be found to have a significant number of repeats. The degree of mental retardation will depend on how many repetitions are on the gene. If you carry it, but have few repetitions, you can have a severely affected child, or one not affected at all. It is never passed from father to son, always passed from father to daughter, and 50/50 shot at passing it on by the mother. You have a 50/50 shot at passing it on with each pregnancy. If you were to give birth to a boy who does have it, he would be severely retarded because he doesn't have that extra X chromosome to help him out. For that reason, it is usually passed my the mother because affected males are usually severely retarded and never have kids of their own.

Answer 7

Of course. I assume from the name that the gene is passed by the X chromosome. Both boys and girls can get it (as I just learned through a quick google search), so it must be a dominant allele (boys have one X chromosome and one Y, so if it were a recessive allele - both alleles have to be this for it to show up - then boys would be carriers but wouldn't be affected).

This means that only one of your X alleles definitely has it. If you pass on an X chromosome with the dominant allele to one daughter, and without it to the other, then assuming your husband did not have it and you did, one daughter would have fragile X syndrome and the other would not.

Basically, yes, it's entirely possible. There's only about a 50-50 chance of passing it on (unless both of your X chromosomes have the allele).

Mind you, if the father is the one with fragile X syndrome, then all of his female children would have it (because he only has one X chromosome to pass on) and none of his sons would have it (unless you had it too, because he would be passing on a Y chromosome to them, not an X chromosome).

That whole response seemed very complicated, but basically, if you have the syndrome but only one of your chromosomes has it, then there is only a 50-50 chance of you passing it on. If your husband has it, or both of your X chromosomes carry it, then all of your female (and male in the second case) children would have it.