Inheritance of fragile X syndrome is complicated. Individuals with a family history of this disorder should consult a genetic counselor to learn more about the risks of passing the disorder to their children.
- Normal number of repeats:
Individuals with a normal number of repeats (5 to 40) cannot pass fragile X syndrome to their offspring. The number of repeats generally does not change when passed from parent to child.
- Intermediate number of repeats:
When a person has 41 to 58 repeats (called the gray zone), the number of repeats can sometimes increase slightly when passed from parent to child. These parents are not at risk of having a child with fragile X syndrome. However, the number of repeats can grow with each generation, so their grandchildren could be at risk.
Individuals with 59 to 200 repeats have a premutation (3). Both men and women can be carriers of a premutation. About 1 in 250 women and 1 in 800 men carries a premutation (8). However, only women who carry a premutation are at risk for having a child with fragile X syndrome.
A mother with a premutation has a 50-percent chance of passing the abnormal gene to her baby in each pregnancy. Some children who inherit the abnormal gene have a premutation and no symptoms of fragile X syndrome. However, the number of repeats is likely to expand when the gene is passed from mother to child. So the number of repeats can increase from a premutation to a full mutation (more than 200 repeats). Children with a full mutation have fragile X syndrome.
A father with a premutation passes it to all of his daughters but to none of his sons. Daughters generally have no symptoms of fragile X syndrome, but they are carriers of a premutation that they can pass on to their own children. Fathers with a premutation do not pass it to their sons because males do not get an X chromosome from their father.
Individuals with more than 200 repeats have a full mutation. A woman with a full mutation has a 50-percent chance of passing it to her baby in each pregnancy. Men with a full mutation generally do not reproduce.
Hi
ReplyDeleteI was diagnosed with 58 repeats(female). the genetic counselor said there is virtually no change for my kids to have FXS, worst case they become PM carriers. Is that correct?
Thanks
Gigi
Dear Gigi,
ReplyDeleteIt is really sad to know about your case. If you were aware about your risk of having kids with Fragile X, you would have tried for some other options to have kids. Now, at this point of time, kids are gift of God, so give care and love to them.
Before going in details I would like to know about your diagnosis method etc, details of your kids--how many boys and how many girls? Age? Symptoms? whether you have diagnosed them or just guessing with physical symptoms?
You belong to which country?
I am working in a private firm, dealing with Fragile X diagnostic kits, patients and carrier mothers. So, I would be more than happy, if can help you in any way...
Best wishes
Padmini
Hi
ReplyDeleteYou misunderstood me. I am currently pregnant with my first kid. I found out that I have 58 repeats. The genetic counselor actually said it's not considered premutation but a gray zone, and therefore the kids are not at risk of FXS. I would like to know if it is the widely accepted opinion in the world, or should I be worried?
I am from Israel, btw..
Thank you