Did I do anything to cause fragile X syndrome?No. There is nothing you did before or during the pregnancy or after your child was born to cause fragile X syndrome. Fragile X syndrome is genetic which means it is caused by a change in a gene, in this case, the FMR1 gene. The change causes the gene not to work the way it should, leading to the problems seen in fragile X syndrome.
Because fragile X syndrome is genetic, it can be passed on and you are at risk for having another child with fragile X syndrome. It is important to know that you have no control over whether this change gets passed on to your child or not. In addition, other family members may also be at risk of having children with fragile X syndrome, so it is important to inform them of your child's diagnosis.
What does cause fragile X syndrome?
Explaining how fragile X happens is not very easy simply because of the way it is inherited. To start, let's talk broadly about genes and chromosomes. Genes are the instructions that tell our bodies how to work and are made up of DNA. We inherit two copies of all of our genes: one copy from our mother and one copy from our father. The DNA is packed into larger structures called chromosomes, and each chromosome contains hundreds to thousands of genes. Most people have 23 pairs of chromosomes, for a total of 46 chromosomes. The first 22 pairs are the same in males and females and are called the autosomes. The 23rd pair, called the sex chromosomes, are different in males and females. Females have two "X" chromosomes, and males have one "X" and one "Y" chromosome.
Fragile X is caused by a change in the FMR1 gene on the X chromosome that causes it not to work properly. Everyone has 6-10 genes that don't work the way they should, but this generally does not cause a problem. However, the change in the FMR1 gene does make a difference. This change (also called a mutation) in the FMR1 gene is complex and occurs over many generations.
The FMR1 gene contains a section of repetitive DNA that in most of the population is only 10-40 repeats long. In those with fragile X syndrome, this repeated region has expanded to over 200 repeats. When a repeat length is greater than 200, it is referred to as a full mutation or expansion. At this size, the FMR1 gene cannot function and the FMR1 protein cannot be produced. It is the inability of cells to make this protein that is responsible for fragile X syndrome.
In general, every person gets two copies of every gene. This is a little bit different for the FMR1 gene because it is on the "X" chromosome. Because males have only one "X" chromosome, they have only one copy of the FMR1 gene. If they have a full mutation, their one copy of the FMR1 gene is not working, and one sees the signs of fragile X syndrome. Because females have two "X" chromosomes and 2 copies of the FMR1 gene, if a girl inherits a full mutation, the other copy of the gene is usually working, so girls with a full mutation are still able to make FMR1 protein. This is why girls usually have fewer signs of fragile X than boys do.
In general, we expect to see the full mutation in every cell of a person with fragile X syndrome. Sometimes, however, an individual with fragile X syndrome can have what is called mosaicism. There are two kinds of mosaicism in fragile X syndrome: repeat size mosaicism and methylation mosaicism. In repeat size mosaicism, an individual has some cells that have a full mutation and some cells that have a premutation. In methylation mosaicism, all the cells have a full mutation, but the methylation pattern may not be the same in all cells. Some research studies have shown that individuals with repeat size or methylation mosaicism may be less affected than those who do not have mosaicism.
What is methylation?
Methylation is a process in which a chemical group, called a methyl group, gets added to the DNA. When enough methyl groups are added to the DNA, the gene gets turned off. When methyl groups are removed, the gene gets turned on. This is a normal process and many of our genes are controlled by methylation. However, in fragile X syndrome, the methylation of the FMR1 gene turns the gene off when it should be turned on. When FMR1 is turned off, its protein is not made, and you see the features of fragile X syndrome.
When someone with fragile X syndrome has methylation mosaicism, not all cells will have the FMR1 gene turned off by methylation. Some cells may have it partially turned off, and some cells may have the FMR1 gene turned on.
I heard only boys have fragile X syndrome. Why does my daughter have it also?
Girls can also have fragile X syndrome even though they have two "X" chromosomes. The reason is that they have a full expansion on one chromosome and a normal repeat section (in most cases) on the other chromosome. The copy with the full expansion is not making any FMR1 protein, while the other copy (the normal repeat section) is making protein. Although some protein is being made, it may not be enough, so we can see characteristics of fragile X syndrome. However, because some protein is being made, girls with fragile X syndrome are generally less affected than boys.
Is there a cure?
At this time, there is no cure for fragile X syndrome. Treatment for fragile X syndrome is provided through therapies such as special education, speech and language therapy, and occupational therapy. Medications may be helpful in managing hyperactivity, short attention span, and other behavioral or emotional problems. In order to determine the best course of action for your child, a comprehensive evaluation is recommended.
Source: www.childrenshospital.org
