What are CGG repeats?
At the beginning of the FMR1 gene there is a repeated sequence of chemical bases, known by the letters CGG. These are repeated a number of times. Most people have less than 55 copies of this CGG repeat. Fragile X premutation carriers can have between 55 and 200 copies of the CGG repeat.
How many CGG repeats do you need to have to have the FMR1 full mutation?
(FMR1) gene. The full mutation is defined as over 200 CGG repeats.
Why do CGG repeats expand?
This CGG trinucleotide repeat is unstable, and therefore the repeat length is variable (polymorpyhic) in the normal population, ranging from 6-55 repeats. The repeat can become unstable upon maternal transmission, usually resulting in the expansion of the repeat in the next generation.
What is CGG triplet repeat?
One region of the FMR1 gene contains a particular DNA segment known as a CGG trinucleotide repeat, so called because this segment of three DNA building blocks (nucleotides) is repeated multiple times within the gene. In most people, the number of CGG repeats ranges from fewer than 10 to about 40.
How many CGG repeats are there?
Most males have about 5 to 44 repeats of the chemical letters, CGG, in their FMR1 gene and most females also have 5 to 44 repeats in each of their FMR1 genes. This is considered a normal number of repeats.
Where is the FMR1 gene located?
FMR1 is located on the X-chromosome and encodes the fragile X mental retardation protein (FMRP). FMRP has been shown to bind mRNA and regulate translation of specific synaptic proteins.
Does everyone have the FMR1 gene?
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.
What does the abnormally expanded CGG segment do to the FMR1 gene?
The abnormally expanded CGG segment turns off (silences) the FMR1 gene, which prevents the gene from producing FMRP. Loss or a shortage (deficiency) of this protein disrupts nervous system functions and leads to the signs and symptoms of fragile X syndrome.
What is CAG in Huntington’s disease?
The HTT mutation that causes Huntington disease involves a DNA segment known as a CAG trinucleotide repeat . This segment is made up of a series of three DNA building blocks (cytosine, adenine, and guanine) that appear multiple times in a row. Normally, the CAG segment is repeated 10 to 35 times within the gene.
Where is FMR1?
The FMR1 gene is located on the X chromosome and contains a repeated CGG trinucleotide. In most people, the CGG segment is repeated approximately 5-44 times. Higher numbers of repeats of the CGG segment are associated with impaired cognitive and reproductive function.
What chromosome is FMR1 in?
The FMR1 gene is located on the X chromosome and contains a repeated CGG trinucleotide.
What causes FMR1 mutation?
Having more than 200 repeats causes the FMR1 gene to “turn off” so that it can’t make FMRP (the protein made by the FMR1 gene). When a person’s FMR1 gene has more than 200 repeats, so that it can’t make FMRP, the person has FXS.
