What is the repeat in Fragile X?

Cloning of the FMR1 gene revealed that the fragile site of the X chromosome contains a CGG repeat in the 5′ untranslated region (UTR) of the gene. This CGG trinucleotide repeat is unstable, and therefore the repeat length is variable (polymorpyhic) in the normal population, ranging from 6-55 repeats.

How many CGG repeats does Fragile X have?

Individuals with Fragile X Syndrome have over 200 CGG repeats. Males with over 200 repeats are almost always affected. Mosaicism, the presence of two different sized repeats or extent of methylation, for pre- and full-mutation alleles has been reported in some individuals with FMR1 full-CGG expansions.

How common is Fragile X premutation?

Fragile X Syndrome (FXS) is the most common form of inherited learning difficulty (1) and has been estimated to affect one in every 2,500–7,000 males and one in 2,500–11,000 females (2).

Does everyone with Fragile X have autism?

Almost 50 percent of men and 16 percent of women with fragile X also have autism, according to the U.S. Centers for Disease Control and Prevention. Other studies have hinted that up to 90 percent of men with fragile X have some autism traits, such as a tendency to avoid eye contact2.

What are CCG repeats?

Fragile X-associated conditions are caused by a lengthening (expansion) in the FMR1 gene on the X chromosome. The FMR1 gene is responsible for producing a protein called FMR1-Protein (FMRP), which is necessary for normal brain development and function.

Why do Trinucleotides repeat?

Mechanism. Triplet expansion is caused by slippage during DNA replication or during DNA repair synthesis. Because the tandem repeats have identical sequence to one another, base pairing between two DNA strands can take place at multiple points along the sequence.

Why do the repeats cause Huntington’s?

Huntington’s disease is caused by a mutation in the HD gene in which the same three bases? (CAG) are repeated many more times than normal. This is known as a CAG trinucleotide repeat expansion. In people who don’t have Huntington’s disease this section of CAG repeats in the gene is usually only repeated 10 to 35 times.

How many repeats does fragile X syndrome have?

It is a dynamic mutation with expansion of the CGG repeat in each generation moving from the premutation range of 55 to 200 repeats and expanding to a full mutation when pass on by a women to her children 3. Patients affected with FXS have more than 200 repeats of the CGG trinucleotide.

Where are trinucleotide repeats located in Fragile X syndrome?

Trinucleotide Repeats: Fragile X Syndrome. Gaze aversion, or the inability to make and hold eye contact, is very common among males and females with Fragile X syndrome. The gene that causes Fragile X syndrome, called FMR1, is located on the X chromosome. Females are usually not as severely affected as males.

What do you need to know about fragile X intermediate?

Understanding a Fragile X Intermediate Result. Fragile X DNA analysis is one of the most commonly ordered medical genetic tests. It is recommended as a standard part of the genetic work-up of children with developmental delay, autism, or intellectual disability.

How is fragile X syndrome passed down from parent to parent?

Fragile X syndrome is inherited, which means it is passed down from parents to children. Anyone with the FMR1 gene mutation can pass it to their children. However, a person who inherits the gene mutation may not develop Fragile X syndrome. Males will pass it down to all of their daughters and not their sons.