What causes CGG 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.
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.
How many CGG repeats do you need to have to have the FMR1 full mutation?
Individuals with fragile X syndrome nearly always have (in greater than 99% of cases) a full mutation of the FMR1 gene which means that they have over 200 CGG repeats and abnormal methylation of the gene.
Does everyone have the FMR1 gene?
Everyone has the FMR1 gene on their X chromosome. 3. The FMR1 gene was identified in 1991. The “job” of the FMR1 gene is to make protein (FMRP) that is important in brain development.
What is CGG triplet?
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.
What is CAG repeat?
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.
Can a male be a carrier?
The term is used in human genetics in cases of hereditary traits in which the observed trait lies on the female sex chromosome, the X chromosome. The carriers are always women. Men cannot be carriers because they only have one X chromosome.
What does Fmrp do in the brain?
FMRP likely carries mRNA molecules from the nucleus to areas of the cell where proteins are assembled. FMRP also helps control when the instructions in these mRNA molecules are used to build proteins, some of which may be important for functioning of the nerves, testes, or ovaries.
Can two parents suffering from the said genetic disorder have normal daughter?
If both parents are carriers, each parent can pass on the changed copy or the normal copy to their children. Children who inherit two changed copies of the CFTR gene are “affected” and have the disease cystic fibrosis.
What is the CGG triplet repeat?
What famous person has Huntington’s disease?
Probably the most famous person to suffer from Huntington’s was Woody Guthrie, the prolific folk singer who died in 1967 at age 55. Ducks football coach Mark Helfrich’s mother also suffers from the disease and lives in a local nursing home.
Why do CAG repeats cause Huntingtons?
The DNA sequence CAG encodes the amino acid glutamine. The CAG repeats in HTT therefore lead to the production of a string of glutamines, known as a polyglutamine chain, which is abnormally long in people with the large numbers of repeats that are associated with Huntington’s disease.
What is the normal repeat length of FMR1?
Methylation of the expanded CGG tract leads to silencing of expression of the FMR1 gene. The American College of Medical Genetics 2, 3 defines a normal repeat length as between 5 and 44. Intermediate alleles of between 45 and 54 repeats almost never expand to full mutations in a single meiosis.
Where is the CGG repeat located in Fragile X?
Fragile-X syndrome (FXS) (OMIM 300624) is caused by the expansion of the CGG repeat in the 5′ untranslated region (UTR) of fragile X mental retardation 1 (FMR1) gene (OMIM 309550) located on the X chromosome (Fu et al., 1991, Verkerk et al., 1991).
How is fragile X syndrome related to FMR1?
Fragile X Syndrome (FXS) is characterized by moderate to severe intellectual disability which is accompanied by macroorchidism and distinct facial morphology. FXS is caused by the expansion of the CGG trinucleotide repeat in the 5′ untranslated region of the Fragile X mental retardation 1 (FMR1) gene.
What kind of PCR is used for CGG expansion?
The use of triplet-primed PCR (TP-PCR) for the detection of CGG expansion in FMR1 was initially described by Daniels et al., 32 who coined the term “repeat primer PCR.”