+what type gene mutation causes fragile x syndrome
Fragile X syndrome is an inherited genetic disease that causes intellectual and developmental disabilities. Inherited means that the disease is passed down from parents to children through their genes. Fragile X syndrome is the most common hereditary source of mental disability in boys. Furthermore, three unrelated fragile X patients were found with a C-to-T point mutation at the 14th nucleotide in intron 10 with normal length CGG·CCG repeats (Fig. 1F) (42). Clearly, these point mutations are sufficient for the development of the fragile X syndrome. Fragile X syndrome is caused by a defect in the FMR1 gene located on the X chromosome. The X chromosome is one of two types of sex chromosomes. The other is the Y chromosome. Women have two X chromosomes while men have one X chromosome and one Y chromosome. The defect (mutation) on the FMR1 gene prevents the gene from properly making a protein called the fragile X mental retardation 1 protein. This protein plays a role in the functioning of the nervous system. Abstract. The fragile X syndrome results from expansions as well as deletions of the repeating CGG·CCG DNA sequence in the 5′-untranslated region of the FMR1 gene on the X chromosome. One interesting aspect of Fragile X is that, even with a full mutation gene, the body may be able to make some FMRP. Three things affect how much FMRP is produced: 1  The number of CGG repeats. 2  People with a full mutation (200 or more repeats) usually have many of the more severe symptoms associated with Fragile X. 3  In contrast, people with a premutation gene may have few, if any, symptoms and may not even know they carry a mutated gene. The principal mutation responsible for the fragile X syndrome is generally considered to be the expansion of an untranslated CGG·CCG repeat in the 5′-untranslated region of the FMR1 gene on the X chromosome (1, 8). 1 People with a full mutation (200 or more repeats) usually have many of the more severe symptoms associated with Fragile X. 2  In contrast, people with a premutation gene may have few, if any, symptoms and may not even know they carry a mutated gene. Hence, the phenomenon of gross deletions of the FMR1 gene causing the fragile X syndrome is not an isolated event. Point Mutations —To this point, the previously described types of mutations are believed to be promoted by the presence of long CGG·CCG repeats. 1 The number of CGG repeats. 2  People with a full mutation (200 or more repeats) usually have many of the more severe symptoms associated with Fragile X. 3  In contrast, people with a premutation gene may have few, if any, symptoms and may not even know they carry a mutated gene. FMR1 (fragile X mental retardation 1) is a human gene that codes for a protein called fragile X mental retardation protein, or FMRP. This protein, most commonly found in the brain, is essential for normal cognitive development and female reproductive function.
C-to-T point mutation