FMR1

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Location of FMR1 on the X chromosome
fragile X mental retardation 1
Identifiers
Symbol	FMR1
HUGO	3775
Entrez	2332
OMIM	309550
RefSeq	NM_002024
UniProt	Q06787
Other data
Locus	Chr. X q27.3

FMR1 (fragile X mental retardation 1) is a human gene that provides instructions to make a protein called fragile X mental retardation 1, or FMRP. This protein is normally made in many tissues, especially in the brain and testes. It may play a role in the development of connections (synapses) between nerve cells in the brain, where cell-to-cell communication occurs. The connections between nerve cells can change and adapt over time in response to experience (a characteristic called synaptic plasticity). FMRP may help regulate synaptic plasticity, which is important for learning and memory.

Researchers believe that FMRP acts as a shuttle within cells by carrying molecules called messenger RNA (mRNA), which contain information for making proteins. FMRP carries mRNA molecules from the nucleus to areas of the cell where proteins are assembled. Some of these mRNA molecules may be important for the function of nerve cells.

One region of the FMR1 gene has a particular sequence of 3 DNA bases, CGG, that is repeated a number of times. (Bases are the building blocks of DNA.) This region is called a trinucleotide repeat. In most people, the number of CGG repeats ranges from fewer than 10 to about 40.

The FMR1 gene is located on the long (q) arm of the X chromosome at position 27.3, from base pair 146,699,054 to base pair 146,738,156.

[edit] Related conditions

Fragile X syndrome: Almost all cases of fragile X syndrome are caused by expansion of the CGG trinucleotide repeat in the FMR1 gene. In these cases, CGG is abnormally repeated from 200 to more than 1,000 times, which makes this region of the gene unstable. As a result, the FMR1 gene is turned off (silenced) and does not make any protein. Without adequate FMRP, severe learning problems or mental retardation and the other features of fragile X syndrome can develop.

Fewer than 1 % of all cases of fragile X syndrome are caused by mutations that delete part or all of the FMR1 gene or change one of the building blocks (amino acids) in FMRP. These mutations disrupt the 3-dimensional shape of FMRP or prevent any protein from being produced, leading to the signs and symptoms of fragile X syndrome.

A CGG sequence in the FMR1 gene that is repeated about 55 to 200 times is described as a premutation expansion. Men, and probably some women, with this premutation do not have fragile X syndrome, but are at increased risk of developing a disorder known as fragile X-associated tremor/ataxia syndrome (FXTAS). FXTAS is characterized by progressive problems with movement (ataxia), tremor, memory loss, loss of sensation in the lower extremities (peripheral neuropathy) and mental and behavioral changes. The disorder usually develops late in life.

Although most men and women with the premutation are intellectually normal, some of these individuals have mild versions of the physical features seen in fragile X syndrome (such as prominent ears) and may experience emotional problems such as anxiety or depression. About 20 % of women who carry a premutation expansion in the FMR1 gene experience premature ovarian failure (POF). POF is a loss of ovarian function in women younger than age 40, which can result in infertility (the inability to conceive a child).

Researchers have found that some children with a premutation expansion in the FMR1 gene have learning disabilities, mental retardation, or disorders in the autism spectrum (developmental disorders that affect communication and social interaction).

[edit] References

Hagerman PJ, Hagerman RJ (2004). "The fragile-X premutation: a maturing perspective". Am J Hum Genet 74 (5): 805-16. PMID 15052536.
Hagerman RJ, Leavitt BR, Farzin F, Jacquemont S, Greco CM, Brunberg JA, Tassone F, Hessl D, Harris SW, Zhang L, Jardini T, Gane LW, Ferranti J, Ruiz L, Leehey MA, Grigsby J, Hagerman PJ (2004). "Fragile-X-associated tremor/ataxia syndrome (FXTAS) in females with the FMR1 premutation". Am J Hum Genet 74 (5): 1051-6. PMID 15065016.
Jacquemont S, Hagerman RJ, Leehey MA, Hall DA, Levine RA, Brunberg JA, Zhang L, Jardini T, Gane LW, Harris SW, Herman K, Grigsby J, Greco CM, Berry-Kravis E, Tassone F, Hagerman PJ (2004). "Penetrance of the fragile X-associated tremor/ataxia syndrome in a premutation carrier population". JAMA 291 (4): 460-9. PMID 14747503.
Jin P, Alisch RS, Warren ST (2004). "RNA and microRNAs in fragile X mental retardation". Nat Cell Biol 6 (11): 1048-53. PMID 15516998.
Jin P, Warren ST (2003). "New insights into fragile X syndrome: from molecules to neurobehaviors". Trends Biochem Sci 28 (3): 152-8. PMID 12633995.
O'Donnell WT, Warren ST (2002). "A decade of molecular studies of fragile X syndrome". Annu Rev Neurosci 25: 315-38. PMID 12052912.
Oostra BA, Chiurazzi P (2001). "The fragile X gene and its function". Clin Genet 60 (6): 399-408. PMID 11846731.
Oostra BA, Willemsen R (2003). "A fragile balance: FMR1 expression levels". Hum Mol Genet 12 Spec No 2: R249-57. PMID 12952862.