Monday, October 31, 2011

Fragile X and mRNA Editing

The article I found describes some new research into Fragile X Syndrome. Fragile X Syndrome is the most common form of heritable cognitive impairment (mental retardation) in boys and results from an expanding tripling repeat mutation on the FMR1 gene. People generally have 30 repeats of the sequence CCG in the fragile X area (long tip of the X chromosome), but people with Fragile X Syndrome have from 200-2,000 CCG repeats in that area. The FMR1 gene encodes the fragile X mental retardation protein (FMRP), which binds to and disables sites critical for brain neuron function when it is dysfunctional. Losing FMR1 completely is the most common cause of autism. Those with Fragile X Syndrome tend to have long faces and protruding ears and are affected by mental retardation, learning disabilities, and social anxiety.

University of Pennsylvania and Brown researchers have discovered that the FMRP protein is critical in mRNA-editing and the neuromuscular junction synapse. mRNA editing is the splicing of introns after transcription and NMJ is the basically the neuron function that stimulates muscles to contract (there’s a great interactive site that explains NMJ here: Mutations in FRMP seem to be connected to overgrowth in the NMJ synapse, which causes problems with nerve function. They studied fruit flies (Drosophila), which have a similar gene (dFRM1) which, when mutated, causes analogous issues to mutated FRM1. Two proteins are necessary for correct NMJ growth—FMRP and ADAR. ADAR affects mRNA editing and is itself directly affected by FMRP. When these proteins are dysfunctional, mRNA editing is damaged, which affects the NMJ synapse and causes the symptoms of Fragile X Syndrome.

This is interesting because, as Prof. Reenan of Brown writes, mRNA editing mistakes have been “implicated in epilepsy, suicidal depression, schizophrenia, and even some neurological cancers. These data are surely pointing in the direction of deep connections between numerous distinct diseases of the brain.” Perhaps mRNA editing flaws are an undercurrent of diseases of the brain.

Main Article:

Works Cited:

Human Genetics, 9 ed. Ricki Lewis

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