080210xf's Blog

L'X fragile sera vaincu | Fragile X will be conquered

Drug trials for fragile X syndrome lead the way for autism therapies

Randi Hagerman, Sfari.org |

A number of targeted trials on drugs that have the potential to reverse many of the behavioral and cognitive features of fragile X syndrome, are under way. Human and animal studies have shown that these medications can reverse many of the neurobiological and phenotypic features of fragile X syndrome. Along with these new trials, we will need accurate endpoints that can reliably measure the drugs’ effectiveness.

Fragile X syndrome is the most common inherited cause of intellectual disability and single-gene cause of autism. The full mutation has more than 200 repeats of a DNA sequence — CGG — at the front end of the FMR1 gene. This repeat number leads to a shutdown of the gene and a lack of the protein that it normally produces, fragile X mental retardation protein, or FMRP. The lack of FMRP causes fragile X syndrome and intellectual disability, in addition to autism, in 30 percent of individuals and pervasive developmental disorder-not otherwise specified in another 30 percent.

Between 55 and 200 repeats in the FMR1 gene causes what is called a premutation. The premutation leads to autism at a much lower rate — approximately ten percent of boys and less than two percent of girls.

The fragile X mutations cause autism through different molecular pathways. The absence or deficiency of FMRP affects the levels of many genes important for synaptic plasticity — how neurons strengthen important connections — and the outgrowth of neurites, the formation of new connections between neurons.

The fragile X premutation leads to higher levels of the RNA message for the FMR1 gene, which can bind to important proteins and dysregulate neuronal functions, leading to early cell death.

Promising trials:

Novartis and Roche both have an inhibitor of mGluR5, which activates a pathway that is overactive in those with fragile X syndrome.

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