Molecular Cause of Fragile X Syndrome


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What is the Molecular Cause of Fragile X Syndrome?

DNA Molecule of life

Copyright DOE Human Genome Program
Used with permission

Our bodies are made up of about 60 trillion cells. Each of those cells manufactures proteins. The kinds of proteins the cell makes, determine the cell's particular characteristics and create the characteristics of the entire body.

The instructions for making these proteins are stored in the DNA which is organized into chromosomes. Genetic differences (mutations) in that stored information establish our individual differences and lead to inherited diseases.

People who do not have fragile X syndrome, make FMRP (fragile X mental retardation protein) in some of their cells. Those cells that do make FMRP are regulated as to when they make it, so that it is present when needed in the places where it is needed.

A person with fragile X syndrome has a mutation in the FMR1 (fragile X mental retardation 1) gene in the DNA that makes up the X chromosome. That mutation causes the cell to methylate a regulatory region of the FMR1 gene. The methylation turns off the FMR1 gene. Since the gene is turned off, the person doesn't make FMRP. That lack of a specific protein triggers fragile X syndrome.

What is the structure of a cell and how does it make proteins?

What do proteins do? Why can't we fix fragile X by adding some protein?

How is the DNA organized into chromosomes?

What is FMRP (fragile X mental retardation protein) and what does it do?

What is the mutation in FMR1 that causes fragile X syndrome?

How does methylation control synthesis of proteins?

For a review of molecular studies, see:
O'Donnell, WT, Warren ST. 2002. A decade of molecular studies of fragile X syndrome. Annu. Rev. Neurosci 25:315-38