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Protein probe may diagnose fragile X syndrome

by  /  29 May 2013

Spot test: A new method uses antibodies to test for fragile X syndrome in dried blood spots. 

Quick tests that detect the protein missing in fragile X syndrome can be used to screen newborns for the disorder and find treatments, according to two studies published in the past two months.

Both studies directly assay levels of the fragile X mental retardation protein (FMRP), whereas traditional fragile X screens focus on the gene, FMR1, that encodes the protein.

This gene typically has up to 55 repeats of three DNA nucleotides. A mutation that leads to more than 200 repeats shuts off the gene’s expression, leading to fragile X syndrome.

Research companies have developed several tests to quickly sequence FMR1 and count its number of repeats. These tests can screen for the disorder using dried blood spots taken from babies at birth. Hospitals don’t routinely screen newborns for fragile X syndrome, but this is likely to change as promising drug candidates enter clinical trials.

The first new study, published 6 May in the Journal of Molecular Diagnostics, describes an antibody-based method that can quantify the amount of FMRP in these blood spots1. Because the antibodies bind to the protein directly, the test is more reliable than assays that analyze the gene repeats. It is also potentially quicker and cheaper, the researchers say.

Using this method with blood samples, the researchers accurately identified 17 men who have fragile X syndrome out of a set of 215 people, including controls and individuals who have a high number of repeats but not enough to develop the syndrome.

In a second study, published 2 April in the Journal of Neurodevelopmental Disorders, researchers developed a test that can detect FMRP in a single step2. This simple and quick test is ideal for large screens of fragile X treatments, the researchers say.

The researchers designed two antibodies that bind to nearby regions on FMRP. These antibodies are each attached to fluorescent molecules. When in close proximity, the molecules interact, emitting a unique spectrum of fluorescence. Using the technique, the researchers measured levels of FMRP in the blood cells of one individual with fragile X syndrome and five controls.

References:

1: Lafauci G. et al. J. Mol. Diagn. Epub ahead of print (2013) PubMed

2: Schutzius G. et al. J. Neurodev. Disord. 5, 8 (2013) PubMed