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Aurora magazine

New genetic test to predict fragile X syndrome

A study published in the journal Frontiers in Genetics exposes a new technique for predicting fragile X syndrome. This is a genetic test that identifies the presence of a specific type of genetic mutation. In this way he predicts the risk that a woman has a child with the disease.

Fragile X syndrome is linked to the expansion of CGG nuclei in the FMR1 gene. One patient with the syndrome shows more than 200 repetitions of CGG, compared with 30 averages. Sometimes the person has between 55 and 200 repetitions and shows milder disorders.

Women with this "premutation" have a high risk of having a child suffering from fragile X syndrome. The presence of repeats of the AGG nuclei reduces the risk, but remains present. A woman with 75 repetitions of CGG and two of AGG has 12% chance of transmitting the disease. The odds rise to 77% without AGG's double. Taking into account these two parameters, it is possible to evaluate the risk of hereditary transmission of the syndrome.

Identifying CGG repetitions is easy, but this does not apply to AGG repetitions. The researchers then developed a new genetic test that identifies AGGs in women with a premature FMR1.

The study involved about 51 women, including 26 carriers of a healthy gene and an intermediate gene, 24 carriers of a premutation. Only 1 woman showed both conditions. 30% of the second group (13 women) showed 60-80 repetitions of CGG. Of these, 3 had no repetition of AGG and were therefore at high risk. Other 2 had more than 85 repetitions of CGG and 1 had 95 repetitions and none of AGG. The latter had 100% chance of transmitting the syndrome.