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​Fragile X Syndrome

updated: June 19, 2024


Fragile X syndrome is a genetic condition that affects a person’s development, in particular their ability to learn and their social behavior. The syndrome results from mutations in a gene on the X chromosome. Because males have only one copy of the X chromosome, they are more likely to show severe symptoms if they inherit the mutated gene compared to females (who have two copies of the X chromosome).



Fragile X syndrome. When I started graduate school, I joined a lab which had just discovered the new mutational mechanism — called dynamic mutation — behind Fragile X syndrome. This was the first example we had seen of a genomic region which had repeated letters. In this case, the base is CGG, over and over. And that repeat region expanded to cause a syndrome in humans. It's called dynamic mutation because the number of repeats that you have might not be the same as your parent or your grandparents. Soon after that, myotonic dystrophy and Huntington's disease were shown to have the same dynamic mutation cause, but with different repeated letters and in different genes. This was such an amazing time to work in human genetics and see how one discovery that took years to pin down can quickly lead to many others, once we learn new things about how the genome works.

Chris Gunter
Chris Gunter, Ph.D.

Associate Investigator

Social and Behavioral Research Branch