A developmental disability caused by a mutated gene on the X chromosome can be reversed by a second mutation, at least in mice. Fragile X syndrome, which causes attention deficiency, anxiety and cognitive dissonance, affects one in 4,000 boys and one in 6,000 girls. It is caused by a mutation of a gene called fragile X mental retardation 1 (FMR1). As a result of this mutation, the body does not produce enough of the gene's corresponding protein. Mansuo Hayashi of the Massachusetts Institute of Technology and his team found a way to counter the deficiency—namely, by suppressing the gene for the enzyme p21-activated kinase. If this process works in humans, then reversing fragile X might be possible with a drug that inhibits the production of p21-activated kinase. The work appears in the July 3 Proceedings of the National Academy of Sciences USA.