The fragile X syndrome is the most common form of intellectual impairment in men, affecting 1 out of 3,600 boys. Now, scientists at the Whitehead Institute used the CRISPR/Cas 9 gene editing method to restore activity to the fragile X syndrome gene in affected neurons. Their work, performed on human brain cells in a dish, paves the way for trying the technique on the brain, with the hope that it may treat a host of genetic conditions.