Rett syndrome seems to appear out of nowhere. Infants with the rare neurological disorder grow and develop normally at first, but then—generally between 6 and 18 months of age—they suddenly regress. Toddlers forget their words, lose the ability to crawl or walk, develop involuntary hand movements and sometimes seizures, and can even struggle to eat or breathe. The children, predominantly girls, “are very sick,” explains Gail Mandel, a molecular neurobiologist at Oregon Health & Science University who has studied the condition for more than a decade.
The symptoms stem from loss-of-function mutations in a gene near the tip of the X chromosome that codes for methyl CpG binding protein 2 (MeCP2). This protein is a transcription factor, and it’s especially abundant in the central nervous system, where it helps to ensure that particular genes are switched off at the right time during development. “We know a lot about how this ...
