Fragile X Premutation Map (image) Rockefeller University Press Caption Researchers used genetic mapping to determine that stem cells derived from mothers carrying a fragile X premutation (above) show a normal pattern of DNA replication when a nearby DNA sequence is similar to normal stem cells. Credit Gerhardt et al., 2014 Usage Restrictions Reporters may freely use these materials in news coverage, with the appropriate credit information. Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.