A research team from the School of Life Sciences at The Chinese University of Hong Kong (CUHK) has recently discovered that SOX9 protein is an essential regulatory factor of choroid plexus function that ensures the correct composition of cerebrospinal fluid (CSF). The finding, recently published in the prestigious scientific journal Proceedings of the National Academy of Sciences (PNAS), has provided the scientific community a novel understanding to the molecular regulatory mechanisms behind the function of the blood-CSF barrier and lays the groundwork for developing novel therapeutic strategies for preventing and treating neurodevelopmental disorders.