Christianson syndrome (CS) is an X-linked brain disorder in males characterized by intellectual disability (ID), lack of language, postnatal microcephaly, ataxia, and epilepsy that is caused by mutations in Na+/H+ Exchanger 6 (NHE6). In the largest CS study to-date, we examined 44 CS probands, from 2 to 32 years old, with 31 unique NHE6 variants. Our natural history study of CS identified a new core symptom (high pain threshold). In longitudinal data, we also define worsening impairments in motor function and declining body weight with age. This study reveals the trajectory of CS symptoms through adulthood, and identifies critical targets for future clinical interventions. (By Dr. Eric M. Morrow, https://jmg.bmj.com/content/early/2024/09/05/jmg-2024-109973 )