This study examined how the type of genetic mutation, function and health affect quality of life in Rett syndrome. Better walking and feeding skills and less frequent seizures were associated with better quality of life and poor sleep and behavioural difficulties with poorer quality of life. Compared to other mutations, individuals with the p.Arg294* mutation experienced the poorest quality of life, explained by poor sleep and more behavioural difficulties and despite better mobility. Genotype, function and health each have implications for quality of life and should be considered when planning clinical and support management strategies. (By Prof Jenny Downs, https://jmg.bmj.com/content/early/2020/08/25/jmedgenet-2020-107120 )