Rett syndrome (RTT) is a rare neurodevelopmental disorder occurring primarily in females (1:10–15,000 female live births) most often caused by loss‐of‐function mutations in the X‐linked methyl‐CpG‐binding protein 2 gene (MECP2; Amir et al., 1999). The gene discussed is MECP2; the disease is Rett syndrome.