Rett syndrome (RTT) is a severe neurodevelopmental disorder, primarily affecting girls and usually caused by heterozygous loss‐of‐function mutations in the X‐linked gene, methyl‐CpG‐binding protein 2 (MECP2),1, 2 encoding an epigenetic reader, MeCP2. The gene discussed is MECP2; the disease is atypical Rett syndrome.