Rett syndrome, related to methyl-CpG binding protein <i>2</i> (<i>MECP2</i>)<i>,</i> primarily affects females, though recent studies have identified additional causative genes, such as IQ motif and SEC7 domain-containing protein 2 (<i>IQSEC2</i>), which mainly affect males and are characterized by prominent developmental encephalopathy. Here, MECP2 is linked to Rett syndrome.