In the end, we identified three pathogenic variants, including only one daughter previously classified as idiopathic (SYNGAP1), while the other two pathogenic mutations (a de novo disruptive missense mutation in TBXLR1 and de novo SV affecting the last exon of MECP2) arose in daughters suspected of Rett syndrome. The gene discussed is SYNGAP1; the disease is atypical Rett syndrome.