Coffin-Siris syndrome 9 (CSS9), a rare congenital disorder caused by SRY-related HMG-box 11 gene (SOX11) deficiency, is characterized by high phenotypic heterogeneity including a wide spectrum of organ anomalies. The gene discussed is SOX11; the disease is intellectual developmental disorder with microcephaly and with or without ocular malformations or hypogonadotropic hypogonadism.