Expanding the Clinical and Molecular Spectrum of FOXG1- and ZBTB18-Associated Neurodevelopmental Disorders

Abstract Introduction: The zinc finger BTB domain-containing protein ZBTB18 binds to FOXG1 to form a transcriptional repressive complex involved in neuronal differentiation. Disruption of the components of this complex results in chromosome 1q43–q44 deletion syndrome/intellectual developmental disorder 22 or in FOXG1 syndrome. Case Presentation: This study reports on five patients with cognitive and behavioral impairment, seizures, microcephaly, and/or congenital brain abnormalities. Whole-exome sequencing identified deleterious ZBTB18 variants in three patients and deleterious FOXG1 variants in the remaining patients. We have detected a missense variant within the BTB domain of ZBTB18 in two affected monozygotic twins. In addition, we observed agenesis of the septum pellucidum in a missense FOXG1 carrier with a severe FOXG1 syndrome. Conclusion: Although the ZBTB18 zinc finger domains harbor the majority of known deleterious variants, we report a novel de novo rare missense variant within the BTB domain. The agenesis of the septum pellucidum observed in a missense FOXG1 carrier could be considered as a novel clinical feature associated with FOXG1 syndrome. The severe FOXG1 syndrome in this patient contrasts with the milder phenotype expected for a missense. Genetic or environmental factors may explain this phenotypic variability in FOXG1 syndrome. Established FactsDeleterious variants in FOXG1 and ZBTB18 are associated with neurodevelopmental disorders.Most of the known deleterious variants in ZBTB18 are located in the zinc finger domains.Deletions, frameshift, and nonsense variants affecting N-terminal and forkhead domains in FOXG1 result in more severe syndrome phenotypes than missense variants located in the same regions.