FOXG1 and Down syndrome: Despite the significant variability in phenotype and severity observed in individuals depending on the genotype, the core FOXG1 syndrome phenotype consists of severe postnatal microcephaly and mental retardation, deficient language development, poor social interactions and eye contact (indicating a link to ASD), postnatal growth deficiency, problematic sleep patterns, epilepsy, and irritability during infancy [4,12].