MECP2 and Down syndrome: The patients' etiologies were identified in 16: tuberous sclerosis complex (n = 5), post-acute encephalopathy (n = 3), post-neonatal hypoglycemia (n = 2), hippocampal sclerosis (n = 1), focal cortical dysplasia (n = 1), chemotherapy-induced leukoencephalopathy (n = 1), methyl-CpG binding protein 2 (MECP2) duplication syndrome (n = 1), post-neonatal hypoxic–ischemic encephalopathy (n = 1), and Down syndrome (n = 1); one patient had both TSC and acute encephalopathy, and one patient had both MECP2 duplication syndrome and acute encephalopathy.