The etiology of seizures in 47 infants, children, and young adults with Down syndrome was examined at The Floating Hospital for Infants and Children, Boston, MA and the Institute for Basic Research in Developmental Disabilities, Staten Island, NY. Of a total of 737 patients with Down syndrome, 47 (6%) had seizures; and 24 had an identifiable etiology usually related to a complication of Down syndrome, including neonatal hypoxia-ischemia, hypoxia from congenital heart disease, or infection. The infections were bacterial meningitis 3, viral meningoencephalitis in 1, brain abscess 1, febrile seizures 2. The patterns of the seizures in those of known etiology were generalized tonic-clonic in 18, infantile spasms in 2, myoclonic 2, absence 1, simple partial 3, and complex partial 1. Mixed partial and generalized seizures occurred in 2. Of 12 patients with seizures related to cardiovascular disease 4 died of complications of acute heart failure. Neonates with hypoxic ischemic injury had relatively poor outcomes. The authors recommend that all Down syndrome patients with seizures be thoroughly evaluated to determine the etiology. 
COMMENT:. Febrile seizures occurred in only two (0.9%) of the author’s patients during the susceptible age range. The relative rarity of febrile seizures in Down syndrome is contrasted with the relatively frequent occurrence of infantile spasms. Wisniewski KE, one of the authors, has previously studied the arrest of neurogenesis and synaptogenesis in brains of patients with Down syndrome . Long necked dendritic spines persist after birth suggesting a dysgenetic process, and neuronal membranes in Down syndrome are abnormally hyperexcitable. The mechanism of increased susceptibility to seizures in children with Down syndrome may involve an interplay between hyperexcitable membranes, altered dendritic spines, and reduction of inhibitory interneurons. The present study suggests that seizures in patients with Down syndrome are frequently caused by additional factors including hypoxia and infection.
The prevalence, onset, and type of seizure disorders and seizure control were studied in 405 individuals with Down syndrome aged six months to 45 years at the Departments of Pediatrics and Neurology, Rhode Island Hospital, Providence, RI. The prevalence of seizures in this group of patients was 8.1%. The onset of seizures occurred before one year of age in 40% and in the third decade of life in another 40%. Infantile spasms and tonic-clonic seizures with myoclonus were most common in the younger age group and partial simple or partial complex seizures and tonic-clonic seizures occurred in the older patients. A bimodal distribution of seizures in patients with Down syndrome was noted.