Down syndrome (DS) is caused by trisomy 21, and is one of the most common chromosomal disorders and etiology of congenital mental retardation. Down syndrome increases the risk of developing acute megakaryoblastic anemia (AMKL) and acute lymphoblastic leukemia (ALL). Approximately 10% of newborns with DS present with transient myeloproliferative disorder (TMD), and 10-20% with TMD develop AMKL before 4 years of age. People with DS have a greatly increased risk of early-onset Alzheimer disease (AD). Epileptic seizures occur in 5-10% of DS patients and prevalence increases with age. Children with DS may exhibit various seizures types, including myoclonic, atonic, tonic-clonic, and, rarely, partial seizures. There is no etiologic treatment for DS, but supportive care and treatment of associated conditions such as cardiac and gastrointestinal abnormalities are indicated. Approximately one-third of patients die in infancy and 50% during the first 5 years from cardiac and respiratory infections.