This book presents Down syndrome, which is the most common chromosomal disorder in humans, occurring at a rate of about 1 in 700 births. It describes the characteristic physical features caused by Down syndrome and the myriad of symptoms and health complications it brings, including heart defects, congenital vision and hearing loss, abnormalities of the musculoskeletal system, digestive problems, epilepsy, leukemia, an increased risk of infectious disease, dementia, and intellectual disability. Readers will learn about methods by which Down syndrome can be diagnosed prenatally or at birth, and the cause of Down syndrome as extra copies of the approximately 250 genes on chromosome 21. The book describes treatments and therapies for Down syndrome, and approaches to the education of children with it. Future prospects for the diagnosis and treatment of Down syndrome are presented, including experimental drugs, stem cell therapies, a process by which embryos produced in a clinical laboratory can be screened for Down syndrome before being used to establish a preg­nancy, and several Down syndrome gene therapy strategies.