Down syndrome (DS or DNS) or Down's syndrome and also known as trisomy 21, is a genetic disorder caused by the presence of all or part of a third copy of chromosome 21. It is a genetic disorder. The parents of the affected individual are typically genetically normal. Those who have one child with Down syndrome have about a 1% risk of having a second child with the syndrome, if both parents are found to have normal karyotypes. It is typically associated with physical growth delays, characteristic facial features, and mild to moderate intellectual disability. The average IQ of a young adult with Down syndrome is 50, equivalent to the mental age of an 8- or 9-year-old child, but this varies widely. Down syndrome can be identified during pregnancy by prenatal screening followed by diagnostic testing, or after birth by direct observation and genetic testing. Since the introduction of screening, pregnancies with the diagnosis are often terminated. Regular screening for health problems common in Down syndrome is recommended throughout the person's life. Education and proper care have been shown to improve quality of life. Some children with Down syndrome are educated in typical school classes, while others require more specialized education. Some individuals with Down syndrome graduate from high school and a few attend post-secondary education. In adulthood, about 20% in the United States do paid work in some capacity with many requiring a sheltered work environment. Support in financial and legal matters is often needed. Life expectancy is around 50 to 60 years in the developed world with proper health care.
Down syndrome is one of the most common chromosome abnormalities in humans, occurring in about one per 1000 babies born each year. In 2013 it resulted in 36,000 deaths down from 43,000 deaths in 1990. It is named after John Langdon Down, the British doctor who fully described the syndrome in 1866. Some aspects of the condition were described earlier by Jean-Étienne Dominique Esquirol in 1838 and Édouard Séguin in 1844. The genetic cause of Down syndrome—an extra copy of chromosome 21—was identified by French researchers in 1959. Globally, as of 2010, Down syndrome occurs in about 1 per 1000 births and results in about 17,000 deaths. More children are born with Down syndrome in countries where abortion is not allowed and in countries where pregnancy more commonly occurs at a later age.
About 1.4 per 1000 live births in the United States and 1.1 per 1000 live births in Norway are affected. In the 1950s, in the United States, it occurred in 2 per 1000 live births with the decrease since then due to prenatal screening and abortions. The number of pregnancies with Down syndrome is more than two times greater with many spontaneously aborting. It is the cause of 8% of all congenital disorders. Maternal age affects the chances of having a pregnancy with Down syndrome. At age 20, the chance is one in 1441; at age 30, it is one in 959; at age 40, it is one in 84; and at age 50 it is one in 44. Although the probability increases with maternal age, 70% of children with Down syndrome are born to women 35 years of age and younger, because younger people have more children. The father's older age is also a risk factor in women older than 35, but not in women younger than 35, and may partly explain the increase in risk as women age. As it is a genetic disorder, consulting a doctor regularly is the only treatment. Utmost care should be taken to that patient. A group of medical specialists like Primary care pediatrician, Pediatric cardiologist, Pediatric gastroenterologist, Pediatric endocrinologist, Developmental pediatrician, Pediatric neurologist, Pediatric ear, nose and throat (ENT) specialist, Pediatric eye doctor (ophthalmologist), Audiologist, Physical therapist, Speech pathologist, and an Occupational therapist.