Down syndrome, also known as trisomy 21, is a genetic disorder caused by the presence of all, or part of a third copy of chromosome 21.
A genetic disorder is a genetic problem caused by one or more abnormalities in the genome, especially a condition that is present from birth.
A trisomy is a type of polysomy in which there are three instances of a particular chromosome, instead of the normal two.
A gene is a locus of DNA which is made up of nucleotides and is the molecular unit of heredity.
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It is typically associated with physical growth delays, characteristic facial features, and mild to moderate intellectual disability.
Intellectual disability, also known as general learning disability, and mental retardation, is a generalized neurodevelopmental disorder characterized by significantly impaired intellectual and adaptive functioning.
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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 can vary widely.
An intelligence quotient is a total score derived from one of several standardized tests designed to assess human intelligence.
The parents of the affected individual are typically genetically normal.
Genetics is the study of genes, genetic variation, and heredity in living organisms.
The extra chromosome occurs by random chance.
The risk increases from less than 0.1% in 20-year-old mothers to 3% in those age 45.
There is no known behavioral activity or environmental factor that changes the risk.
Down syndrome can be identified during pregnancy by prenatal screening followed by diagnostic testing, or after birth by direct observation and genetic testing.
Prenatal diagnosis and prenatal screening are aspects of prenatal care that focus on detecting anatomic and physiologic problems with the zygote, embryo, or fetus as early as possible, either before gestation even starts or as early in gestation as practicable.
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.
There is no cure for Down syndrome.
Education and proper care have been shown to improve quality of life.
Quality of life is the general well-being of individuals and societies, outlining negative and positive features 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.
Higher education, post-secondary education, or third level education is an optional final stage of formal learning that occurs after 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.
A developed country, industrialized country, or "more economically developed country", is a sovereign state that has a highly developed economy and advanced technological infrastructure relative to other less industrialized nations.
Down syndrome is one of the most common chromosome abnormalities in humans.
It occurs in about one per 1000 babies born each year.
In 2013, Down syndrome was present in 8.5 million individuals and resulted in 36,000 deaths down from 43,000 deaths in 1990.