children s health issues
Down Syndrome (Trisomy 21)
Introduction
Down syndrome is a chromosome disorder caused by an extra chromosome 21 that results in intellectual disability and physical abnormalities. Down syndrome is caused by an extra chromosome 21. Children with Down syndrome have delayed physical and mental development, specific head and facial features, and are often short. Before birth, Down syndrome may be suspected based on ultrasonography or tests on the mother's blood and confirmed using Chorionic Villus Sampling and/or After birth, the diagnosis is suggested by the child’s physical appearance and is confirmed by finding an extra chromosome 21, usually by testing a blood sample. There is no cure for Down syndrome, but some specific symptoms and problems caused by the syndrome can be treated. Most children with Down syndrome survive to adulthood. (See also Overview of Chromosome and Gene Disorders .) Chromosomes are structures within cells that contain An extra chromosome, making three of the same chromosome (instead of the normal two), is called trisomy. The most common trisomy in a newborn is Down Syndrome (Trisomy 21) (an extra chromosome 21, which is the smallest human chromosome). It is possible for an embryo to have trisomy of any chromosome; however, an extra of one of the larger chromosomes is more likely to end in Trisomy 21 causes about 95% of the cases of Down syndrome. Thus, most people with Down syndrome have 47 chromosomes instead of the normal 46. However, about 4% of people with Down syndrome have 46 chromosomes, but the extra chromosome 21 is attached to another chromosome, creating an abnormal, but not extra, chromosome. This abnormal attachment is called translocation. The extra chromosome usually comes from the mother, and a couple's risk of having a baby with an extra chromosome gradually increases with the mother's age. Yet, because most births occur to younger women, just 20% of infants with Down syndrome are born to mothers older than 35. Women who have Down syndrome have a 50% chance of having a child with Down syndrome. However, there seems to be an increased risk of miscarriage of affected fetuses. Men with Down syndrome are usually infertile, unless they have mosaic Down syndrome. People who have mosaic Down syndrome have a mixture of two types of cells. Some of the cells contain the usual 46 chromosomes and some cells contain 47 chromosomes. The cells that have 47 chromosomes contain an extra chromosome 21. 