Dec 3 2014
Down syndrome (DS) or Trisomy 21 is a complex developmental genetic disorder in which a person has 47 chromosomes instead of 46. Normally, a fertilized egg has 23 pairs of chromosomes. But in most cases, people living with Down syndrome have an extra copy of chromosome 21 also known as Trisomy 21, which is responsible for 95% Down syndrome cases and most common genetic cause of human mental retardation, with an incidence of 1-600/1-1000 live births. It is also responsible for premature pregnancy failure. It is the leading cause of cognitive impairment. Down syndrome occurs because of an abnormality characterized by an extra copy of ...view middle of the document...
When cells divide, the chromosomes in each are supposed to split apart and move to different places in the dividing cell, so that each new cell will have a single set of chromosomes. Nondisjunction occurs when one pair of chromosomes doesn't divide, meaning that in the resulting divided cells, one cell will have 23 chromosomes and the other will have 22. Ninety-five percent of Down syndrome cases are caused by a sperm or an egg with an abnormal number of chromosomes merging with its mate, creating a fertilized egg which also has an abnormal number of chromosomes.
Down syndrome can be diagnosed in two categories of tests that can be performed before a baby is born: screening tests and diagnostic tests. Prenatal screens estimate the chance of the fetus having Down syndrome. Most of these tests only provide a probability. Diagnostic tests can provide a definitive diagnosis with almost 100% accuracy. Most screening tests involve a blood test and an ultrasound (sonogram). The blood tests (or serum screening tests) measure quantities of various substances. These blood tests are often performed in conjunction with a detailed sonogram to check for "markers" (characteristics that some researchers feel may have a significant association with Down syndrome. People with Down syndrome have a distinct facial appearance. A person with Down syndrome has some distinct facial features which can include almond shaped eyes, light-colored spots in their eyes a small, somewhat flat nose, a small mouth with a protruding tongue, and small ears. They also have round faces and somewhat flatter profiles. Other physical features seen in Down syndrome include a single crease across the palms of their hands, short stubby fingers and a fifth finger or pinky that curves inward. They have a smaller head that is somewhat flattened in the back and straight hair that is fine and thin. In general, they tend to have short stature with short limbs, and can have a larger than normal space between the big and second toes.
Some of the medical issues associated with Down syndrome are Children with Down syndrome are at an increased risk for a wide range of medical problems. These potential problems include congenital heart defects, increased susceptibility to infection, respiratory problems, gastrointestinal disorders, and childhood leukemia. However, not every baby with Down syndrome develops health problems and most of these health problems are now treatable. Down's syndrome will also affect your child's development. The physical development of children with Down's syndrome tends to be slower than that of other children of a similar age. They may also be slower to develop socially and mentally. It might take them longer to learn to speak, or to read. All people with Down's syndrome will have some degree of learning disability, although some people are more severely affected than others. If your child has Down's syndrome, it will not stop them from developing at all. Many people...