Down Syndrome
Uploaded by Whittee999 on May 13, 2001
Sometimes when meiosis ( the division of reproductive cells ) occurs, chromosomes may be lost, left behind, or too many may be passed on, resulting in the birth of a child with a genetic or congenital defect or disease. One of the most common of these genetic disorders is Down syndrome. This disorder takes its name from Dr. Langdon Down, who was the first to describe it formally, in 1866.
Down syndrome is a condition marked by abnormal physical and mental development that is caused by a genetic defect. This genetic defect is caused by an extra chromosome. People born with Down syndrome have 47 chromosomes compared to the normal amount of 46, 23 chromosomes inherited from each parent. This extra chromosome originates more often in the mother's egg than the father's sperm. Chromosomes are individual, large DNA molecules in a cell nucleus. They contain the genes along with structures that hold the DNA and aid it in expressing heredity by orchestrating cellular operations.
Down syndrome is one of the most common chromosomal abnormalities, occurring in about 1 out of 800 births. However, the frequency of the disorder varies greatly according to the age of the mother. For women in their twenties the rate is 1 in 2,000 but it rises steeply to 1 in 100 by the time a woman reaches 40.
Down syndrome is usually recognized soon after birth because of characteristic facial features such as a flattened nose, upward slanting of the eyes, a large tongue that often protrudes from a small mouth, a small, rounded head, and a short stature. Other symptoms that might only be noticed by doctors include congenital malformations of the heart of gastrointestinal system, flabby muscle tone and poor coordination due to poor control over the motor nerves, poorly functioning endocrine glands, narrow ear canals, low resistance to infection, weak vision, and misshapen teeth with thin enamel. All children with Down syndrome also have learning difficulties to some extent and there is a large variation in handicap. In some cases Down syndrome may be discovered before birth through a test known as amniocentesis in which fluid is taken from around the baby and the fetal cells are examined for the extra chromosome.
People with Down syndrome are usually exceptionally happy, gentle, and loving. As children, they need loving care and extra attention to make sure that their minds are stimulated. Special teaching is...