DOWN SYNDROME Essays - Chromosomal Abnormalities, Cytogenetics

DOWN SYNDROME Essays - Chromosomal Abnormalities, Cytogenetics DOWN SYNDROME By; Theodore Kirk INTRODUCTION In every cell in the human body there is a nucleus, where genetic material is stored in genes. Genes carry the codes responsible for all our inherited traits and are grouped along rod-like structures called chromosomes. Typically, the nucleus of each cell contains 23 pairs of chromosomes, half of which are inherited from each parent. Down syndrome occurs when an individual has a full or partial extra copy of chromosome 21. The cause of the extra full or partial chromosome is still unknown. Maternal age is the only factor that has been linked to an increased chance of having a baby with Down syndrome resulting from nondisjunction or mosaicism. However, due to higher birth rates in younger, 80% of children with Down syndrome are born to women under 35 years of age. In my research paper I will be taking a closer look at the genetic disorders cause and effect. What is Down syndrome? Overview Down syndrome is a chromosomal condition that is associated with intellectual disability, a characteristic facial appearance, and weak muscle tone in infancy. All affected individuals experience cognitive delays, but the intellectual disability is usually mild to moderate. Case in point: I had a set of fraternal twins (boy/girl), and my son was Down syndrome and so this is why this subject is of great importance to me. Babies that are born with this genetic disorder may have a variety of birth defects. About half of all affected children are born with heart defect. Such as the case with my son, he was born with two holds in his heart and also suffered with digest abnormalities. Children with Down syndrome have increased risk of developing several medical conditions. These include gastro esophageal reflux, which is a backflow of acidic stomach contents into the esophagus, and celiac disease, which is an intolerance of a wheat protein called gluten. About 15% of children with Down syndrome have an underactive thyroid gland. The thyroid gland is a butterfly-shaped organ in the lower neck that produces hormones. Individuals with Down syndrome also have an increased risk of hearing and vision problems. Additionally, a small percentage of children with Down syndrome develop cancer of blood-forming cells (leukemia). Delayed development and behavioral problems are often reported in children with Down syndrome. Affected individuals speech and language develop later and more slowly than in children without Down syndrome, and affected individual speech may be more difficult to understand. Behavioral issues can include attention problems, obsessive/compulsive behavior, and stubbornness or tantrums. A small percentage of people with Down syndrome are also diagnosed with developmental conditions called autism spectrum disorders, which affect communication and social interaction. People with Down syndrome often experience a gradual decline in thinking ability (cognition) as they age, usually starting around age 50. Down syndrome is also associated with an increase risk of developing Alzheimer disease, a brain disorder that result in a gradual loss of memory, judgment, and ability to function. Cause for Down syndrome In 1959, the French physician Jerome Jejune identified Down syndrome as a chromosomal condition. Instead of the usual 46 chromosomes present in each cell, Lejeune observed 47 in the cells of individuals with Down syndrome. It was later determined that an extra partial or whole copy of chromosome 21 resulted in the characteristics associated with Down syndrome. In the year 2000, an international team of scientists successfully identified and catalogued each of the approximately 329 genes on chromosome 21. This accomplishment opened the door to great advances in Down syndrome research. There are three types of Down syndrome: trisomy 21 (nondisjunction), translocation and mosaicism. My research focus will be on trisomy 21, because this one was my sons condition and it accounts for 95% of cases. TRISOMY 21 (NONDISJUNCTION) Down syndrome is usually caused by an error in cell division called nondisjunction. Nondisjunction results in early embryo with three copies of chromosome 21 instead of the usual two. Prior to or at conception, a pair of 21st chromosomes in either the sperm or egg fails to separate. As the embryo develops, the extra chromosome is replicated in every cell of the body. DOWN SYNDROME DIAGNOSED There are two categories of tests for Down syndrome that can be performed before a baby is born: screening tests and diagnostic tests.