Trisomy 21: The Most Common Cause Of Down Syndrome

Trisomy 21 or more commonly known as down syndrome is a condition in which an individual has a full or partial extra copy of chromosome 21 (What is Down Syndrome?, 2012). It was first described as a disorder in 1866 by doctor John Langdon Down and it is the most common cause of cognitive impairment (Heyn, 2014). Today there are three known types of down syndrome trisomy 21 or called nondisjunction, translocation, and mosaicism. Regardless of the type of down syndrome a child may have, they all have an extra portion of chromosome 21 present and the cause is still unknown today (What is Down Syndrome?, 2012). With the cause unknown many people have misconceptions or don’t understand what down syndrome is. That is why I chose to research down

Down syndrome results when abnormal cell division involving chromosome 21 occurs. The risk factors include the mother's maternal age and being carriers of genetic translocation (Mayo, 2014). According to Mayo (2014) a woman's chances of giving birth to a baby with down syndrome increase with age because older eggs have a greater risk of improper chromosome division. By age thirty-five the risk of conceiving a child with down syndrome is about 1 in 350. By age forty, the risk is about 1 in 100 and by age forty-five, the risk is about 1 in 30. However, due to higher birth rates in younger women 80% of children with down syndrome are born to women under thirty-five years of age (What is Down Syndrome?,

The parent is considered a balanced carrier and can have no signs or symptoms of down syndrome. Approximately 3% of the cases are linked to the father and between 10 and 15% of the cases are linked to the mother (Mayo, 2014). As of today there are no definite scientific research that indicates that down syndrome is caused by environmental factors or the parents’ activities before or during pregnancy (What is Down Syndrome?, 2012).
There are two types of test available to detect down syndrome during pregnancy, screening tests and diagnostic tests. A screening test estimates the chances of the baby having down syndrome but does not tell for sure whether or not the baby has it. Diagnostic test can provide a almost 100% accuracy of the diagnosis (What is Down Syndrome?, 2012). According to Mayo (2014), screening tests include the first trimester combined test, integrated screening test, and cell-free fetal DNA analysis. The first trimester combined test is done in two steps, blood test and