C+&+GD+--+Trisomy+21

Cancer & Genetic Defects -
﻿Trisomy 21


 * Down's Syndrome**

Down syndrome is a genetic condition in which a person has 47 chromosomes instead of the usual 46. In most cases, Down syndrome occurs when there is an extra copy of chromosome 21. This form of Down syndrome is called Trisomy 21. The extra chromosome causes problems with the way the body and brain develop. It is named after John Langdon Down, the British physician who described the syndrome in 1866. Many of the common physical features of Down syndrome may also appear in people with a standard set of chromosomes, including microgenia (an abnormally small chin), an unusually round face, macroglossia (protruding or oversized tongue), an almond shape to the eyes caused by an epicanthic fold of the eyelid, upslanting palpebral fissures (the separation between the upper and lower eyelids), shorter limbs, a single transverse palmar crease (a single instead of a double crease across one or both palms), poor muscle tone, and a larger than normal space between the big and second toes.

In Down's Syndrome (Trisomy 21), 95% of all cases are caused by one cell having two 21st chromosomes instead of one. So the resulting fertilized egg has three 21st chromosomes.

Down Syndrome Karyotype

Health concerns for individuals with Down syndrome include:
 * Risks of Down's Syndrome**
 * a higher risk for congenital heart defects
 * gastroesophageal reflux disease
 * recurrent ear infections
 * obstructive sleep apnea
 * and thyroid dysfunctions

The following diseases are some of those related to genes on chromosome 21:
 * Chromosome 21 - Associations**
 * Alzheimer's disease
 * Amyotrophic lateral sclerosis
 * Down syndrome
 * Erondu-Cymet Syndrome
 * Holocarboxylase synthetase deficiency
 * Homocystinuria
 * Jervell and Lange-Nielsen syndrome
 * Leukocyte adhesion deficiency
 * Majewski osteodysplastic primordial dwarfism type II
 * Nonsyndromic deafness

Also, rearrangements of genetic material between chromosome 21, and other chromosomes, have been linked to several types of cancer.