Chromosome+21

= = __**EXCERPT FROM GENOME**__ "//In all other cases, having an extra copy of a whole// //chromosome so upsets the balance of the human genome that the// //body cannot properly develop at all. Children are occasionally born// //with an extra chromosome 13 or 18, but they never survive more// //than a few days. Children born with an extra chromosome 21 are// //healthy, conspicuously happy and destined to live for many years.// //But they are not considered, in that pejorative word, 'normal'. They// //have **Down syndrome** .//"

====Humans normally have 46 chromosomes in each cell, divided into 23 pairs. Two copies of chromosome 21, one copy inherited from each parent, form one of ﻿the pairs. Chromosome 21 is the smallest human chromosome, spanning about 47 million base pairs (the building blocks of DNA) and representing approximately 1.5 percent of the total DNA in cells. ==== =Identifying genes on each chromosome is an active area of genetic research. Because researchers use different approaches to predict the number of genes on each chromosome, the estimated number of genes varies. Chromosome 21 likely contains between 300 and 400 genes. These genes perform a variety of different roles in the body. = = =

1. AIRE (autoimmune regulator)

 * ====Cytogenetic Location: 21q22.3 ====
 * ====Molecular Location on chromosome 21: base pairs 45,705,762 to 45,718,109 ====
 * ====The AIRE gene provides insructions for making a protein called the autoimmune regulator. This is active primarily in the thymus which is a gland located behind the breastbone that plays an important role in the immune system function. Specifically, the thymus produces infection-fighting cells called T cells. For a person to remain healthy, immune system cells such as T cells must be able to identify and destroy potentially harmful invaders (such as bacteria and viruses) while sparing the body's normal tissues. The autoimmune regulator protein plays an important role in this process by helping T cells distinguish the body's own proteins from those of foreign invaders. When this system is working properly, it prevents the immune system from turning against itself and attacking healthy tissues by mistake. This abnormal reaction is called autoimmunity. In the thymus, the autoimmune regulator protein helps control the activity of certain genes that protect against autoimmunity. ====
 * ====//Autoimmune Polyglandular Syndrome Type 1// is caused by mutations in the AIRE gene. More than 60 mutations in the AIRE gene have been identified in people with autoimmune polyglandular syndrome, type 1. Some of these genetic changes lead to the production of an abnormally short, nonfunctional version of the autoimmune regulator protein. Other mutations change single protein building blocks (amino acids) in critical regions of the protein. AIRE mutations reduce or eliminate the function of the autoimmune regulator protein. Without enough of this protein, the immune system can malfunction, resulting in autoimmunity. ====

2. APP (amyloid beta A4 precursor protein)

 * Cytogenetic Location: 21q21.2 [[image:http://ambassadors.net/archives/images/chromosome21.jpg width="566" height="306" align="right"]]
 * ====Molecular Location on chromosome 21: base pairs 27,252,860 to 27,543,137 ====
 * ====The APP gene provides instructions for making a protein called amyloid precursor protein. This protein is found in many tissues and organs, including the brain and spinal cord (central nervous system). Little is known about the function of amyloid precursor protein. Researchers speculate that it may bind to other proteins on the surface of cells or help cells attach to one another. ====
 * ====Amyloid precursor protein is cut by enzymes to create smaller fragments (peptides), some of which are released outside the cell. Two of these fragments are called soluble amyloid precursor protein (sAPP) and amyloid beta peptide. Recent evidence suggests that sAPP has growth-promoting properties and may play a role in the formation of nerve cells (neurons) in the brain both before and after birth. Other functions of sAPP and amyloid beta peptide are under investigation. ====
 * ====//[|Alzheimer disease]// - caused by mutations in the APP gene. More than 25 different mutations in the APP gene can cause early-onset Alzheimer disease. These mutations are responsible for 10 percent to 15 percent of all early-onset cases of the disorder. The most common APP mutation changes one of the protein building blocks (amino acids) in the amyloid precursor protein. This mutation replaces the amino acid valine with the amino acid isoleucine at protein position 717 (written as Val717Ile or V717I). Mutations in the APP gene can lead to an increased amount of the amyloid beta peptide or to the production of a slightly longer and stickier form of the peptide. When these protein fragments are released from the cell, they can accumulate in the brain and form clumps called amyloid plaques. These plaques are characteristic of Alzheimer disease. A buildup of toxic amyloid beta peptide and amyloid plaques may lead to the death of neurons and the progressive signs and symptoms of this disorder. ====
 * ====The E22Q mutation likely affects processing of this protein, leading to the formation of amyloid plaques in brain tissue and the walls of blood vessels that serve the brain. ====

3. CSTB <span style="font-family: Arial,Helvetica,sans-serif; font-weight: normal;">(cystatin B or stefin B)

 * ====<span style="font-family: Arial,Helvetica,sans-serif; line-height: 21px;">Cytogenetic Location: 21q22.3 ====
 * ====<span style="font-family: Arial,Helvetica,sans-serif; font-size: 14px; line-height: 21px;">Molecular Location on chromosome 21: base pairs 45,193,830 to 45,196,258 ====
 * ====<span style="font-family: Arial,Helvetica,sans-serif; line-height: 21px;">The CSTB gene provides instructions for making a protein called cystatin B. This protein reduces the activity of (inhibits) enzymes called cathepsins. Cathepsins help break down certain proteins in the lysosomes (compartments in the cell that digest and recycle materials). While the specific function of cystatin B is unclear, it may help protect the cells' proteins from cathepsins that leak out of the lysosomes. ====
 * ====<span style="font-family: Arial,Helvetica,sans-serif; font-size: 14px; line-height: 21px;">One region of the CSTB gene has a particular repeating sequence of 12 DNA building blocks (nucleotides) written as CCCCG-CCCCG-CG. This sequence, called a dodecamer repeat, is usually repeated two or three times within a part of the gene that helps regulate cystatin B protein production. ====
 * ====<span style="font-family: Arial,Helvetica,sans-serif; line-height: 21px;">Unverricht-Lundborg disease is caused by mutations in the CSTB gene.In almost all affected individuals, Unverricht-Lundborg disease is caused by an increased number of copies (expansion) of the dodecamer repeat in the CSTB gene. Most people with this disorder have more than 30 repeats of the dodecamer sequence in both copies of the CSTB gene. In a small number of individuals, one copy of the CSTB gene has the expanded dodecamer repeat while the second copy carries one of nine other identified mutations. Some of these mutations substitute one protein building block (amino acid) for another amino acid in the cystatin B protein. Others result in a shortened protein that may function improperly or not at all, or cause the protein to be pieced together incorrectly. Only one individual with Unverricht-Lundborg disease has been reported to have mutations other than the dodecamer repeat expansion in both copies of the gene in each cell. ====

====//Down Syndrone// - Is the abnormality of having an extra 21st chomosome in anyones DNA if its present. Down syndrone babies are generally born to elder moms. The chances of having a baby with Down syndrone rise rapidly as the mother ages, age of twenty would be 1 in 2300, and age of forty 1 in 400. "====

<span style="background-color: transparent; color: #000000; display: block; font-family: Arial; text-align: left; text-decoration: none;">FIGURE 1<span style="font-family: arial,helvetica,sans-serif;">shows the <span style="font-family: Arial,Helvetica,sans-serif; font-size: 14px; line-height: 21px;">estimated risk of Down syndrome according to maternal age. Data from reference 8. <span style="font-family: Arial,Helvetica,sans-serif; font-size: 14px; line-height: 21px;">There are three types of Down Syndrome. An error in cell division is the most common type, which results in 3 21 chromosomes instead just two. The other name for this genetic disorder, Trisomy 21. The other two types of this disorder are Mosaic and Translocation Down Syndrome. It is very important to remember that Down Syndrome is not caused by anything the mother did or did not do before or during the pregnancy. Children with down syndrome are mostly from mothers who were thrity-five or older, but not always it could happen to a younger mother. Down syndrome can be determined at a young age.Usually children with down syndrome have flat faces, large eyes and, a small nose along with other features. The incidence of Down syndrome in the United States is estimated to be 1 in every 800 - 1,000 live births. Of all children born in this country annually, approximately 5,000 will have Down syndrome. In the United States there are approximately 1/4 million families affected by Down syndrome. While the likelihood of giving birth to a child with Down syndrome increases with maternal age; nevertheless, 80% of babies with Down syndrome are born to women under 35 years of age, as women in that age group give birth to more babies overall. Each individual has his/her own unique personality, capabilities and talents. 30% - 50% of the individuals with Down syndrome have heart defects and 8% - 12% have gastrointestinal tract abnormalities present at birth. Most of these defects are now correctable by surgery. <span style="background-color: transparent; color: #810081; display: block; font-family: 'Times New Roman'; font-size: 16px; text-align: left;">

**<span style="font-family: Arial,Helvetica,sans-serif; font-size: 14px;">Eugenics "The Genome", Matt Ridley, 287 **
====<span style="font-family: Arial,Helvetica,sans-serif; font-size: 14px; line-height: 19px;">**Chromosome 21 - Genetics Home Reference. (n.d.). //Genetics Home Reference - Your guide to understanding genetic conditions//. Retrieved April 13, 2011, from http://ghr.nlm.nih.gov/chromosome/21** ==== ====**<span style="color: black; font-family: Arial,sans-serif; font-size: 11.5pt;">APP - amyloid beta (A4) precursor protein - Genetics Home Reference. (n.d.). ** **//<span style="color: black; font-family: Arial,sans-serif; font-size: 11.5pt;">Genetics Home Reference - Your guide to understanding genetic conditions //**. **Retrieved April 24, 2011, from** **<span style="color: black; font-family: Arial,sans-serif; font-size: 11.5pt;">[] **==== ====<span style="font-family: Arial,Helvetica,sans-serif; line-height: 21px;">**CSTB - cystatin B - Genetics Home Reference. (n.d.). //Genetics Home Reference - Your guide to understanding genetic conditions//. Retrieved April 13, 2011, from http://ghr.nlm.nih.gov/gene/CSTB** ==== ====<span style="font-family: Arial,Helvetica,sans-serif; line-height: 19px;">**AIRE - autoimmune regulator - Genetics Home Reference. (n.d.). //Genetics Home Reference - Your guide to understanding genetic conditions//. Retrieved April 13, 2011, from http://ghr.nlm.nih.gov/gene/AIRE** ====