DOWN'S SYNDROME
Down syndrome (DS) or Down's syndrome, also known as trisomy 21, is a chromosomal condition caused by the presence of all or part of a third copy of chromosome 21. Down syndrome is the most common chromosome abnormality in humans. It is typically associated with a delay in cognitive ability (mental retardation, or MR) and physical growth, and a particular set of facial characteristics. The physical features and medical problems associated with Down syndrome can vary widely from child to child. While some kids with DS need a lot of medical attention, others lead healthy lives.
The average IQ of young adults with Down syndrome is around 50, whereas young adults without the condition typically have an IQ of 100. (MR has historically been defined as an IQ below 70.) A large proportion of individuals with Down syndrome have a severe degree of intellectual disability.
Though Down syndrome can't be prevented, it can be detected before a child is born. The health problems that may go along with DS can be treated, and many resources are available to help kids and their families who are living with the condition. [1]
Down syndrome is named after Doctor Langdon Down, who in 1866 first described the syndrome as a disorder. Although Doctor Down made some important observations about Down syndrome, he did not correctly identify what causes the disorder. It wasn't until 1959 that scientists discovered the genetic origin of Down syndrome. [2]
TYPES OF DOWN SYNDROME
Three Types Of Down Syndrome:
1. NONDISJUNCTION - This is the most common reason. Cells containing 46 chromosomes are split equally to create eggs and sperm, which then contain 23 chromosomes. Nondisjunction means that the cells did not equally divide the genetic information. This creates a sperm or egg that contains 24 chromosomes with two copies of the 21st chromosome. That egg/sperm joins with a typical egg/sperm with 23 chromosomes making a cell that has 47 chromosomes and three copies of the 21st chromosome. This is known as Trisomy 21. This is a random occurrence.
2. TRANSLOCATION - The egg or sperm have 23 chromosomes, however part of the 21st chromosome has attached itself to one of the other chromosomes during the division processes that occur when the egg or sperm were made. Therefore, even though they have the right number of chromosomes there is actually extra 21st chromosome material. This can be an inherited condition, which increases your risk of having another child with Down syndrome. Both parents will be tested.
3. MOSAIC - Not all of the cells are affected, so the baby would have cells with 46 chromosomes and also 47. This can occur in two ways. The baby either started with 46 chromosomes, however nondisjunction occurred with further cell division in only part of the cell lines creating some cells with three copies of the 21st chromosome. The other way is that the baby started out as trisomy 21 and nondisjunction occurred creating cells that now contain 46 chromosomes. This is a random occurrence.
The average IQ of young adults with Down syndrome is around 50, whereas young adults without the condition typically have an IQ of 100. (MR has historically been defined as an IQ below 70.) A large proportion of individuals with Down syndrome have a severe degree of intellectual disability.
Though Down syndrome can't be prevented, it can be detected before a child is born. The health problems that may go along with DS can be treated, and many resources are available to help kids and their families who are living with the condition. [1]
Down syndrome is named after Doctor Langdon Down, who in 1866 first described the syndrome as a disorder. Although Doctor Down made some important observations about Down syndrome, he did not correctly identify what causes the disorder. It wasn't until 1959 that scientists discovered the genetic origin of Down syndrome. [2]
TYPES OF DOWN SYNDROME
Three Types Of Down Syndrome:
1. NONDISJUNCTION - This is the most common reason. Cells containing 46 chromosomes are split equally to create eggs and sperm, which then contain 23 chromosomes. Nondisjunction means that the cells did not equally divide the genetic information. This creates a sperm or egg that contains 24 chromosomes with two copies of the 21st chromosome. That egg/sperm joins with a typical egg/sperm with 23 chromosomes making a cell that has 47 chromosomes and three copies of the 21st chromosome. This is known as Trisomy 21. This is a random occurrence.
2. TRANSLOCATION - The egg or sperm have 23 chromosomes, however part of the 21st chromosome has attached itself to one of the other chromosomes during the division processes that occur when the egg or sperm were made. Therefore, even though they have the right number of chromosomes there is actually extra 21st chromosome material. This can be an inherited condition, which increases your risk of having another child with Down syndrome. Both parents will be tested.
3. MOSAIC - Not all of the cells are affected, so the baby would have cells with 46 chromosomes and also 47. This can occur in two ways. The baby either started with 46 chromosomes, however nondisjunction occurred with further cell division in only part of the cell lines creating some cells with three copies of the 21st chromosome. The other way is that the baby started out as trisomy 21 and nondisjunction occurred creating cells that now contain 46 chromosomes. This is a random occurrence.