Is down syndrome always caused by a defect in the 21st chromosome???

could down syndrome be caused by any other chromosomal abnormalities?

Down's is always caused by a defect in the 21st chromosome. However, other abnormalities can come along with it which would lead to Downs and an additional diagnosis--this one is just always present... Hope I helped

NO, ANY OTHER ANORMALITY IN ANY OTHER CHROMOSOME CAUSES COMPLETELY DIFFERENT SYNDROME.

Down Syndrome is named after John Langdon Down, who was in charge of an asylum for mentally retarded children. He made a distinction between those who had hypothyroidism (cretinism) and those with what he termed 鈥淢ongoloids鈥? considering that they resembled people from Mongolia. This term caused problems and the name was dropped and his name, 鈥淒own鈥? was substituted during the 1960s. This British doctor was the first to describe the condition in 1887. It was not until 72 years later, in 1959, that an extra chromosome was identified as the cause. Chromosomes are thread-like structures composed of DNA and other proteins. They are present in every cell of the body and carry the genetic information needed for that cell to develop. Genes, which are units of information, are "encoded" in the DNA. Human cells normally have 46 chromosomes which can be arranged in 23 pairs. Of these 23, 22 are alike in males and females; these are called the "autosomes." The 23rd pair are the sex chromosomes ('X' and 'Y'). Each member of a pair of chromosomes carries the same information, in that the same genes are in the same spots on the chromosome. However, variations of that gene ("alleles") may be present. (Example: the genetic information for eye color is a "gene;" the variations for blue, green, etc. are the "alleles.") Human cells divide in two ways. The first is ordinary cell division ("mitosis"), by which the body grows. In this method, one cell becomes two cells which have the exact same number and type of chromosomes as the parent cell. The second method of cell division occurs in the ovaries and testicles ("meiosis") and consists of one cell splitting into two, with the resulting cells having half the number of chromosomes of the parent cell. So, normal eggs and sperm cells only have 23 chromosomes instead of 46. Though Down syndrome can't be prevented, it can be detected before a child is born. The health problems that can go along with DS can be treated, and there are many resources within communities to help kids and their families who are living with the condition. Normally, at the time of conception, a baby inherits genetic information from its parents in the form of 46 chromosomes: 23 from the mother and 23 from the father. In most cases of Down syndrome, however, a child gets an extra chromosome -21, or part of it - for a total of 47 chromosomes instead of 46. It's this extra genetic material that causes the physical and cognitive delays associated with DS. Although no one knows for sure why DS occurs and there's no way to prevent the chromosomal error that causes it, scientists do know that women age 35 and older have a significantly higher risk of having a child with the condition. At age 30, for example, a woman has less than a 1 in 1,000 chance of conceiving a child with DS. Those odds increase to 1 in 400 by age 35. By 42, it jumps to about 1 in 60.
Hope this helps
Matador 89

Down's syndrome is caused by a defect in the 21st chromosome. The 21st chromosome can be extra in number (non-disjunction), or the number of chromosomes can be normal and one 21st chromosome of the pair has extra genetic material added to it from another chromosome, often the 14th.This is known as translocation. The person can also be mosaic, with some cells having an extra 21st chromosome and others having a normal number.

down syndrome (Trisomy 21) is caused by an extra copy of the 21st chromosome, not a defect.
and no, if there was an extra copy of any other chromosome, it is a different Trisomy.

Down syndrome is caused by a triplication of the 21st chromosome. Plain and simple.