What are chromosomal abnormalities?

Chromosomal abnormalities are caused by errors in the number or structure of chromosomes. Some examples of chromosomal abnormalities cause by an error in the number of chromosomes are:

• Down’s syndrome or trisomy 21: The individual has an extra chromosome 21.
• Trisomy 18 or Edwards’s syndrome: The individual has an extra chromosome 18.
• Trisomy 13 or Patau syndrome: The individual has an extra chromosome 13
• Turner’s syndrome: Girls with Turner syndrome have one X chromosome and are missing all or part of the other X chromosome
• Klinefelter syndrome: Boys with Klinefelter syndrome have two, or occasionally more, X chromosomes along with their Y chromosome.

Some examples of chromosomal abnormaliities cause by an error in the structure of the chromosomes are:

• Cri-du-chat (cat cry) syndrome: the individual is missing the short arm on chromosome 5
• Prader-Willi syndrome: The individual has a deletion on chromosome 15

In humans, chromosomes contain the genetic information that makes us who we are. In general, human beings have 23 sets of chromosomes or 46 total, one set from each parent. The chromosomes are contained in all of our cells and are constantly being copied to produce more cells. However, this process does not occur without mistakes but our body had inherent mechanisms to detect mistakes and correct them. But from time to time, mistakes do go uncorrected. When this happens, this can lead to various diseases such as Down's syndrome, chronic lymphocytic leukemia, etc. There are various mistakes that can occur with this copying of our chromosomes such as:  a section of the chromosome is duplicated, deleted, a part of a chromosome can break off and attach to another. This events are called chromosomal abnormalities. This is what geneticists look for when doing genetic counseling as certain diseases have linked to specific chromosomal abnormalities that can be discovered when doing genetic testing.