Overview
Chromosomal disorders, alterations, and aberrations are the root cause of numerous genetic disorders and traits. Chromosomal disorders frequently lead to birth defects and congenital abnormalities that can develop throughout a person's lifetime.
What is a chromosome?
Genes are made up of chromosomes, which are the body's genetic building blocks. Genes are the distinctive instructions that inform the body about how to develop and work. They regulate physical and physiological traits like blood type, eye and hair colour, susceptibility to certain diseases, etc.
What is Chromosomal Disorder?
Though there are several varieties of chromosomal disorders, they can generally be divided into the two following basic types:
Numerical disorders
In the case of numerical disorders, a person may have one missing chromosome from their pair of chromosomes, and then the condition is known as monosomy. On the other hand, when a person has more than two chromosomes instead of the normal two, the condition is referred to as trisomy.
Structural Disorders: There are several ways the structure of a chromosome can become changed.
- Deletion: When this occurs, a section of the chromosome gets omitted or missing.
- Duplication: Here, a part of a chromosome's section gets duplicated, causing the development of extra genetic materials.
- Translocation: In this phenomenon, a part of one chromosome moves to another. The process of translocation happens via two processes. One is when segments from two separate chromosomes get switched in a process called reciprocal translocation. Another is when a complete chromosome attaches to another one at the centromere, a process known as Robertsonian translocation.
- Inversion: When this happens, a chromosomal segment brakes off, turns inside out, and then reattaches. Due to this, the genetic code gets reversed.
- Rings: In this occurrence, a part of a chromosome brakes off and forms a ring or a circle. This may happen with or without losing the genetic materials.
What are some examples of chromosomal disorders?
Some of the most common chromosomal disorders are:
- Jacobsen syndrome
- Klinefelter's syndrome
- XYY syndrome and XXX syndrome
- Cri du chat syndrome
- Down's syndrome
- Turner syndrome
- Edward's syndrome
- Wolf-Hirschhorn syndrome
- Patau syndrome
How do chromosomal disorders happen?
Chromosomal disorders are caused by common cell division errors. The two distinct methods of cell division are meiosis and mitosis.
- The original cell is duplicated during mitosis. When a single cell with 46 chromosomes divides, two cells, each with 46 chromosomes, are produced. The body goes through this kind of cell division all over, with the exception of the reproductive organs. This is how most of the cells that make up our body are made and replaced.
- Meiosis creates cells with 23, rather than the usual 46, chromosomes. This type of cell division occurs in the reproductive organs and helps in the development of the egg and sperm.
Both of these procedures generally produce cells with the appropriate number of chromosomes. However, mistakes in cell division can develop cells with either an abnormally high or low number of copies of a particular chromosome.
Below are some other factors that can enhance the risk of chromosomal disorders:
- Maternal Age: When a woman is born, she has all the eggs she will ever have in her lifetime. Some researchers believe that as those eggs age, their genetic makeup may change. Older women are more prone than younger ones to develop chromosomal disorders during pregnancy.
- Environment: Even though there is no conclusive evidence that specific environmental factors can cause chromosomal disorders, it's still possible that the environment may play a role in the development of such aberrations.
Conclusion
Chromosomal disorders can be identified by examining the karyotypes of the chromosomes in a sample of cells. If any chromosomal disorders are found, then physicians provide counselling and guidance to the parents or families whose children are at risk of acquiring a genetic disorder.
In this syndrome, a chromosome remains missing and is an example of monosomy. Turner syndrome causes a woman to have only one X chromosome at birth which causes her to be shorter than average, unable to have children, etc.
Down syndrome, is characterized by a person having a mental disability, learning difficulties, a distinctive facial appearance, and also decreased muscular tone (hypotonia) in infancy, etc.
Down syndrome is also known as trisomy 21, in which an individual has three copies of chromosome 21 rather than the normal two.
Most chromosomal disorders occur accidentally in either the egg or sperm. In these conditions, the disorders are present in every single cell of the newborn child. Certain diseases, however, may manifest after conception, at which point some cells of the child are affected while others are unaffected.
Chromosomal conditions can either develop "de novo" or be passed down from a parent (such as a translocation). This is why when a child is found to have a chromosomal disorder, chromosomal exams on the parents are routinely done.
