Difference Between Monogenic Disorders and Chromosomal Disorders

The key difference between monogenic disorders and chromosomal disorders is that monogenic disorders are disorders associated with single genes, while chromosomal disorders are diseases associated with abnormalities in chromosomes and part of the chromosomes.

Gene is the structural and functional unit of heredity. Gene has a specific nucleotide sequence. There are thousands of genes in chromosomes. Chromosomes are thread-like structures composed of nucleotide sequences or DNA. A mutation in the nucleotide sequence of a gene can cause diseases. They are known as monogenic disorders. Sickle cell anaemia is an example of a monogenic disorder. Disorders can also occur when nucleotide sequence of a chromosome or a part of a chromosome is changed or missing. We call such disorders as chromosomal disorders. Down syndrome is an example of a chromosomal disorder. Chromosomal disorders may be a mutation of several genes.

CONTENT

1. Overview and Key Difference
2. What are Monogenic Disorders
3. What are Chromosomal Disorders
4. Similarities Between Monogenic Disorders and Chromosomal Disorders
5. Side by Side Comparison – Monogenic Disorders vs Chromosomal Disorders in Tabular Form
6. Summary

What are Monogenic Disorders?

A gene is a segment of DNA which has a specific nucleotide sequence. In this nucleotide sequence, crucial information is hidden in order to make a protein. A mutation is a nucleotide sequence change which can be deleterious. It can produce a different protein or no protein. A disease associated with a single gene mutation is known as a monogenic disorder. A change in a single gene within the genome does not change the chromosome structure or number. But it can result in genetic disorders such as Osteogenesis Imperfecta (OGI), Retinoblastoma (RB), Cystic Fibrosis, Thalassemia, Fragile X Syndrome (FXS), Hypophosphatemia, Hemophilia and Ichthyosis, etc.

Majority of monogenic disorders are rare. They can be inherited to the next generations as well. They are mainly autosomal dominant, autosomal recessive or X linked. Affected people show a decrease in fitness. Gene therapy, stem cell transplantation and bone marrow transplant are several treatments for monogenic disorders.

What are Chromosomal Disorders?

Chromosomal disorders are genetic disorders caused by chromosomal abnormalities. A part of the chromosome can be missing or extra. This type of changes can cause deleterious effects since the missing part might contain important genes. Moreover, extrachromosomal parts can add extra genes to the genome. Similar to structural changes in chromosomes, the total number of chromosomes in a cell can also be changed.

Figure 01: Down Syndrome Karyotype

Down syndrome is one such disorder caused due to trisomy of chromosome number 21. Chromosomal disorders mainly occur as a result of an error in cell division following meiosis or mitosis. These disorders are detected by the examination of an individual’s karyotype. Turner’s syndrome is another chromosomal disorder caused due to monosomy of the X chromosome. Wolf-Hirschhorn syndrome and Jacobsen syndrome are two chromosomal disorders caused by deletions of some parts of the chromosomes.

What are the Similarities Between Monogenic Disorders and Chromosomal Disorders?

• Monogenic disorders and chromosomal disorders are genetic disorders.
• They occur as a result of an abnormality in the genome.
• These disorders can transmit from parents to offspring.

What is the Difference Between Monogenic Disorders and Chromosomal Disorders?

A single mutated gene is responsible for a monogenic disorder while abnormalities in structure or number of chromosomes are responsible for chromosomal disorders. Thus, this is the key difference between monogenic disorders and chromosomal disorders.

The below infographic shows more differences between monogenic disorders and chromosomal disorders in tabular form.

Summary – Monogenic Disorders vs Chromosomal Disorders

Monogenic disorders are genetic diseases caused by single mutated genes. Chromosomal disorders are genetic diseases caused by abnormalities in chromosomal number or structures. So, this is the key difference between monogenic disorders and chromosomal disorders. Monogenic disorders do not change the structure or number of chromosomes.

Reference:

1. “Genetic Disorder.” Wikipedia, Wikimedia Foundation, 18 Jan. 2021, Available here.
2. “Monogenic Disorders (Single Abnormal Gene).” University of Leicester, 9 Aug. 2011, Available here.

Image Courtesy:

1. “Down Syndrome Karyotype” By National Human Genome Research Institute – Human Genome Project (Public Domain) via Commons Wikimedia

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