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Defining Disorders
A disorder is a disruption to the normal structure or function of the body. Disorders are often distinguished from diseases, though the terms are sometimes used interchangeably. A disease usually refers to a condition that develops when the body responds to harmful internal or external factors, and it often has a recognizable set of signs and symptoms (for example, heart disease). A disorder, on the other hand, may simply mean that something in the body is not working properly, even if the exact cause is unclear (for example, an irregular heartbeat).
Genetic disorders are a specific class of disorders that arise from abnormalities in an individual’s genetic material. These abnormalities can involve a single gene, multiple genes, or entire chromosomes.
"I got excited about genetics as a first-year medical student [when] a pediatric geneticist [brought] a young man with sickle cell disease [to class] who talked about the experience of sickle cell crises and how incredibly painful those are. And yet, it was all because of one single letter in the DNA that is misplaced, a 'T' that should have been an 'A.' And that was profound. You could have all of that happen because of one letter that was misspelled."
— Francis Collins, former Director of the NIH, in a 60 Minutes interview (2019)
Categories of Genetic Disorders
Genetic disorders are typically grouped into three broad categories:
- Monogenic (single-gene) disorders — caused by mutations in a single gene.
- Polygenic or multifactorial disorders — influenced by the combined effect of multiple genes, often in interaction with environmental factors.
- Chromosomal disorders — resulting from structural or numerical abnormalities in chromosomes.
Genetic Anomalies and Mutations
The underlying cause of genetic disorders is variation or damage to DNA. Several types of anomalies can occur:
- Point mutations – single nucleotide changes that alter gene function.
- Deletions – loss of a section of DNA.
- Chromosomal abnormalities – larger scale changes that may include:
- Duplication (extra copies of a chromosome segment)
- Translocation (segments exchanged between chromosomes)
- Inversion (a segment reversed within the chromosome)
- Insertion (addition of extra DNA into a chromosome)
"There are 7,000 genetic diseases for which we know the precise DNA misspelling. Couldn't this same strategy, this same set of principles [of gene therapy] work for lots of those, maybe someday all of them? ... to see that emerging not just as hoped-for advances, but real data showing cures for people. I believe that this looks like a cure."
— Francis Collins, former Director of the NIH, in a 60 Minutes interview (2019)
1.1: Defining Disorders is shared under a CC BY-SA 4.0 license and was authored, remixed, and/or curated by LibreTexts.
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