UNDERSTANDING GENETIC DISEASES
What is a Genetic Disease?
Genetic diseases (also called genetic disorders ) occur when changes to DNA (referred to as a genetic mutation) result in an alteration in the encoded protein that prevents or alters its function or prevent protein expression entirely. Genetic mutations can be passed down from parents. But they can also occur randomly or can be due to environmental factors. Some genetic mutations are harmless, but others can result in genetic diseases that affect our health.
What is an example of a
One example of a genetic disease is hemophilia, an inherited blood disorder in which the blood does not clot properly. In hemophilia, a gene that codes for a protein involved in blood clotting is mutated. This gene resides on the X chromosome and the disease occurs mainly in males.
is a bone growth disorder that causes short-limbed
blood does not clot properly in which there is a problem converting cartilage into bone3
See glossary for more terms >, an inherited blood disorder in which the blood does not clot properly. In hemophilia, a gene that codes for a protein involved in blood clotting is mutated. This gene resides on the X chromosome and the disease occurs mainly in males.3
What causes genetic diseases?
Although genetic diseases are usually inherited from a person's parents, there are instances of genetic diseases occurring spontaneously. This means that a child can be born with a genetic mutation without either parent having the genetic change (or mutation) themselves. This is called a de novo occurrence of the disease.
When a person acquires a genetic disease that is inherited, there are several ways it can happen.
See glossary for more terms > occurrence of the disease.2
When a person acquires a genetic disease that is inherited, there are several ways it can happen.4
Next Level Knowledge
Different ways a single-gene disease can be inherited4:
Remember that, even though diseases often fit into categories like the ones below, every disease is different. If you have questions about a specific disease, you should speak to your doctor or another healthcare professional.
- Individuals carrying 1 mutated copy of a gene in each cell will be affected by the disease
- Each affected person usually has 1 affected parent
- Tends to occur in every generation of an affected family
- Affected individuals must carry 2 mutated copies of a gene
- Parents of affected individual are usually unaffected, and each carry a single copy of the mutated gene (known as carriers)
- Not typically seen in every generation of an affected family
- Only females can pass on mitochondrial conditions to their children (maternal inheritance)
- Both males and females can be affected
- Can appear in every generation of an affected family
- Females are more frequently affected than males
- Fathers cannot pass X-linked traits to their sons (no male-to-male transmission)
- Males are more frequently affected than females
- Families with an X-linked recessive disease often have affected males, but rarely affected females, in each generation
- Both parents of an affected daughter must be carriers
- Mothers of affected sons are carriers (fathers cannot pass X-linked traits to their sons)
See glossary for more terms >. These cancers may be caused by exposure to things in the environment, such as cigarette smoke or radiation. In these cancers, genes are mutated later in life and are found in only certain types of cells. Lung cancer is an example. These cancers are not considered genetic diseases because they are not inherited.5,6
A small portion of cancers are Germline mutationsa gene change in a body's reproductive cell that is incorporated into the DNA of a person’s offspring
See glossary for more terms >, which are inherited. These mutations are present from the time sperm fertilizes an egg (in the zygote) or in the sperm or egg themselves. In contrast to acquired mutations, germline mutations are present in every cell in the body.5 Hereditary retinoblastoma is an example of a disease caused by a germline mutation.7
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1. National Institutes of Health. Medline Plus. Genetic disorders. Accessed March 4, 2020. https://medlineplus.gov/geneticdisorders.html 2. National Institutes of Health. Genetics Home Reference. Help me understand genetics. Accessed March 4, 2020. https://ghr.nlm.nih.gov/primer 3. Centers for Disease Control and Prevention. What is hemophilia? Accessed March 16, 2020. https://www.cdc.gov/ncbddd/hemophilia/facts.html 4. Genetic Alliance; The New York–Mid-Atlantic Consortium for Genetic and Newborn Screening Services. Understanding Genetics: A New York, Mid-Atlantic Guide for Patients and Health Professionals. Genetic Alliance Monographs and Guides; 2009. https://www.ncbi.nlm.nih.gov/books/NBK115563/pdf/Bookshelf_NBK115563.pdf 5. American Society of Clinical Oncology. Cancer.Net. The genetics of cancer. Accessed March 26, 2020. https://www.cancer.net/navigating-cancer-care/cancer-basics/genetics/genetics-cancer 6. Jackson M, Marks L, May GHW, Wilson JB. The genetic basis of disease. Essays Biochem. 2018;62(5):643-723. 7. National Institutes of Health. Genetics Home Reference. Retinoblastoma. Accessed March 4, 2020. https://ghr.nlm.nih.gov/condition/retinoblastoma