A genetic disease is a disease caused in some way by a change in the genetic material of a person. They are also referred to as genetic disorders. Genetic diseases can be grouped into three main types.
- Single Gene or Monogenic Disorders: These are diseases caused by defects in a very specific gene. These diseases follow a simple and predictable inheritance pattern – often referred to as Mendelian inheritance. These diseases can show certain types of inheritance and they could be:
- Dominant: Only one copy of the gene has to be mutated for someone to show symptoms of the disease. For example, Marfan Syndrome, Huntington’s Disease.
- Recessive: Both copies of the gene has to be mutated to see observable disease. For example, Sickle Cell Anemia, Cystic Fibrosis.
- X-linked disorders: Genes on the X chromosomes are altered. Can be dominant or recessive. Males have one X chromosome (and a Y chromosome) and females have two X chromosomes. Dominant inheritance refers to only one copy of the mutation causing the disease and can result in death of affected males. Examples include Rett syndrome, Incontinentia pigmenti type 1. In the case of recessive disorders, a male carrying the mutation will be affected, as he has only one copy on one X chromosome. A female carrying a mutation in one copy of the gene will be unaffected as the other copy will be normal. Examples include red-green color blindness and hemophilia A.
- Chromosomal Disorders: These are genetic disorders that occur due to changes in the structure or number of chromosomes. Examples include Down Syndrome and Fragile X syndrome.
- Complex Disorders or Multi-gene disorders: These are genetic disorders caused by changes in multiple genes and also influenced by external conditions like diet, chemicals, medications, lifestyle (tobacco or alcohol use) etc. They are also called multi-factorial diseases. Examples include Cancer, Diabetes, Coronary artery disease etc.
For more information on genetic diseases:
https://www.genome.gov/For-Patients-and-Families/Genetic-Disorders
More information on basic genetics and about Gregor Mendel can be found here:
https://www.nature.com/scitable/topicpage/gregor-mendel-and-the-principles-of-inheritance-593/