Single Gene Disorders
This type of human genetic disorder occurs when a change happens in part of a gene's DNA sequence. Genes make proteins, and a mutation in the gene will result in the protein not being able to function properly. It's this that causes the problems we associate with disease.
Cystic fibrosis is an example of a single-gene disorder. Patients with the condition have a defective gene on chromosome 7 called CFTR (cystic fibrosis transmembrane conductance regulator).
The abnormality on the CFTR gene causes the protein produced by this gene to affect how salt (sodium chloride) moves in and out of cells. This single-gene disorder affects mainly lung cells producing an abnormally thick mucus that blocks the lungs. It can make breathing and digestion difficult, as well as causing many other complications such as lung infections.
Cystic fibrosis is also known as a recessive disorder. A recessive genetic disorder is one in which both parents pass the defective gene to their children. In this situation both parents are carriers. They have the defective gene but do not express the disease themselves. If only one parent has the affected gene then the child does not expresses it, because the good version of the gene from the other parent will make the protein that the body needs. Around 5% of the US population carries a copy of the affected gene for Cystic fibrosis.
A dominant disorder is one in which only one copy of the affected gene is needed for a disease to appear. An example of a dominant genetic disorder is Marfan syndrome. Because it is dominant, people who have inherited one affected gene (named FBN1 gene) from either parent will have Marfan's, which is a disease related to the connective tissue.