What kind of genetic disorder is cystic fibrosis

Every person has two copies of the cystic fibrosis transmembrane conductance regulator CFTR gene. A person must inherit two copies of the CFTR gene that contain mutations -- one copy from each parent -- to have cystic fibrosis. Cystic fibrosis occurs when the cystic fibrosis transmembrane conductance regulator CFTR protein is either not made correctly, or not made at all. By understanding how the protein is made, scientists have been able to develop treatments that target the protein and restore its function.

Carrier or genetic testing not only plays a key role in the diagnosis of cystic fibrosis, but testing also allows parents to find out what their chances are of having a child with CF to help inform important family planning decisions. In an international research project, scientists are examining cystic fibrosis transmembrane conductance regulator CFTR mutations to determine which ones cause CF and to provide additional information associated with these mutations.

Their findings are available in an online searchable database. Tsui and his team discovered that the gene that contains the instructions for production of the CFTR protein, when mutated, was responsible for the majority of cystic fibrosis cases. Certain specialized epithelial cells that generate mucus in the stomach lining, nasal cavity, and lungs have the CFTR protein in their cell membranes.

The CFTR protein regulates the passage of chloride ions through a channel in the membrane that adjusts the percentage of water that these cells secrete. The deletion of the amino acid mentioned above renders these specialized skin cells unable to regulate their chloride channels properly, making the mucus they produce thick and sticky.

People with CF produce sweat with a very high salt content. While most cases of cystic fibrosis result from the single amino acid deletion, well over a thousand additional mutations of the CFTR gene have been found that account for a small percentage of cystic fibrosis cases.

Adults and children can be tested to see if they carry the mutated CF gene. Genetic carrier testing analyzes a sample of the DNA from each parent via a mouth swab or blood sample that is examined for any mutations in the CF gene. Carrier testing is highly accurate, but some mutations are undetectable. Therefore, a person who tests negative for a cystic fibrosis mutation may be a carrier. For parents that are known carriers for the disease, doctors can conduct prenatal screening such as chorionic villus sampling CVS or amniocentesis to determine if the fetus has the genetic disorder.

A doctor performs amniocentesis at approximately fifteen to twenty weeks of pregnancy. In amniocentesis, the doctor takes a small sample of the amniotic fluid surrounding the fetus.

The cells there are then cultured in a lab and examined for cystic fibrosis mutations. Cystic fibrosis has traditionally been tested in children with a sweat test, which involves sampling the sweat of an individual who might have CF in order to determine if the salt content is higher than normal. However, with the advent of genetic testing, use of the sweat test has diminished.

Health professionals conduct newborn screening for CF by taking a blood sample at birth, and sometimes taking a second blood sample several weeks later. The disease occurs in 1 in 2, to 3, white newborns. Cystic fibrosis is less common in other ethnic groups, affecting about 1 in 17, African Americans and 1 in 31, Asian Americans. Mutations in the CFTR gene cause cystic fibrosis.

The CFTR gene provides instructions for making a channel that transports negatively charged particles called chloride ions into and out of cells. Chloride is a component of sodium chloride, a common salt found in sweat.

Chloride also has important functions in cells; for example, the flow of chloride ions helps control the movement of water in tissues, which is necessary for the production of thin, freely flowing mucus. Mutations in the CFTR gene disrupt the function of the chloride channels, preventing them from regulating the flow of chloride ions and water across cell membranes.

As a result, cells that line the passageways of the lungs, pancreas, and other organs produce mucus that is unusually thick and sticky. This mucus clogs the airways and various ducts, causing the characteristic signs and symptoms of cystic fibrosis. Other genetic and environmental factors likely influence the severity of the condition.

For example, mutations in genes other than CFTR might help explain why some people with cystic fibrosis are more severely affected than others. Most of these genetic changes have not been identified, however. This condition is inherited in an autosomal recessive pattern , which means both copies of the gene in each cell have mutations.

The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition. Genetics Home Reference has merged with MedlinePlus. Learn more. The information on this site should not be used as a substitute for professional medical care or advice. Contact a health care provider if you have questions about your health. Cystic fibrosis.

From Genetics Home Reference.