Cystic fibrosis (CF) is a chronic and inherited disease that affects the secretory glands, causing an excessive production of mucus and salty sweat. While in healthy people mucus is a watery and slippery substance, in CF patients, it is thick and sticky. The production and accumulation of the mucus damages the lungs, pancreas, digestive tract and sex organs. The most common CF features are progressive damage to the respiratory system and chronic digestive system problems.
However, the symptoms and severity of the disease vary depending on the patient’s characteristics and age. Most commonly, mucus clogs the airways, causing breathing difficulties and bacterial infections in the lungs. Over time, it can cause chronic coughing, wheezing and inflammation, and develop into permanent lung damage, the formation of scar tissue (fibrosis), and cysts in the lungs.
How Are Genetics Related to Cystic Fibrosis?
The development of cystic fibrosis is caused by genetics. The disease occurs when there is a mutation in the cystic fibrosis transmembrane conductance regulator (CFTR) gene, which is the gene responsible for the movements of negatively charged particles known as chloride ions into and out of cells. The component chloride comes from sodium chloride, which is a common salt present in sweat. The component holds important roles in the cells, including controlling the flow of chloride ions that control the water movement in tissues, a function that results in the production of thin, freely flowing mucus.
There are more than 180 known mutations in the CFTR gene that causes cystic fibrosis and disrupt the normal work of the chloride channels. Due to the defect, the chloride is unable to properly regulate the flow of chloride ions and water through the cells. Therefore, the cells near the lungs, pancreas, and other organs end up producing thick and sticky mucus instead of the normal watery and slippery substance. Genetics and environmental factors also impact the severity of the disease. The very existence of 180 known mutations and numerous other unknowns make it difficult to find a cure or define an effective treatment for the disease.
How Do Genetics Impact CF Development
Since genetics are responsible for the development of cystic fibrosis, the condition is inherited. However, there is no direct transmission and the genetic heredity process is very complex.
Cystic fibrosis runs in families in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. In CF cases, each parent has one CFTR (mutated) gene and one normal CF gene, but if the normal gene dominates the parent might never know they have the faulty gene and are potential “carriers.” A child only gets CF when the faulty CFTR gene from both parents is genetically passed down.
About 1 in every 20 Americans is an unaffected carrier of an abnormal CF gene, but most of those 12 million people are unaware that they are carriers.
“The presence of two mutant genes (g) is needed for CF to appear. Each parent carries one defective gene (g) and one normal gene (G). The single normal gene is sufficient for normal function of the mucus glands, and the parents are therefore CF-free. Each child has a 25 percent risk of inheriting two defective genes and getting CF, a 25 percent chance of inheriting two normal genes, and a 50 percent chance of being an unaffected carrier like the parents,” explains the Centers for Disease Control and Prevention about the development of cystic fibrosis.
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