Cystic fibrosis is an inherited, genetic disease that mainly affects the lungs and the digestive system. In the average unaffected individual, the cystic fibrosis transmembrane regulator (CFTR) protein sit within the cell membrane on the surface of our cells. These CFTR proteins, when functioning normally, open in order to allow for chloride ions (charged molecules) to flow freely into and out of the cell as needed. Therefore, in the average unaffected individual, the lungs, digestive tract, and sweat glands secrete thin, slippery fluids as the ions flow freely and there is a balance between salt and water. These thin, slippery fluids that act as a natural lubricant in the body.
However, in individuals affected with cystic fibrosis, their CFTR proteins do not rise to the cell surface where they are normally located, nor do they open properly. This defect prevents the chloride ions from flowing freely, leading to an imbalance of salt and water. The typically thin, slippery bodily fluids are instead thick and sticky. These abnormally thick and sticky bodily fluids clog tubes, ducts, and passageways, especially the lungs and pancreas. Clogging of the lungs often leads to life-threatening lung infections. Obstruction of the pancreas prevents the body’s natural enzymes from digesting (breaking down) and absorbing food. Male individuals with cystic fibrosis are typically infertile. Given the severity of the disease, some individuals have a shortened lifespan.
Like many different genetic diseases, cystic fibrosis is inherited in a recessive pattern. Usually, people have two working copies of the CFTR gene, which is currently the only known gene associated with cystic fibrosis. Most individuals inherit two functional copies of the CFTR gene, one from their mother and father (one copy of the CFTR gene on each chromosome). Some people only have one working copy of the CFTR gene; however, if you have at least one working copy of the CFTR gene, an individual is expected to be healthy and unaffected. If you have mostly Caucasian (White) ancestry, you have a 4% (1 in 25) chance to have only one working copy of CFTR gene instead of the characteristic two. If you only have one functional copy of the CFTR gene, you are referred to as a carrier for cystic fibrosis. If two carriers conceive a child together, there is a 25% (1 in 4) chance that their child will be affected with cystic fibrosis.
Previously, the average individual affected with cystic fibrosis was only expected to live into their twenties. Fortunately, the current expected lifespan has been improving and is now approximately 40 years of age. Of the various advancements that have occurred to treat cystic fibrosis, one of the most astounding are various medications which target the mutated (altered) CFTR gene itself. For example, a new medication, marketed as Orkambi® (combination drug of lumacaftor/ivacaftor), was invented in recent years for individuals with two deltaF508 mutations and approved by the FDA in 2015. The deltaF508 is one of the most common mutations within the CFTR gene that can keep the gene from functioning properly. As Orkambi® has been available for several years, it is now approved for children as young as 2 years of age. Other combination medications, such as Symdeko® and Trikafta™, were approved in 2018 and 2019, respectively. Individuals with at least one deltaF508 mutation usually may take these medications. Therefore, these medications are available to even more individuals affected with cystic fibrosis than Orkambi®. Symdeko® (ivacaftor/tezacaftor and ivacaftor) has now been approved for children as young as 6 years of age. Trikafta™, the newest of these targeted combination medications (elexacaftor/tezacaftor/ivacaftor and ivacaftor), remains only available for use by children of at least 12 years of age.
All of these combination therapies work by targeting the mutations within the CFTR gene that cause abnormal CFTR proteins. Ivacaftor works by helping the abnormal CFTR proteins stay open longer, like normal CFTR proteins should. Lumacaftor, elexacaftor, and tevacaftor allow more CFTR proteins to travel from within the cell to the cell’s outside surface where they belong.
As nearly all of these new medications rely on the knowledge of the underlying mutations that have caused an individual to be affected with cystic fibrosis, genetic carrier screening and genetic testing is highly recommended to determine if an individual is eligible for these new and improved therapies. Ideally, genetic carrier screening and genetic testing is completed prior to conception, or even during pregnancy. However, if you choose not to complete genetic carrier screening or genetic testing, cystic fibrosis is included in the newborn screening programs across the United States. Please contact Advanced Tele-Genetic Counseling for information regarding telemedicine for genetic carrier screening or go to nsgc.org to find a prenatal genetic counselor near you.