CFTR rs121908702: Understanding Gating Mutations
The rs121908702 variant is a specific genetic change within the CFTR gene known as a gating mutation. It is associated with cystic fibrosis, a condition where the body's ability to transport chloride ions is impaired, and it is a target for specific precision medicines.
What each genotype means
Typical CFTR function
This genotype represents the common, non-mutated sequence at this specific location in the CFTR gene. It is associated with normal production of the CFTR protein, which helps regulate chloride and water transport in the body.
This is the most common genotype found in the general population across all ancestries.
Carrier of gating mutation
This genotype indicates you carry one copy of the rs121908702 variant, which is classified as a gating mutation in the CFTR gene. Carriers typically do not have cystic fibrosis, but you should discuss your status with a genetic counselor or clinician if you are planning a family, as this variant can be passed to children.
This genotype is rare and typically identified in clinical settings or specific population screenings.
Gating mutation present
This genotype indicates the presence of the rs121908702 variant on both copies of the CFTR gene. This variant is known to impair the gating function of the CFTR protein, which is associated with cystic fibrosis and related conditions; please consult with a specialized medical professional or a cystic fibrosis center to discuss clinical implications and potential modulator therapies.
This genotype is extremely rare in the general population.
What is the rs121908702 Variant?
The rs121908702 variant, often referred to in clinical literature as G551D, is a single nucleotide variant located within the CFTR gene. Specifically, it involves a substitution where a guanine is replaced by an adenine at a precise location in the gene's sequence. This change results in an amino acid alteration in the resulting protein, where glycine is replaced by aspartate at position 551. This specific location is critical because it sits within the nucleotide-binding domain of the CFTR protein, which acts as the engine for the channel's activity. Because this change occurs in a functional part of the protein, it is classified as a gating mutation. This means that while the protein may be produced and reach the cell surface, it fails to open and close properly to allow the necessary flow of ions, effectively acting like a gate that is stuck in the closed position.
The Role of the CFTR Gene
The CFTR gene provides instructions for making the cystic fibrosis transmembrane conductance regulator protein. This protein functions as a channel across the membranes of cells that produce mucus, sweat, saliva, tears, and digestive enzymes. Its primary job is to transport negatively charged particles called chloride ions into and out of cells. The movement of chloride ions helps control the movement of water in tissues, which is necessary for the production of thin, freely flowing mucus. When the CFTR protein is dysfunctional, as seen with gating mutations like rs121908702, chloride transport is severely impaired. This leads to the production of thick, sticky mucus that can clog airways and ducts in the lungs, pancreas, and other organs. Understanding the specific nature of a mutation is essential because different types of CFTR defects require different therapeutic approaches to restore channel function.
Research and Clinical Associations
Research has extensively characterized the rs121908702 variant as a pathogenic mutation associated with cystic fibrosis. Studies have shown that this mutation significantly reduces the probability of the CFTR channel opening, often by a factor of approximately 100 compared to the normal, wild-type channel. Because the protein is present at the cell surface but simply fails to function correctly, it has become a primary target for a class of drugs known as CFTR potentiators. These medications are designed to bind to the defective protein and increase the probability that the channel will open, thereby facilitating ion transport. The evidence for this association is strong, and the development of targeted therapies for this specific gating defect represents a significant milestone in precision medicine. Individuals with this variant should consult with their healthcare provider or a specialized cystic fibrosis center to discuss how current clinical guidelines and available modulator therapies may apply to their specific health profile.
Population Frequency
The rs121908702 variant is considered rare in the general population. Within the specific population of individuals diagnosed with cystic fibrosis, it is recognized as one of the more common gating mutations, with reported incidences typically ranging between 2% and 5% of the CF patient population depending on the cohort studied.
What You Can Do With This Information
Genetic information regarding the rs121908702 variant is primarily used in clinical settings to guide personalized treatment plans. If you or a family member have been identified as carrying this variant, it is important to understand that this information is not a diagnosis on its own but a piece of a larger clinical picture. You cannot use this information to self-diagnose or determine treatment protocols. Instead, use this knowledge to facilitate a conversation with a genetic counselor or a specialized physician. They can explain how this variant fits into your overall health, discuss the availability of targeted modulator therapies, and provide guidance on monitoring and management. Always rely on professional medical advice for any decisions regarding your health, and never change or start any medication without consulting your clinician or pharmacist, who can provide the most accurate information based on your complete medical history.
How common is this variant?
The rs121908702 variant is rare in the general population, though it is identified in approximately 2% to 5% of individuals diagnosed with cystic fibrosis.
Frequently asked questions
Is rs121908702 the same as G551D?
Yes, rs121908702 is the identifier used in genetic databases for the G551D mutation in the CFTR gene. They refer to the exact same genetic change.
Can this variant be treated with medication?
Yes, the G551D mutation is a known target for specific CFTR modulator therapies, such as ivacaftor, which help improve the function of the protein. You should discuss with your doctor whether such treatments are appropriate for your specific clinical situation.
Does having this variant mean I have cystic fibrosis?
Cystic fibrosis is a complex condition, and the presence of this variant is a significant factor in its development. A diagnosis is typically made by a physician based on a combination of genetic testing, clinical symptoms, and sweat chloride testing.
Where can I find more information about CFTR mutations?
You can find reliable information through resources like MedlinePlus Genetics, the Cystic Fibrosis Foundation, or by speaking with a certified genetic counselor. These sources provide evidence-based information on how different mutations affect health.
Sources & further reading
Educational information only, last refreshed 10/2/2026. Not medical advice — these associations describe population statistics, not individual predictions.
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Severe pathogenic mutation (p.Gly542Ter) associated with cystic fibrosis.
Classic cystic fibrosis in-frame 3-bp deletion variant (p.Phe508del / deltaF508) causing misfolding and impaired chloride channel trafficking.
Pathogenic frameshift mutation (c.3659delC) in CFTR linked to cystic fibrosis.
Pathogenic nonsense variant (p.Gly542Ter / G542X) causing autosomal recessive cystic fibrosis when inherited in trans with another CFTR pathogenic allele.
Also known as p.Arg117His (R117H), this CFTR variant is associated with mild or atypical cystic fibrosis and congenital bilateral absence of the vas deferens, with clinical severity influenced by the poly-T tract background.
A CFTR mutation associated with cystic fibrosis and CFTR-related disorders.