CFTR rs121907998: Understanding This Genetic Variant
The rs121907998 variant is a specific change in the CFTR gene, also known as p.Gly85Glu. It is identified in research as a carrier variant associated with autosomal recessive cystic fibrosis.
What each genotype means
Non-carrier
You have two standard functional copies of the CFTR gene at position c.254 and do not carry the pathogenic G85E (c.254G>A) variant. This genotype does not increase your risk of cystic fibrosis or CFTR-related disorders at this specific site. However, it does not rule out being a carrier for other variants in the CFTR gene.
Carried by more than 99.9% of individuals across all major global populations.
Cystic fibrosis carrier
You carry one copy of the pathogenic c.254G>A (p.Gly85Glu, commonly referred to as G85E) variant in the CFTR gene. Carriers typically do not develop cystic fibrosis themselves because the condition is autosomal recessive, but there is a 50% chance of passing this variant to biological offspring. If reproductive planning is relevant, discussing CFTR carrier screening for a partner with a genetic counselor or healthcare provider is standard practice.
Carried by roughly 1 in 2,500 to 1 in 5,000 individuals of European ancestry, and is extremely rare or virtually absent in other populations.
Affected cystic fibrosis genotype
You carry two copies of the pathogenic c.254G>A (p.Gly85Glu) variant in the CFTR gene. In clinical databases such as ClinVar, homozygosity or compound heterozygosity for this variant is associated with classic cystic fibrosis, characterized by chloride channel dysfunction, elevated sweat chloride levels, and pulmonary or pancreatic involvement. Consultation with a medical geneticist or pulmonologist is standard to evaluate clinical context and management.
Extremely rare globally, estimated to occur in fewer than 1 in 25 million individuals.
What is the rs121907998 Variant?
The rs121907998 variant is a single nucleotide polymorphism (SNP) located within the CFTR gene. In genetic notation, this specific change is often referred to as c.254G>A, which results in an amino acid substitution where glycine is replaced by glutamic acid at position 85 of the protein (p.Gly85Glu). This location is significant because it sits within the first membrane-spanning domain of the CFTR protein. Because this variant alters the protein's primary structure, researchers study it to understand how it might affect the protein's ability to fold or function correctly within the cell membrane. It is categorized in genetic databases as a carrier variant, meaning it is typically studied in the context of recessive inheritance patterns where an individual would need to inherit a pathogenic variant from both parents to potentially manifest the associated condition.
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. The channel is responsible for transporting negatively charged particles called chloride ions into and out of cells. This 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 absent or dysfunctional, the transport of chloride ions and water is disrupted. This leads to the production of thick, sticky mucus that can clog airways and ducts in various organs, particularly the lungs and the pancreas. Understanding how variants like rs121907998 impact this protein is a major focus of ongoing genetic research.
Research and Evidence Strength
The evidence linking rs121907998 to clinical outcomes is currently considered limited. While the variant is recognized in scientific literature as a carrier variant for cystic fibrosis, the functional impact of this specific amino acid change requires further investigation to fully characterize its clinical severity. Genetic research often relies on large-scale registries and functional studies to determine if a variant is disease-causing or benign. Because cystic fibrosis is an autosomal recessive condition, being a carrier of a single variant typically does not result in the disease itself. However, the classification of such variants is essential for genetic counseling and carrier screening programs. Researchers continue to collect data from diverse populations to better understand the penetrance and expressivity of various CFTR variants, ensuring that clinical interpretations remain grounded in the most current and robust scientific evidence available.
Population Frequency
The rs121907998 variant is considered rare in the general population. Current data indicates an allele frequency of approximately 0.0001 to 0.0002 in European populations. Because this variant is infrequent, it is not commonly encountered in the general public. Carrier frequencies for CFTR variants can vary significantly based on ancestral background, with some populations showing higher rates of specific mutations than others. Large-scale genomic databases like gnomAD are instrumental in providing these frequency estimates, which help geneticists distinguish between common benign variations and rare, potentially pathogenic ones. If you are concerned about your carrier status, it is important to consult with a qualified genetic counselor or healthcare provider who can interpret your specific genetic information in the context of your personal and family medical history.
What This Information Means for You
Information about genetic variants like rs121907998 is intended for educational purposes and should not be used for self-diagnosis or medical decision-making. If you have received a report indicating you carry this variant, it is important to understand that this does not necessarily mean you have or will develop cystic fibrosis. Carrier status is a common finding in genetic testing, and most people carry several recessive variants in their genome. You cannot change your genetic code, but you can use this information to have informed conversations with your doctor. If you are planning a family or have concerns about hereditary conditions, a genetic counselor can provide personalized guidance. Always discuss any medical questions or concerns with a healthcare professional who can provide context based on your full clinical picture and family history.
How common is this variant?
The rs121907998 variant is rare, with an estimated allele frequency of approximately 0.0001 to 0.0002 in European populations.
Frequently asked questions
What does it mean to be a carrier of a CFTR variant?
Being a carrier means you have one copy of a gene variant that is associated with a recessive condition. Carriers typically do not show symptoms of the condition themselves but can pass the variant to their children.
Is rs121907998 the same as having cystic fibrosis?
No, identifying a single carrier variant does not mean you have cystic fibrosis. Cystic fibrosis is an autosomal recessive condition, meaning it generally requires two pathogenic variants to be present.
Should I get tested for cystic fibrosis if I have this variant?
If you are concerned about your health or family planning, you should speak with a healthcare provider or a genetic counselor. They can determine if further clinical testing or screening is appropriate for you.
Where can I find more information about CFTR variants?
Resources like MedlinePlus Genetics and the CFTR2 database provide extensive information on the CFTR gene and its associated variants. These sites are excellent for learning about the science behind genetic testing.
Sources & further reading
Educational information only, last refreshed 10/18/2026. 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.