CFTR rs121908785: Understanding This Rare Genetic Variant
The rs121908785 variant is a rare, pathogenic insertion in the CFTR gene. It is clinically associated with cystic fibrosis, a condition that affects the body's ability to transport salt and water across cell membranes.
What each genotype means
Cystic fibrosis carrier status
You carry one copy of the c.1153_1154insAT insertion, also known as p.Asn386Ilefs. This variant is classified as pathogenic and is associated with cystic fibrosis, an autosomal recessive condition; carriers typically do not show symptoms but should discuss reproductive risks and family planning with a genetic counselor.
This genotype is rare in the general population.
Cystic fibrosis associated genotype
This genotype indicates the presence of the c.1153_1154insAT insertion on both copies of the CFTR gene. This variant is documented as pathogenic and is associated with the development of cystic fibrosis, which requires clinical management by a specialized healthcare provider.
This genotype is extremely rare.
What is the rs121908785 Variant?
The rs121908785 variant is a specific genetic alteration located within the CFTR gene on chromosome 7. In scientific literature, this variant is often described as an insertion, specifically c.1153_1154insAT. This means that two extra nucleotides, adenine and thymine, are inserted into the DNA sequence at this position. This type of change is known as a frameshift mutation, which can significantly alter how the cell reads the genetic instructions to build a protein. Because this change occurs in a critical region of the gene, it is classified as pathogenic, meaning it is known to disrupt the normal function of the resulting protein. Genetic variants like this are tracked in databases such as ClinVar, which aggregate information from clinical testing and research to help healthcare professionals understand the potential health implications of specific DNA changes.
The Role of the CFTR Gene
The CFTR gene provides instructions for making a protein called the cystic fibrosis transmembrane conductance regulator. This protein functions as a channel across the membranes of cells that produce mucus, sweat, saliva, tears, and digestive enzymes. By transporting negatively charged particles called chloride ions into and out of cells, the CFTR protein helps control the movement of water in tissues, which is necessary for the production of thin, freely flowing mucus. When the CFTR gene is mutated, the resulting protein may be missing, non-functional, or present in insufficient quantities. This leads to the production of thick, sticky mucus that can clog airways and ducts in various organs, particularly the lungs and pancreas. Understanding the function of this gene is essential for grasping why specific variants, such as rs121908785, can lead to significant health challenges.
Research and Clinical Associations
Research has firmly established that pathogenic variants in the CFTR gene are the underlying cause of cystic fibrosis. Cystic fibrosis is an autosomal recessive condition, meaning that an individual typically must inherit two copies of a disease-causing variant—one from each parent—to manifest the full clinical symptoms of the disease. The rs121908785 variant is recognized in clinical databases as a pathogenic mutation linked to cystic fibrosis. Because it is a rare variant, most of the evidence regarding its impact comes from clinical genetic testing and specialized research studies that characterize the molecular consequences of such insertions. While the association with cystic fibrosis is clear, the specific clinical presentation can vary between individuals based on other genetic factors and environmental influences. It is important to note that this information is for educational purposes and does not constitute a medical diagnosis.
Population Frequency and Prevalence
The rs121908785 variant is considered rare in the general population. Unlike more common variants, such as the well-known F508del mutation which accounts for a large percentage of cystic fibrosis cases worldwide, rs121908785 is not frequently observed in large-scale genomic studies. Because it is rare, it is not typically included in standard, broad-spectrum carrier screening panels unless those panels are specifically designed to detect a wide array of rare, pathogenic CFTR mutations. The rarity of this variant means that there is limited data on its distribution across different ancestral groups. In the context of genetic testing, the rarity of such variants underscores the importance of comprehensive sequencing when a clinical suspicion of cystic fibrosis exists, as standard targeted panels might miss less common, pathogenic insertions.
Navigating Genetic Information
If you have received information about this variant, it is natural to have questions about what it means for your health or your family. It is important to understand that carrying a single copy of a pathogenic CFTR variant typically does not cause cystic fibrosis, but it does make you a carrier. Carriers are generally healthy but have a chance of passing the variant to their children. If you are concerned about your carrier status or family history, the most appropriate step is to consult with a certified genetic counselor or a medical geneticist. These professionals can help interpret your specific results in the context of your personal and family health history. They can also provide guidance on whether further testing is appropriate for you or your partner. Never make medical decisions based solely on online information; always discuss your genetic findings with a qualified healthcare provider.
How common is this variant?
The rs121908785 variant is rare in the general population, with limited data available regarding its specific frequency across different ancestral groups.
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 pathogenic variant in the CFTR gene. Carriers typically do not show symptoms of cystic fibrosis but can pass the variant to their children.
Is rs121908785 the same as the common F508del mutation?
No, rs121908785 is a distinct, rare insertion mutation. F508del is the most common CFTR mutation, while rs121908785 is much less frequent.
Can I be tested for this specific variant?
Yes, this variant can be detected through clinical genetic testing, such as full gene sequencing of the CFTR gene. You should speak with a healthcare provider or genetic counselor to determine if such testing is appropriate for you.
Does having this variant mean I have cystic fibrosis?
Cystic fibrosis is typically an autosomal recessive condition, meaning it usually requires two pathogenic variants to manifest. A single copy makes you a carrier, but you should discuss your specific results with a doctor to understand your health status.
Sources & further reading
Educational information only, last refreshed 10/6/2026. Not medical advice — these associations describe population statistics, not individual predictions.
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This variant (p.Arg117His) is a well-documented pathogenic mutation associated with CFTR-related disorders, including atypical cystic fibrosis and congenital bilateral absence of the vas deferens, with severity modulated by the poly-T tract.
This variant is associated with cystic fibrosis, affecting chloride channel function in epithelial cells.
The most common mutation (DeltaF508) causing Cystic Fibrosis.
A "gating" mutation in Cystic Fibrosis that responds to specific modulators.
This variant is a known mutation associated with cystic fibrosis clinical presentation.
A variant associated with cystic fibrosis transmembrane conductance regulator function.