BEST1 rs118204417: Understanding This Rare Genetic Variant
The rs118204417 variant is a rare genetic change located within the BEST1 gene. It is associated with Best vitelliform macular dystrophy type 2, an inherited condition that affects the retina.
What each genotype means
Typical vision risk
You carry two copies of the common reference allele at this position in the BEST1 gene. This genotype is not associated with Best vitelliform macular dystrophy type 2 or related bestrophinopathies. It reflects the standard baseline profile observed in the vast majority of the general population.
Carried by greater than 99.9% of individuals across all major global populations.
Increased Best vitelliform dystrophy risk
You carry one copy of the rare missense variant in the BEST1 gene. In clinical databases such as ClinVar, this heterozygous alteration is linked to autosomal dominant Best vitelliform macular dystrophy (BVMD), which can cause gradual central vision alterations due to retinal pigment epithelium disruption. However, clinical penetrance and expressivity can be variable among carriers, and evidence strength for some specific presentations remains limited.
Extremely rare, observed in fewer than 1 in 10,000 individuals globally in population reference databases like gnomAD.
High risk of severe bestrophinopathy
You carry two copies of the rare variant allele in the BEST1 gene. Homozygosity for pathogenic BEST1 variants is exceptionally uncommon and is typically associated with autosomal recessive bestrophinopathy (ARB) or severe, early-onset vitelliform macular degeneration. Because of the extreme rarity of this genotype, published clinical observations for this specific homozygous change are very limited.
Extremely rare; virtually unobserved in broad population reference cohorts.
What is the rs118204417 Variant?
The rs118204417 variant is a specific change in the DNA sequence of the BEST1 gene. In genetics, a variant like this is often referred to as a single nucleotide polymorphism (SNP) or a missense mutation, where one building block of DNA is swapped for another. This specific variant is categorized as a pathogenic missense change, meaning it alters the instructions for building a protein, which can potentially disrupt normal biological processes. Because this variant is extremely rare, it is not commonly found in the general population. Geneticists study such variants to understand how small changes in our genetic code can lead to significant differences in health outcomes, particularly in the context of inherited eye conditions.
The Role of the BEST1 Gene
The BEST1 gene provides the essential instructions for creating a protein known as bestrophin-1. This protein is primarily found in the retinal pigment epithelium (RPE), a layer of cells in the eye that supports the light-sensing cells of the retina. Bestrophin-1 functions as an ion channel, helping to regulate the movement of chloride ions and maintaining the proper environment for retinal health. When the BEST1 gene is altered, the resulting bestrophin-1 protein may not function correctly. This dysfunction can lead to a group of conditions collectively known as bestrophinopathies, which include Best vitelliform macular dystrophy. These conditions are characterized by the accumulation of deposits in the macula, the part of the eye responsible for sharp, central vision.
Research and Clinical Associations
Scientific research has linked various mutations in the BEST1 gene to several distinct ocular phenotypes, including Best vitelliform macular dystrophy type 2. The evidence for rs118204417 specifically is currently classified as limited, meaning that while it is identified as a pathogenic variant, ongoing research is required to fully characterize its clinical impact across different individuals. Studies often utilize techniques like electrooculography (EOG) and electroretinography (ERG) to assess how these genetic changes affect the electrical activity of the eye. It is important to note that the presence of a variant does not always guarantee a specific clinical outcome, as factors like other genetic modifiers and environmental influences can play a role in how these conditions manifest.
Population Frequency
The rs118204417 variant is extremely rare in the general population. According to data from large-scale genomic databases like gnomAD, its frequency is estimated to be less than 0.0001. This rarity is typical for variants associated with specific, inherited retinal dystrophies, which often do not reach high frequencies in the broader human population. Because it is so uncommon, most individuals will not carry this variant. When it is identified, it is usually in the context of clinical genetic testing for individuals or families experiencing symptoms of macular dystrophy.
What This Information Means for You
If you have received information about this variant, it is essential to understand that genetic data is complex and should be interpreted by a qualified healthcare professional, such as a genetic counselor or an ophthalmologist. This information is for educational purposes and is not a medical diagnosis. You cannot use this information to self-diagnose or make decisions about your health without professional guidance. If you are concerned about your vision or a family history of eye disease, consult with a clinician who can provide a comprehensive evaluation, including clinical exams and appropriate genetic testing. They can help you understand what these findings mean for your specific situation and discuss any necessary steps for monitoring or care.
How common is this variant?
The rs118204417 variant is extremely rare in gnomAD, with a frequency of less than 0.0001 across global populations.
Frequently asked questions
What is Best vitelliform macular dystrophy?
Best vitelliform macular dystrophy is an inherited eye condition that causes the buildup of yellowish, egg-yolk-like deposits in the macula. This can lead to a gradual loss of central vision over time.
Is rs118204417 common?
No, this variant is extremely rare. It is found in less than 0.01% of the population according to major genomic databases.
Can I be tested for this variant?
Genetic testing for BEST1 variants is typically performed in a clinical setting for individuals with symptoms of retinal dystrophy. You should discuss the necessity and implications of such testing with an ophthalmologist or a genetic counselor.
Does having this variant mean I will lose my vision?
Genetic variants in BEST1 are associated with a range of outcomes, and the severity can vary significantly between individuals. A clinical evaluation by an eye specialist is necessary to understand the potential impact on your vision.
Sources & further reading
Educational information only, last refreshed 10/19/2026. Not medical advice — these associations describe population statistics, not individual predictions.
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Encodes the Thr6Arg (T6R) missense change in Bestrophin 1 associated with autosomal dominant Best vitelliform macular dystrophy.
A missense alteration in bestrophin-1 linked to Best vitelliform macular dystrophy and central visual impairment.
Pathogenic missense variant in BEST1 (p.Ala146Thr) linked to autosomal dominant Best vitelliform macular dystrophy causing progressive loss of central vision.
Missense mutation in BEST1 causing classical Best vitelliform macular dystrophy type 2.
A pathogenic missense variant (p.Tyr227Asn) in BEST1 associated with Best vitelliform macular dystrophy.
Pathogenic missense mutation (p.Arg218Cys) in bestrophin-1 causing Best vitelliform macular dystrophy with subretinal egg-yolk-like lesions.