IQGAP1 rs117555778: Tritan Color Vision Association
The single nucleotide polymorphism rs117555778 is a genetic variant situated within the IQGAP1 gene on chromosome 15. Published genome-wide association studies have linked this variant with tritan-type color vision defects, which affect an individual's perception along the blue-yellow color axis. The evidence supporting this association is classified as moderate, representing a statistical signal identified within specific population cohorts.
What each genotype means
Typical Tritan Color Vision
You carry two copies of the common C allele at rs117555778 in the IQGAP1 gene. In published genome-wide association studies, this baseline genotype is not associated with an increased predisposition to tritan-type (blue-yellow) color perception alterations. Your color vision depends on multiple genetic and environmental factors.
Carried by the vast majority of individuals globally, accounting for over 90% of genotypes across European, Asian, and other ancestral populations.
Moderately Increased Tritan Defect Risk
You carry one copy of the T effect allele at rs117555778, which has been identified in Silk Road cohort association studies as a signal associated with tritan-type (blue-yellow) color discrimination differences. Having this variant confers a statistical association rather than a clinical diagnosis, and most heterozygous carriers maintain standard color vision. Evidence remains preliminary and ancestry-specific, requiring validation across broader cohorts.
Carried by approximately 5% to 10% of individuals in Eurasian populations, while being uncommon or rare in African ancestries.
Elevated Tritan Defect Association
You carry two copies of the T effect allele at rs117555778 in the IQGAP1 gene. While homozygous status is linked statistically to a higher probability of blue-yellow (tritan) color perception variations compared to non-carriers, color vision defects exhibit variable penetrance and cannot be diagnosed from this marker alone. Formal clinical vision screening remains the standard method to evaluate functional color perception.
Carried by less than 1% of individuals worldwide, occurring primarily at low frequencies in certain Eurasian groups.
Genomic Location and the IQGAP1 Gene
The single nucleotide polymorphism rs117555778 maps to the IQGAP1 locus located on chromosome 15. IQGAP1 encodes IQ motif-containing GTPase-activating protein 1, a ubiquitous scaffolding protein involved in cellular architecture, signaling cascades, cell adhesion, and cytoskeletal dynamics. In ocular tissues, IQGAP1 has been studied in connection with retinal biology and choroidal vascular regulation. While classic forms of inherited color blindness typically involve cone opsin genes, broader genomic screens have illuminated loci like IQGAP1 that may influence retinal cell structure, photoreceptor signaling pathways, or support tissue integrity.
Association with Tritan Color Vision Variation
Genome-wide association studies evaluating color discrimination traits have highlighted rs117555778 as a notable signal linked to tritan-type color vision defects. Tritan defects alter the short-wavelength (S-cone) pathway, reducing the ability to distinguish blue from yellow hues. While monogenic, Mendelian tritanopia is classical caused by rare disruptive variants in the blue-sensitive opsin gene (OPN1SW), population research indicates that milder or complex forms of color vision defects exhibit multifactorial genetics. The association between rs117555778 and tritan deficits suggests non-opsin cellular pathways may modulate visual discrimination thresholds.
Strength of the Evidence and Scientific Caveats
The current evidence connecting rs117555778 to color perception is ranked as moderate. The association was revealed through systematic statistical mapping in cohort studies, specifically in isolated and cross-continental Silk Road Eurasian populations. However, statistical significance in a discovery cohort does not inherently demonstrate biological causality. Functional bench assays have not yet confirmed how this specific variant alters IQGAP1 expression or affects photoreceptor function. Consequently, researchers treat this finding as an association signal rather than a definitive, deterministic cause of tritan defects.
Interpreting Results in Everyday Context
Learning that you carry a specific genotype at rs117555778 cannot diagnose or rule out color vision deficiency. Standard direct-to-consumer genetic profiles are educational screening tools and cannot substitute for clinical eye examinations. Clinical assessments, such as the Farnsworth-Munsell 100-Hue test, Hardy-Rand-Rittler (HRR) pseudoisochromatic plates, or anomaloscopy, remain the gold standard for evaluating real-world visual function. If you notice difficulties differentiating blue and green or yellow and violet, an optometric or ophthalmologic evaluation provides definitive answers that genetics alone cannot offer.
How common is this variant?
The variant rs117555778 is observed across Eurasian ancestry sets at low-to-moderate frequencies. In discovery cohorts studying color vision defects, the minor allele occurs as a polymorphic trait signal rather than a ubiquitous global variant.
Frequently asked questions
What is tritan color blindness?
Tritan color blindness, or tritanopia, is a condition that impairs the ability to distinguish blue from yellow and violet from red-green shades. It occurs when the short-wavelength sensitive cones (S-cones) in the retina do not function optimally.
Does having rs117555778 mean I will develop color blindness?
No, carrying a variant allele at rs117555778 does not mean you have or will develop color blindness. It represents a statistical association identified in research studies, and most carriers exhibit normal everyday vision.
How does IQGAP1 affect vision if it is not an opsin gene?
Unlike opsin genes that code directly for light-sensitive photopigments, IQGAP1 produces a scaffolding protein that regulates cytoskeletal organization and vascular tissue maintenance. Researchers hypothesize that variations in such structural proteins may subtly influence retinal cell function or resilience.
How can I get an accurate check of my color vision?
An eye care professional can administer validated functional assessments, such as pseudoisochromatic color plates or hue-arrangement tests. These non-invasive clinical tests accurately determine color discrimination ability.
Sources & further reading
Educational information only, last refreshed 9/12/2026. Not medical advice — these associations describe population statistics, not individual predictions.
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