What you carry at this position in your DNA and what research says about it.
Macular Degeneration Risk: 8/10 evidence, 14 publications.
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Sample genotype (not yours): T/T
Higher Macular Degeneration Risk
Two copies of the T allele are associated with a significantly higher risk of developing age-related macular degeneration. This includes both dry and wet forms of the condition.
What this genotype means: Significantly higher risk of dry macular degeneration; Significantly higher risk of wet macular degeneration; Lower levels of complement factor I protein.
Sample genotype (not yours): C/C
Typical Macular Degeneration Risk
Two copies of the C allele are associated with a lower risk of age-related macular degeneration. This genotype is linked to higher, more protective levels of complement factor I.
What this genotype means: Lower risk of dry macular degeneration; Lower risk of wet macular degeneration; Higher levels of complement factor I protein.
Sample genotype (not yours): T/C
Increased Macular Degeneration Risk
A single copy of the T allele is associated with a moderately increased risk of developing age-related macular degeneration. This intermediate genotype results in slightly lower protective protein levels.
What this genotype means: Moderately higher risk of dry macular degeneration; Moderately higher risk of wet macular degeneration; Intermediate levels of complement factor I protein.
Gene function and biological role
Gene Function: The CFI gene encodes complement factor I, a crucial regulatory protein in the immune system's complement cascade [1]. This serine protease is responsible for cleaving and inactivating key complement proteins like C3b and C4b [2]. By controlling these proteins, complement factor I prevents the overactivation of the complement system, which can otherwise lead to chronic inflammation and tissue damage [3]. Proper functioning of this gene is essential for protecting delicate tissues, particularly in the retina of the eye, from autoimmune-like attacks [4]. Genetic variations that reduce complement factor I activity are strongly linked to increased susceptibility to age-related macular degeneration [5].
Variant Impact: The rs10033900 variant is an intronic change located within the CFI gene that influences the expression levels of complement factor I [1]. The C allele of this variant is associated with increased production of the complement factor I protein [6]. Conversely, the T allele is linked to lower protein levels, which can lead to insufficient regulation of the complement system [2]. This reduction in regulatory control allows for increased complement activation and subsequent inflammation in the retina [4]. Consequently, this single nucleotide polymorphism is a well-established genetic marker for susceptibility to both dry and wet forms of age-related macular degeneration [3].
Key Insight: This variant acts as a genetic thermostat for complement system activity in the eye, where lower protein levels directly translate to higher risk of retinal damage.
Location: CFI. Chromosome 4 · 4q25 · 109.7 Mb
Estimated prevalence by population
Global 22.1%; European 23.1%; African 14.7%; East Asian 38.1%; South Asian 42.7%; Americas 21.0%; Ashkenazi 24.0%; Finnish 29.0%; Middle Eastern 22.0%; Amish 15.0%.
Estimated TT genotype frequency.
Global 48.9%; European 49.9%; African 47.3%; East Asian 47.3%; South Asian 45.3%; Americas 49.7%; Ashkenazi 50.0%; Finnish 49.7%; Middle Eastern 49.8%; Amish 47.5%.
Estimated TC genotype frequency.
Global 29.0%; European 26.9%; African 38.0%; East Asian 14.7%; South Asian 12.0%; Americas 29.3%; Ashkenazi 26.0%; Finnish 21.3%; Middle Eastern 28.2%; Amish 37.5%.
Estimated CC genotype frequency.
Showing effects for T/T genotype
Organ Systems
Vision & Eye Health
Macular Degeneration. Evidence: 8/10. Source: PMID 26691988. ~1.3x Higher Risk.
Immunity & Inflammation
Inflammatory & Circulating Protein Markers
Complement Factor I. Evidence: 8/10. Source: PMID 36168886. Lower Levels.
Showing effects for C/C genotype
Macular Degeneration. Evidence: 8/10. Source: PMID 26691988. Typical Risk.
Complement Factor I. Evidence: 8/10. Source: PMID 36168886. Higher Levels.
Showing effects for T/C genotype
Macular Degeneration. Evidence: 8/10. Source: PMID 26691988. Increased Risk.
Complement Factor I. Evidence: 8/10. Source: PMID 36168886. Intermediate Levels.
What this genotype means for the people who carry it
Sample genotype: TT (Homozygous)
Two copies of the T allele are linked to a higher risk of developing age-related macular degeneration [1]. This genetic variant is located near the CFI gene, which plays a crucial role in regulating the complement system [2]. The T allele is associated with lower levels of complement factor I, a protein that helps prevent chronic inflammation in the retina [3]. Without sufficient complement factor I, the body's immune response can mistakenly attack healthy eye tissue, leading to the accumulation of cellular debris known as drusen [4]. Over time, this damage can progress to both dry and wet forms of macular degeneration, potentially causing severe vision loss [5].
Significantly higher risk of dry macular degeneration; Significantly higher risk of wet macular degeneration; Lower levels of complement factor I protein.
Sample genotype: CC (Homozygous)
Two copies of the C allele are associated with a lower risk of developing age-related macular degeneration [1]. This protective genotype is linked to higher circulating levels of complement factor I, a key regulatory protein in the immune system [2]. Complement factor I helps control the complement cascade, preventing the chronic low-grade inflammation that can damage the retina [3]. By maintaining adequate levels of this protein, individuals with the C/C genotype are less likely to experience the retinal cell damage and drusen accumulation characteristic of macular degeneration [4]. This protective effect applies to both the dry and wet forms of the disease [5].
Lower risk of dry macular degeneration; Lower risk of wet macular degeneration; Higher levels of complement factor I protein.
Sample genotype: TC (Heterozygous)
One copy of the T allele and one copy of the C allele is associated with a moderate increase in the risk of age-related macular degeneration [1]. This heterozygous genotype typically results in intermediate levels of complement factor I, which regulates the immune system's complement pathway [2]. While the single C allele provides some protective benefit by boosting complement factor I levels compared to the T/T genotype, the presence of the T allele still elevates overall susceptibility to retinal inflammation [3]. Research indicates that individuals with this genotype have a moderately higher likelihood of developing both dry and wet subtypes of macular degeneration [4]. Managing modifiable risk factors like smoking and diet can be particularly beneficial for individuals with this intermediate genetic profile [5].
Moderately higher risk of dry macular degeneration; Moderately higher risk of wet macular degeneration; Intermediate levels of complement factor I protein.
Variants with shared genetic architecture
rs10468017 · LIPC Gene · Chr 15 · Cholesterol and Eye Health
rs10490924 · ARMS2 Gene · Chr 10 · Macular Degeneration Risk
rs704 · VTN Gene · Chr 17 · Macular Degeneration Risk
Content updated August 2026.
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