rs3798220 — LPA Ile4399Met (I4399M)

The Lp(a) Missense Variant — Cardiovascular Risk with an Aspirin Twist

Lipoprotein(a), or Lp(a), is an LDL-like particle distinguished by an additional apolipoprotein(a) protein component¹¹ LDL-like particle distinguished by an additional apolipoprotein(a) protein component
making Lp(a) structurally and functionally distinct from ordinary LDL. The rs3798220 variant causes an isoleucine-to-methionine substitution (p.Ile1891Met, also written Ile4399Met in legacy numbering) in the protease-like domain of apolipoprotein(a)²² protease-like domain of apolipoprotein(a)
a region structurally homologous to plasminogen but catalytically inactive. Carriers of the C allele have markedly elevated Lp(a) levels — median 79.5 mg/dL in heterozygotes versus 10.0 mg/dL in non-carriers — and face substantially higher rates of coronary artery disease, peripheral vascular disease, and aortic valve stenosis. This variant is independent of rs10455872 and operates through a distinct mechanism.

The Mechanism

The rs3798220 C allele correlates with smaller apolipoprotein(a) isoforms³³ smaller apolipoprotein(a) isoforms
fewer kringle IV-2 repeat copies in the LPA gene, the same feature that drives the Lp(a)-elevating effect of the related rs10455872 variant. However, the Ile4399Met substitution is a coding change in the protease-like domain that appears to independently influence isoform size, secretion efficiency, or metabolic clearance, independently of the KIV-2 repeat number alone.

Elevated Lp(a) contributes to cardiovascular disease through three convergent mechanisms: atherogenic cholesterol delivery to arterial plaques⁴⁴ cholesterol delivery to arterial plaques
similar to LDL, but resistant to statin therapy; pro-inflammatory oxidized phospholipids (OxPL) carried by the apolipoprotein(a) kringle domains⁵⁵ pro-inflammatory oxidized phospholipids (OxPL) carried by the apolipoprotein(a) kringle domains
OxPL drives macrophage activation and arterial wall inflammation; and anti-fibrinolytic activity⁶⁶ anti-fibrinolytic activity
apolipoprotein(a)'s structural similarity to plasminogen allows it to compete with plasminogen for fibrin binding, impairing clot breakdown and increasing thrombotic risk. The thrombotic mechanism is why aspirin provides disproportionate benefit in carriers.

Notably, the Ile4399Met substitution is not associated with elevated Lp(a) in East and Southeast Asian populations⁷⁷ not associated with elevated Lp(a) in East and Southeast Asian populations
the variant is not in linkage disequilibrium with small KIV-2 alleles in these populations, so the standard risk interpretation does not apply.

The Evidence

The landmark evidence base for rs3798220 is anchored by two large independent studies. Clarke et al. 2009 in the New England Journal of Medicine⁸⁸ Clarke et al. 2009 in the New England Journal of Medicine
Genetic Variants Associated with Lp(a) Lipoprotein Level and Coronary Disease. N Engl J Med 2009;361:2518-28 found rs3798220 associated with coronary disease with an odds ratio of 1.92 (95% CI 1.48-2.49)⁹⁹ odds ratio of 1.92 (95% CI 1.48-2.49)
a remarkably large effect size for a common variant — the C allele frequency is only ~2% in Europeans, and showed that rs3798220 and rs10455872 together predicted risk with an odds ratio of 4.87 for individuals carrying two or more risk alleles across both variants.

The Chasman et al. 2009 Women's Health Study¹⁰¹⁰ Chasman et al. 2009 Women's Health Study
Polymorphism in the Apolipoprotein(a) Gene, Plasma Lipoprotein(a), Cardiovascular Disease, and Low-dose Aspirin Therapy. Atherosclerosis 2009;203:371-6 followed 25,131 initially healthy Caucasian women for 9.9 years. The 3.7% who carried the C allele had 2.21-fold higher cardiovascular risk in the placebo group¹¹¹¹ 2.21-fold higher cardiovascular risk in the placebo group
HR 2.21, 95% CI 1.39-3.52, but a critical finding emerged: among carriers assigned to low-dose aspirin, cardiovascular risk was reduced by 56% (HR 0.44, p=0.033) versus only 9% in non-carriers¹²¹² 56% (HR 0.44, p=0.033) versus only 9% in non-carriers
the gene-aspirin interaction p=0.048, suggesting a genotype-specific aspirin benefit.

The Heart Protection Study (n=12,236)¹³¹³ Heart Protection Study (n=12,236)
Lipoprotein(a) Genetic Variants Associated With Coronary and Peripheral Vascular Disease but Not With Stroke Risk. Circ Cardiovasc Genet 2011;4:129-38 confirmed that rs3798220 (as part of an LPA combined score) is strongly associated with coronary disease and peripheral vascular disease but not with ischemic stroke¹⁴¹⁴ not with ischemic stroke
suggesting the thrombotic and atherogenic mechanisms of Lp(a) are site-specific rather than pan-vascular.

A large-scale EHR study of 44,703 individuals¹⁵¹⁵ large-scale EHR study of 44,703 individuals
Association of LPA Variants With Aortic Stenosis. JAMA Cardiol 2018;3:400-408 confirmed rs3798220 associated with aortic valve stenosis (OR 1.31, 95% CI 1.09-1.58, p=0.0036), extending the Lp(a) cardiovascular phenotype beyond atherosclerosis to valvular disease.

A meta-analysis of 55,647 participants¹⁶¹⁶ meta-analysis of 55,647 participants
including 12,406 CHD cases examining both rs3798220 and rs10455872 confirmed significant CHD association under allelic (OR 1.49), dominant (OR 1.53), and other genetic models for rs3798220.

Practical Implications

Carriers of the C allele should measure serum Lp(a)¹⁷¹⁷ measure serum Lp(a)
a single test is sufficient as levels are highly stable over time. Because Lp(a) levels are 70-90% genetically determined and statins do not lower Lp(a), this variant represents a source of residual cardiovascular risk that requires targeted attention beyond standard LDL lowering.

The aspirin finding from the Women's Health Study has generated clinical interest in rs3798220 testing as a decision aid for aspirin therapy in primary prevention¹⁸¹⁸ decision aid for aspirin therapy in primary prevention
particularly relevant given the increased bleeding risk of aspirin, which makes personalized rather than universal aspirin use more attractive. This remains an active area and some health insurers now cover the test for this indication.

Pelacarsen¹⁹¹⁹ Pelacarsen
an antisense oligonucleotide targeting LPA mRNA in hepatocytes reduces Lp(a) by 80-96% and completed a Phase 3 trial (Lp(a) HORIZON) in 8,323 patients; importantly, pelacarsen's Lp(a)-lowering efficacy is unaffected by whether the patient carries rs3798220 or rs10455872²⁰²⁰ pelacarsen's Lp(a)-lowering efficacy is unaffected by whether the patient carries rs3798220 or rs10455872
the antisense mechanism targets all apo(a) mRNA equally regardless of isoform size. PCSK9 inhibitors (evolocumab, alirocumab) provide more modest Lp(a) reduction (~20-27%) plus substantial LDL lowering.

Interactions

The rs3798220 variant interacts additively with rs10455872²¹²¹ rs10455872
the other major LPA cardiovascular risk variant, located in an intron and associated with fewer KIV-2 repeats through a different mechanism. Together, these two SNPs capture the major genetic determinants of elevated Lp(a) in Europeans. Individuals carrying variant alleles at both positions face dramatically elevated risk²²²² dramatically elevated risk
OR 4.87 compared to non-carriers at both variants, which is substantially greater than the sum of individual effects.

The cardiovascular risk from rs3798220 is independent of and additive to LDL cholesterol²³²³ independent of and additive to LDL cholesterol
meaning Lp(a) contributes residual risk beyond what statins and LDL targets address. Carriers with concurrent elevated LDL face compounded atherosclerotic burden.

For the interaction between rs3798220 and rs10455872 producing amplified Lp(a) risk: both CT/CC genotypes at rs3798220 combined with AG/GG at rs10455872 produce an extremely high-risk haplotype warranting aggressive Lp(a)-targeted therapy, with OR 4.87 for coronary disease representing one of the highest effect sizes for common variant combinations in cardiovascular genetics.