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 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) | 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) 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 plaques | similar to LDL, but resistant to statin
therapy; pro-inflammatory oxidized
phospholipids (OxPL) carried by the apolipoprotein(a) kringle domains |
OxPL drives macrophage activation and arterial wall inflammation;
and 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 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 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)
| 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 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 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-carriers | the gene-aspirin
interaction p=0.048, suggesting a genotype-specific aspirin benefit.
The 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 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 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 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) | 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 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.
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 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 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 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 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.
All Genotypes
Common genotype with no rs3798220-related elevation in Lp(a) or cardiovascular risk
You carry two copies of the common T allele at rs3798220, meaning this specific variant does not elevate your lipoprotein(a) levels or increase your cardiovascular risk above baseline. About 96% of people of European ancestry share your genotype. Your Lp(a) levels are determined by other genetic factors — primarily the KIV-2 repeat count and other LPA variants — and are likely in the population-typical range (median ~10 mg/dL in Europeans). A one-time Lp(a) measurement remains clinically useful as independent assessment of this important risk factor.
One C allele markedly elevates Lp(a) levels and approximately doubles cardiovascular event risk
You carry one copy of the C risk allele at rs3798220 (Ile4399Met). This heterozygous genotype is associated with median Lp(a) levels of approximately 79.5 mg/dL — roughly 8 times higher than the non-carrier median of 10.0 mg/dL. The Women's Health Study found that C allele carriers had a 2.21-fold higher risk of major cardiovascular events (MI, stroke, cardiovascular death). About 3.7% of people of European ancestry carry the C allele. Critically, this genotype also predicts a 56% reduction in cardiovascular risk with low-dose aspirin, compared to only 9% in non-carriers.
Two C alleles produce extremely elevated Lp(a) and the highest genetic cardiovascular risk from this variant
You carry two copies of the C risk allele at rs3798220 — a rare genotype found in fewer than 0.1% of people of European ancestry. Homozygosity for this missense variant is associated with very high Lp(a) levels, typically well above 150 mg/dL (median reported in the Women's Health Study cohort was 153.9 mg/dL). This represents the extreme end of Lp(a)-driven cardiovascular risk from this variant, and warrants specialist evaluation. Like the heterozygous CT genotype, you may derive particular benefit from aspirin therapy.