rs17222842 — ALOX5AP ALOX5AP variant (SG13S32)

The Leukotriene Switch: ALOX5AP, Inflammation, and Heart Attack Risk

A genetic variant in the ALOX5AP gene — encoding the 5-lipoxygenase-activating protein (FLAP) — tags a risk haplotype that has been linked to myocardial infarction and stroke across multiple European cohorts. FLAP is the membrane scaffold that enables 5-lipoxygenase (5-LOX) to process arachidonic acid into pro-inflammatory leukotrienes, particularly leukotriene B4 (LTB4)¹¹ leukotriene B4 (LTB4)
a potent lipid mediator that recruits neutrophils, activates macrophages, and promotes atherosclerotic plaque formation. Without FLAP, 5-LOX cannot dock on the nuclear membrane and remains catalytically inactive.

The Mechanism

rs17222842 is an intronic tag SNP — a marker, not a functional mutation — that travels with the four-SNP HapB haplotype (rs17216473A–rs10507391A–rs9315050A–rs17222842*G*). Carriers of this haplotype show evidence of increased leukotriene pathway activity, which promotes:

• Macrophage activation and foam-cell formation in arterial plaques
• Endothelial dysfunction via LTB4-driven oxidative stress
• Platelet aggregation and vasospasm through cysteinyl leukotrienes
• Systemic low-grade inflammation measurable as elevated hs-CRP

The minor A allele at rs17222842 is absent from HapB and correlates with reduced haplotype burden — i.e., the A allele tags the absence of the full risk haplotype. Carriers of the A allele therefore represent a genetically lower-risk subgroup.

The Evidence

The story begins with the landmark Helgadottir et al. 2004 Nature Genetics paper²² Helgadottir et al. 2004 Nature Genetics paper
"The gene encoding 5-lipoxygenase activating protein confers risk of myocardial infarction and stroke", which identified ALOX5AP haplotypes as conferring approximately twice the risk of MI and stroke in Icelandic and British populations. A 2005 Scottish replication study³³ 2005 Scottish replication study
Helgadottir A et al., Am J Hum Genet, 2005 confirmed HapA's stroke association (RR 1.36, P=0.007) in 450 stroke patients vs 710 controls.

For HapB specifically — the haplotype defined by the rs17222842 G allele — evidence has accumulated across multiple cohorts:

• A 2010 meta-analysis by Huang et al.⁴⁴ 2010 meta-analysis by Huang et al.
  Arch Med Res, 2010 found HapB associated with CHD (OR 1.33, 95% CI 1.10–1.62) and rs17222842 alone showed a marginal CHD association (OR 1.17, 95% CI 1.00–1.36) across studies published through January 2010.
• An angiography-based Italian study of 1,431 patients (Girelli et al. 2007)⁵⁵ angiography-based Italian study of 1,431 patients (Girelli et al. 2007)
  Eur J Hum Genet, 2007 found HapB associated with angiographically confirmed CAD (OR 1.67, 95% CI 1.04–2.67, P=0.032).
• In a cohort of 1,817 familial hypercholesterolemia patients (van der Net et al. 2009)⁶⁶ cohort of 1,817 familial hypercholesterolemia patients (van der Net et al. 2009)
  Atherosclerosis, 2009, HapB conferred HR 1.48 (95% CI 1.17–1.89, P=0.001) for CHD — rising to HR 1.82 in the highest-LDL subgroup, suggesting synergy between leukotriene-driven inflammation and lipid burden.
• A US European-American study of 1,000 participants (Tsai et al. 2009)⁷⁷ US European-American study of 1,000 participants (Tsai et al. 2009)
  Atherosclerosis, 2009 reported HapB associated with premature CAD with an adjusted OR of 2.05.

Importantly, the A allele itself shows a directly protective signal: Oosterveer et al. 2009⁸⁸ Oosterveer et al. 2009 found the A allele at rs17222842 was protective against tendon xanthomas in 945 FH patients (OR 0.62, 95% CI 0.43–0.90, P=0.01), consistent with reduced inflammatory drive.

However, effect sizes vary across populations and some prospective studies in non-European cohorts found no association, highlighting that this is a moderate-evidence haplotype marker rather than a high-penetrance causal variant.

Practical Actions

For individuals carrying GG (the common genotype, without the protective A allele), strategies that reduce leukotriene-driven inflammation are most relevant:

• Omega-3 fatty acids (EPA/DHA): EPA competes with arachidonic acid for 5-LOX, directly reducing the substrate available for leukotriene synthesis
• Monitoring cardiovascular inflammatory biomarkers (hs-CRP, Lp-PLA2): more informative than standard lipid panels for leukotriene-pathway risk
• Targeted anti-inflammatory diet: reducing dietary arachidonic acid (red meat, high-fat dairy) limits leukotriene precursor availability

For A allele carriers (AG or AA), the protective signal at this locus is reassuring, though it does not override other cardiovascular risk factors.

Interactions

rs17222842 is one of four tag SNPs constituting the ALOX5AP HapB haplotype. The full haplotype is defined by: rs17216473 (A allele) + rs10507391 (A allele) + rs9315050 (A allele) + rs17222842 (G allele). Haplotype carriers who also carry high-LDL variants (e.g. LDLR, APOB, PCSK9) face compounded risk — the Oosterveer/van der Net FH cohorts showed the strongest effects in high-LDL subgroups, suggesting leukotriene- driven inflammation and lipid accumulation act synergistically in plaque development. Interaction with COX-2 (PTGS2) pathway variants may also modulate net eicosanoid balance in favor of or against resolution of arterial inflammation.