rs78117248 — ABCA7 ABCA7 AD risk variant

ABCA7 — The Brain's Lipid-Linked Garbage Collector

Your brain generates amyloid-beta peptides continuously, and healthy ageing depends on clearing them efficiently. ABCA7 — an ATP-binding cassette transporter expressed most highly in microglia and excitatory neurons — sits at the intersection of this clearance system and the brain's lipid economy. The rs78117248 variant is an intronic marker that tags an expanded VNTR¹¹ tags an expanded VNTR
Variable Number Tandem Repeat: a stretch of repeating DNA in intron 18 of ABCA7 that can expand beyond 5.6 kb, disrupting how the gene is read and the protein it produces.

The Mechanism

rs78117248 itself is a deep intronic SNP with no direct effect on protein sequence. Its significance comes from what it tracks: carriers of the G allele are significantly more likely to carry an expanded VNTR in ABCA7 intron 18²² VNTR in ABCA7 intron 18. When this repeat expands beyond roughly 5.6 kb, two things happen: overall ABCA7 expression falls (the expanded repeat recruits transcriptional repressors including ZNF263 and PLAG1), and exon 19 is skipped during mRNA splicing³³ exon 19 is skipped during mRNA splicing, removing 44 amino acids from the first nucleotide-binding domain of the protein.

The downstream effects cascade through two well-characterised pathways. First, microglia lacking functional ABCA7 cannot efficiently engulf amyloid-beta oligomers⁴⁴ cannot efficiently engulf amyloid-beta oligomers — in mouse knockouts, hippocampal amyloid clearance is substantially reduced both in cell culture and in the living brain. Second, excitatory neurons with ABCA7 loss-of-function show disrupted phosphatidylcholine metabolism, impaired mitochondrial respiration, elevated oxidative stress, and increased amyloid-beta secretion⁵⁵ disrupted phosphatidylcholine metabolism, impaired mitochondrial respiration, elevated oxidative stress, and increased amyloid-beta secretion — a constellation of changes that mirrors early-stage Alzheimer's pathology.

The Evidence

The VNTR expansion study⁶⁶ VNTR expansion study
De Roeck et al. An intronic VNTR affects splicing of ABCA7 and increases risk of Alzheimer's disease. Acta Neuropathol. 2018 showed that expanded alleles were present in 7.3% of AD patients versus 1.7% of controls in a Belgian cohort (OR 4.5, 95% CI 1.3–24.2). rs78117248 was in strong LD with all three major European GWAS sentinel SNPs for ABCA7 (rs3764650, rs4147929, rs3752246).

A comprehensive 2024 review by Duchateau et al. Alzheimer's & Dementia. 2024⁷⁷ Duchateau et al. Alzheimer's & Dementia. 2024 quantified rs78117248's population-level effect at OR 1.16 (95% CI 1.11–1.20, p = 8.47 × 10⁻⁹) — a modest but robustly replicated association consistent with rs78117248 being an incomplete tag for the higher-penetrance VNTR expansion. The VNTR expansion itself explains the apparently paradoxical finding that this intronic SNP outperforms the coding GWAS variants as a statistical predictor of AD.

The most actionable recent finding comes from a 2025 Nature study by von Maydell et al.⁸⁸ von Maydell et al.: using human iPSC-derived neurons from ABCA7 loss-of-function carriers, the researchers showed that supplementing with CDP-choline (citicoline) — a precursor for phosphatidylcholine synthesis — restored choline-containing phospholipid levels, reversed mitochondrial dysfunction, reduced oxidative stress, normalised amyloid-beta secretion, and reduced neuronal hyperexcitability. This is the first mechanistically direct intervention demonstrated in human neuronal models of ABCA7 dysfunction.

Practical Actions

rs78117248 G carriers face approximately 1.15–1.20-fold elevated AD risk at the population level, with the subset who carry an expanded VNTR facing roughly 4-fold higher risk. Because the SNP tags but does not equal the functional variant, the clearest response is to support the pathways ABCA7 governs: phosphatidylcholine availability and microglial health.

CDP-choline (citicoline), sold as a cognitive supplement and studied in neurological conditions, directly feeds the phosphatidylcholine synthesis pathway that ABCA7 dysfunction impairs. Cognitive monitoring — baseline neuropsychological testing followed by regular reassessment — enables early detection of decline when interventions are most effective. Elevated homocysteine accelerates phospholipid degradation and amplifies cognitive risk; this is especially relevant in ABCA7 risk carriers given the shared neurodegeneration pathway.

Interactions

The ABCA7 locus interacts additively with APOE ε4 status: published studies confirm that ABCA7 risk variant associations remain significant after adjustment for APOE genotype, and dual carriers (ABCA7 risk + APOE ε4) show greater amyloid accumulation than either alone. The compound effect of rs78117248 (or the underlying VNTR) and APOE ε4 (rs429358) represents the strongest common-variant AD risk combination in the neurology category.