rs968567 — FADS2 FADS2 Promoter D6D Activity Variant

Promoter variant in FADS2 that increases delta-6 desaturase (D6D) expression via ELK1 transcription factor binding; the minor T allele elevates D6D activity, accelerating conversion of dietary omega-6 and omega-3 precursors to long-chain PUFAs with downstream effects on arachidonic acid production and inflammatory mediator balance.

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FADS2 rs968567 — The Promoter Dial for Delta-6 Desaturase

Most genetic variants in the FADS gene cluster reduce enzyme activity. rs968567 works differently: the minor T allele turns up delta-6 desaturase (D6D11 D6D
FADS2 — the enzyme that adds a double bond at the sixth carbon position, the rate-limiting first step in converting dietary linoleic acid to GLA and alpha-linolenic acid to stearidonic acid). Instead of blocking PUFA synthesis, T allele carriers push the omega-6 and omega-3 pathways faster — generating more downstream products from dietary precursors. The consequences are nuanced: accelerated conversion boosts EPA production from plant ALA, but also drives more arachidonic acid from omega-6 sources, with opposing effects on inflammatory signalling depending on dietary context.

The Mechanism

rs968567 sits in the promoter region of FADS2 on chromosome 11 (position 61,828,092, GRCh38). The critical molecular finding22 critical molecular finding
Lattka et al. A common FADS2 promoter polymorphism increases promoter activity and facilitates binding of transcription factor ELK1. J Lipid Res, 2010 is that the T allele creates a binding site for ELK1, a member of the ETS transcription factor family. When ELK1 binds, it drives higher FADS2 mRNA transcription. The C allele does not create this binding site, leaving D6D expression at its baseline. Luciferase reporter assays across three cell lines confirmed allele-dependent differences in promoter activity, establishing rs968567 as a functional, mechanistically-explained regulatory variant — not simply a tag for a nearby causal site.

D6D catalyses two parallel reactions: (1) linoleic acid (LA, the dominant dietary omega-6) → gamma-linolenic acid (GLA) → DGLA → arachidonic acid (AA); (2) alpha-linolenic acid (ALA, the plant omega-3) → stearidonic acid (SDA) → eicosatetraenoic acid (ETA) → EPA. Higher D6D activity in T allele carriers means both pathways run faster from the same precursor intake, but whether that produces a net benefit or a net risk depends critically on the ratio of omega-6 to omega-3 in the diet.

The Evidence

The functional promoter finding was validated physiologically in the HELENA study33 HELENA study
Bokor et al. Single nucleotide polymorphisms in the FADS gene cluster are associated with delta-5 and delta-6 desaturase activities estimated by serum fatty acid ratios. J Lipid Res, 2010 — 1,144 European adolescents across seven countries. Of all FADS2 SNPs tested, rs968567 was the only one specifically and significantly associated with higher estimated D6D activity (p=1.5×10⁻⁶). This directly connects the ELK1-driven promoter upregulation seen in cell assays to measurable enzyme activity variation in living humans.

The effect extends to the earliest stage of human development. In the ALSPAC birth cohort44 ALSPAC birth cohort
Lattka et al. Umbilical cord PUFA are determined by maternal and child fatty acid desaturase (FADS) genetic variants in the Avon Longitudinal Study of Parents and Children (ALSPAC). Br J Nutr, 2013, analysing >2,000 mother-child pairs, rs968567 was one of only two FADS2 variants with specific, independent effects on umbilical cord plasma PUFA composition. This means D6D activity differences from rs968567 are not a post-natal diet interaction — they shape fetal fatty acid availability during development.

The net effect on circulating fatty acids in healthy young adults55 healthy young adults
Roke et al. Variation in the FADS1/2 gene cluster alters plasma n-6 PUFA. Prostaglandins Leukot Essent Fatty Acids, 2013 follows predictably: FADS gene cluster minor allele carriers (including rs968567 T allele carriers) showed lower circulating AA and reduced desaturase indices. This appears paradoxical given the T allele elevates D6D — but the explanation lies in genetic LD: rs968567 T allele tags a haplotype that, across the cluster, tracks with different product ratios than the isolated promoter effect would predict. The promoter activity study and the desaturase index study together frame the actual phenotype: elevated D6D at rs968567 specifically shifts flux through both pathways, but the net plasma AA outcome depends on the full FADS haplotype background.

Practical Actions

The key dietary implication of elevated D6D activity is that the balance between omega-6 and omega-3 precursor intake matters more than for people with baseline D6D. T allele carriers convert LA to AA more efficiently: on a Western diet high in linoleic acid (from vegetable oils, processed foods), this produces more arachidonic acid and its pro-inflammatory eicosanoids. The same elevated D6D also converts ALA to SDA and further to EPA more efficiently — meaning T allele carriers are better responders to plant-based omega-3 sources, and better responders to EPA/DHA supplementation when baseline intake is adequate.

The practical priority is managing the omega-6 load specifically — reducing high-LA vegetable oils (soybean, sunflower, corn oil) and replacing with low-LA alternatives (olive oil, macadamia oil, avocado oil) directly limits the AA overproduction that elevated D6D can drive.

Interactions

rs968567 sits on chromosome 11q12.2 in proximity to the broader FADS1/FADS2/FADS3 gene cluster. The promoter variant acts upstream of the FADS2 coding sequence; coding or intronic variants in the same gene (rs174568, rs174575, rs174553) that reduce D6D expression can partially offset the T allele's upregulation effect when co-inherited on the opposite haplotype. For users with both rs968567 T allele and a FADS1 reduced-activity variant (such as rs174541 or rs174547), the downstream pathway is complex: FADS2 elevates EPA substrate supply via faster ALA conversion, but the impaired FADS1 delta-5 step still limits the final EPA yield. The net omega-3 status in this combination depends on both steps — supplementing with preformed EPA/DHA remains the most reliable strategy regardless of which FADS enzyme is rate-limiting.

Nutrient Interactions

linoleic acid (LA) altered_metabolism
alpha-linolenic acid (ALA) altered_metabolism
gamma-linolenic acid (GLA) altered_metabolism
arachidonic acid (AA) altered_metabolism
eicosapentaenoic acid (EPA) altered_metabolism

Genotype Interpretations

What each possible genotype means for this variant.

CC Baseline Converter Normal

Standard FADS2 promoter activity — normal delta-6 desaturase expression

The CC genotype lacks the ELK1 transcription factor binding site that the T allele creates. Without this additional transcriptional driver, FADS2 mRNA levels are at their baseline, and D6D enzyme activity reflects the population norm. In the HELENA study (Bokor et al. 2010), CC homozygotes showed the reference-level desaturase indices used as the comparison group against which T allele effects were measured.

For CC carriers, dietary omega-6:omega-3 ratio remains the dominant determinant of downstream fatty acid balance. Plant-based ALA sources (flaxseed, chia, walnuts) contribute to EPA status through the normal D6D-to-FADS1 cascade, though conversion efficiency is limited by the inherent substrate competition and pathway inefficiency in omnivores on typical Western diets.

CT Elevated Converter Intermediate

One T allele — moderately increased FADS2 promoter activity and D6D expression

Heterozygous CT carriers show intermediate promoter activity between the C-only baseline and the full T/T upregulation. The Bokor et al. 2010 HELENA study confirmed an additive allele-dose relationship at this locus, with each T allele copy incrementally increasing estimated D6D activity in adolescents.

The dual nature of D6D elevation — acting on both omega-6 and omega-3 pathways simultaneously — means the net effect on inflammatory status in CT carriers depends heavily on dietary omega-6 load. In populations eating traditional diets low in linoleic acid (pre-industrial European diets, Mediterranean patterns with olive oil rather than seed oils), elevated D6D would primarily increase beneficial LC-PUFA production. In the context of modern Western diets where LA from soybean and sunflower oil dominates, the elevated D6D drives a disproportionate AA surplus.

CT carriers are better responders to plant omega-3 sources than CC individuals due to moderately faster ALA conversion, but preformed EPA/DHA from marine sources remains more direct and reliable regardless of genotype.

TT High-Activity Converter High

Two T alleles — substantially elevated FADS2 promoter activity and D6D expression with increased arachidonic acid production risk on high omega-6 diets

TT homozygotes carry the maximum ELK1-driven transcriptional upregulation at both FADS2 alleles. In the HELENA study (Bokor et al. 2010), the association between rs968567 minor allele and D6D activity was dose-dependent, meaning TT individuals show the most pronounced enzyme activity elevation. In the ALSPAC cohort (Lattka et al. 2013), rs968567 effects on umbilical cord PUFA levels were present from fetal development — TT carriers enter postnatal life with a D6D-elevated fatty acid phenotype that persists through dietary exposure across the lifespan.

The clinical concern for TT homozygotes on Western diets is the unchecked omega-6 amplification loop: linoleic acid (12-15% of calories in typical Western diets) enters an overactive D6D pipeline and produces elevated DGLA and AA. AA is the precursor to prostaglandins and leukotrienes of the 2-series and 4-series — pro-inflammatory mediators involved in pain, fever, and immune activation. Chronically elevated AA-to-EPA ratios are associated with increased low-grade systemic inflammation markers, including hsCRP.

The same elevated D6D that drives excess AA also accelerates ALA-to-EPA conversion, making TT individuals among the most efficient plant omega-3 converters. However, given the extreme LA dominance in modern diets, the net result without active dietary intervention still favours AA accumulation over EPA. Measuring the AA:EPA ratio directly (via a fatty acid panel or omega-3 index test) is the only way to confirm whether omega-6 or omega-3 products are predominating in this genotype.