rs2727270 — FADS2

Intronic regulatory variant in FADS2 that tags a 10-SNP haplotype reducing basal FADS1 and FADS2 expression, lowering long-chain PUFA synthesis capacity and arachidonic acid levels; T allele carriers have lower D5D and D6D activity and reduced fasting insulin.

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FADS2 rs2727270 — The Desaturase Dimmer Switch

Deep in chromosome 11's FADS gene cluster, rs2727270 sits inside the first intron of FADS2 — not in a coding region, but in a regulatory hotspot that acts as a volume control for the entire fatty acid desaturation cascade. The T allele tags a 10-SNP haplotype spanning FADS2 intron 1 that reduces how much of the key desaturase enzymes your cells produce, affecting your ability to convert dietary fats into the biologically active long-chain polyunsaturated fatty acids (LC-PUFAs) that your brain, heart, and immune system depend on.

The Mechanism

The FADS2 intron 1 region containing rs2727270 harbors a conserved regulatory locus11 conserved regulatory locus
a region flanking predicted SREBP and PPARγ transcription factor binding sites, identified by Reardon et al. 2012 as the functional core of the haplotype effect. Two insertion-deletion (INDEL) polymorphisms sit 137 bp and 81–83 bp downstream of a putative sterol response element: all carriers of the minor (T) haplotype carry deletions at these sites, while major haplotype carriers carry insertions.

This structural difference in the regulatory region suppresses basal FADS1 and FADS2 transcription22 FADS1 and FADS2 transcription
FADS1 encodes delta-5 desaturase (D5D), which converts DGLA to arachidonic acid; FADS2 encodes delta-6 desaturase (D6D), which converts linoleic acid to GLA and alpha-linolenic acid to stearidonic acid — both are rate-limiting steps for long-chain PUFA synthesis. The result: T allele carriers have a lower baseline capacity to desaturate dietary omega-6 and omega-3 fatty acid precursors into their long-chain bioactive forms.

The 10-SNP haplotype anchored by rs2727270 (spanning rs2727270 through rs2851682) is present in approximately 24% of Japanese study populations and shows significant population variation — the T allele reaches 33–41% in East Asian populations but stays below 4% in African populations.

The Evidence

Desaturase activity and PUFA composition. A cross-sectional study of 576 healthy Korean men33 cross-sectional study of 576 healthy Korean men
Kim et al. 2011, Nutrition and Metabolism, PMID 21513558 found that rs2727270 T allele carriers had significantly lower serum phospholipid proportions of DGLA (p=0.035) and arachidonic acid (AA, p<0.001), with higher linoleic acid (LA, p=0.026) — the signature of reduced D6D activity, which leaves the omega-6 precursor (LA) partially unconverted. The DGLA/LA ratio, a direct measure of D6D activity, was lower in T allele carriers, confirming the enzymatic bottleneck.

Longitudinal aging effects. A 3-year follow-up study of 122 nonobese Korean men aged 35–5944 3-year follow-up study of 122 nonobese Korean men aged 35–59
Kwak et al. 2013, Clinical Interventions in Aging, PMID 23818766 tracked how FADS genotypes influenced fatty acid trajectories over time. T allele carriers at rs2727270 maintained lower AA concentrations at both baseline (3.99% vs 4.73%, p=0.008) and 3-year follow-up (4.16% vs 5.42%, p=0.001), and showed a significantly attenuated increase in urinary 8-epi-PGF2α — a marker of oxidative stress — over the follow-up period (p=0.003). This lower oxidative stress trajectory in T allele carriers may reflect the reduced AA-derived pro-inflammatory eicosanoid production.

Insulin resistance. Notably, the Korean men's study also found that fasting insulin and HOMA-IR were significantly lower in rs2727270 T allele carriers compared to CC homozygotes — suggesting that reduced AA production and lower D5D/D6D activity may be protective against insulin resistance, at least in this population. This adds a nuanced dimension: the T haplotype's reduced desaturase activity has both costs (impaired EPA/DHA synthesis from plant precursors) and apparent benefits (lower AA-driven inflammation, lower insulin resistance).

T2D and HDL-C. A study of 176 type 2 diabetes patients55 study of 176 type 2 diabetes patients
reported in Int J Environ Res Public Health, PMID 27004414 found progressively lower D5D activity (p-trend=0.039) and D6D activity (p-trend<0.001) with increasing T allele copies, along with a trend toward lower HDL-C (p-trend=0.025). After multivariate adjustment, desaturase activities (not genotype directly) independently predicted HDL-C.

Statin pharmacogenomics. The Reardon et al. 2012 functional study66 Reardon et al. 2012 functional study
Prostaglandins, Leukotrienes and Essential Fatty Acids, PMID 22564485 revealed a striking reversal: while the minor haplotype shows lower basal FADS1/FADS2 expression, simvastatin and the LXR agonist GW3965 induced 20–40% greater upregulation of both desaturases in minor haplotype homozygotes compared to major haplotype carriers. This pharmacogenomic interaction suggests T allele carriers may derive greater PUFA-related benefits from statin therapy.

Practical Actions

For CC homozygotes (the large majority): baseline desaturase activity is higher, but the well-documented omega-6:omega-3 imbalance of modern diets still means that relying on plant ALA alone is insufficient for optimal EPA and DHA status.

For CT and TT genotypes: reduced D5D and D6D activity means the conversion bottleneck from dietary LA to AA, and from ALA to EPA, is more pronounced. Preformed EPA and DHA from marine or algae sources bypasses both impaired steps. The lower AA production may also reduce pro-inflammatory eicosanoid output — a distinction that matters when selecting omega-3 supplementation targets.

Interactions

rs2727270 sits in a large linkage disequilibrium block with rs174537, rs174547, rs174575, rs174576, and rs2851682. However, studies in Mediterranean metabolic syndrome patients identified rs2727270 as a relatively independent association signal77 relatively independent association signal
unlike most top-ranked FADS SNPs which are highly correlated with lead SNP rs174547, rs2727270 showed lower LD with the lead signal in the GWAS by Coltell et al. 2020, PMID 31991592, suggesting it may capture unique functional variation beyond what the rs174537 or rs174547 loci explain. Carriers of multiple FADS risk alleles across the cluster face compounded reductions in desaturase activity.

The pharmacogenomic interaction with statins is also relevant for users who take simvastatin or other statins: T allele carriers at rs2727270 may upregulate desaturase expression more strongly in response to statin treatment, potentially improving long-chain PUFA synthesis capacity as a pleiotropic statin effect.

Nutrient Interactions

omega-3 fatty acids (ALA) impaired_conversion
arachidonic acid (AA) altered_metabolism
eicosapentaenoic acid (EPA) increased_need

Genotype Interpretations

What each possible genotype means for this variant.

CC Full Desaturase Capacity Normal

Standard FADS2 activity — typical long-chain PUFA conversion

You carry two copies of the C allele at rs2727270, the common genotype associated with higher basal expression of FADS1 and FADS2 desaturase enzymes. About 77% of people globally share this genotype (higher in African populations where C allele frequency exceeds 96%). Your cells produce the standard amount of these enzymes, supporting efficient conversion of dietary omega-6 linoleic acid through to arachidonic acid and of omega-3 alpha-linolenic acid toward EPA.

Even with standard desaturase capacity, the typical Western diet's high ratio of omega-6 to omega-3 still limits EPA and DHA status — but this is a dietary issue rather than a genetic conversion bottleneck.

CT Intermediate Desaturase Activity Intermediate

One T allele — mildly reduced FADS2 activity and lower arachidonic acid production

You carry one copy of the T allele at rs2727270, which tags a regulatory haplotype that partially reduces FADS1 and FADS2 expression. About 22% of people globally are CT heterozygotes (CT is more common in East Asian populations where the T allele reaches 34%). Research in Korean men found that T allele carriers had lower serum phospholipid arachidonic acid and DGLA than CC homozygotes, reflecting modestly reduced delta-6 desaturase (D6D) activity in the omega-6 pathway.

The same studies found that fasting insulin and HOMA-IR were lower in T allele carriers — suggesting the reduced AA production carries some metabolic benefit. Your capacity to synthesize EPA from plant-based ALA is also modestly reduced; preformed EPA from marine sources is a more reliable omega-3 source than flaxseed or walnuts for this genotype.

TT Reduced Desaturase Capacity Poor Converter

Two T alleles — substantially reduced FADS1 and FADS2 expression with impaired long-chain PUFA synthesis

The TT genotype places you on the minor FADS2 intron 1 haplotype in both copies. The functional mechanism involves deletions at two insertion-deletion polymorphisms flanking a sterol response element in the FADS2 intron 1 regulatory region. These deletions reduce the transcriptional response of the FADS1 and FADS2 promoters to their normal activating signals, producing less desaturase enzyme under baseline dietary conditions.

The consequence for fatty acid metabolism is a slower rate of conversion at two steps: (1) D6D converts linoleic acid (LA, 18:2 omega-6) to gamma-linolenic acid (GLA) and ALA to stearidonic acid — both of these are slowed; (2) D5D converts DGLA to arachidonic acid and ETA to EPA — also slowed. The net result: higher LA and lower AA in the omega-6 pathway, and slower ALA-to-EPA conversion in the omega-3 pathway.

There is a pharmacogenomic twist: the same regulatory region that reduces basal expression appears more responsive to SREBP-activating signals. Simvastatin and LXR agonists (GW3965) induced 20–40% greater upregulation of both desaturases in minor haplotype homozygotes versus major haplotype carriers. If you take a statin, this variant may amplify the statin's pleiotropic effect on LC-PUFA synthesis — though this finding comes from a single mechanistic study and has not been confirmed in clinical outcomes.