rs7944926 — DHCR7

DHCR7 Vitamin D Synthesis — Array Coverage Proxy Variant

Your skin makes vitamin D through a two-step process: ultraviolet B light converts 7-dehydrocholesterol (7-DHC)¹¹ 7-dehydrocholesterol (7-DHC)
A cholesterol precursor concentrated in the outer skin layers. It is the substrate for both vitamin D synthesis and DHCR7-mediated cholesterol production in the outer skin into previtamin D3, which spontaneously rearranges into vitamin D3 (cholecalciferol). But the same 7-DHC molecule is also the substrate for DHCR7 (7-dehydrocholesterol reductase), the enzyme that converts it into cholesterol — making DHCR7 a molecular switch governing how much sunlight exposure translates into vitamin D.

rs7944926 is an intronic variant in the NADSYN1 gene on chromosome 11, situated within the same large haplotype block²² haplotype block
A segment of DNA inherited as a unit, typically because recombination within the block is rare. SNPs within a haplotype block track together through generations as the canonical DHCR7 vitamin D variant rs12785878, spanning 63–102 kb depending on the population. The two variants are in near-perfect linkage disequilibrium³³ linkage disequilibrium
LD measures how strongly two variants travel together in a population. r² ≈ 1.0 means the two SNPs are essentially interchangeable as genetic proxies for each other (r² ≈ 1.0 in Europeans), meaning rs7944926 tags exactly the same biological signal as rs12785878. The A allele at rs7944926 co-segregates with the G allele at rs12785878 — both associated with lower circulating 25-hydroxyvitamin D.

The Mechanism

The functional effect at this locus is attributed to regulatory changes that alter DHCR7 transcription or activity. Higher DHCR7 activity channels more 7-DHC toward cholesterol synthesis via the Kandutsch-Russell pathway⁴⁴ Kandutsch-Russell pathway
One of two routes for cellular cholesterol synthesis. DHCR7 reduces the C7-8 double bond in 7-DHC using NADPH, producing cholesterol on the smooth endoplasmic reticulum, leaving less 7-DHC available for UV-driven vitamin D synthesis in the skin. Cholesterol itself accelerates the proteasomal degradation of DHCR7 protein, creating a feedback loop: when cholesterol is plentiful, DHCR7 degrades, 7-DHC accumulates, and vitamin D production is favored. Risk-allele carriers appear to disrupt this balance, sustaining higher DHCR7 activity and reducing vitamin D synthesis capacity.

The Evidence

The landmark 2010 Lancet GWAS⁵⁵ landmark 2010 Lancet GWAS
Wang TJ et al. Common genetic determinants of vitamin D insufficiency: a genome-wide association study. Lancet, 2010 in 33,996 Europeans identified the DHCR7/NADSYN1 locus as one of three genome-wide significant loci for 25(OH)D concentration (P = 2.1 × 10⁻²⁷). Carriers of two risk alleles had mean 25(OH)D approximately 8 nmol/L lower than non-carriers under the same conditions. Each additional risk allele increased the odds of vitamin D insufficiency (below 75 nmol/L) by about 21%.

An evolutionary genetics study⁶⁶ evolutionary genetics study
Kuan V et al. DHCR7 mutations linked to higher vitamin D status allowed early human migration to northern latitudes. BMC Evol Biol, 2013 demonstrated that rs7944926 specifically showed signatures of strong positive selection in European and East Asian populations, with FST values⁷⁷ FST values
FST measures allele frequency differentiation between populations. Values above the 95th percentile relative to genome-wide SNPs indicate selection pressures, not just genetic drift above the 95th percentile on chromosome 11. The G allele (protective, higher vitamin D) rose dramatically in frequency at northern latitudes — from ~15–16% in sub-Saharan Africa to ~72% in Europeans — consistent with selection pressure to maintain vitamin D synthesis in low-UVB environments. This population differentiation is among the strongest seen anywhere in the human genome for this region.

The findings have been confirmed in massive replication. A UK Biobank GWAS⁸⁸ UK Biobank GWAS
Manousaki D et al. Genome-wide association study for vitamin D levels reveals 69 independent loci. Am J Hum Genet, 2020 in 401,460 participants and a concurrent 143-loci study⁹⁹ 143-loci study
Revez JA et al. Genome-wide association study identifies 143 loci associated with 25 hydroxyvitamin D concentration. Nat Commun, 2020 in 417,580 Europeans both confirmed DHCR7/NADSYN1 among the strongest vitamin D loci. rs7944926 has been used as a direct instrument in Mendelian randomization studies of vitamin D-disease relationships, with each A allele associated with approximately 2–3 nmol/L lower serum 25(OH)D.

Practical Implications

Because rs7944926 is an LD proxy for rs12785878, its clinical meaning is identical to that of its canonical partner: a genetic tendency toward reduced vitamin D3 synthesis from sunlight. The per-allele effect is modest in isolation, but it compounds with other vitamin D pathway variants (CYP2R1 rs10741657 for hepatic hydroxylation, GC rs2282679 for D-binding protein transport, CYP24A1 rs6013897 for active D degradation), limited sun exposure, higher latitude, and darker skin pigmentation.

The A allele does not impair absorption of dietary or supplemental vitamin D, making supplementation an effective countermeasure.

Array Coverage Note

This SNP is included in the GeneOps database as an array coverage proxy. If your genome file includes rs12785878 directly, that entry provides equivalent information. If rs12785878 was not genotyped on your array, rs7944926 captures the same biological signal. Both cannot give discordant results in a person with a high-quality genome file — if both are present, results should be consistent.

Evolutionary Context

The stark frequency gradient of the G (protective) allele — from ~12% in West African populations to ~72% in Europeans and ~42% in East Asians — is one of the clearest signatures of latitude-driven natural selection in the human genome. As populations migrated from equatorial Africa to regions with weaker UV radiation, variants that redirected more 7-DHC toward vitamin D synthesis conferred survival advantages against rickets, immune dysfunction, and reproductive impairment. rs7944926 marks this same adaptive sweep.

Interactions

rs7944926 is functionally equivalent to rs12785878 and participates in the same four-locus vitamin D pathway network. Wang et al. (2010) found that individuals in the highest quartile of a combined genetic risk score across DHCR7, CYP2R1 (rs10741657), GC (rs2282679), and CYP24A1 (rs6013897) had 2.47 times the odds of vitamin D insufficiency compared to the lowest quartile. If you carry risk alleles at multiple loci, compound vitamin D supplementation guidance is warranted.