rs1369481 — NPAS2

NPAS2 rs1369481 — A Circadian Clock Variant with Thin but Suggestive Evidence

NPAS2 (Neuronal PAS Domain Protein 2) is the brain-specific paralog of the master circadian clock gene CLOCK. In the forebrain and limbic system, NPAS2 forms heterodimers with BMAL1 to drive the transcription of downstream clock-controlled genes — those that regulate sleep timing, hormone secretion, cell-cycle checkpoints, and DNA repair. NPAS2 is expressed predominantly in the cortex, hippocampus, and striatum¹¹ NPAS2 is expressed predominantly in the cortex, hippocampus, and striatum
Unlike CLOCK, which is expressed ubiquitously, NPAS2 provides brain-specific circadian rhythm generation. The rs1369481 variant sits within an intron of NPAS2 and has been studied primarily in the context of cancer risk — but the evidence for this specific variant is currently limited to a single unreplicated study.

The Variant

Rs1369481 is an intronic single nucleotide variant in which the common allele is C (~79% globally) and the minor allele is T (~21%). The T allele is the GRCh38 reference base at this position, but it is the minor allele in every major population database. The variant does not change the NPAS2 protein sequence — it sits within an intron — and its functional consequence, if any, is unknown. CADD scores (C allele: 5.1, T allele: 4.8) place this well below the threshold typically associated with functional significance. No regulatory feature disruption has been experimentally confirmed.

The Evidence

The primary study naming rs1369481 is Zhu et al. 2009 (Cancer Research)²² Zhu et al. 2009 (Cancer Research)
Testing the Circadian Gene Hypothesis in Prostate Cancer: A Population-Based Case-Control Study, a candidate-gene study of 1,308 prostate cancer cases and 1,266 controls among Caucasian men. The investigators genotyped 41 SNPs across 10 circadian genes and found rs1369481 to be among 11 variants significantly associated with prostate cancer susceptibility — either overall or for aggressive disease. NPAS2 was the only gene with three independent associated variants.

Critical limitation: This study has not been independently replicated for rs1369481 specifically. Two subsequent EPICAP studies by Wendeu-Foyet et al. 2019 (Int J Cancer)³³ Wendeu-Foyet et al. 2019 (Int J Cancer)
Circadian genes and risk of prostate cancer: Findings from the EPICAP study and 2020⁴⁴ 2020
Circadian genes polymorphisms, night work and prostate cancer risk replicated NPAS2 gene-level associations with prostate cancer (including among night workers), but found that no individual SNP reached significance — consistent with rs1369481 being a weak signal within a gene that collectively shows circadian-cancer links. The GWAS Catalog contains no genome-wide significant associations for rs1369481. ClinVar has no entry for this variant.

Separate from prostate cancer, the broader NPAS2 literature documents cancer-relevant biology: Zhu et al. 2007 (Int J Cancer)⁵⁵ Zhu et al. 2007 (Int J Cancer)
Ala394Thr polymorphism in the clock gene NPAS2: a circadian modifier for the risk of non-Hodgkin's lymphoma found that the NPAS2 Ala394Thr variant (rs2305160, a different coding SNP) reduced NHL risk by 34% (OR=0.66, 95% CI 0.51-0.85). This provides biological plausibility — NPAS2 participates in circadian regulation of DNA repair and cell-cycle checkpoints — but does not validate rs1369481 specifically.

For mood and sleep, Soria et al. 2010 (Neuropsychopharmacology)⁶⁶ Soria et al. 2010 (Neuropsychopharmacology)
CRY1 and NPAS2 associated with unipolar major depression identified NPAS2 rs11123857 (not rs1369481) as associated with major depressive disorder in 534 mood disorder patients. Shift-work studies have documented NPAS2 polymorphism effects on sleep phase and daytime sleepiness, again using different SNPs in the gene.

Bottom line on evidence: The association between rs1369481 and prostate cancer is based on one study with no replication, no genome-wide significance, and no known functional mechanism. The honest evidence grade is emerging. Users with the T allele should be aware of this signal but should not treat it as established risk.

Practical Implications

For men carrying the T allele (TC or TT genotype), the available evidence supports discussing prostate cancer screening timing with their physician — not because this variant alone confers high risk, but because it is one of several circadian gene signals associated with prostate cancer in studies of men with European ancestry. Standard PSA testing guidelines apply; this variant does not yet justify altered surveillance schedules on its own.

For circadian health generally: NPAS2 function depends on consistent light-dark cycle entrainment. Regular wake times, morning light exposure, and avoiding artificial light after dark support NPAS2-BMAL1 heterodimer activity regardless of genotype.

For women and for sleep phenotypes: No replicated evidence exists linking rs1369481 to sleep timing, chronotype, mood disorders, or any female-specific outcome.

Interactions

NPAS2 works in concert with CLOCK (its paralog) and the repressor arm of the circadian clock: CRY1, CRY2, PER1, PER2, PER3. Loss of NPAS2 function is partially compensated by CLOCK in most tissues, but not in the forebrain. The CRY1 splice variant rs184039278 (CRY1Δ11), associated with Delayed Sleep Phase Disorder, affects the same transcriptional complex that NPAS2 drives. Whether rs1369481 and CRY1 variants interact additively has not been studied.

The NPAS2 Ala394Thr coding variant (rs2305160) is more extensively studied and is a stronger candidate for cancer risk modification than rs1369481. Individuals who want to assess NPAS2 cancer biology should prioritize rs2305160 data where available.