rs10918594 — NOS1AP

NOS1AP and the QT Interval — A Common Variant in the Heart's Electrical Timing

The QT interval¹¹ QT interval
the time between the start of ventricular depolarization and the end of repolarization, measured on an electrocardiogram is one of medicine's most important cardiac biomarkers. A prolonged QTc interval predisposes to torsades de pointes²² torsades de pointes
a dangerous polymorphic ventricular tachycardia that can degenerate into ventricular fibrillation and sudden cardiac death. Genetics account for roughly 30% of QTc variation in the population — and the NOS1AP gene harbors one of the strongest common genetic contributors ever discovered.

NOS1AP (also called CAPON — Carboxy-terminal PDZ ligand of Neuronal nitric Oxide synthase) encodes an adaptor protein that physically binds to neuronal nitric oxide synthase (nNOS). Though originally studied in the brain, nNOS is expressed in cardiac myocytes where it plays a key role in modulating calcium handling and action potential duration.

The Mechanism

nNOS in cardiomyocytes inhibits the L-type calcium channel³³ L-type calcium channel
the main inward calcium current that drives and prolongs cardiac contraction and activates the delayed rectifier potassium current. Together, these effects accelerate ventricular repolarization — shortening the action potential and therefore the QT interval. NOS1AP/CAPON interacts with nNOS and modulates the efficiency of this signaling cascade.

rs10918594 is a C>G variant located upstream of NOS1AP, approximately 55 kb from a second functional SNP in the same gene (rs10494366, r²=0.63, D′=0.89). Neither SNP is a coding variant — they sit in regulatory or non-coding sequence and have no known functional effect on the protein itself. Instead, they appear to tag a causal regulatory variant that alters NOS1AP expression in cardiac tissue. Direct evidence supports this interpretation: analysis of NOS1AP RNA levels in human right ventricular tissue⁴⁴ analysis of NOS1AP RNA levels in human right ventricular tissue
cardiac samples from 17 patients undergoing pacemaker lead extraction found that CC homozygotes (major allele) had lower NOS1AP expression than GG minor homozygotes. Lower NOS1AP expression correlates with shorter QTc — meaning the G allele raises NOS1AP/CAPON expression, which amplifies nNOS signaling and paradoxically reduces nNOS's ability to shorten the action potential. The net effect is prolonged repolarization.

The Evidence

The original discovery came from the landmark Rotterdam Study⁵⁵ Rotterdam Study
a prospective population-based cohort of 3,761 individuals aged ≥55 years in the Netherlands. The rs10918594 G allele (31% frequency in this European cohort) was associated with a 3.6-ms increase in QTc per additional allele copy (95% CI 2.7–4.4; P=6.9×10⁻¹⁷) — a highly significant genome-wide association replicated across dozens of subsequent studies. GG homozygotes averaged 7.2 ms longer QTc than CC homozygotes.

Replication in the Diabetes Heart Study⁶⁶ Diabetes Heart Study
European-American families with and without type 2 diabetes confirmed and extended the finding. Minor homozygotes had QT intervals 12.5 ms longer than major homozygotes overall (P=1.5×10⁻⁶). Critically, the effect was stronger among diabetic individuals (13.9-ms difference), suggesting that diabetic cardiomyopathy creates a permissive background in which NOS1AP-dependent calcium dysregulation is amplified.

Beyond QTc prolongation, NOS1AP variation is associated with sudden cardiac death (SCD) risk⁷⁷ NOS1AP variation is associated with sudden cardiac death (SCD) risk
in 233 SCD cases over 11.9 years of follow-up in the Rotterdam Study — and this SCD association appears to be at least partially independent of the effect on QT duration, suggesting NOS1AP influences arrhythmia susceptibility through mechanisms beyond simple QT prolongation.

NOS1AP has also emerged as a genetic modifier of congenital Long QT syndrome (LQTS)⁸⁸ genetic modifier of congenital Long QT syndrome (LQTS)
inherited channelopathies caused by loss-of-function mutations in KCNQ1, KCNH2, and SCN5A. Among LQTS patients, G allele carriers had higher rates of life-threatening cardiac events (24.8% vs 17.8%), and the variant independently predicted arrhythmia risk beyond QTc alone — meaning NOS1AP genotyping adds prognostic information on top of standard clinical assessment in these patients.

Drug-induced QT prolongation⁹⁹ Drug-induced QT prolongation
a major cause of drug withdrawal and black-box warnings across multiple drug classes is also modified by NOS1AP variants. The G allele was associated with increased risk of amiodarone-induced ventricular arrhythmia. The Rotterdam Study specifically showed that G allele carriers had a significantly potentiated QTc-prolonging response to verapamil (a calcium channel blocker) — consistent with the mechanistic role of NOS1AP in L-type calcium channel regulation.

A systematic meta-analysis published in 2019¹⁰¹⁰ systematic meta-analysis published in 2019
pooling data across multiple cohorts confirmed that the NOS1AP QTc association is particularly strong in women and in patients with diabetes mellitus, and that the sudden death association is significant in Caucasian populations.

Practical Actions

For carriers of one or two G alleles, the primary concern is QTc prolongation. A QTc above 450 ms in men or 460 ms in women is considered borderline prolonged; above 500 ms substantially elevates arrhythmia risk. NOS1AP's 3.6-ms-per-allele effect is modest in isolation — GG homozygotes average about 7 ms longer QTc — but the clinical stakes rise when other QT-prolonging factors stack on top.

Key risks to manage: certain medications (including many antiarrhythmics, antibiotics, antipsychotics, and antihistamines) prolong the QT interval independently, and G allele carriers face an amplified combined effect. Electrolyte disturbances — particularly hypokalemia and hypomagnesemia — further extend the QT interval and lower the threshold for torsades de pointes. Diabetics with G alleles face a compounded risk because both diabetic autonomic neuropathy and NOS1AP variants independently prolong QTc.

Interactions

The two principal NOS1AP SNPs — rs10918594 and rs10494366 — are in moderate linkage disequilibrium (r²=0.63) and are typically co-inherited. Their combined effects have not been formally quantified in a compound-genotype analysis, but given their shared locus and similar effect sizes, they likely tag the same functional regulatory variant rather than act through independent mechanisms.

Interaction with rs12143842 (and its proxy rs16847549), a neighboring NOS1AP variant, was the strongest SCD signal in the Rotterdam Study follow-up analysis. In the congenital LQTS context, NOS1AP G allele carriers with KCNQ1 variants also showed elevated risk — suggesting the NOS1AP-nNOS pathway compounds with the primary channelopathy.