What you carry at this position in your DNA and what research says about it.
QT Interval Duration: 10/10 evidence, 21 publications.
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Sample genotype (not yours): C/C
Typical Heart Recharging Time
A typical QT interval duration and normal cardiac electrical activity are expected with this genetic profile. There is no genetically elevated risk of rhythm-related complications from this variant.
What this genotype means: Typical QT interval duration; Baseline risk of long QT syndrome; Normal ventricular repolarization.
Sample genotype (not yours): C/T
Slightly Prolonged Heart Recharging Time
One copy of the T allele is associated with a slightly longer QT interval of about 4.4 milliseconds on average. This can slightly increase the time it takes for the heart's ventricles to electrically recharge.
What this genotype means: Slightly prolonged QT interval; Modestly increased risk of long QT syndrome; Altered ventricular repolarization.
Sample genotype (not yours): T/T
Prolonged Heart Recharging Time
Two copies of the T allele are associated with a prolonged QT interval of about 8.8 milliseconds on average. This slower electrical recharging of the heart ventricles is linked to a higher risk of rhythm irregularities.
What this genotype means: Prolonged QT interval; Increased risk of long QT syndrome; Altered T-wave morphology.
Gene function and biological role
Gene Function: Nitric oxide synthase 1 adaptor protein (NOS1AP) is a signaling adapter molecule that modulates the activity of neuronal nitric oxide synthase [1]. In cardiac tissue, this protein plays a crucial role in regulating the electrical activity of the heart, particularly during the repolarization phase when the ventricles recharge after a heartbeat [2]. Variations in this gene can alter the function of cardiac ion channels, which directly impacts the timing of the heart's electrical cycle [3]. Researchers have consistently linked genetic changes in and around this gene to variations in the QT interval on electrocardiograms [4].
Variant Impact: The rs12143842 variant is a single nucleotide polymorphism located near the NOS1AP gene on chromosome 1. This genetic change is one of the most strongly associated markers with QT interval duration discovered to date [1]. The presence of the variant T allele is associated with a prolonged QT interval, representing a slower electrical recovery of the heart ventricles [5]. This prolongation can alter ventricular repolarization dynamics and T-wave morphology on an electrocardiogram [6]. Consequently, this variant has been studied for its potential to modify the risk of cardiac events and sudden cardiac arrest [7].
Key Insight: This variant is the single strongest common genetic predictor of QT interval duration discovered to date, yet it lies in a non-coding region near the NOS1AP gene rather than directly inside a cardiac ion channel gene.
Location: NOS1AP. Chromosome 1 · 1q23.3 · 162.1 Mb
Estimated prevalence by population
Global 60.7%; European 55.7%; African 76.8%; East Asian 41.8%; South Asian 34.7%; Americas 60.5%; Ashkenazi 48.4%; Finnish 56.6%; Middle Eastern 49.6%; Amish 50.2%.
Estimated CC genotype frequency.
Global 33.8%; European 37.9%; African 21.7%; East Asian 45.7%; South Asian 48.4%; Americas 34.6%; Ashkenazi 42.3%; Finnish 37.3%; Middle Eastern 41.7%; Amish 41.3%.
Estimated CT genotype frequency.
Global 5.5%; European 6.4%; African 1.5%; East Asian 12.5%; South Asian 16.9%; Americas 4.9%; Ashkenazi 9.2%; Finnish 6.1%; Middle Eastern 8.8%; Amish 8.5%.
Estimated TT genotype frequency.
Showing effects for C/C genotype
Cardiovascular & Metabolic
Heart Rhythm & Conduction
QT Interval. Evidence: 10/10. Source: PMID 18927126. Typical.
Long QT Syndrome. Evidence: 5/10. Source: PMID 32429735. Typical Risk.
Tachycardia. Evidence: 3/10. Source: PMID 28827735. Typical Risk.
T Wave Morphology. Evidence: 6/10. Source: PMID 31607149. Typical.
Showing effects for C/T genotype
QT Interval. Evidence: 10/10. Source: PMID 18927126. ~4.4 ms Increase.
Long QT Syndrome. Evidence: 5/10. Source: PMID 32429735. Slightly Increased.
Tachycardia. Evidence: 3/10. Source: PMID 28827735. Slightly Increased.
T Wave Morphology. Evidence: 6/10. Source: PMID 31607149. Altered.
Showing effects for T/T genotype
QT Interval. Evidence: 10/10. Source: PMID 18927126. ~8.8 ms Increase.
Long QT Syndrome. Evidence: 5/10. Source: PMID 32429735. Increased Risk.
Tachycardia. Evidence: 3/10. Source: PMID 28827735. Increased Risk.
What this genotype means for the people who carry it
Sample genotype: CC (Homozygous)
Two copies of the common C allele are associated with a baseline, typical QT interval duration on electrocardiograms [1]. This means the heart's ventricles recharge their electrical system at a standard rate after each contraction [2]. Studies indicate that individuals with this genotype do not experience the genetic prolongation of ventricular repolarization linked to the variant allele [3]. Consequently, this genetic profile is associated with a typical baseline risk for long QT syndrome and related ventricular arrhythmias [4]. Maintaining healthy cardiovascular habits remains important, but this specific genetic marker does not add any extra risk to your cardiac electrical profile [5]. The absence of the T allele means there is no genetic predisposition to altered T-wave morphology from this locus [6]. Most clinical guidelines view this genotype as the standard reference for cardiac repolarization studies [7]. Overall, this result represents a highly favorable genetic baseline for heart rhythm stability [8].
Typical QT interval duration; Baseline risk of long QT syndrome; Normal ventricular repolarization.
Sample genotype: CT (Heterozygous)
A single copy of the T allele is associated with an average increase of approximately 4.4 milliseconds in the QT interval duration [1]. This prolongation reflects a slightly slower electrical recovery or repolarization of the heart's lower chambers [2]. Large-scale genetic studies have confirmed this association across multiple diverse populations [3]. While a few milliseconds' difference is generally small and often asymptomatic, it represents a measurable shift in cardiac electrical dynamics [4]. This genetic variation has also been linked to a modest increase in the susceptibility to long QT syndrome and ventricular repolarization changes [5]. It is a common genetic factor that contributes to the natural variation in heart rhythms observed among individuals [6]. For most people, this slight increase does not cause any noticeable health issues or require medical intervention [7]. However, it may interact with other risk factors, such as certain medications that are known to prolong the QT interval [8].
Slightly prolonged QT interval; Modestly increased risk of long QT syndrome; Altered ventricular repolarization.
Sample genotype: TT (Homozygous)
Two copies of the T allele are associated with a more pronounced prolongation of the QT interval, averaging about 8.8 milliseconds [1]. This represents a slower electrical recharging process in the heart's ventricles after each beat [2]. This specific variant is recognized as one of the strongest common genetic influences on QT interval duration [3]. The prolonged repolarization can be detected as changes in T-wave morphology and JT intervals on an electrocardiogram [4]. Clinical studies have shown that this prolongation is associated with an elevated risk of long QT syndrome and ventricular arrhythmias [5]. While many individuals with this genotype never experience symptoms, the slower electrical recovery can make the heart more sensitive to certain triggers, such as specific medications or electrolyte imbalances [6]. Understanding this genetic tendency can be useful when discussing new prescriptions with a healthcare provider [7]. It highlights the importance of maintaining overall cardiovascular health and avoiding known QT-prolonging substances [8].
Prolonged QT interval; Increased risk of long QT syndrome; Altered T-wave morphology.
Variants with shared genetic architecture
rs10494366 · NOS1AP Gene · Chr 1 · Cardiac QT Interval
rs11153730 · PLN Gene · Chr 6 · QT Interval Duration
rs1805123 · KCNH2 Gene · Chr 7 · Heart Rhythm
Identification of a common variant at the NOS1AP locus strongly associated to QT-interval duration.
Impact of ancestry and common genetic variants on QT interval in African Americans.
Common variants at ten loci modulate the QT interval duration in the QTSCD Study.
Cardiovascular Predictive Value and Genetic Basis of Ventricular Repolarization Dynamics.
Common variants at ten loci influence QT interval duration in the QTGEN Study.
Content updated August 2026.
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