Endothelial Nitric Oxide Synthase (eNOS)

Clinical Usage

  • To identify individuals with increased risk of developing Coronary Artery Disease
  • Evaluate patients with symptoms of coronary spasm

Background Information

Nitric oxide plays an important role in maintaining vascular tone. A deficiency in its synthesis may predispose individuals to various coronary vascular disorders, such as coronary spasm, angina pectoris and myocardial infarction. 
eNOS protein catalyses the synthesis of nitric oxide. Presence of a T-786C mutation in the eNOS gene results in decreased synthesis of nitric oxide and confers a 3-fold greater risk for coronary spasm. Since coronary spasm is difficult to diagnose, screening for this eNOS mutation in families with risk for coronary artery disease would enable early and appropriate therapy.

Gene Information

eNOS gene is located on chromosome 7q36 position. T-786C mutation is located upstream of the transcription start site and influences the gene expression level. 
The following three possible genotypes for eNOS genes are reported:
– Normal (-/-)
– Heterozygous (+/- for T-786C) 
– Homozygous (+/+ for T-786C)

Population Information

This mutant form of eNOS gene (T-786C) is generally very rare in healthy population. Some researchers report about 3% of individuals with the mutation.

Test Method

The test was developed using CLSI guidelines.  Control DNA samples of known genotype are tested together with each patient sample to monitor the performance of the test.  Genomic DNA is extracted from the submitted blood specimen and analyzed by Polymerase chain reaction (PCR) followed by restriction digest.



Whole blood in a purple top (EDTA) tube

Rejection Criteria

Blood specimen:
• It is collected in a heparin-containing tube because heparin can inhibit the PCR reaction.
• It leaked in the shipping container.
• The name on the tube does not match the name on the paperwork.
• It is older than 10 days.


Normal (-/-): Generally, no change in nitric oxide. 

  • Heterozygous (+/- for T-786C): Heterozygosity for eNOS mutation (T-786C) may be associated with reduced nitric oxide synthesis and increased risk for coronary spasms. 
  • Homozygous (+/+ for T-786C): Homozygosity for eNOS mutation (T-786C) may be associated with reduced synthesis of nitric oxide and greater risk for coronary spasm and vascular disorders.

CPT code


Test Limitations

Other genetic variants of the eNOS gene that are not detected in this assay may influence the enzyme activity. Other genetic and non-genetic factors may also influence the risk of coronary disease progression.  The detection of genetic variants does not replace the need for appropriate clinical monitoring by the health care provider.  This test was developed and the performance characteristics were determined by MDL. This test has not been cleared or approved by the US Food and Drug Administration.  The FDA has determined that such approval is not necessary.


Scientific Articles on eNOS. Free PDF copies of some of these articles can be 
obtained from PubMed at NCBI (National Center for Biotechnology Information):

Ghilardi G, Biondi ML, DeMonti M, Bernini M, Turri O, Massaro F, Guagnellini E, Scorza R. Independent risk factor for moderate to severe internal carotid artery stenosis: T786C mutation of the endothelial nitric oxide synthase gene.

Clin Chem. 2002 Jul;48(7):989-93. Free pdf copy.

Rossi GP, Cesari M, Zanchetta M, Colonna S, Maiolino G, Pedon L, Cavallin M, 
Maiolino P, Pessina AC. The T-786C endothelial nitric oxide synthase genotype 
is a novel risk factor for coronary artery disease in Caucasian patients of the GENICA study. J Am Coll Cardiol. 2003 Mar 19;41(6):930-7.

Nakayama M, Yoshimura M, Sakamoto T, Shimasaki Y, Nakamura S, Ito T, Abe 
K, Yamamuro M, Miyamoto Y, Saito Y, Nakao K, Yasue H, Ogawa H. 
Synergistic interaction of T-786–>C polymorphism in the endothelial nitric oxide synthase gene and smoking for an enhanced risk for coronary spasm.

Pharmacogenetics. 2003 Nov;13(11):683-8.

Yoshimura M, Nakayama M, Shimasaki Y, Ogawa H, Kugiyama K, Nakamura 
S, Ito T, Mizuno Y, Harada E, Yasue H, Miyamoto Y, Saito Y, Nakao K. A 
T-786–>C mutation in the 5′-flanking region of the endothelial nitric oxide 
synthase gene and coronary arterial vasomotility. Am J Cardiol. 2000 Mar 

Miyamoto Y, Saito Y, Nakayama M, Shimasaki Y, Yoshimura T, Yoshimura M, 
Harada M, Kajiyama N, Kishimoto I, Kuwahara K, Hino J, Ogawa E, Hamanaka 
I, Kamitani S, Takahashi N, Kawakami R, Kangawa K, Yasue H, Nakao K. 
Replication protein A1 reduces transcription of the endothelial nitric oxide 
synthase gene containing a -786T–>C mutation associated with coronary 
spastic angina. Hum Mol Genet. 2000 Nov 1;9(18):2629-37.

Nakayama M, Yasue H, Yoshimura M, Shimasaki Y, Ogawa H, Kugiyama K, 
Mizuno Y, Harada E, Nakamura S, Ito T, Saito Y, Miyamoto Y, Ogawa Y, Nakao 
K. T(-786)–> C mutation in the 5′-flanking region of the endothelial nitric oxide synthase gene is associated with myocardial infarction, especially without coronary organic stenosis. Am J Cardiol. 2000 Sep 15;86(6):628-34.

Nakayama M, Yasue H, Yoshimura M, Shimasaki Y, Kugiyama K, Ogawa H, 
Motoyama T, Saito Y, Ogawa Y, Miyamoto Y, Nakao K. T-786–>C mutation in 
the 5′-flanking region of the endothelial nitric oxide synthase gene is associated with coronary spasm. Circulation. 1999 Jun 8;99(22):2864-70. Free pdf copy:

Barbera JA, Peinado VI, Santos S, Ramirez J, Roca J, Rodriguez-Roisin R. 
Reduced expression of endothelial nitric oxide synthase in pulmonary arteries of smokers. Am J Respir Crit Care Med. 2001 Aug 15;164(4):709-13.

Free pdf copy:

Barua RS, Ambrose JA, Eales-Reynolds LJ, DeVoe MC, Zervas JG, Saha DC. 
Dysfunctional endothelial nitricoxide biosynthesis in healthy smokers with 
impaired endothelium-dependent vasodilatation. Circulation. 2001 Oct 
16;104(16):1905-10. Free pdf copy.

Barua RS, Ambrose JA, Srivastava S, DeVoe MC, Eales-Reynolds LJ. Reactiveoxygen species are involved in smoking-induced dysfunction of nitric oxide biosynthesis and upregulation of endothelial nitric oxide synthase: an in vitro demonstration in human coronary artery endothelial cells.

Circulation. 2003 May 
13;107(18):2342-7. Free pdf copy.
Barua RS, Ambrose JA, Saha DC, Eales-Reynolds LJ. Smoking is associated 
with altered endothelial-derived fibrinolytic and antithrombotic factors: an in vitro demonstration. Circulation. 2002 Aug 20;106(8):905-8. Free pdf copy.

Nasreen S, Nabika T, Shibata H, Moriyama H, Yamashita K, Masuda J, 
Kobayashi S. T-786C polymorphism in endothelial NO synthase gene affects
cerebral circulation in smokers: possible gene-environmental interaction.

Arterioscler Thromb Vasc Biol. 2002 Apr 1;22(4):605-10. Free pdf copy.

Wang J, Dudley D, Wang XL. Haplotype-specific effects on endothelial NO 
synthase promoter efficiency: modifiable by cigarette smoking. Arterioscler 
Thromb Vasc Biol. 2002 May 1;22(5):e1-4.

Perez-Ruiz A, Montes R, Velasco F, Lopez-Pedrera C, Antonio Paramo J, Orbe 
J, Hermida J, Rocha E. Regulation by nitric oxide of endotoxin-induced tissue
factor and plasminogen activator inhibitor-1 in endothelial cells. Thromb 
Haemost. 2002 Dec;88(6):1060-5.

Articles on Stromelysin-1 (aka, MMP3)

Liu PY, Chen JH, Li YH, Wu HL, Shi GY. Synergistic effect of stromelysin-1 
(matrix metallo-proteinase-3) promoter 5A/6A polymorphism with smoking on the 
onset of young acute myocardial infarction. Thromb Haemost. 2003 

Humphries SE. The stromelysin-1 (MMP-3) gene and risk of coronary artery 
disease: a candidate gene that has won the election? Thromb Haemost. 2003