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TNNI3 gene
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Gene

TNNI3 gene

The TNNI3 gene encodes cardiac troponin I, a protein essential for regulating contraction and relaxation of heart muscle.

Overview

The TNNI3 gene provides instructions for making a protein called cardiac troponin I, which is found solely in the heart (cardiac) muscle. Cardiac troponin I is one of three proteins that make up the troponin protein complex in cardiac muscle cells. The troponin complex is associated with a structure called the sarcomere, the basic unit of muscle contraction. Sarcomeres are made up of thick and thin filaments that overlap, bind, and release to allow muscle contraction.

The troponin complex, together with calcium, helps regulate tension (contraction) of cardiac muscle. When calcium levels are low, the troponin complex binds to the thin filament, blocking interaction between thick and thin filaments and preventing contraction. An increase in calcium causes structural changes in troponin C, triggering the complex to detach from the thin filament and allowing the heart muscle to contract. Cardiac troponin I therefore coordinates normal heartbeats by mediating contraction and relaxation.

Health Conditions Related to Genetic Changes

Familial restrictive cardiomyopathy

Approximately 10 mutations in the TNNI3 gene have been found to cause familial restrictive cardiomyopathy, which is characterized by stiffening of the heart muscle. Most of these mutations change single amino acids in the cardiac troponin I protein, impairing the protein's function. The altered protein typically cannot bind to actin. As a result, heart muscle relaxation is disrupted, leading to abnormal heart function, impaired blood flow, and the signs and symptoms of familial restrictive cardiomyopathy, such as fatigue and fainting.

Nonsyndromic dilated cardiomyopathy

MedlinePlus Genetics provides information about Nonsyndromic dilated cardiomyopathy.

Nonsyndromic hypertrophic cardiomyopathy

MedlinePlus Genetics provides information about Nonsyndromic hypertrophic cardiomyopathy.

Other Names for This Gene

  • cardiac troponin I
  • cTnI
  • TNNI3_HUMAN
  • troponin I type 3 (cardiac)
  • troponin I, cardiac muscle

Additional Information & Resources

Tests Listed in the Genetic Testing Registry

  • Tests of TNNI3

Scientific Articles on PubMed

  • PubMed

Catalog of Genes and Diseases from OMIM

  • CARDIOMYOPATHY, DILATED, 1FF; CMD1FF
  • CARDIOMYOPATHY, DILATED, 2A; CMD2A
  • TROPONIN I, CARDIAC; TNNI3

Gene and Variant Databases

  • NCBI Gene
  • ClinVar

References

  • Bashyam MD, Savithri GR, Kumar MS, Narasimhan C, Nallari P. Molecular genetics of familial hypertrophic cardiomyopathy (FHC). J Hum Genet. 2003;48(2):55-64. doi: 10.1007/s100380300007.
  • Gomes AV, Liang J, Potter JD. Mutations in human cardiac troponin I that are associated with restrictive cardiomyopathy affect basal ATPase activity and the calcium sensitivity of force development. J Biol Chem. 2005 Sep 2;280(35):30909-15. doi: 10.1074/jbc.M500287200.
  • Gomes AV, Potter JD. Cellular and molecular aspects of familial hypertrophic cardiomyopathy caused by mutations in the cardiac troponin I gene. Mol Cell Biochem. 2004 Aug;263(1-2):99-114. doi: 10.1023/B:MCBI.0000041852.42291.aa.
  • Kaski JP, Syrris P, Burch M, et al. Idiopathic restrictive cardiomyopathy in children is caused by mutations in cardiac sarcomere protein genes. Heart. 2008 Nov;94(11):1478-84. doi: 10.1136/hrt.2007.134684.
  • Keren A, Syrris P, McKenna WJ. Hypertrophic cardiomyopathy: the genetic determinants of clinical disease expression. Nat Clin Pract Cardiovasc Med. 2008 Mar;5(3):158-68. doi: 10.1038/ncpcardio1110.
  • Marston SB. How do mutations in contractile proteins cause the primary familial cardiomyopathies? J Cardiovasc Transl Res. 2011 Jun;4(3):245-55. doi: 10.1007/s12265-011-9266-2.
  • Sen-Chowdhry S, Syrris P, McKenna WJ. Genetics of restrictive cardiomyopathy. Heart Fail Clin. 2010 Apr;6(2):179-86. doi: 10.1016/j.hfc.2009.11.005.
  • Willott RH, Gomes AV, Chang AN, et al. Mutations in Troponin that cause HCM, DCM AND RCM: what can we learn about thin filament function? J Mol Cell Cardiol. 2010 May;48(5):882-92. doi: 10.1016/j.yjmcc.2009.10.031.
  • Xu Q, Dewey S, Nguyen S, Gomes AV. Malignant and benign mutations in familial cardiomyopathies: insights into mutations linked to complex cardiovascular phenotypes. J Mol Cell Cardiol. 2010 May;48(5):899-909. doi: 10.1016/j.yjmcc.2010.03.005.

Genomic Location

The TNNI3 gene is found on chromosome 19.

Medical Encyclopedia

  • Genes
  • Genetics

Understanding Genetics

  • What is DNA?
  • What is a gene?
  • What is a gene variant and how do variants occur?

Frequently Asked Questions

Early signs often include unexplained fatigue, shortness of breath with mild activity, and occasional fainting (syncope). As stiffness of the heart walls worsens, patients may develop swelling in the legs or abdomen, reduced exercise tolerance, and a rapid or irregular heartbeat. New onset of chest discomfort or worsening shortness of breath at rest should trigger immediate medical attention.
Because TNNI3 mutations are inherited in an autosomal‑dominant manner, first‑degree relatives have a 50 % chance of carrying the same variant. Cascade genetic testing—targeted sequencing of the known family mutation—offers the most efficient approach. A baseline cardiac evaluation (echocardiogram, ECG, and possibly cardiac MRI) is advised for anyone who tests positive, even if asymptomatic.
Yes. Prenatal diagnostic testing (chorionic villus sampling or amniocentesis) can detect the known TNNI3 variant. For couples undergoing in‑vitro fertilization, pre‑implantation genetic testing for monogenic disorders (PGT‑M) allows selection of embryos without the mutation. Genetic counseling should be sought to discuss success rates, risks, and ethical considerations.
Patients benefit from low‑sodium diets, regular moderate‑intensity aerobic activity as tolerated, and avoidance of excessive alcohol or stimulants. Medications such as beta‑blockers, ACE inhibitors, or angiotensin‑receptor blockers can reduce cardiac workload and improve filling pressures. In some cases, anticoagulation is added if atrial fibrillation develops. Close follow‑up with a cardiologist experienced in genetic cardiomyopathies is essential.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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