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, which is the basic unit of muscle contraction. Sarcomeres are made up of thick and thin filaments. The overlapping thick and thin filaments attach (bind) to each other and release, which allows the filaments to move relative to one another so that muscles can contract. The troponin complex, along with calcium, helps regulate tensing (contraction) of cardiac muscle.
For the heart to beat normally, cardiac muscle must contract and relax in a coordinated way. Cardiac troponin I helps to coordinate contraction of the heart. When calcium levels are low, the troponin complex binds to the thin filament. This binding blocks the interaction between the thick and thin filaments that is needed for muscle contraction. An increase in calcium levels causes structural changes in another troponin complex protein called troponin C, which then triggers the troponin complex to detach from the thin filament, allowing the heart muscle to contract.
Health Conditions Related to Genetic Changes
Familial hypertrophic cardiomyopathy
Mutations in the TNNI3 gene can cause familial hypertrophic cardiomyopathy, a condition characterized by thickening (hypertrophy) of the cardiac muscle. TNNI3 gene mutations are found in less than 5 percent of people with this condition. Although some people with hypertrophic cardiomyopathy have no obvious health effects, all affected individuals have an increased risk of heart failure and sudden death.
Most TNNI3 gene mutations in familial hypertrophic cardiomyopathy change single protein building blocks (amino acids) in the cardiac troponin I protein. The altered protein is likely incorporated into the troponin complex, but it may not function properly. It is unclear how these mutations lead to the features of familial hypertrophic cardiomyopathy.
In some people, hypertrophic cardiomyopathy develops into restrictive cardiomyopathy (described below), although it can be difficult to distinguish these two disorders.More About This Health Condition
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, which impairs 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.More About This Health Condition
Familial dilated cardiomyopathy
MedlinePlus Genetics provides information about Familial dilated cardiomyopathyMore About This Health Condition
Mutations in the TNNI3 gene can also cause another heart conditions called dilated cardiomyopathy. This condition weakens and enlarges the heart, preventing it from pumping blood efficiently. Dilated cardiomyopathy increases the risk of heart failure and premature death.
Other Names for This Gene
- cardiac troponin I
- troponin I type 3 (cardiac)
- troponin I, cardiac muscle
Additional Information & Resources
Tests Listed in the Genetic Testing Registry
Scientific Articles on PubMed
- 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. Review. Citation on PubMed
- 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. Epub 2005 Jun 15. Citation on PubMed
- 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. Review. Citation on PubMed
- Kaski JP, Syrris P, Burch M, Tomé-Esteban MT, Fenton M, Christiansen M, Andersen PS, Sebire N, Ashworth M, Deanfield JE, McKenna WJ, Elliott PM. 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. Epub 2008 May 8. Citation on PubMed
- 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. Epub 2008 Jan 29. Review. Erratum in: Nat Clin Pract Cardiovasc Med. 2008 Nov;5(11):747. Citation on PubMed
- 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. Epub 2011 Mar 22. Review. Citation on PubMed
- 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. Review. Citation on PubMed
- Willott RH, Gomes AV, Chang AN, Parvatiyar MS, Pinto JR, Potter JD. 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. Epub 2009 Nov 12. Review. Citation on PubMed
- 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. Epub 2010 Mar 16. Review. Citation on PubMed