rs74315379 — TNNT2 R141W / R151W

TNNT2 R141W — When the Heart's Tension Sensor Goes Quiet

Every heartbeat is a precisely timed surge of calcium flooding the cardiac muscle cell, binding to troponin C, and pulling troponin T¹¹ troponin T
Cardiac troponin T (encoded by TNNT2) is the tropomyosin-binding subunit of the troponin complex — it anchors the regulatory machinery to the thin filament and transmits the calcium signal into mechanical force into a conformation that lets the myosin motors fire. When calcium retreats, troponin T reverts, the motors disengage, and the heart relaxes. The TNNT2 R141W variant — an arginine-to-tryptophan substitution at codon 141 (or 151, depending on transcript isoform) — breaks this feedback loop by making the troponin T–tropomyosin complex abnormally stable. The motors do not disengage as completely; the heart struggles to generate force proportional to the available calcium signal. The result is dilated cardiomyopathy (DCM)²² dilated cardiomyopathy (DCM)
Dilated cardiomyopathy: the left ventricle enlarges and weakens, reducing pump efficiency. In genetic forms, onset often occurs in the second to fourth decade and can progress to heart failure, arrhythmia, or sudden death — and in some families, left ventricular noncompaction (LVNC).

The variant is classified Pathogenic/Likely pathogenic by ClinVar (VCV000012414) with 16 of 20 independent submitters in agreement and a two-star review status. OMIM lists it as allelic variant 191045.0007. It is absent from gnomAD population databases at meaningful frequency, consistent with a disease allele under strong negative selection.

The Mechanism

Arginine 141 sits within the tropomyosin-binding domain³³ tropomyosin-binding domain
The region of TNNT2 that physically contacts alpha-tropomyosin along the thin filament; mutations here alter how tightly the troponin complex holds tropomyosin in the "off" position of cardiac troponin T. The arginine residue is positively charged and normally forms a salt bridge with glutamic acid 257 of alpha-tropomyosin. Replacing it with tryptophan — a bulky, hydrophobic residue — destroys this salt bridge and instead locks tropomyosin into an over-stabilized interaction with troponin T; quartz-crystal microbalance experiments⁴⁴ quartz-crystal microbalance experiments
A technique that measures binding kinetics between purified proteins with nanogram sensitivity by detecting changes in oscillation frequency as mass accumulates on a crystal surface showed the R141W mutation increases troponin T affinity for alpha-tropomyosin approximately three-fold compared to wild-type.

The functional consequence is paradoxical: stronger troponin T–tropomyosin binding makes it harder to open the thin filament, not easier. Troponin I, the inhibitory subunit, retains the thin filament more effectively in the blocked state, requiring higher intracellular calcium concentrations to generate the same contractile force — a state called calcium desensitization⁵⁵ calcium desensitization
Reduced myofilament sensitivity to calcium: the heart must work harder to sustain output, which over time drives maladaptive remodeling — chamber dilation, fibrosis, and impaired systolic function.

The Evidence

Lu et al., 2003⁶⁶ Lu et al., 2003
Lu QW et al., J Mol Cell Cardiol 2003;35:1377–83 — in vitro reconstitution with recombinant human TNNT2 R141W and alpha-tropomyosin; quartz-crystal microbalance binding assays and skinned fiber mechanics in rabbit cardiac muscle provided the first molecular explanation for R141W's DCM mechanism: three-fold tighter tropomyosin binding and direct demonstration of reduced Ca²⁺ sensitivity of force development.

Ramratnam et al., 2016⁷⁷ Ramratnam et al., 2016
Ramratnam M et al., PLoS One 2016;11(12):e0167681 — gene-targeted knock-in mouse model (Tnnt2^R141W/+); optical mapping, echocardiography, skinned fiber mechanics, and β-adrenergic stress testing in heterozygous mice demonstrated that heterozygous mice develop overt DCM with left ventricular dilation, reduced contractility, and significant Ca²⁺ desensitization. Hearts compensated by raising peak systolic calcium transient amplitude by 54% above wild-type — but this compensation prolonged the diastolic calcium fall and impaired cardiac responses to stress. Male mice had significantly worse survival than females (P<0.001), suggesting sex-modifying factors.

Hershberger et al., 2009⁸⁸ Hershberger et al., 2009
Hershberger RE et al., Circ Cardiovasc Genet 2009;2(4):306–13 — bidirectional resequencing of TNNT2 in 313 DCM probands; functional testing in porcine cardiac fiber preparations found TNNT2 mutations in 2.9% of DCM probands, characterized by early-onset aggressive disease (median onset 32.5 years) with Ca²⁺ desensitization as the consistent functional hallmark. The R141W variant was found in 3 individuals with DCM and segregated with disease in 16 affected relatives from 2 families; it also occurred de novo in one individual with LVNC — the first documented de novo R141W case.

Klaassen et al., 2008⁹⁹ Klaassen et al., 2008
Klaassen S et al., Circulation 2008;117(22):2893–901 — systematic sequencing of MYH7, ACTC, and TNNT2 in 63 unrelated adult LVNC probands identified heterozygous sarcomeric mutations in 11 of 63 cases (17%), including one TNNT2 mutation, establishing that the same sarcomeric gene variants that cause HCM and DCM can also present as LVNC — a phenotypically distinct condition sharing overlapping genetic architecture.

An iPSC model of pediatric DCM from TNNT2 R151W confirmed the calcium desensitization and sarcomere disorganization in patient-derived cardiomyocytes, and showed that overexpression of wild-type TNNT2 partially rescued the contractile defect — early evidence supporting future gene-therapy approaches.

Practical Actions

The autosomal dominant nature of R141W means a single copy is sufficient to cause disease. Each first-degree relative of a carrier has a 50% chance of inheriting the variant. Penetrance is high but variable: in the original R141W family, 5 of 19 carriers were phenotypically unaffected at evaluation ages ranging from 1 to 47 years, indicating that age-dependent penetrance and environmental modifiers influence expression.

Cardiac management follows current DCM and LVNC guidelines: establish baseline left ventricular dimensions and function, monitor for arrhythmias (atrial fibrillation affects 25–30% of LVNC patients; ventricular arrhythmias drive sudden death risk), consider anticoagulation (thromboembolism risk in LVNC is 21–38% over a lifetime), and use guideline-directed heart failure therapy (ACE inhibitors/ARBs, beta-blockers, diuretics) once systolic dysfunction develops.

Interactions

The R141W mutation has been reported in combination with an MYPN (myopalladin) S1296T variant in a family with severe LVNC — the compound digenic combination appeared to produce a more penetrant noncompaction phenotype than either variant alone, with Tnnt2 R141W/+ mice (but not Mypn S1296T/+ mice) showing cardiac hypertrabeculation and noncompaction in the murine model.

Other sarcomeric gene mutations in MYH7 (rs104894664), TPM1 (rs104894502, rs104894503), MYBPC3 (rs36211723), and ACTC (rs193922385) can produce overlapping DCM/LVNC/HCM phenotypes. "Double positive" sarcomeric genotypes — two pathogenic variants in different sarcomeric genes — are associated with earlier onset and more severe disease.