rs104894654 — DTNA P121L

Missense variant in alpha-dystrobrevin disrupting the EF-hand calcium-binding domain, associated with left ventricular noncompaction cardiomyopathy in a single Japanese family

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Alpha-Dystrobrevin P121L — A Rare Structural Variant in the Heart's Scaffolding Complex

Alpha-dystrobrevin (encoded by DTNA) is a structural adaptor protein that anchors the dystrophin-glycoprotein complex (DGC)11 dystrophin-glycoprotein complex (DGC)
A macromolecular scaffold connecting the cytoskeleton to the extracellular matrix in muscle cells to the inner surface of the cardiac muscle cell membrane. It acts as a molecular linchpin, physically coupling dystrophin to syntrophins and other signalling proteins. Without it, the DGC loses mechanical resilience under the cyclic stress of every heartbeat. The rs104894654 variant introduces a proline-to-leucine substitution at position 121, inside the protein's calcium-binding EF-hand domain — a region critical for maintaining the protein's three-dimensional shape. This variant has been reported in one Japanese family with left ventricular noncompaction (LVNC), though its current classification is uncertain significance following re-evaluation against population databases.

The Mechanism

The EF-hand domain in alpha-dystrobrevin contains two calcium-binding loop-helix motifs that stabilize the protein's tertiary structure. The P121L substitution replaces the structurally rigid proline — a residue that enforces tight turns in protein chains — with a flexible leucine. Protein sequence modelling predicts that this change shortens a nearby alpha-helix by two residues and removes a loop22 Protein sequence modelling predicts that this change shortens a nearby alpha-helix by two residues and removes a loop
Structural prediction from Ichida et al. 2001, Circulation, potentially destabilizing the EF-hand domain and disrupting its calcium-binding geometry. A weakened DGC anchor in the cardiomyocyte membrane may impair the mechanical buffering that normally prevents trabeculae (the finger-like muscular projections lining the left ventricle) from becoming pathologically prominent — the hallmark of LVNC.

DTNA is expressed on the plus strand of chromosome 18 (GRCh38 position 34,794,249). The C-to-T transition at this locus changes codon 121 from proline (CCG) to leucine (CTG).

The Evidence

Ichida et al. (2001)33 Ichida et al. (2001)
Novel gene mutations in patients with left ventricular noncompaction or Barth syndrome. Circulation 103(9):1256–63 identified the P121L mutation in six affected members across four generations of a Japanese family with LVNC. Five of the six had additional congenital heart defects, primarily ventricular septal defects. The mutation was absent in 300 age- and sex-matched controls (200 Japanese, 100 Caucasian), originally supporting pathogenicity. However, re-examination by Labcorp Genetics (2025)44 Labcorp Genetics (2025) found the T allele present in gnomAD at ~0.002% overall frequency — higher than expected for a dominant, fully penetrant disease allele — and predictive algorithms scored the substitution as likely tolerated, leading to reclassification as uncertain significance (VUS).

A 2006 study55 2006 study
Genetic analysis in 79 Japanese LVNC patients confirming genetic heterogeneity re-identified the same 362C>T change in the DTNA gene, further supporting its association with non-isolated LVNC, but no independent large-scale replication has been published.

Functional support for DTNA's role in LVNC comes from a 2017 transgenic mouse model66 2017 transgenic mouse model
Phenotype and functional analyses in a DTNA N49S mouse model of LVNC in which a different DTNA missense variant (N49S) produced progressive LV hypertrabeculation, LV dilation, and cardiac systolic dysfunction — providing in vivo proof-of-concept that alpha-dystrobrevin dysfunction can cause the LVNC phenotype.

In a broader LVNC outcomes study, Habib et al. (2019)77 Habib et al. (2019)
Genotype-positive status associated with HR 2.49 for death/transplantation found that genotype-positive LVNC patients had twice the rate of death or heart transplantation versus genotype-negative patients (50.0% vs 23.5% over 4.5 years, adjusted HR 2.49, 95% CI 1.15–5.37). This supports close cardiac follow-up for all genotype-positive individuals, regardless of symptom burden at diagnosis.

Practical Actions

Carriers of the T allele at rs104894654 detected in a clinical genetic workup warrant cardiac evaluation to assess for LVNC phenotype — specifically, echocardiography using Jenni criteria (noncompacted-to-compacted myocardial ratio >2:1 in end-systole) and, if equivocal, cardiac MRI (CMR) with a noncompacted-to-compacted ratio >2.3:1 in diastole. Because LVNC clusters in families, first-degree relatives should undergo the same screening. The VUS classification means this variant alone does not confirm disease, but given the family history context and the gene's established LVNC link, clinical surveillance is warranted. Atrial fibrillation develops in 25–30% of LVNC patients and merits periodic ECG or Holter monitoring.

Interactions

DTNA P121L does not have well-characterized gene-gene interactions documented in the literature. LVNC is genetically heterogeneous — other pathogenic genes include MYH7 (beta-myosin heavy chain), MYBPC3 (cardiac myosin-binding protein C), TTN (titin), LDB3, and TAZ. If a proband with this DTNA variant undergoes a comprehensive cardiomyopathy panel and carries an additional pathogenic variant in one of these genes, the combined phenotype may be more severe than either variant alone, as is common in compound-genetic cardiomyopathies.

Genotype Interpretations

What each possible genotype means for this variant.

CC No Variant Detected Normal

Standard alpha-dystrobrevin sequence — no DTNA P121L variant

You carry two copies of the common reference allele at this position in the DTNA gene. The P121L substitution is absent. Nearly all individuals globally share this genotype; the T allele occurs in approximately 1–2 per 100,000 people in most populations, with slightly higher frequency in East Asian populations (~1.3 per 10,000 based on the Japanese population database). Your DTNA protein has the standard proline at position 121, which preserves the normal geometry of the EF-hand calcium-binding domain.

TT Homozygous P121L High Risk

Two copies of the DTNA P121L variant — homozygous state has not been reported; specialist evaluation essential

Because homozygous P121L has never been described, its phenotypic consequences are unknown. By analogy with other autosomal dominant cardiomyopathy genes, biallelic disease variants often produce more severe and earlier-onset phenotypes than heterozygous carriage. For genes like MYH7, TTN, and MYBPC3, compound heterozygosity or homozygosity is associated with pediatric-onset dilated cardiomyopathy, very low ejection fraction, and early need for transplantation.

In clinical practice, a TT result should prompt verification of sequencing quality (rule out technical artifact), followed by referral to a cardiomyopathy specialist with experience interpreting LVNC genetics. Comprehensive cardiac workup including echocardiography, CMR with late gadolinium enhancement (LGE) for fibrosis, and 24-hour Holter monitoring is appropriate.

CT P121L Carrier Carrier

One copy of the DTNA P121L variant — uncertain significance, cardiac evaluation recommended

LVNC is characterized by prominent ventricular trabeculations and deep intertrabecular recesses in the left ventricle, resulting from incomplete compaction of the fetal myocardium during development. Clinically it ranges from asymptomatic (found incidentally) to severe heart failure, arrhythmia, or thromboembolic stroke. Genotype-positive LVNC patients have approximately 2.5 times the rate of death or heart transplantation compared to genotype-negative patients, underscoring the prognostic relevance of genetic findings even when variant classification is uncertain.

The P121L variant disrupts proline 121 in the EF-hand domain of alpha-dystrobrevin, likely altering local protein structure. Proline residues enforce rigid turns in protein chains; replacing one with flexible leucine may destabilize the nearby calcium-binding loop. Whether this structural change is sufficient to disrupt DGC function in the heart is not yet experimentally resolved in humans.

Because LVNC can be familial (autosomal dominant inheritance is common), first-degree relatives who have not undergone genetic testing should be offered cardiac screening with echocardiography regardless of symptoms.