Sarcomere Variants of Uncertain Significance identify an Intermediate Clinical Risk Profile in Hypertrophic Cardiomyopathy

Technical Deep Dive: Sarcomere Variants of Uncertain Significance in Hypertrophic Cardiomyopathy

Overview

This study examined the clinical significance of sarcomere variants of uncertain significance (VUS) in patients with hypertrophic cardiomyopathy (HCM). The researchers aimed to evaluate the associations between variant pathogenicity and clinical characteristics, imaging phenotypes, and patient outcomes.

Problem & Context

HCM is a genetic heart disease characterized by thickening of the heart muscle, which can lead to serious complications like heart failure and sudden cardiac death. Pathogenic or likely pathogenic (P/LP) sarcomere variants are established drivers of HCM, but the clinical impact of sarcomere VUS remains unclear. As VUS are increasingly identified in genetic testing, understanding their significance is crucial for patient management.

Methodology

The researchers conducted a multicenter retrospective cohort study of 438 patients with HCM who underwent genetic testing. Patients were classified into three groups based on their sarcomere variant status: P/LP variants, VUS, and no sarcomere mutations. The researchers compared clinical characteristics, imaging phenotypes, and patient outcomes across these groups.

Data & Experimental Setup

• The study included 438 patients with HCM from two tertiary hospitals.
• Genetic testing was performed using next-generation sequencing.
• Patients were classified into three groups: P/LP variants (39.0%), VUS (36.3%), and no sarcomere mutations.
• The primary endpoint was a composite of cardiovascular death, aborted sudden cardiac death, appropriate implantable cardioverter-defibrillator therapy, and heart transplantation.

Results

• Patients with sarcomere VUS demonstrated intermediate clinical and phenotypic features between P/LP variant carriers and genotype-negative patients.
• Kaplan-Meier analysis showed a graded difference in event-free survival across variant classifications, with P/LP variant carriers having the worst outcomes and genotype-negative patients having the best.
• While VUS were not independently associated with adverse outcomes when modeled as a categorical variable, increasing pathogenicity from genotype-negative to VUS and P/LP variants was associated with a stepwise increase in risk of the primary endpoint.
• Identified VUS were preferentially enriched in Z-disc and giant sarcomere scaffolding proteins.

Interpretation

These findings suggest that sarcomere VUS may not be entirely clinically neutral and represent an intermediate level of sarcomere dysfunction between P/LP variants and the absence of sarcomere mutations. Sarcomere VUS are associated with distinct phenotypic features and clinical outcomes in HCM patients, and should be interpreted within a broader genetic and structural context.

Limitations & Uncertainties

• The study was retrospective, and a prospective validation is needed.
• The analysis was limited to the specific cohort of patients from two tertiary hospitals, and the findings may not be generalizable to all HCM populations.
• The underlying mechanisms linking sarcomere VUS to intermediate clinical features and outcomes are not fully elucidated.

What Comes Next

The researchers recommend further investigation into the structural and functional consequences of sarcomere VUS to better understand their pathogenic potential. Prospective studies are also needed to validate the clinical relevance of sarcomere VUS in HCM and explore their utility for risk stratification and management.