His108Arg Transthyretin Amyloidosis-Shedding Light on a Distinctively Malignant Variant

Variant transthyretin amyloidosis cardiomyopathy (ATTRv-CM) is a rare form of cardiac amyloidosis associated with many possible mutations in the transthyretin gene, presenting as various distinct clinical phenotypes. Among these, the His108Arg mutation is the most prevalent TTR variant in Austria. However, data describing its clinical phenotype are lacking. This study aims to describe the characteristics, clinical manifestations, and outcomes of patients with the His108Arg variant focusing on cardiac involvement, disease progression, response to therapy, and imaging findings. Methods: Patients were enrolled from a prospective cardiac amyloidosis registry. The baseline assessment included comprehensive echocardiography, cardiac magnetic resonance imaging, a biomarker analysis, and a clinical evaluation. Patients were followed longitudinally, with outcomes such as arrhythmias, heart failure hospitalizations, and response to disease-targeted therapies recorded. Results: Between March 2012 and June 2024, a total of 20 carriers of the His108Arg variant were identified, with 12 exhibiting clear cardiac involvement and 8 remaining asymptomatic. The median age at diagnosis was 62.3 years with significant heterogeneity in the clinical presentation. Patients with ATTRv-CM had a high prevalence of atrial and ventricular arrhythmias, a reduced left ventricular ejection fraction, and elevated cardiac biomarkers. The majority received specific disease-modifying therapies, with varying tolerance and responses. A longitudinal follow-up indicated frequent arrhythmic events, heart failure exacerbations, and three cases of heart transplantation, underscoring the need for stringent monitoring and individualized management strategies. Conclusions: This study represents a unique, comprehensive analysis of the His108Arg variant in ATTR-CM, highlighting its clinical heterogeneity and significant impact on cardiac function and clinical outcomes.