Sex- and Exercise-Dependent Modulation of Hypertrophic Remodeling by the MCT1 rs1049434 Polymorphism

Background: The monocarboxylate transporter 1 (MCT1) plays a central role in myocardial lactate handling and metabolic adaptation. The functional rs1049434 polymorphism (T1470A; Asp490Glu) affects MCT1-mediated lactate transport and substrate utilization, but its clinical relevance in sarcomere-related hypertrophic cardiomyopathy (HCM) remains poorly defined. Methods: We studied 56 carriers of pathogenic or likely pathogenic sarcomeric variants followed in a familial HCM program. All participants underwent standardized clinical phenotyping, including electrocardiography, transthoracic echocardiography and cardiac magnetic resonance imaging. Genotyping of MCT1 rs1049434 was performed on genomic DNA. Analyses focused on sex-stratified genotype distribution, phenotypic expression among the 26 individuals who fulfilled diagnostic criteria for HCM, and the influence of habitual vigorous exercise. Septal wall thickness was the primary structural endpoint. Results: Among the 26 patients with established HCM (10 women, 16 men), a marked sex-specific effect emerged. Female carriers of the T-allele (TT/TA) exhibited significantly greater interventricular septal thickness compared with AA homozygotes (23.2 vs. 14.2 mm; p = 0.037). In men, septal thickness did not differ by genotype. However, male patients engaged in vigorous physical activity showed a consistently milder structural phenotype, including lower septal thickness (18.3 vs. 19.9 mm; p = 0.585) and directionally favorable markers of mechanical severity. Phenotypic distribution was predominantly asymmetric septal hypertrophy in both sexes, without genotype-dependent differences. Conclusions: The phenotypic impact of MCT1 rs1049434 in sarcomere-positive HCM is context-dependent. In women, impaired monocarboxylate handling is associated with greater hypertrophic remodeling, whereas in men, exercise-related metabolic conditioning appears to attenuate disease severity. These findings support a genotype–sex–environment interaction relevant to precision medicine approaches in HCM..