The heart muscle diseases hypertrophic (HCM) and dilated (DCM) cardiomyopathies are leading causes of sudden death and heart failure in young otherwise healthy individuals. We conducted genome-wide association studies (GWAS) and multi-trait analyses in HCM (1,733 cases), DCM (5,521 cases), and nine left ventricular (LV) traits in 19,260 UK Biobank participants with structurally normal hearts. We identified 16 loci associated with HCM, 13 with DCM, and 23 with LV traits. We show strong genetic correlations between LV traits and cardiomyopathies, with opposing effects in HCM and DCM. Two-sample Mendelian randomization supports a causal association linking increased contractility with HCM risk. A polygenic risk score (PRS) explains a significant portion of phenotypic variability in carriers of HCM-causing rare variants. Our findings thus provide evidence that PRS may account for variability in Mendelian diseases. More broadly, we provide insights into how genetic pathways may lead to distinct disorders through opposing genetic effects.

Cardiac amyloidosis is an under-recognized and potentially fatal cause of heart failure and other cardiovascular manifestations. It is caused by deposition of misfolded precursor proteins as fibrillary amyloid deposits in cardiac tissues. The two primary subtypes of systemic amyloidosis causing cardiac involvement are immunoglobulin light chain (AL), a plasma cell dyscrasia, and transthyretin (ATTR), itself subdivided into a hereditary subtype caused by a gene mutation of the ATTR protein, and an age-related wild type, which occurs in the absence of a gene mutation. Clinical recognition requires a high index of suspicion, inclusive of the extracardiac manifestations of both subtypes. Diagnostic workup includes screening for serum and/or R ESUM E L'amylose cardiaque est une cause sous-reconnue et potentiellement mortelle d'insuffisance cardiaque et d'autres manifestations cardiovasculaires. Elle est caus ee par le d epôt, dans les tissus cardiaques, de prot eines pr ecurseurs mal repli ees prenant la forme de fibrilles amyloïdes. On distingue deux grands sous-types d'amylose syst emique entraînant une atteinte cardiaque : l'amylose à chaînes l egères d'immunoglobulines (AL), une forme de dyscrasie plasmocytaire; et l'amylose à transthyr etine (ATTR), dont il existe un sous-type h er editaire, caus e par une mutation du gène codant pour la TTR, et un sous-type à TTR sauvage, li e au vieillissement et se produisant en l'absence de mutation g enique. La reconnaissance clinique n ecessite

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