Abstract Background Dilated cardiomyopathy (DCM) is characterised by left ventricular or biventricular systolic dysfunction and dilatation, in the absence of abnormal loading conditions or coronary artery disease (1). Up to 30% of cases have an identified monogenic cause, usually with autosomal dominant (AD) inheritance (2). The disease appears to be twice as common in males, suggesting either a sex specific penetrance or a potential difference in expressivity. This sex ratio has not been systematically evaluated for genetic forms of DCM. Purpose To assess the sex ratio in patients with all-cause DCM compared to genetic (monogenic) and gene-elusive subtypes, defined by the presence or absence of a pathogenic variant in DCM-associated genes. Methods A literature search was conducted to identify cohorts of DCM patients with identifiable sex ratios. Exclusion criteria were patients with syndromic, X-linked, mitochondrial, or autosomal recessive (AR) DCM. Studies with a small cohort size (n<100), a paediatric population, unidentifiable sex ratio, or ischaemic and peripartum DCM were excluded. 98 studies with a total of 36,662 participants were included in this study. A random-effects meta-analysis generated a pooled proportion of female participants with a 95% confidence interval (95% CI) for an overall DCM cohort as well as for the subtypes – all genetic DCM, individual gene level for 10 key DCM genes (including titin, TTN, and lamin, LMNA), and gene elusive DCM. Results The overall DCM cohort had a 0.30 female proportion (95% CI: 0.28-0.32; Figure 1). This corresponds to a male:female (M:F) ratio of 2.38:1. This ratio did not significantly change in patients with an identified causative DCM variant (0.31 [95% CI 0.26-0.36]; M:F ratio of 2.22:1; p=0.563). There was also no significant difference when compared to patients who had been genetically tested with no identified variant (0.30 [95% CI 0.24-0.37]; M:F ratio of 2.29:1; p=0.814). Furthermore, the ratio within participants with AD gene variants was not significantly different for the specific genes of TTN (0.28 [95% CI 0.22-0.36]; M:F ratio of 2.51:1) and LMNA (0.35 [95% CI 0.27-0.44]; M:F ratio of 1.84:1). Overall, the sex ratio amongst patients with these AD gene variants was similar to the all-cause group (0.34 [95% CI 0.28-0.40]; M:F ratio of 1.98:1; p=0.18); Figure 2. Conclusions This meta-analysis suggests that DCM is twice as prevalent in males than females, even in pooled monogenic genetic subtypes with an equally prevalent genetic risk factor, indicating a difference in penetrance between the sexes. Further studies are required to determine the drivers of this sex specific penetrance.Forest plots: overall DCM cohortForest plots: gene-specific DCM cohort