Survival patterns and cancer determinants in families with myotonic dystrophy type 1

Background and purpose Research indicates that patients with myotonic dystrophy type 1 (DM1) are at increased risk of cancer and early death. Family data may provide insights given DM1 phenotypic heterogeneity, the broad range of non‐muscular manifestations and the usual delays in the diagnosis of DM1. Method Family history data were collected from 397 genetically and/or clinically confirmed DM1 patients (respondents) enrolled in the US or UK myotonic dystrophy registries. Standardized mortality ratios were calculated for DM1 first‐degree relatives (parents, siblings and offspring) by their reported DM1 status (affected, unaffected or unknown). For cancer‐related analyses, mixed effects logistic regression models were used to evaluate factors associated with cancer development in DM1 families, including familial clustering. Results A total of 467 deaths and 337 cancers were reported amongst 1737 first‐degree DM1 relatives. Mortality risk amongst relatives reported as DM1‐unaffected was comparable to that of the general population [standardized mortality ratio (SMR) 0.82, P = 0.06], whilst significantly higher mortality risks were noted in DM1‐affected relatives (SMR = 2.47, P