Increased Cancer Risk Among Patients with Myotonic Muscular Dystrophy

Myotonic muscular dystrophy (MMD) is a multisystem disorder characterized by myotonic myopathy, cardiac conduction disturbances, insulin resistance, infertility, cognitive impairment, frontal balding, and premature cataracts. Case reports have suggested that the phenotypic spectrum may extend to include an increased risk for cancer, but this putative association has remained somewhat speculative. Now, researchers have examined the risk for cancer among 1658 patients with MMD identified through the Swedish Hospital Discharge Register, the Danish National Patient Registry, and their respective national cancer registries.

During 14,170 person-years of follow-up, there were 104 observed cases of cancer, compared with 52.3 expected cases based on local population-based incidence rates. Thus, the overall cancer risk was increased twofold in those with MMD (standardized incidence ratio, 2.0; 95% confidence interval, 1.6–2.4). The greatest increased risks in MMD patients were for endometrial, brain, ovarian, and colon cancers. The pathological basis for this association remains unclear, but the authors suggest the possibility of RNA-mediated alterations in tumor suppressor gene or oncogene function and defective nucleotide mismatch repair, among other putative mechanisms. This idea derives support from the known biology of myotonic dystrophy, which is caused by repeat expansions in noncoding segments of the DMPK and ZNF9 genes. These genes exert their pathogenic influence via an effect on RNA processing and transcriptional dysregulation.