The scientists suggest that some of the genetic changes that lead to MMD may also be responsible for the observed increase in cancer risk, but more research is needed to confirm this hypothesis. The study appeared Dec. 14, 2011, in the Journal of the American Medical Association.
MMD is part of a group of inherited disorders and the most common form of muscular dystrophy in adults. There are two main types of MMD, type 1 and type 2, which are caused by mutations in two different genes. In both cases, the mutation is a result of greater than normal repetition of part of the gene along a segment of DNA. Repetition of parts of genes is common but, in these cases, the repeat length is so excessive that it disrupts normal gene function. Doctors who treat MMD patients occasionally observe the development of benign and malignant tumors. However, it has not been clear whether these cancers were part of the myotonic dystrophy syndrome or just a coincidence.
To determine if MMD patients were at higher risk of cancer than the general population, the scientists identified 1,658 Scandinavian patients with this disorder who were reported to the Swedish Inpatient Hospital Discharge Register from 1987 through 2004 or the Danish National Patient Discharge Registry between 1977 and 2008. The researchers then linked the patients to the corresponding cancer registry in Sweden and Denmark.
In this study, the investigators describe risks of all cancers combined and by cancer type. In addition, they analyzed risks according to age and sex. The investigators found that the cancer risk of MMD patients was twice that of the general population, with the majority of the excess explained by cancers of the colon, brain, endometrium, and ovaries. The excess risk was similar in both the Swedish and Danish cohorts. The researchers also found that, after they excluded cancers of the genital organs, both females and males with MMD had the same excess risk of developing cancer.
“Our study suggests that cancer screening strategies with proven clinical utility in the general population should not be neglected in MMD patients, particularly with regard to colon cancer, since early stage cancers are most easily and effectively treated,” said Mark H. Greene, M.D., chief of the Clinical Genetics Branch, Division of Cancer Epidemiology and Genetics, NCI.
A limitation of this work, according to the scientists, was that they did not have information about known cancer risk factors, such as smoking. They also lacked information on which MMD type each patient had, so they were unable to determine if the increased cancer risk they observed in those with MMD was common to both or confined to a specific type.
“We are conducting studies to examine a number of important questions about MMD and cancer risk, including whether MMD type 1 or type 2 are differentially related to cancer risk; if excess risk can be explained by known risk factors for cancer; and whether there is a relationship between the length of repeated DNA segments and cancer risk,” said Greene.
This study is part of the DCEG’s clinical genetic studies of familial and hereditary cancer syndromes portfolio, and was funded under project 1Z1ACP010144-13, as well as the National Institute of Arthritis and Musculoskeletal and Skin Diseases (contracts: N01-AR-5-2274 and NO1-AR-0-2250), and the National Institute of Neurological Disorders and Stroke (grant: U54-NS048843). Among colleagues who participated in this work are scientists from the Department of Neurology, Neuromuscular Disease Center, University of Rochester (N.Y.) Medical Center, the Karolinska University Hospital Solna and Karolinska Institute, Sweden, and the Statens Serum Institute, Denmark.
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S M Gadalla et al. Cancer risk among patients with myotonic dystrophy.JAMA, Dec. 14, 2011.
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