ORPHAN DISEASE

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People with a Form of Muscular Dystrophy May Have Elevated Cancer Risk

 

Myotonic muscular dystrophy (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.

 

According to a study published online in the Journal of the American Medical Association (14 December 2100), adults with MMD may be at increased risk of developing cancer. The authors 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.

 

To determine if MMD patients were at higher risk of cancer than the general population, the authors identified 1,658 Scandinavian patients with MMD 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 the study, the investigators describe risks of all cancers combined and by cancer type. In addition, they analyzed risks according to age and gender. Results showed 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 study also found that, after cancers of the genital organs were excluded, both females and males with MMD had the same excess risk of developing cancer.

 

A limitation of this work, according to the authors, 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.

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