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Patients with myotonic muscular dystrophy at increased risk of cancer

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By David Liu

A study in the December 14 issue of JAMA found patients with a severe form of myotonic muscular dystrophy were at increased risk of cancer, primarily of the brain, ovary, colon and endometrium, compared to the general population. 

The study showed that patients with MMD were twice as likely as those without the disease to develop cancers including eye cancer, other female genital organ cancer, thyroid cancer, and pancreatic cancer.

The findings came after authors of the study Shahinaz M. Gadalla, M.D., Ph.D., of the National Cancer Institute, National Institutes of Health, Bethesda, Md., and colleagues analysed data on 1658 patients with MMD registered to the Swedish Hospital Discharge Register or Danish National Patient Registry from 1997 through 2008.

Myotonic muscular dystrophy (MMD) is a form of muscular dystrophy with symptoms like generalized weakness and muscular wasting that affects the face, feet, hands and neck.  Early studies have suggested that patients with MMD may be at increased risk of benign and malignant tumors, according to background information in the article.

From the current study, the researchers found 104 cases of cancer among the patients with MMD, 100 percent higher than the incidence expected in the general population.

"Most notably, we observed significant excesses of endometrial cancer, brain cancer, ovarian cancer, and colon cancer. Our data also suggested possible excesses of eye cancer, other female genital organ cancer, thyroid cancer, and pancreatic cancer. Close similarity in overall and site-specific cancer excess was observed in both Swedish and Danish MMD patients," the authors wrote.

The elevated risk for cancer is the same for both male and female patients with myotonic muscular dystrophy and ages- younger than 50 versus older than 50 years did not make any significant difference in the risk.

"Our findings have implications for the clinical management of MMD patients, including at a minimum the implementation of appropriate validated routine population-based cancer screening strategies, particularly for colon cancer, and careful assessment of therapy-related risks and benefits. The incidence rates for a number of the excess cancers are relatively low, despite their large relative risks. Screening for these uncommon cancers should not be implemented in the absence of demonstrated clinical utility," the researchers concluded.

It is unknown what caused the increase in the cancer risk. It could be that treatments for myotonic muscular dystrophy boost the risk or both cancer and MMD share the same risk factors.

Here is something about MMD cited from http://rarediseases.info.nih.gov/GARD/Disease.aspx?PageID=4&DiseaseID=10419

Myotonic dystrophy is an inherited condition that affects the muscles and other body systems. It is the most common form of muscular dystrophy that begins in adulthood; usually during a person's twenties or thirties. This condition is characterized by progressive muscle loss and weakness, particularly in the lower legs, hands, neck, and face. People with myotonic dystrophy often have prolonged muscle tensing (myotonia) and are not able to relax certain muscles after use. The severity of the condition varies widely among affected people, even among members of the same family.

There are two types of myotonic dystrophy: myotonic dystrophy type 1 and myotonic dystrophy type 2. The symptoms seen in patients with myotonic dystrophy type 2 tends to be milder than those observed in type 1. Although both types are inherited in an autosomal dominant pattern, they are caused by mutations in different genes. Myotonic dystrophy type 1 is caused by mutations in the DMPK gene, while mutations in the CNBP gene are responsible for myotonic dystrophy type 2.

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