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Genetic Testing Challenges in Oncology: Myotonic Dystrophy Signs Missed in Uterine Cancer Patient

myotonic dystrophy

Precision Oncology News and My Gene Counsel have partnered to produce the "Genetic Testing Challenges in Oncology" series to highlight real-world issues that genetics experts and medical professionals are encountering as genetic tests are increasingly used in cancer care. Experts submit anonymized case reports to My Gene Counsel, and based on the details in these reports, Precision Oncology News writes a feature that describes the case history, challenges encountered by professionals in dealing with the case, and strategies they used in response to challenges or errors. The features also include a discussion with My Gene Counsel genetic counseling experts on better approaches that could be considered if similar cases are encountered in the future. In publishing this series, our aim is to educate experts in the field and foster discussion. If you would like to submit a case report, please email [email protected].

What happened?

An oncologist referred an endometrial cancer patient to a genetic counselor because she was diagnosed at a young age — before age 50. The patient had already undergone surgical treatment before the oncologist referred her to a genetic counselor.

After taking a thorough medical history of this patient and her relatives, the genetic counselor discovered the patient had a strong family history of myotonic dystrophy, an inherited disorder caused by mutations in the DMPK or CNBP gene and characterized by muscle weakness or wasting. Type 1 myotonic dystrophy affects muscles in the lower legs, hands, neck, and face, while type 2 disease impacts the muscles in the center of the body, like in the neck, shoulders, elbows, and hips.

Patients with this condition can have difficulty relaxing their muscles, slurred speech, temporary lockjaw, cataracts, cardiac defects, and diabetes mellitus. When myotonic dystrophy occurs at birth, it can cause more severe, life-threatening congenital defects. Symptoms of myotonic dystrophy can begin in adults in their twenties or thirties and may be mild enough to allow them to have a normal life span or may manifest more severely such that they are physically disabled and live a shorter life.

In addition to a strong family history of myotonic dystrophy, the genetic counselor noted that this patient had clinical signs of the condition prior to her endometrial cancer workup.

How was the case resolved?

Given the patient's experience with early-onset cancer, the genetic counselor ordered genetic testing to assess if she had any pathogenic variants in genes known to increase the risk of endometrial and related cancers. The test did not identify any pathogenic hereditary cancer risk variants.

However, genetic tests for assessing hereditary cancer risk would not analyze the genes associated with myotonic dystrophy, which studies have shown can increase the risk of thyroid, skin, and uterine malignancies, such as early-onset endometrial cancer, in patients. Recognizing this, the genetic counselor referred the patient to the adult genetics department for a full evaluation.

Why is this case concerning?

While the results of this genetic workup are not known, based on the patient's personal and family medical history, the genetic counselor expects that genetic testing will likely confirm her strong suspicions that this woman has myotonic dystrophy. It is concerning that no medical professional, neither her oncologist nor another doctor, had connected this patient’s symptoms and family history of myotonic dystrophy earlier and performed the appropriate diagnostic evaluations, said Meagan Farmer, genetic clinical operations director at My Gene Counsel.

"It's fair to say that these physical symptoms should have been noted and genetic testing should have been ordered earlier by a physician," said Farmer, who is also the director of the cancer genetic counseling program at the University of Alabama at Birmingham. "The oncologist missed this, but it's also a lot to expect that the oncologist should have captured all this at the same time as trying to come up with a treatment plan for the patient, especially when myotonic dystrophy would have been outside of scope of this physician."

The Myotonic Dystrophy Foundation has issued recommendations for managing the cardiac, muscle weakness, ocular, and other symptoms associated with type 1 and type 2 forms of the disease. With regard to the cancer risks, experts "strongly encourage" patients to follow general population screening guidelines for colon, breast, testicular, and cervical cancers, and be on the watch for symptoms that could indicate cancers of the brain, uterus, ovaries, and thyroid.

Increased cancer screening isn't recommended for myotonic dystrophy patients, and it's unclear if greater awareness of endometrial cancer symptoms would have led to an earlier diagnosis in her case, but it certainly should have impacted her surgical planning. Myotonic dystrophy patients can have erratic responses to anesthesia, and the Myotonic Dystrophy Foundation recommends closely monitoring patients' cardiac rhythm, and ventilatory and gastrointestinal functions while they're receiving anesthesia for surgery.

By the time the genetic counselor in this case noted that this patient needed to undergo formal genetic evaluation for myotonic dystrophy, she had already had surgery. If the oncologist had referred the woman for a genetic evaluation before surgery, it would have delayed her treatment, Farmer said, but she added that the alternative also isn’t ideal in this case. This patient's surgeon, for example, likely would have wanted to know in advance if she needed to be monitored closely for myotonic dystrophy-related complications while under anesthesia.

key takeaways_myotonic dystrophy

What could have been done differently?

Information about patients' family history of illness is "one of the most critical pieces of data we have" when diagnosing diseases, Farmer said, and that's why "we often harp on the need to take a thorough family history." But she also recognized that, in practice, doctors may only ask about the risk of specific diseases based on their specialty.

"For instance, I'll see a breast oncologist just ask about a family history of breast or ovarian cancer … when we know pathogenic variants in cancer predisposition genes are often linked with multiple cancers," Farmer said. "And, in this case, even family history beyond cancer mattered."

While it may not be possible or realistic to expect that all doctors will take a complete family history of all diseases for all patients, Farmer noted that a case like this highlights the need for health technology tools that help doctors collect family health history within electronic medical records and consistently integrate that information into patient care. Such tools certainly could have helped doctors flag much earlier this patient's concerning family history of myotonic dystrophy that warranted further follow-up.

"I would have loved to have seen this patient's primary care physician notice the clinical signs and refer her to neurology or genetics," Farmer said. "If she ended up with a genetic diagnosis, they could have flagged her cancer risks earlier instead of doing all this backwards."