Genetic Testing for Myotonic Dystrophy

Myotonic community members often contact the Foundation with questions about genetic testing. Their questions range from how to find facilities that conduct genetic testing for myotonic dystrophy (DM) types 1 and 2 to whether or not they should be tested and how to assess the benefits and risks of having a genetic test.

The question of whether or not to be tested is best answered in partnership with a physician or genetic counselor who understands your family history, your personal circumstances and reasons for exploring genetic testing. Implications associated with DM genetic testing are financial as well as emotional. For this reason, the question of whether to get genetic testing for DM should be considered carefully.

We spoke with Carly Siskind, MS, LCGC, senior genetic counselor on the Stanford University Neuromuscular Disorders Team about the pros and cons of testing and the impact it can have on issues such as insurability.

What do you do as a genetic counselor?

Usually people are referred to me by a specialist such as a neurologist. Sometimes individuals call my office directly. My job is two-fold: to provide basic information about genetics and the implications of testing, and to be the person between the doctor and the patient to help interpret “doctor speak.”

I’d like to emphasize that while genetic testing can provide definitive answers with regard to the presence of disorders like DM, the decision of whether to pursue genetic testing is a personal one with significant potential impacts, both positive and negative. I encourage anyone considering genetic testing to consult with his or her physician or qualified medical professional first, and to consider working with a genetic counselor; we can be helpful in navigating this process.

Do most people understand how DM gets passed along?

Most people I’ve met with to discuss myotonic dystrophy are already fairly well educated on the topic, but I find it helpful to go through some of the basics nonetheless. DM is a complicated disease; for instance, if someone has not inherited the CTG (DM1) or CCTG (DM2) repeat expansion and both copies of this gene—one from each parent—are in the normal range, then he or she won’t develop DM or pass it on to future generations. Only if someone has the expansion will that person potentially experience symptoms or risk passing DM on to his or her children.

What are some of the pros and cons of genetic testing for DM?

If a person isn’t experiencing any DM symptoms but has a family history of DM, it is important to consider the consequences of being tested. Insurability is probably the biggest concern. Even if someone doesn’t have symptoms or a DM diagnosis, if his or her genetics indicate that there is potential to develop DM in the future, it can—and probably will—impact that person’s ability to secure life, disability and long term care insurance. While it is sometimes possible to get this insurance with a family history of DM, it is nearly impossible to get it with a diagnosis, and a diagnosis might still delay access to health insurance.

Because of this, we generally recommend that people think about setting up insurance policies prior to being tested in case their test comes back positive. Unlike health insurance, there’s no federal protection against discrimination for these other three types of insurance.

What are some of the reasons to consider getting tested?

Having a genetic test for DM provides information that, should the test result be positive, can assist the attending physician in anticipating complications, and can also allow for easier insurance approval for other diagnostic testing such as an EKG to detect arrhythmia, a common issue for those with DM. While clinicians typically use the repeat number to help inform diagnosis and care considerations, I have found that people in the community like to use this number as a way to help tell their personal stories and create connections to others living with DM.

Is the DM genetic test widely available? Where can people find a lab if they want to be tested?

There are a number of labs that conduct testing for DM, including academic or institutional settings such as Baylor College of Medicine, etc., and for-profit corporations such as Athena Diagnostics and Medical Neurogenetics. There are a number of labs in the U.S. that offer testing for DM. Prices can vary considerably depending on the lab and whether someone is being tested for DM1 or DM2. I would advise people to do their research in advance, and call their insurance plan before testing to see if the insurance company will cover a particular lab.

Insurance plans may request a CPT code to consider a request for genetic test reimbursement. CPT stands for Current Procedural Terminology and is generated by the American Medical Association for coding, billing and insurance purposes. CPT codes can be found on each lab’s website and are publically available.

The insurance company may also want an ICD-9 code, which is a diagnosis code used by the US Centers for Disease Control (CDC) and other international public health agencies to assist with disease reporting. ICD stands for International Classification of Diseases. The current diagnostic code for myotonic dystrophy is 359.21. Updated ICD-10 codes will be implemented in October 2014 and at that time the DM code will change to G71.1.

Insurance companies should be able to explain what percentage of the cost of a DM genetic test they will cover. Individuals with very low incomes can sometimes qualify for financial assistance programs.

What does the testing involve?

It requires a blood draw. It takes about three weeks to get the results, although timing varies from lab to lab. For those with DM in their family who choose not to get the genetic test, I recommend talking with their doctor about scheduling an EKG every year or two, at least until they’re 18 years old. While an abnormal EKG may not imply a DM diagnosis, when coupled with a family history of DM, an abnormal EKG should direct the physician to conduct additional follow up testing.

What do you discuss with individuals who have a family history of DM and are considering getting pregnant?

Reproductive options are definitely an issue we discuss when appropriate. The risk of having a child born with DM is 50/50 for each pregnancy. In this situation, prospective parents can think about options for testing the pregnancy. Tests can be run to look for the repeat expansion at 10-12 weeks of pregnancy through chorionic villus sampling (CVS) or by amniocentesis after 15 weeks.

It’s important to note that the expansions can grow and change as the baby develops. The number of repeat expansions found by CVS or amnio are not necessarily going to be the same number that the baby has when it is born, so those numbers can be used to determine whether the baby will be affected by DM, but not to predict disease severity. The implication for this type of testing would be that the parents can decide if they want to proceed with the pregnancy.

For those who don’t want to go that route, there’s also the option of pursuing in vitro fertilization (IVF) and getting the appropriate testing done before implantation to ensure the DM genetic mutation has not been passed along to the baby. This pre-implantation genetic diagnosis (PGD) test is done after the sperm and egg are fertilized and have developed up to eight cells. At that point, one or two of those cells are removed and tested for the DM repeat expansion. Doctors can then transfer to the mother only embryos that don’t have the expansion, so the disease won’t be passed on.

Generally, it can be assumed that about 50% of these fertilized eggs have the expansion. IVF/PGD is a very expensive option, usually costing at least $20,000 per cycle so, depending on state and insurance plan, prospective parents may or may not be able to get some help with these costs.


Note: Athena Diagnostics offers qualifying patients a substantial discount on its regular price for clinical laboratory services. If you cannot afford to pay for testing ordered from Athena, you may obtain a 75% discount off the list price if you meet certain income guidelines. For more information, see call (800) 394-4493 and ask to speak with a Reimbursement Services Representative.


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