Below are some of the more frequently asked questions about Centronuclear/Myotubular Myopathy. Many of these topics are covered in greater detail elsewhere in the web site. Also, please remember that none of these questions or answers should be used as a replacement for proper genetic counselling.
This depends largely on the severity of the disorder and on the interventions taken. Contrary to what is said in much of the available literature, MTM expresses itself in a range of severities. In some cases, it is only slightly noticeable, in some cases it is quite severe.
In the milder cases, it is often managed syptomatically. The kids have more difficulty breathing at first and are very susceptible to the flu, pneumonia and other respiratory diseases. In these cases, the muscles are weaker than they would be if unaffected but are still strong enough to enable many everyday functions. For example, some of these kids are able to walk.
In the more severe cases, long-term survival is unlikely without a tracheotomy and mechanical ventilation. In these cases the patients are usually wheelchair bound and require significant assistance for daily living.
Much of the literature indicates very high mortality rates (as high as 90%) for kids born with MTM. Our experience is different. While mortality in the first year is still very, very high when compared to the general population, with appropriate interventions it nowhere approaches the virtual certainties implied in the literature. Data on this is tough to get and tougher to verify, so we are unable to give any validated statistics supporting our position. However, our experience in discussions with over 200 families is that, with the proper interventions, approximately two-thirds of kids with MTM survive past the first year.
Unfortunately, at this time, no. The root cause of MTM is genetic. A problem in a person's genes cause, for reasons still unknown, a structural defect in the skelatal muscles. There is much to do to prepare the MTM community for a clinical trial towards a cure. Including participating in the patient registry, the natural history study and more.
We think this is not seen with the X-linked form. All X-linked patients we know of presented at birth or within a few months of life. It could be autosomal recessive or dominant centronuclear myopathy. Again, we think the dominant is milder and might be more likely to present later in life. However, until the autosomal genes are isolated this is only a guess, unless there is a clear history in the family that tells us what type of autosomal CNM this is.
In the past, doctors have performed muscle biopsies on mothers of isolated males with MTM1. The biopsy can detect some abnormal muscle cells in 50-70% of carrier females. A normal test, however, does not rule out being a carrier.
Genetic testing for all forms of CNM, including MTM, can be done at the University of Chicago Genetic Services Laboratory. Click here for an information sheet.
If a research group finds a mutation (change in the MTM1 gene itself), then the mother can usually be tested for the presence of this mutation. This is the best way to determine if a woman is a carrier.
In some families with more than one male affected with MTM1, an indirect molecular test, called linkage analysis can be used to determine if someone is carrier. This usually involved testing several people in the family rather than just one affected male and the potential carrier female.
This mutation test is now available as a fee for service through the University of Chicago (888-UC-GENES is the phone number). It is our understanding that the success rate at detecting a mutation is ~80%. For more information see the university of Chicago genetic clinical services website.
Studies from Dr. Herman's laboratory on a relatively small sample of sporadic cases (~20) suggest that at least 90% of mothers of affected boys are carriers. This is significantly higher than the predicted 2/3 (66%) from theoretical calculations.
Just as in carrier testing, there is no easy, simple standard prenatal test for MTM. If a mutation has been found in a family, a pregnancy can be tested for the presence of that mutation. A few specialized diagnostic laboratories are willing to do this sort of prenatal test. It is extremely important to already know the mutation prior to undertaking another pregnancy since there may not be sufficient time to first find a mutation and then test a pregnancy. For cases with more than one affected in a family, linkage testing can be performed without knowing an exact mutation. For many affected pregnancies, there is decreased fetal movement and accumulation of too much fluid, but this may occur too late to be helpful in prenatal testing. Again, please consult your geneticist or genetics counsellor.
There are 3 types of CNM based on their pattern of inheritance: X-linked, autosomal dominant, and autosomal recessive.
X-linked appears to be the most common and is seen in boys almost exclusively. Typically, males are severely affected at birth with decreased tone and problems breathing. However, our mutation and clinical studies have shown that a few boys with X-linked disease have a much milder course.
The autosomal recessive form can affect males and females equally. It may start after birth and become worse over time. The gene for this (and the dominant form) has not been identified as yet.
The autosomal dominant form also affects males and females and can be transmitted from a parent to a child. It may be the mildest of the 3 forms and begin in childhood, again becoming worse with age.
This video explains about the different genes
involved in all forms of CNM, including MTM.
One way to tell if someone has CNM at all is through a muscle biopsy. Genetic testing is another way. Click here for a form to give to your doctor to help you get genetic testing approved by insurance. If no genetic variants are found, this may be caused by a yet unknown mutation. Experience from Dr Herman's lab as well as others suggest that ~80% of boys suspected of having X-linked MTM will have mutations found in this gene.
If MTM is known to exist within a family, the chances that any particular child will be affected depend on the form of MTM present and, if the form is x-linked, the sex of the child. The inheritence of the MTM gene in any single child is an event independent of what happened in any other child with the same parents. In other words, whether earlier children were affected or not does not have any bearing on the odds that the next child will be affected.
If a mother is known to be a carrier of MTM (either through previous children or through carrier testing) and the form of MTM is known, then the chart below describes the probabilities of any particular child being affected.
Sex of Child
(same parents for each pregnancy)
|1 in 2||1 in 2|
|Autosomal Recessive||1 in 4||1 in 4|
|X-Linked||1 in 2||zero|
Note: this table should not be used as
If the mother is not a carrier then the risk of another affected child is on the order of 1-3%.
These different risks underscore the value of DNA mutation testing and the need to seek appropriate genetic counseling any time a child is diagnosed with MTM. It also explains why it is so important to find the other autosomal MTM genes so we can, hopefully, identify which type of MTM it is in all patients.
There are a few other disorders that seem to accompany x-linked MTM. There have not been any additional disorders associated with the other forms of MTM.
A number of kids with confirmed XMTM also have shown a variety of other disorders, most notably hydrocephalus, liver dysfunction, blood disorders (often in the form of spherocytosis), gall stones and genitourinary abnormalities in addition to undescended testes. These other disorders accompany MTM far too frequently to be unrelated. Physicians caring for MTM patients should be aware of their possible occurrence.
An article describing these other disorders and their relationship to MTM has just been published. See the page on Research for more details.
Yes. Research is underway at several centers in the USA and in Europe. See the page in this website on Research for more details.
Special thanks to Gail Herman, PhD, MD for supplying answers to many of these questions and to our good friend, Jerome McCombs, PhD, for reviewing these FAQs.
Click here to learn more about how to get involved with the registry, tissue repository and biobanking.