Limb-Girdle Muscular Dystrophy (LGMD)
In diagnosing any form of muscular dystrophy, a doctor usually begins by taking a patient and family history and performing a physical examination. Much can be learned from these, including the pattern of weakness. The history and physical go a long way toward making the diagnosis, even before any laboratory tests are done.
The doctor also wants to determine whether the patient’s weakness results from a problem in the muscles themselves (as is the case in muscular dystrophy), or in the muscle-controlling nerves, called motor neurons, that control them.
Early in the diagnostic process, doctors often order a special blood test called CK level. CK stands for creatine kinase, an enzyme that leaks out of damaged muscle. When elevated CK levels are found in a blood sample, it usually means muscle is being destroyed by some abnormal process, such as a muscular dystrophy or inflammation. Therefore, a high CK level suggests that the muscles themselves are the likely cause of the weakness, but it doesn’t tell exactly what the muscle disorder might be.
Sometimes, special testing called electromyography is done. In this kind of test, the electrical activity of the muscles is measured and nerves stimulated to see where the problem lies. Electromyography is uncomfortable but not usually very painful.
In some cases it is necessary for a doctor to order a muscle biopsy, the surgical removal of a small sample of muscle from the patient. By examining this sample, doctors can tell a great deal about what’s actually happening inside the muscles. Using a variety of techniques, muscular dystrophies can be distinguished from inflammatory and other disorders. Specific testing of the biopsy also may distinguish among different forms of muscular dystrophy.
Tests on the biopsy sample also can provide information about which muscle proteins are present in the muscle cells, and whether they’re present in the normal amounts and in the right locations. This can reveal what’s wrong with the cells’ proteins and point toward the genes that may be responsible for the problem. The correlation between missing proteins on the muscle biopsy and genetic flaws isn’t perfect, however.
Today, DNA testing is available for several forms of LGMD and is rapidly expanding. If a particular type of LGMD is suspected, DNA testing (from a blood sample) may be undertaken relatively early in the diagnostic process, often before the doctor considers a more invasive procedure.
Genetic testing is commercially available that can determine the exact type of several, but not all, forms of LGMD. If there are clues as to what gene is involved (from previously tested family members, biopsy findings or symptoms clearly associated with one or two types of LGMD), it may be practical to do DNA testing to pinpoint the gene defect. However, if there are no such clues, testing can get very expensive.
In 2015, with support from Sanofi Genzyme, MDA launched the limb-girdle muscular dystrophy genetic testing program in partnership with EGL Genetics. Since then, more than 2,800 testing samples have been submitted by MDA Care Centers and MDA Care Affiliates to EGL Genetics for testing. Through this program, individuals with limb-girdle muscle weakness can be tested to find out if they have one of the known subtypes of LGMD or any of a number of other disorders that can sometimes cause similar symptoms (such as Emery-Dreifuss muscular dystrophy or Bethlem myopathy, for example). The test is an important first step for anyone living with limb-girdle muscle weakness who has not received a definitive genetic diagnosis. That’s why MDA and Sanofi Genzyme are proud to work together to continue offering MDA’s LGMD genetic testing program.
Understanding your inheritance pattern may be important for family planning. Your family history can help determine the inheritance pattern of your disorder.
No matter the exact genetic cause, treatment is essentially the same for all forms of LGMD — physical and occupational therapy, assistive devices, and monitoring for heart and breathing complications.