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WINTER 2026 InTouch | 13 WHAT IS BECKER MUSCULAR DYSTROPHY? two copies of the X chromosome. A woman who has one correct dystrophin gene and one faulty dystrophin gene can nearly always produce enough dystrophin to have normal muscle function. She is therefore a “carrier” of the mutation or a “genetic carrier” or DMD or BMD. Males have only one X chromosome and therefore one dystrophin gene copy. So if a male has a faulty dystrophin gene he will be affected with DMD or BMD since he cannot produce the correct amount or type of the dystrophin protein. A small number of BMD female carriers (10%) may have issues with cardiomyopathy, therefore it is important for carrier mothers to have engagement with cardiology and intermittent screening echocardiograms. The pattern of inheritance of BMD is called X-linked recessive (see accompanying genetics fact sheet). If a woman is a carrier of the mutation (she has one copy of the faulty dystrophin gene), and she has a daughter, there is one chance in two that the daughter will be a carrier of the mutation and one chance in two that she will not, i.e. a 50% probability of being a genetic carrier of DMD or BMD and an equal chance of not being a carrier. For each son of a genetic carrier, there is one chance in 2, i.e. a 50% probability, of being affected and an equal chance of not being affected. Since women have two X chromosomes, if one X chromosome has the defective gene, the other X chromosome functions to produce enough dystrophin for normal muscle function. Males on the other hand, have one X and one Y chromosome; thus they do not have a compensatory X chromosome, and will develop symptoms. Spontaneous mutations are responsible for approximately one-third of BMD cases, with the genetic fault arising in the affected boy himself. This happens when the mutation in the dystrophin gene happens by chance in the formation of the egg or sperm. With a spontaneous mutation, the affected boy will be the first in his family to have BMD. • Both BMD and DMD are caused by mutations in the dystrophin gene • DMD is caused by an “out of frame”mutation in the dystrophin gene which disrupts the reading frame which results in a truncated protein lacking function. • BMD is caused by an “in frame” mutation in the dystrophin gene which does not disrupt the reading frame and therefore Results in a shorter, but still partially functional protein which is why the clinical manifestations are often less severe than DMD Diagnosis of Becker Muscular Dystrophy Once BMD is suspected, diagnostic tests will be offered to establish a definite diagnosis. These may include: • CPK (CK) Testing : A positive blood test for BMD will demonstrate higher than normal levels of the muscle protein creatine phosphokinase. This enzyme leaks out of damaged muscles, and into the blood serum. This is not, however, a conclusive test, as an elevated amount of CPK is also a feature of other muscular dystrophies. This could also be a marker of inflammation in muscles due to other reasons, not just muscular dystrophies • DNA Studies: In some cases, DNA studies are able to give definitive information about the genetic abnormality responsible for the faulty BMD gene, whilst in others the abnormality is not able to be exactly defined. • Muscle Biopsy: If the fault in the BMD gene is too small to be detected by DNA analysis, then a muscle biopsy may be the best option. Whilst under local anaesthetic, a small piece of muscle is taken from the thigh. Using special staining techniques in the laboratory, the muscle tissue is examined microscopically for the muscle protein dystrophin. The test is positive for BMD if there is an abnormally low level of dystrophin present. • Electromyography: An EMG gives information on the electrical activity of the muscle tested. It tells whether the muscle weakness is caused by damage to the muscles, as in BMD, or damage to the nerves in other conditions. • Genetic Counselling: Soon after the diagnosis of a BMD boy, it is essential that genetic counselling is arranged. Genetic testing and counselling in BMD families usually focus on one or both of two issues. The first is the probability that a particular Continued over ...