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Becker Muscular Dystrophy

Becker muscular dystrophy (BMD) is a disorder that causes progressive weakness of muscles and, for some, progressive dilation and weakness of the heart (dilated cardiomyopathy). BMD can also cause intellectual disability and/or autism in some patients. BMD is caused by genetic variants in the DMD gene. The DMD gene is important in the development of dystrophin, which is an essential protein needed to protect muscles, including muscles in the heart.

Variants in the DMD gene also cause the condition Duchenne muscular dystrophy (DMD) which is more severe than BMD. The mutations that cause DMD cause complete loss of dystrophin, whereas mutations that cause a malformed form of dystrophin (which does not function as well as it should, but still functions some) cause BMD. The diseases are similar, but DMD is more severe, usually resulting in impaired movement in males in early childhood with inability to walk by late childhood or early teenage years, followed by heart and respiratory failure and eventual death in the male patient’s 20s or 30s1. In contrast, male patients with BMD usually begin to experience muscle weakness later in childhood (average age about 12 years old) and maintain the ability to walk longer if not forever, with only 13.5% of patients losing their ability to walk at an average age of 69 years in one large study1,2. Dilated cardiomyopathy (a heart disease) develops in about 70% of male patients with BMD with a usual onset in late teenage years or later. Heart failure is the leading cause of death amongst patients with BMD, however this usually occurs later. Life expectancy for males with BMD is historically in the 40s-60s though many individuals live longer if they do not develop heart disease, and medical advancements are continuing to improve outcomes for those that do1.

BMD affects different individuals in different ways with varying severity. Some individuals remain mostly without symptoms for their entire life, others might have strictly myalgias (muscle pains) or mild weakness, while others have severe disease that is more similar to DMD. The way that someone is affected depends on the specific gene variant that they have and how much residual dystrophin function they have in their muscles2. Importantly, the development of heart disease can happen in patients without significant muscular symptoms and often does not correlate with the severity of muscle disease.

 

Females with BMD

Females with BMD disease-causing variants in the DMD gene on one of their two X chromosomes (heterozygotes) were historically thought to be asymptomatic carriers of BMD.  However, it is becoming increasingly clear that many if not most females do develop some signs and symptoms of disease1.

Female carriers of BMD can develop muscular symptoms including muscle weakness, myalgias (muscle pains), cramping, enlargement of calf muscles, and fatigue. The rates of female carriers experiencing these symptoms is thought to be below 20%, and when present, the disease features are typically milder and slower to progress compared to male patients. Some recent studies have used muscle strength measurements and imaging techniques to compare the muscles of females carrying DMD gene mutations to those without (these studies thus include carriers of both DMD disease and BMD). In these studies, 40% of female carriers had reduced muscle strength and 81% had evidence of reduced muscle strength or fat replacement on imaging (when a muscle is weak and dies, it gets replaced by fat, so this can be used as a sign of muscle decay)3. Female carriers can also have elevated CK levels, which is a marker in the blood that indicates muscle breakdown. Females with symptoms generally have higher CK levels than females without symptoms, but it is possible to have an elevated level or irregular findings on imaging even without symptoms1. Thus, some sub-clinical (i.e. not symptom-causing) muscle disease seems to be present in a majority of female carriers of DMD gene mutations, while symptoms only develop in a minority.

In addition to muscle disease, female carriers of BMD are at risk for dilated cardiomyopathy (heart disease). Across seven large research studies, the percentage of female carriers of BMD who had dilated cardiomyopathy was 0-13% and of all the female carriers of DMD or BMD who had any symptoms of disease, ~17% had heart disease4. More recent studies have found that early signs of heart disease may be even more common: in studies from 2016 and 2020, up to 49% of female carriers of BMD or DMD had at least one irregular finding on imaging of their heart by their mid-40s. Another study found that 62% of carrier females (again including both carriers of BMD and of DMD) had irregularities on echocardiography (ultrasound of the heart), 49% had irregularity on cardiac MRI (image of the heart), and 70% has irregularity on their EKG (electrical pattern of the heart)5. Female carriers of BMD specifically were compared with carriers of DMD, and it was seen that females with BMD were much less likely to have an abnormal image of the heart (19% compared to 65% in DMD) despite being significantly older in age (average age of 50 compared to 40) at the time of testing6. Since all of these studies include signs of heart disease that may not result in symptoms or significant health concerns, it is hard to say what the real likelihood is of developing clinically-significant heart disease in a female carrier of BMD. At this time, the best estimate seems to be a risk at or below 13%. The risk increases with age, so it is recommended that female carriers undergo monitoring with echocardiography (ultrasound of the heart) every 5 years4.

Skewed X-inactivation, with more cells expressing the mutant X chromosome, is thought to be the reason why some females develop symptoms of BMD7. In general, the presence of one normal copy of the DMD gene on one of the X chromosomes is enough to compensate for the mutated gene on the other, allowing for females to typically have milder disease (or no disease) compared to males.

It is rare for female carriers of BMD to develop the “full” features of disease like males with BMD or DMD, but it has happened. When this does occur, it is due to a rare genetic event, such as extreme X-inactivation, Turner syndrome (absence of 1 X chromosome), or other uncommon genetic features. Of note, the rare females who do develop early-onset, severe BMD disease have been seen to have a high rate of intellectual disability and mental health disorders, even higher than in affected male patients8. Apart from these extreme cases, female carriers of BMD are not known to have intellectual challenges.

It is difficult to determine a clear percentage of female carriers of BMD who will develop symptoms of the disease. While many studies have attempted to do so, they each have looked at different populations and many use different classifications for symptoms, making it challenging to unify the information. Additionally, many studies do not separate female carriers of BMD from female carriers of DMD, since the mutations exist in the same gene (the DMD gene) and the diseases thus exist on a spectrum. In the few studies who have separated female carriers by BMD vs DMD, the females with DMD were at higher risk for more severe, earlier symptoms of disease compared to females who carry BMD. This is not surprising given that females carrying DMD have more detrimental genetic variants compared to those carrying BMD.

Overall, many female carriers of BMD seem to remain asymptomatic throughout their lives, while others will develop signs or symptoms of muscle disease and/or heart disease. In general, disease features in females will be less severe than in their affected male family members.

This page was last updated in August, 2026. Please note that research into females with this condition is limited. As a result, percentages and prevalence rates may not be accurate or widely applicable. Decisions regarding your own health should be made in consultation with your medical provider.

  1. Pickart AM, Martin AS, Gross BN, et al. Genetic counseling for the dystrophinopathies—Practice resource of the National Society of Genetic Counselors. J Genet Couns. 2025;34(1):e1892. doi:10.1002/jgc4.1892
  2. Gorgoglione D, Sabbatini D, Riguzzi P, et al. Natural history of Becker muscular dystrophy: DMD gene mutations predict clinical severity. Brain. 2025;148(5):1695-1706. doi:10.1093/brain/awae358
  3. Fornander F, Solheim TÅ, Eisum ASV, et al. Quantitative Muscle MRI and Clinical Findings in Women With Pathogenic Dystrophin Gene Variants. Front Neurol. 2021;12. doi:10.3389/fneur.2021.707837
  4. Ishizaki M, Kobayashi M, Adachi K, Matsumura T, Kimura E. Female dystrophinopathy: Review of current literature. Neuromuscul Disord. 2018;28(7):572-581. doi:10.1016/j.nmd.2018.04.005
  5. Solheim TÅ, Fornander F, Raja AA, et al. Cardiac Involvement in Women With Pathogenic Dystrophin Gene Variants. Front Neurol. 2021;12:707838. doi:10.3389/fneur.2021.707838
  6. Florian A, Rösch S, Bietenbeck M, et al. Cardiac involvement in female Duchenne and Becker muscular dystrophy carriers in comparison to their first-degree male relatives: a comparative cardiovascular magnetic resonance study. Eur Heart J – Cardiovasc Imaging. 2016;17(3):326-333. doi:10.1093/ehjci/jev161
  7. Viggiano E, Picillo E, Ergoli M, Cirillo A, Del Gaudio S, Politano L. Skewed X-chromosome inactivation plays a crucial role in the onset of symptoms in carriers of Becker muscular dystrophy. J Gene Med. 2017;19(4):e2952. doi:10.1002/jgm.2952
  8. Imbornoni L, Price ET, Andrews J, Meaney FJ, Ciafaloni E, Cunniff C. Diagnostic and clinical characteristics of early-manifesting females with Duchenne or Becker muscular dystrophy. Am J Med Genet A. 2014;164(11):2769-2774. doi:10.1002/ajmg.a.36728