dilated cardiomyopathy 3B

Dilated cardiomyopathy 3B (CMD3B) is a genetic heart muscle disorder in which the left ventricle becomes enlarged and weakened. The condition results from pathogenic variants in the DMD gene, which encodes dystrophin, a protein that lends structural stability to muscle cells, including those in the heart. Because the gene is located on the X chromosome, CMD3B primarily affects males, while females with one altered copy may have milder or no symptoms. Precise prevalence figures have not been established, but available data suggest the condition is very uncommon.

Two findings are considered characteristic of CMD3B. All affected individuals show an increased left-ventricular end-diastolic volume, meaning the main pumping chamber of the heart is dilated. In addition, blood tests consistently reveal elevated levels of the cardiac enzyme creatine kinase-MB, reflecting stress or injury to heart muscle cells. These changes can be detected before significant clinical symptoms emerge. Not all individuals experience the same degree of ventricular enlargement or enzyme elevation, and severity varies considerably.

CMD3B is caused by disease-causing variants in the DMD gene. Dystrophin, the protein produced by this gene, forms part of a complex that anchors muscle cell membranes; when dystrophin is deficient or absent in the heart, the cell walls become fragile and the ventricle can stretch and thin. The condition follows an X-linked inheritance pattern: one altered copy of the gene is sufficient to cause disease in males, who have a single X chromosome. Female carriers usually have a healthy second copy on their other X chromosome, but they may experience mild cardiac changes and should discuss routine heart monitoring with their healthcare provider. Each son of a carrier female has a 50 percent chance of being affected, and each daughter has a 50 percent chance of being a carrier. Genetic counseling is strongly recommended for families.

Currently, management focuses on supportive care tailored to each individual’s cardiac status. Standard heart-failure therapies, lifestyle measures, and regular follow-up with a cardiologist experienced in inherited cardiomyopathies form the cornerstone of care. In many cases, a multidisciplinary team that may include cardiologists, genetic counselors, and primary care physicians oversees surveillance and adjustment of therapy as needed. Because no targeted or FDA-approved disease-modifying treatments are available at this time, participation in registries and close clinical monitoring remain important. Families should discuss all treatment options, including advanced heart-failure interventions if necessary, with their healthcare team.

Outcomes for individuals with CMD3B vary widely. Some maintain stable heart function for years with standard medical therapy, while others experience progressive ventricular dilation that requires more intensive management. Early diagnosis, routine cardiac surveillance, and prompt treatment of heart-failure symptoms can improve quality of life and may slow disease progression. Ongoing follow-up at specialized centers helps ensure that emerging interventions and evolving care guidelines are considered for each patient.