In a recent study entitled “Progression of cardiac involvement in patients with limb-girdle type 2 and Becker muscular dystrophies: A 9-year follow-up study,” researchers describe a higher risk for cardiac dysfunction in patients suffering from Becker muscular dystrophy and limb-girdle muscular dystrophy, particularly subtypes 2I and 2E. The study was published in the International Journal of Cardiology.
Becker muscular dystrophy (BMD) and recessively inherited limb-girdle muscular dystrophy type 2 (LGMD2) are both rare muscle diseases. While BMD is caused by mutations in the dystrophin coding gene (dystrophin protein is a key structure linking the cytoskeleton of a muscle fiber to the extracellular matrix in order to maintain muscle integrity), LGMD2 is caused by multiple defective proteins within muscle cells. Thus, both diseases are characterized by progressive muscle weakness and wasting of the lower body, including the legs and pelvic area; in LGMD2 the proximal upper extremities are also affected.
A major concern in both BMD and LGMD2 is the involvement of cardiac muscle. In fact, in LGMD2, both skeletal myofibers (functional contractile units of skeletal muscle) and cardiomyocytes (cardiac muscle cells) degenerate and die and are ultimately replaced with non-functioning fibrotic tissue.
As part of their research, the authors sought to determine the extent and progression of cardiac involvement in patients with BMD and LGMD2. In this longitudinal study (a type of observational study where repeated observations of the same variables are performed over long periods of time), the authors followed 30 BMD and 100 LGMD2 patients (types A–L) over a span of 9 years who were registered at the University Hospital, Rigshospitalet in Copenhagen, Denmark and evaluated their cardiac morbidity and mortality as well as the progression of cardiac involvement by measuring cardiac function with electrocardiogram (ECG) and echocardiography.
Because muscular dystrophy patients are at risk of developing both cardiomyopathy and left-ventricular dysfunction, the authors paid particular attention to these features and determined left ventricular ejection fraction (LVEF), a measure of how much blood is pumped out of the left ventricle of the heart in each contraction.
They observed that LVEF was significantly decreased in both BMD and LGMD type 2I patients, a 10% (from 60 to 50%) and 4% decrease (from 59% to 55%), respectively. In the LGMD2I group, patients with LVEF below 50% exhibited increased mortality. Additionally, the majority of patients with LGMD2E, a second subtype, presented left ventricular systolic dysfunction.
The authors highlight that their findings support the need, according to genetic subtypes, for a close cardiac supervision, particularly among patients with BMD and LGMD types 2I and 2E.