A subtype of autosomal recessive limb-girdle muscular dystrophy characterized by a childhood onset of progressive shoulder and pelvic girdle muscle weakness and atrophy frequently associated with calf hypertrophy, diaphragmatic weakness, and/or variable cardiac abnormalities. Mild to moderate elevated serum creatine kinase levels and positive Gowers sign are reported.

6q25 microdeletion syndrome is a recently described syndrome characterized by developmental delay, facial dysmorphism and hearing loss.

Atrial fibrillation is the most common sustained cardiac rhythm disturbance, affecting more than 2 million Americans, with an overall prevalence of 0.89%. The prevalence increases rapidly with age, to 2.3% between the ages of 40 and 60 years, and to 5.9% over the age of 65. The most dreaded complication is thromboembolic stroke (Brugada et al., 1997). For a discussion of genetic heterogeneity of atrial fibrillation, see 608583.

Arrhythmogenic right ventricular cardiomyopathy/dysplasia-13 (ARVD13) is characterized by progressive fibrofatty myocardial replacement, primarily of the right ventricle. The main clinical features are structural and functional abnormalities of the ventricles, electrocardiographic depolarization/repolarization changes, reentrant arrhythmias, and sudden death (summary by van Hengel et al., 2013).

Arrhythmogenic right ventricular cardiomyopathy/dysplasia-14 (ARVD14) is characterized by palpitations, chest pain, and presyncope. Electrocardiography shows epsilon waves, T-wave inversion across anterior leads, premature ventricular contractions, ventricular tachycardia, and left bundle branch block. Dilation of the right ventricle with hypokinesia and aneurysmal changes are seen on echocardiography. Cardiac MRI may show fibrofatty infiltration, which has been confirmed by endocardial biopsy in some patients. Sudden death may occur (Mayosi et al., 2017). For a discussion of genetic heterogeneity of ARVD, see ARVD1 (107970).

VISS syndrome is a generalized connective tissue disorder characterized by early-onset thoracic aortic aneurysm and other connective tissue findings, such as aneurysm and tortuosity of other arteries, joint hypermobility, skin laxity, and hernias, as well as craniofacial dysmorphic features, structural cardiac defects, skeletal anomalies, and motor developmental delay (Van Gucht et al., 2021). Immune dysregulation has been observed in some patients (Ziegler et al., 2021).

Immunodeficiency-93 and hypertrophic cardiomyopathy (IMD93) is an autosomal recessive disorder characterized by onset of recurrent viral and bacterial infections, particularly with encapsulated bacteria, and hypertrophic cardiomyopathy in the first months or years of life. Immunologic workup typically shows decreased circulating B cells and hypo- or agammaglobulinemia, sometimes with neutropenia or T-cell lymphocytosis, although laboratory findings may be variable among patients. Ig replacement therapy is beneficial. Cardiac involvement can also include atrial septal defect, valvular insufficiency, and pre-excitation syndrome. Rare myopathic or neurologic involvement has been reported, but these features are not consistently part of the disorder and may be related to other genetic defects (summary by Niehues et al., 2020 and Saettini et al., 2021).