An autosomal dominant subtype of dilated cardiomyopathy caused by mutation(s) in the RBM20 gene, encoding RNA-binding protein 20.

MDDGB2 is an autosomal recessive congenital muscular dystrophy associated with impaired intellectual development and mild structural brain abnormalities (Yanagisawa et al., 2007). It is part of a group of similar disorders, collectively known as 'dystroglycanopathies,' resulting from defective glycosylation of alpha-dystroglycan (DAG1; 128239) (Godfrey et al., 2007). For a discussion of genetic heterogeneity of congenital muscular dystrophy-dystroglycanopathy type B, see MDDGB1 (613155).

Some individuals with left ventricular noncompaction experience no symptoms at all; others have heart problems that can include sudden cardiac death. Additional signs and symptoms include abnormal blood clots, irregular heart rhythm (arrhythmia), a sensation of fluttering or pounding in the chest (palpitations), extreme fatigue during exercise (exercise intolerance), shortness of breath (dyspnea), fainting (syncope), swelling of the legs (lymphedema), and trouble laying down flat. Some affected individuals have features of other heart defects. Left ventricular noncompaction can be diagnosed at any age, from birth to late adulthood. Approximately two-thirds of individuals with left ventricular noncompaction develop heart failure.\n\nLeft ventricular noncompaction is a heart (cardiac) muscle disorder that occurs when the lower left chamber of the heart (left ventricle), which helps the heart pump blood, does not develop correctly. Instead of the muscle being smooth and firm, the cardiac muscle in the left ventricle is thick and appears spongy. The abnormal cardiac muscle is weak and has an impaired ability to pump blood because it either cannot completely contract or it cannot completely relax. For the heart to pump blood normally, cardiac muscle must contract and relax fully.

Mitochondrial complex II deficiency nuclear type 3 (MC2DN3) is an autosomal recessive multisystemic metabolic disorder with a highly variable phenotype. Some patients may have an encephalomyopathic picture with episodic developmental regression, loss of motor skills, hypotonia, ataxia, dystonia, and seizures or myoclonus. Other patients present in infancy with hypertrophic cardiomyopathy, which may be fatal. Laboratory studies show increased serum lactate and mitochondrial complex II deficiency in muscle and fibroblasts (summary by Jackson et al., 2014 and Alston et al., 2015). For a discussion of genetic heterogeneity of MC2DN, see MC2DN1 (252011).

Hypotaurinemic retinal degeneration and cardiomyopathy (HTRDC) is an autosomal recessive disorder characterized by low plasma taurine, childhood-onset progressive retinal degeneration, and cardiomyopathy (Ansar et al., 2020).

Intellectual disability and myopathy syndrome (IDMYS) is an autosomal recessive developmental disorder characterized by global developmental delay with mildly impaired intellectual development, hypotonia, muscle weakness and fatigue, and white matter abnormalities on brain imaging. Variable additional features may include sensorineural hearing loss, dysmorphic facies, and progressive heart disease (summary by Smeland et al., 2019).

Arrhythmogenic cardiomyopathy with variable ectodermal abnormalities (ARCME) is characterized by severe dilated cardiomyopathy resulting in death or cardiac transplantation in childhood. Ventricular tachycardia, sustained or nonsustained, has been reported. In addition, some patients exhibit ectodermal manifestations including woolly or wiry hair, dental anomalies, dry skin, and/or dystrophic nails. Cleft lip and palate and corneal abnormalities have also been observed (Robinson et al., 2020; Henry et al., 2022).