MedGen

Emery-Dreifuss muscular dystrophy (EDMD) is characterized by the clinical triad of: joint contractures that begin in early childhood; slowly progressive muscle weakness and wasting initially in a humero-peroneal distribution that later extends to the scapular and pelvic girdle muscles; and cardiac involvement that may manifest as palpitations, presyncope and syncope, poor exercise tolerance, and congestive heart failure along with variable cardiac rhythm disturbances. Age of onset, severity, and progression of muscle and cardiac involvement demonstrate both inter- and intrafamilial variability. Clinical variability ranges from early onset with severe presentation in childhood to late onset with slow progression in adulthood. In general, joint contractures appear during the first two decades, followed by muscle weakness and wasting. Cardiac involvement usually occurs after the second decade and respiratory function may be impaired in some individuals. [from GeneReviews]

Primary hyperoxaluria type 1 (PH1) is caused by a deficiency of the liver peroxisomal enzyme alanine:glyoxylate-aminotransferase (AGT), which catalyzes the conversion of glyoxylate to glycine. When AGT activity is absent, glyoxylate is converted to oxalate, which forms insoluble calcium oxalate crystals that accumulate in the kidney and other organs. Individuals with PH1 are at risk for recurrent nephrolithiasis (deposition of calcium oxalate in the renal pelvis / urinary tract), nephrocalcinosis (deposition of calcium oxalate in the renal parenchyma), or end-stage renal disease (ESRD). Age at onset of symptoms ranges from infancy to the sixth decade. Approximately 10% of affected individuals present in infancy or early childhood with nephrocalcinosis, with or without nephrolithiasis, and failure to thrive related to renal failure. The majority of individuals with PH1 present in childhood or early adolescence, usually with symptomatic nephrolithiasis and normal or reduced kidney function. The remainder of affected individuals present in adulthood with recurrent renal stones and a mild-to-moderate reduction in kidney function. The natural history of untreated PH1 is one of progressive decline in renal function as a result of calcium oxalate deposits in kidney tissue and complications of nephrolithiasis (e.g., obstruction and infection) with eventual progression to oxalosis (widespread tissue deposition of calcium oxalate) and death from ESRD and/or complications of oxalosis. [from GeneReviews]

Carnitine-acylcarnitine translocase (CACT) is a critical component of the carnitine shuttle, which facilitates the transfer of long-chain fatty acylcarnitines across the inner mitochondrial membrane. CACT deficiency causes a defect in mitochondrial long-chain fatty acid ß-oxidation, with variable clinical severity. Severe neonatal-onset disease is most common, with symptoms evident within two days after birth; attenuated cases may present in the first months of life. Hyperammonemia and cardiac arrhythmia are prominent in early-onset disease, with high rates of cardiac arrest. Other clinical features are typical for disorders of long-chain fatty acid oxidation: poor feeding, lethargy, hypoketotic hypoglycemia, hypotonia, transaminitis, liver dysfunction with hepatomegaly, and rhabdomyolysis. Univentricular or biventricular hypertrophic cardiomyopathy, ranging from mild to severe, may respond to appropriate dietary and medical therapies. Hyperammonemia is difficult to treat and is an important determinant of long-term neurocognitive outcome. Affected individuals with early-onset disease typically experience brain injury at presentation, and have recurrent hyperammonemia leading to developmental delay / intellectual disability. Affected individuals with later-onset disease have milder symptoms and are less likely to experience recurrent hyperammonemia, allowing a better developmental outcome. Prompt treatment of the presenting episode to prevent hypoglycemic, hypoxic, or hyperammonemic brain injury may allow normal growth and development. [from GeneReviews]

While most people with familial hypertrophic cardiomyopathy are symptom-free or have only mild symptoms, this condition can have serious consequences. It can cause abnormal heart rhythms (arrhythmias) that may be life threatening. People with familial hypertrophic cardiomyopathy have an increased risk of sudden death, even if they have no other symptoms of the condition. A small number of affected individuals develop potentially fatal heart failure, which may require heart transplantation.

The symptoms of familial hypertrophic cardiomyopathy are variable, even within the same family. Many affected individuals have no symptoms. Other people with familial hypertrophic cardiomyopathy may experience chest pain; shortness of breath, especially with physical exertion; a sensation of fluttering or pounding in the chest (palpitations); lightheadedness; dizziness; and fainting.

Nonfamilial hypertrophic cardiomyopathy tends to be milder. This form typically begins later in life than familial hypertrophic cardiomyopathy, and affected individuals have a lower risk of serious cardiac events and sudden death than people with the familial form.

In familial hypertrophic cardiomyopathy, cardiac thickening usually occurs in the interventricular septum, which is the muscular wall that separates the lower left chamber of the heart (the left ventricle) from the lower right chamber (the right ventricle). In some people, thickening of the interventricular septum impedes the flow of oxygen-rich blood from the heart, which may lead to an abnormal heart sound during a heartbeat (heart murmur) and other signs and symptoms of the condition. Other affected individuals do not have physical obstruction of blood flow, but the pumping of blood is less efficient, which can also lead to symptoms of the condition. Familial hypertrophic cardiomyopathy often begins in adolescence or young adulthood, although it can develop at any time throughout life.

Hypertrophic cardiomyopathy is a heart condition characterized by thickening (hypertrophy) of the heart (cardiac) muscle. When multiple members of a family have the condition, it is known as familial hypertrophic cardiomyopathy. Hypertrophic cardiomyopathy also occurs in people with no family history; these cases are considered nonfamilial hypertrophic cardiomyopathy.  [from MedlinePlus Genetics]

Mutations in the PRKAG2 gene (602743) give rise to a moderate, essentially heart-specific, nonlysosomal glycogenosis with clinical onset typically in late adolescence or in the third decade of life, ventricular pre-excitation predisposing to supraventricular arrhythmias, mild to severe cardiac hypertrophy, enhanced risk of sudden cardiac death in midlife, and autosomal dominant inheritance with full penetrance (summary by Burwinkel et al., 2005). [from OMIM]

Any familial isolated dilated cardiomyopathy in which the cause of the disease is a mutation in the SCN5A gene. [from MONDO]

Dilated cardiomyopathy-1G (CMD1G) is an autosomal dominant disorder characterized by ventricular dilatation and systolic contractile dysfunction (Siu et al., 1999). For a general phenotypic description and a discussion of genetic heterogeneity of dilated cardiomyopathy (CMD), see CMD1A (115200). [from OMIM]

Any familial isolated dilated cardiomyopathy in which the cause of the disease is a mutation in the ACTN2 gene. [from MONDO]

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is characterized by episodic syncope occurring during exercise or acute emotion. The underlying cause of these episodes is the onset of fast ventricular tachycardia (bidirectional or polymorphic). Spontaneous recovery may occur when these arrhythmias self-terminate. In other instances, ventricular tachycardia may degenerate into ventricular fibrillation and cause sudden death if cardiopulmonary resuscitation is not readily available. The mean onset of symptoms (usually a syncopal episode) is between age seven and 12 years; onset as late as the fourth decade of life has been reported. If untreated, CPVT is highly lethal, as approximately 30% of affected individuals experience at least one cardiac arrest and up to 80% have one or more syncopal spells. Sudden death may be the first manifestation of the disease. [from GeneReviews]

Long QT syndrome (LQTS) is a cardiac electrophysiologic disorder, characterized by QT prolongation and T-wave abnormalities on the EKG that are associated with tachyarrhythmias, typically the ventricular tachycardia torsade de pointes (TdP). TdP is usually self-terminating, thus causing a syncopal event, the most common symptom in individuals with LQTS. Such cardiac events typically occur during exercise and emotional stress, less frequently during sleep, and usually without warning. In some instances, TdP degenerates to ventricular fibrillation and causes aborted cardiac arrest (if the individual is defibrillated) or sudden death. Approximately 50% of untreated individuals with a pathogenic variant in one of the genes associated with LQTS have symptoms, usually one to a few syncopal events. While cardiac events may occur from infancy through middle age, they are most common from the preteen years through the 20s. Some types of LQTS are associated with a phenotype extending beyond cardiac arrhythmia. In addition to the prolonged QT interval, associations include muscle weakness and facial dysmorphism in Andersen-Tawil syndrome (LQTS type 7); hand/foot, facial, and neurodevelopmental features in Timothy syndrome (LQTS type 8); and profound sensorineural hearing loss in Jervell and Lange-Nielson syndrome. [from GeneReviews]

Long QT syndrome (LQTS) is a cardiac electrophysiologic disorder, characterized by QT prolongation and T-wave abnormalities on the EKG that are associated with tachyarrhythmias, typically the ventricular tachycardia torsade de pointes (TdP). TdP is usually self-terminating, thus causing a syncopal event, the most common symptom in individuals with LQTS. Such cardiac events typically occur during exercise and emotional stress, less frequently during sleep, and usually without warning. In some instances, TdP degenerates to ventricular fibrillation and causes aborted cardiac arrest (if the individual is defibrillated) or sudden death. Approximately 50% of untreated individuals with a pathogenic variant in one of the genes associated with LQTS have symptoms, usually one to a few syncopal events. While cardiac events may occur from infancy through middle age, they are most common from the preteen years through the 20s. Some types of LQTS are associated with a phenotype extending beyond cardiac arrhythmia. In addition to the prolonged QT interval, associations include muscle weakness and facial dysmorphism in Andersen-Tawil syndrome (LQTS type 7); hand/foot, facial, and neurodevelopmental features in Timothy syndrome (LQTS type 8); and profound sensorineural hearing loss in Jervell and Lange-Nielson syndrome. [from GeneReviews]

The term 'sick sinus syndrome' encompasses a variety of conditions caused by sinus node dysfunction. The most common clinical manifestations are syncope, presyncope, dizziness, and fatigue. Electrocardiogram typically shows sinus bradycardia, sinus arrest, and/or sinoatrial block. Episodes of atrial tachycardias coexisting with sinus bradycardia ('tachycardia-bradycardia syndrome') are also common in this disorder. SSS occurs most often in the elderly associated with underlying heart disease or previous cardiac surgery, but can also occur in the fetus, infant, or child without heart disease or other contributing factors, in which case it is considered to be a congenital disorder (Benson et al., 2003). Genetic Heterogeneity of Sick Sinus Syndrome Sick sinus syndrome-2 (SSS2; 163800) is caused by mutation in the HCN4 gene (605206). Susceptibility to sick sinus syndrome-3 (SSS3; 614090) is influenced by variation in the MYH6 gene (160710). Sick sinus syndrome-4 (SSS4; 619464) is caused by mutation in the GNB2 gene (139390). [from OMIM]

Most cases of heart block are not genetic and are not considered progressive familial heart block. The most common cause of heart block is fibrosis of the heart, which occurs as a normal process of aging. Other causes of heart block can include the use of certain medications or an infection of the heart tissue.

Progressive familial heart block can be divided into type I and type II, with type I being further divided into types IA and IB. These types differ in where in the heart signaling is interrupted and the genetic cause. In types IA and IB, the heart block originates in the bundle branch, and in type II, the heart block originates in the atrioventricular node. The different types of progressive familial heart block have similar signs and symptoms.

Heart block occurs when the electrical signaling is obstructed anywhere from the atria to the ventricles. In people with progressive familial heart block, the condition worsens over time: early in the disorder, the electrical signals are partially blocked, but the block eventually becomes complete, preventing any signals from passing through the heart. Partial heart block causes a slow or irregular heartbeat (bradycardia or arrhythmia, respectively), and can lead to the buildup of scar tissue (fibrosis) in the cells that carry electrical impulses. Fibrosis contributes to the development of complete heart block, resulting in uncoordinated electrical signaling between the atria and the ventricles and inefficient pumping of blood in the heart. Complete heart block can cause a sensation of fluttering or pounding in the chest (palpitations), shortness of breath, fainting (syncope), or sudden cardiac arrest and death.

Progressive familial heart block is a genetic condition that alters the normal beating of the heart. A normal heartbeat is controlled by electrical signals that move through the heart in a highly coordinated way. These signals begin in a specialized cluster of cells called the sinoatrial node (the heart's natural pacemaker) located in the heart's upper chambers (the atria). From there, a group of cells called the atrioventricular node carries the electrical signals to another cluster of cells called the bundle of His. This bundle separates into multiple thin spindles called bundle branches, which carry electrical signals into the heart's lower chambers (the ventricles). Electrical impulses move from the sinoatrial node down to the bundle branches, stimulating a normal heartbeat in which the ventricles contract slightly later than the atria. [from MedlinePlus Genetics]

An autosomal dominant subtype of familial hypertrophic cardiomyopathy caused by mutation(s) in the FLNC gene, encoding filamin-C. [from NCI]

Congenital heart block (CHB) is a rare disorder of atrioventricular conduction, characterized by absence of conduction of atrial impulses to the ventricles with slower ventricular rhythm (atrioventricular dissociation). CHB can occur in association with immunological evidence of maternal connective disease (autoimmune CHD), fetal structural CHD or can be idiopathic. [from ORDO]

Progressive familial heart block type II (PFHB2) is an autosomal dominant disorder, similar to type I progressive familial heart block (PFHB1; see 113900). The pattern of PFHB2, however, tends to develop along the lines of a sinus bradycardia with a left posterior hemiblock, presenting clinically as syncopal episodes, Stokes-Adams seizures, or sudden death when complete heart block supervenes (Brink and Torrington, 1977). [from OMIM]

The Zaki-Gleeson syndrome is an autosomal recessive neurodevelopmental disorder characterized by profound mental retardation, severe microcephaly, poor growth, cerebellar hypoplasia, and second-degree cardiac conduction defects (Zaki et al., 2011). [from OMIM]

Multiple types of congenital heart defects-3 (CHTD3) is an autosomal dominant condition characterized by various types of congenital heart defects and low atrial rhythm (van de Meerakker et al., 2011). For a general phenotypic description and a discussion of genetic heterogeneity of multiple types of congenital heart defects, see 306955. [from OMIM]

Sick sinus syndrome-4 (SSS4) is characterized by early and progressive sinus node and atrioventricular conduction dysfunction. Patients show bradycardia and chronotropic incompetence, and may experience syncope. Atrioventricular conduction block ranges from mild to severe, and some patients also have intermittent atrial fibrillation. Many require implantation of a pacemaker, but sudden cardiac death has not been reported (Stallmeyer et al., 2017). For a general phenotypic description and discussion of genetic heterogeneity of sick sinus syndrome, see SSS1 (608567). [from OMIM]