Wolff-Parkinson-White syndrome is a condition characterized by abnormal electrical pathways in the heart that cause a disruption of the heart's normal rhythm (arrhythmia).\n\nThe heartbeat is controlled by electrical signals that move through the heart in a highly coordinated way. A specialized cluster of cells called the atrioventricular node conducts electrical impulses from the heart's upper chambers (the atria) to the lower chambers (the ventricles). Impulses move through the atrioventricular node during each heartbeat, stimulating the ventricles to contract slightly later than the atria.\n\nPeople with Wolff-Parkinson-White syndrome are born with an extra connection in the heart, called an accessory pathway, that allows electrical signals to bypass the atrioventricular node and move from the atria to the ventricles faster than usual. The accessory pathway may also transmit electrical impulses abnormally from the ventricles back to the atria. This extra connection can disrupt the coordinated movement of electrical signals through the heart, leading to an abnormally fast heartbeat (tachycardia) and other changes in heart rhythm. Resulting symptoms include dizziness, a sensation of fluttering or pounding in the chest (palpitations), shortness of breath, and fainting (syncope). In rare cases, arrhythmias associated with Wolff-Parkinson-White syndrome can lead to cardiac arrest and sudden death. The most common arrhythmia associated with Wolff-Parkinson-White syndrome is called paroxysmal supraventricular tachycardia.\n\nComplications of Wolff-Parkinson-White syndrome can occur at any age, although some individuals born with an accessory pathway in the heart never experience any health problems associated with the condition.\n\nWolff-Parkinson-White syndrome often occurs with other structural abnormalities of the heart or underlying heart disease. The most common heart defect associated with the condition is Ebstein anomaly, which affects the valve that allows blood to flow from the right atrium to the right ventricle (the tricuspid valve). Additionally, the heart rhythm problems associated with Wolff-Parkinson-White syndrome can be a component of several other genetic syndromes, including hypokalemic periodic paralysis (a condition that causes episodes of extreme muscle weakness), Pompe disease (a disorder characterized by the storage of excess glycogen), Danon disease (a condition that weakens the heart and skeletal muscles and causes intellectual disability), and tuberous sclerosis complex (a condition that results in the growth of noncancerous tumors in many parts of the body).

Naxos disease (NXD) is characterized by arrhythmogenic right ventricular cardiomyopathy associated with abnormalities of the skin, hair, and nails. The ectodermal features are evident from birth or early childhood, whereas the cardiac symptoms develop in young adulthood or later. Clinical variability of ectodermal features has been observed, with hair anomalies ranging from woolly hair to alopecia, and skin abnormalities ranging from mild focal palmoplantar keratoderma to generalized skin fragility or even lethal neonatal epidermolysis bullosa (Protonotarios et al., 1986; Cabral et al., 2010; Pigors et al., 2011; Erken et al., 2011; Sen-Chowdhry and McKenna, 2014). Another syndrome involving cardiomyopathy, woolly hair, and keratoderma (DCWHK; 605676) is caused by mutation in the desmoplakin gene (DSP; 125647). Also see 610476 for a similar disorder caused by homozygous mutation in the DSC2 gene (125645).

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).

ARVC may not cause any symptoms in its early stages. However, affected individuals may still be at risk of sudden death, especially during strenuous exercise. When symptoms occur, they most commonly include a sensation of fluttering or pounding in the chest (palpitations), light-headedness, and fainting (syncope). Over time, ARVC can also cause shortness of breath and abnormal swelling in the legs or abdomen. If the myocardium becomes severely damaged in the later stages of the disease, it can lead to heart failure.\n\nArrhythmogenic right ventricular cardiomyopathy (ARVC) is a form of heart disease that usually appears in adulthood. ARVC is a disorder of the myocardium, which is the muscular wall of the heart. This condition causes part of the myocardium to break down over time, increasing the risk of an abnormal heartbeat (arrhythmia) and sudden death.

A rare glycogen storage disease with fetal or neonatal onset of severe cardiomyopathy with non-lysosomal glycogen accumulation and fatal outcome in infancy. Patients present with massive cardiomegaly, severe cardiac and respiratory complications and failure to thrive. Non-specific facial dysmorphism, bilateral cataracts, macroglossia, hydrocephalus, enlarged kidneys and skeletal muscle involvement have been reported in some cases.

ARVC may not cause any symptoms in its early stages. However, affected individuals may still be at risk of sudden death, especially during strenuous exercise. When symptoms occur, they most commonly include a sensation of fluttering or pounding in the chest (palpitations), light-headedness, and fainting (syncope). Over time, ARVC can also cause shortness of breath and abnormal swelling in the legs or abdomen. If the myocardium becomes severely damaged in the later stages of the disease, it can lead to heart failure.\n\nArrhythmogenic right ventricular cardiomyopathy (ARVC) is a form of heart disease that usually appears in adulthood. ARVC is a disorder of the myocardium, which is the muscular wall of the heart. This condition causes part of the myocardium to break down over time, increasing the risk of an abnormal heartbeat (arrhythmia) and sudden death.

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a form of heart disease that usually appears in adulthood. ARVC is a disorder of the myocardium, which is the muscular wall of the heart. This condition causes part of the myocardium to break down over time, increasing the risk of an abnormal heartbeat (arrhythmia) and sudden death.\n\nARVC may not cause any symptoms in its early stages. However, affected individuals may still be at risk of sudden death, especially during strenuous exercise. When symptoms occur, they most commonly include a sensation of fluttering or pounding in the chest (palpitations), light-headedness, and fainting (syncope). Over time, ARVC can also cause shortness of breath and abnormal swelling in the legs or abdomen. If the myocardium becomes severely damaged in the later stages of the disease, it can lead to heart failure.

A rare genetic developmental defect during embryogenesis disorder with characteristics of craniofacial dysmorphism (including brachycephaly, prominent forehead, sparse lateral eyebrows, severe hypertelorism, upslanting palpebral fissures, epicanthal folds, protruding ears, broad nasal bridge, pointed nasal tip, flat philtrum, anteverted nostrils, large mouth, thin upper vermilion border, highly arched palate and mild micrognathia) associated with osteopenia leading to repeated long bone fractures, severe myopia, mild to moderate sensorineural or mixed hearing loss, enamel hypoplasia, sloping shoulders and mild intellectual disability. There is evidence the disease can be caused by homozygous mutation in the IRX5 gene on chromosome 16q11.2.

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 familial atrial fibrillation, see ATFB1 (608583).