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).

LMNA-related dilated cardiomyopathy (DCM) is characterized by left ventricular enlargement and/or reduced systolic function preceded (sometimes by many years) by or accompanied by conduction system disease and/or arrhythmias. LMNA-related DCM usually presents in early to mid-adulthood with symptomatic conduction system disease or arrhythmias, or with symptomatic DCM including heart failure or embolus from a left ventricular mural thrombus. Sudden cardiac death can occur, and in some instances is the presenting manifestation; sudden cardiac death may occur with minimal or no systolic dysfunction.

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

This syndrome is characterized by congenital lymphedema of the lower limbs, atrial septal defect and a characteristic facies (a round face with a prominent forehead, a flat nasal bridge with a broad nasal tip, epicanthal folds, a thin upper lip and a cleft chin). It has been described in two brothers and a sister. Transmission appears to be autosomal recessive.

An autosomal dominant subtype of familial hypertrophic cardiomyopathy caused by mutation(s) in the ACTC1 gene, encoding actin, alpha cardiac muscle 1.

Brugada syndrome is characterized by cardiac conduction abnormalities (ST segment abnormalities in leads V1-V3 on EKG and a high risk for ventricular arrhythmias) that can result in sudden death. Brugada syndrome presents primarily during adulthood, although age at diagnosis may range from infancy to late adulthood. The mean age of sudden death is approximately 40 years. Clinical presentations may also include sudden infant death syndrome (SIDS; death of a child during the first year of life without an identifiable cause) and sudden unexpected nocturnal death syndrome (SUNDS), a typical presentation in individuals from Southeast Asia. Other conduction defects can include first-degree AV block, intraventricular conduction delay, right bundle branch block, and sick sinus syndrome.

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.

Myotonic dystrophy type 1 (DM1) is a multisystem disorder that affects skeletal and smooth muscle as well as the eye, heart, endocrine system, and central nervous system. The clinical findings, which span a continuum from mild to severe, have been categorized into three somewhat overlapping phenotypes: mild, classic, and congenital. Mild DM1 is characterized by cataract and mild myotonia (sustained muscle contraction); life span is normal. Classic DM1 is characterized by muscle weakness and wasting, myotonia, cataract, and often cardiac conduction abnormalities; adults may become physically disabled and may have a shortened life span. Congenital DM1 is characterized by hypotonia and severe generalized weakness at birth, often with respiratory insufficiency and early death; intellectual disability is common.

Primary pulmonary hypertension is a rare progressive disease characterized by increased pulmonary artery pressure in the absence of common causes of pulmonary hypertension, such as chronic heart, lung, or thromboembolic disease. There is often vascular remodeling. The clinical presentation can be nonspecific, and patients often receive a diagnosis late in their clinical course (summary by Ma et al., 2013). For a general phenotypic description and a discussion of genetic heterogeneity of primary pulmonary hypertension, see PPH1 (178600).

Atrial fibrillation (AF) is a supraventricular tachyarrhythmia characterized by uncoordinated atrial activation with consequent deterioration of atrial mechanical function. It is the most common sustained cardiac rhythm disturbance, and its prevalence increases as the population ages. An estimated 70,000 strokes each year are caused by atrial fibrillation (summary by Oberti et al., 2004). For a discussion of genetic heterogeneity of atrial fibrillation, see 608583.

A rare genetic cardiac disease characterized by variably expressed atrial tachyarrhythmia (such as atrial flutter, paroxysmal or chronic atrial fibrillation, ectopic atrial tachycardia, or multifocal atrial tachycardia), infra-Hisian conduction system disease, and vulnerability to dilated cardiomyopathy. Age of onset ranges between childhood and adulthood.

Syndrome with characteristics of sick sinus syndrome and intestinal pseudo-obstruction. The heart and digestive issues develop at the same time, usually by age 20. The syndrome is caused by mutations in the SGO1 gene. This gene provides instructions for making part of a protein complex cohesin. This protein complex helps control the placement of chromosomes during cell division. Research suggests that SGO1 gene mutations may result in a cohesin complex that is less able to hold sister chromatids together, resulting in decreased chromosomal stability during cell division. This instability is thought to cause senescence of cells in the intestinal muscle and in the sinoatrial node, resulting in problems maintaining proper rhythmic movements of the heart and intestines.

Brugada syndrome is characterized by cardiac conduction abnormalities (ST segment abnormalities in leads V1-V3 on EKG and a high risk for ventricular arrhythmias) that can result in sudden death. Brugada syndrome presents primarily during adulthood, although age at diagnosis may range from infancy to late adulthood. The mean age of sudden death is approximately 40 years. Clinical presentations may also include sudden infant death syndrome (SIDS; death of a child during the first year of life without an identifiable cause) and sudden unexpected nocturnal death syndrome (SUNDS), a typical presentation in individuals from Southeast Asia. Other conduction defects can include first-degree AV block, intraventricular conduction delay, right bundle branch block, and sick sinus syndrome.

Familial atrial hypertrophic cardiomyopathy-30 (CMH30) is characterized by atrial arrhythmias, including flutter and fibrillation, atrial structural abnormalities with hypertrophic cardiomyopathy and fibrosis, and hypertension (Baris Feldman et al., 2023).

Primary pulmonary hypertension-6 (PPH6) is characterized by markedly elevated pulmonary arterial hypertension, associated with reduced oxygen saturation and diffuse ground-glass opacities on chest x-ray. Lung biopsy shows thickening of the alveolar septae and abnormally proliferating capillaries (Postma et al., 2023). For a general phenotypic description and a discussion of genetic heterogeneity of primary pulmonary hypertension, see PPH1 (178600).