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Ancestor membership does not transfer phenotype values between groups.","importantHtml":""},"sections":[{"bodyHtml":"<p>Mutations in the SCN5A and TRPM4 genes cause most cases of progressive familial heart block types IA and IB, respectively. The proteins produced from these genes are channels that allow positively charged atoms (cations) into and out of cells. Both channels are abundant in heart (cardiac) cells and play key roles in these cells&#x27; ability to generate and transmit electrical signals. These channels play a major role in signaling the start of each heartbeat, coordinating the contractions of the atria and ventricles, and maintaining a normal heart rhythm.</p><p>The SCN5A and TRPM4 gene mutations that cause progressive familial heart block alter the normal function of the channels. As a result of these channel alterations, cardiac cells have difficulty producing and transmitting the electrical signals that are necessary to coordinate normal heartbeats, leading to heart block. Death of these impaired cardiac cells over time can lead to fibrosis, worsening the heart block.</p><p>Mutations in other genes, some of which are unknown, account for the remaining cases of progressive familial heart block.</p><p class=\"section-source\"><a href=\"https://medlineplus.gov/genetics/condition/progressive-familial-heart-block/#causes\">MedlinePlus Genetics: Causes</a></p>","key":"forms","title":"What causes Progressive familial heart block?"},{"bodyHtml":"<p>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.</p><p>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.</p><p>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.</p><p class=\"section-source\">Source: <a href=\"https://medlineplus.gov/genetics/condition/progressive-familial-heart-block\">MedlinePlus Genetics</a></p>","key":"overview","title":"Condition overview"}],"sharedSources":[],"slug":"progressive-familial-heart-block","sourceDocuments":[{"name":"Progressive familial heart block","reviewed":"2015-04","sections":{"causes":{"fetchedAt":"2026-10-20T20:24:26.703821+00:00","label":"Causes","pageSha256":"83147d7b9907f541ad9fd0ba55d6937b43a237dfdd0130a6bb3f369ee30138ec","sourceUrl":"https://medlineplus.gov/genetics/condition/progressive-familial-heart-block/#causes","status":"available"}},"source_release":"2026-10-01","url":"https://medlineplus.gov/genetics/condition/progressive-familial-heart-block"}],"sourceNote":"MedlinePlus descriptions and Causes; original HPO annotations.","takeawayHtml":"Cause explanations are from MedlinePlus Genetics. Feature values below retain their original sources and patient groups.","title":"Progressive familial heart block"},"schemaVersion":1}