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Ancestor membership does not transfer phenotype values between groups.","importantHtml":""},"sections":[{"bodyHtml":"<p>Infantile-onset ascending hereditary spastic paralysis is caused by mutations in the ALS2 gene. This gene provides instructions for making the alsin protein. Alsin is produced in a wide range of tissues, with highest amounts in the brain, particularly in motor neurons. Alsin turns on (activates) multiple proteins called GTPases that convert a molecule called GTP into another molecule called GDP. GTPases play important roles in several cell processes. The GTPases that are activated by alsin are involved in the proper placement of the various proteins and fats that make up the cell membrane, the transport of molecules from the cell membrane to the interior of the cell (endocytosis), and the development of specialized structures called axons and dendrites that project from neurons and are essential for the transmission of nerve impulses.</p><p>Mutations in the ALS2 gene alter the instructions for making alsin, often resulting in the production of an abnormally short alsin protein that is unstable and rapidly broken down. It is unclear exactly how ALS2 gene mutations cause infantile-onset ascending hereditary spastic paralysis. Research suggests that a lack of alsin and the subsequent loss of GTPase functions, such as endocytosis and the development of axons and dendrites, contribute to the progressive atrophy of motor neurons that is characteristic of this condition.</p><p class=\"section-source\"><a href=\"https://medlineplus.gov/genetics/condition/infantile-onset-ascending-hereditary-spastic-paralysis/#causes\">MedlinePlus Genetics: Causes</a></p>","key":"forms","title":"What causes Infantile-onset ascending hereditary spastic paralysis?"},{"bodyHtml":"<p>Affected infants are typically normal at birth, then within the first 2 years of life, the initial symptoms of infantile-onset ascending hereditary spastic paralysis appear. Early symptoms include exaggerated reflexes (hyperreflexia) and recurrent muscle spasms in the legs. As the condition progresses, affected children develop abnormal tightness and stiffness in the leg muscles and weakness in the legs and arms. Over time, muscle weakness and stiffness travels up (ascends) the body from the legs to the head and neck. Muscles in the head and neck usually weaken during adolescence; symptoms include slow eye movements and difficulty with speech and swallowing. Affected individuals may lose the ability to speak (anarthria). The leg and arm muscle weakness can become so severe as to lead to paralysis; as a result affected individuals require wheelchair assistance by late childhood or early adolescence. Intelligence is not affected in this condition.</p><p>A condition called juvenile primary lateral sclerosis shares many of the features of infantile-onset ascending hereditary spastic paralysis. Both conditions have the same genetic cause and significantly impair movement beginning in childhood; however, the pattern of nerve degeneration is different. Because of their similarities, these conditions are sometimes considered the same disorder.</p><p class=\"section-source\">Source: <a href=\"https://medlineplus.gov/genetics/condition/infantile-onset-ascending-hereditary-spastic-paralysis\">MedlinePlus Genetics</a></p>","key":"overview","title":"Condition overview"}],"sharedSources":[],"slug":"infantile-onset-ascending-hereditary-spastic-paralysis","sourceDocuments":[{"name":"Infantile-onset ascending hereditary spastic paralysis","reviewed":"2016-04","sections":{"causes":{"fetchedAt":"2026-10-20T20:22:27.878008+00:00","label":"Causes","pageSha256":"9d6fdf9e0fe3c791ea5abc5bab425fc4836b1cc804f5a1e20db66026ca847221","sourceUrl":"https://medlineplus.gov/genetics/condition/infantile-onset-ascending-hereditary-spastic-paralysis/#causes","status":"available"}},"source_release":"2026-10-01","url":"https://medlineplus.gov/genetics/condition/infantile-onset-ascending-hereditary-spastic-paralysis"}],"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":"Infantile-onset ascending hereditary spastic paralysis"},"schemaVersion":1}