Each column keeps its native condition scope. Initial features are displayed alphabetically, not ranked by clinical importance. Counts remain separate, and an empty cell does not mean a feature cannot occur.
"},"coverage":{"countRecords":0,"emptyColumnKeys":[],"hpoRelease":"2026-06-23","narrativeSourceChanges":[],"records":12,"sourceGroups":{"omim":0,"orphanet":12,"published":0}},"features":[{"hpoId":"HP:0000708","label":"Atypical behavior","primary":false},{"hpoId":"HP:0002353","label":"EEG abnormality","primary":false},{"hpoId":"HP:0200134","label":"Epileptic encephalopathy","primary":false},{"hpoId":"HP:0011153","label":"Focal motor seizure","primary":false},{"hpoId":"HP:0001510","label":"Growth delay","primary":false},{"hpoId":"HP:0001249","label":"Intellectual disability","primary":false},{"hpoId":"HP:0001268","label":"Decline in thinking abilities","primary":false},{"hpoId":"HP:0012758","label":"Neurodevelopmental delay","primary":false},{"hpoId":"HP:0031951","label":"Nocturnal seizures","primary":false},{"hpoId":"HP:0032671","label":"Non-convulsive status epilepticus without coma","primary":false},{"hpoId":"HP:0000736","label":"Short attention span","primary":false},{"hpoId":"HP:0001328","label":"Specific learning disability","primary":false}],"ledeHtml":"Ring chromosome 20 syndrome is a condition that affects the normal development and function of the brain. The most common feature of this condition is recurrent seizures (epilepsy) in childhood. The seizures may occur during the day or at night during sleep. They are described as partial seizures because they affect only one area of the brain, a region called the frontal lobe. In many cases, the seizures are complex and resistant to treatment with anti-epileptic drugs. Prolonged seizure episodes known as non-convulsive status epilepticus also appear to be characteristic of ring chromosome 20 syndrome. These episodes involve confusion and behavioral changes.","mondoId":"MONDO:0015436","records":[{"frequencyKind":"range","key":"085622eda2ee7866bc22969412570264a7a913ffebbb8eab317571e65c0234e8","raw":{"aspect":"P","body_system":"nervous_system","disease_id":"ORPHA:1444","disease_name":"Ring chromosome 20 syndrome","evidence":"TAS","frequency_raw":"HP:0040281","hpo_id":"HP:0032671","is_excluded":false,"label":"Non-convulsive status epilepticus without coma","onset_id":null,"reference":"ORPHA:1444","source_release":"2026-06-23"},"sourceGroups":["orphanet"]},{"frequencyKind":"range","key":"2b91233ad9559e392503afddd656b8157c54ad9a1852166fb6e940abae980740","raw":{"aspect":"P","body_system":"nervous_system","disease_id":"ORPHA:1444","disease_name":"Ring chromosome 20 syndrome","evidence":"TAS","frequency_raw":"HP:0040283","hpo_id":"HP:0012758","is_excluded":false,"label":"Neurodevelopmental 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span","onset_id":null,"reference":"ORPHA:1444","source_release":"2026-06-23"},"sourceGroups":["orphanet"]}],"referenceLabels":{},"references":{"causeHtml":"","identityNote":"MONDO cross-references identify native condition entries. Ancestor membership does not transfer phenotype values between groups.","importantHtml":""},"sections":[{"bodyHtml":"Ring chromosome 20 syndrome is caused by a chromosomal abnormality known as a ring chromosome 20 or r(20). A ring chromosome is a circular structure that occurs when a chromosome breaks in two places and its broken ends fuse together. People with ring chromosome 20 syndrome have one copy of this abnormal chromosome in some or all of their cells.
It is not well understood how the ring chromosome causes the signs and symptoms of this syndrome. In some affected individuals, genes near the ends of chromosome 20 are deleted when the ring chromosome forms. Researchers suspect that the loss of these genes may be responsible for epilepsy and other health problems. However, most affected individuals do not have these gene deletions. In these people, the ring chromosome may change the activity of certain genes on chromosome 20, or the chromosome may be unable to copy (replicate) itself normally during cell division. Researchers are still working to determine the precise relationship between the ring chromosome 20 and the characteristic features of the syndrome.
","key":"forms","title":"What causes Ring chromosome 20 syndrome?"},{"bodyHtml":"Most people with ring chromosome 20 syndrome also have intellectual disabilities and behavioral difficulties. Although these problems can appear either before or after the onset of epilepsy, they tend to worsen after seizures develop. Major birth defects and differences in facial features can occur in people with ring chromosome 20 syndrome, though these are rare.
Source: MedlinePlus Genetics
","key":"overview","title":"Condition overview"}],"sharedSources":[],"slug":"ring-chromosome-20-syndrome","sourceDocuments":[{"name":"Ring chromosome 20 syndrome","reviewed":"2024-01","sections":{"causes":{"fetchedAt":"2026-10-20T20:24:46.297314+00:00","label":"Causes","pageSha256":"ffa645f79d566aac6a264e33f85e453ab6adc5a49f77ced25ac6d36b0bf39102","sourceUrl":"https://medlineplus.gov/genetics/condition/ring-chromosome-20-syndrome/#causes","status":"available"}},"source_release":"2026-10-01","url":"https://medlineplus.gov/genetics/condition/ring-chromosome-20-syndrome"}],"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":"Ring chromosome 20 syndrome"},"schemaVersion":1}