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Chromosome 20 ring: a chromosomal disorder associated with a particular electroclinical pattern
M P Canevini1, V Sgro, O Zuffardi
1Centro Regionale Epilessia, Ospedale San Paolo, Università degli Studi, Milan, Italy.
Epilepsia
|September 17, 1998
Summary
Ring chromosome 20 syndrome (r(20)) presents a unique electroclinical pattern, including abnormal theta waves and generalized spike waves, even without clear physical markers or significant intellectual disability. This suggests r(20) syndrome may be present in individuals with these specific EEG findings.
Area of Science:
- Genetics
- Neurology
- Cytogenetics
Background:
- Ring chromosome 20 [r(20)] is a rare chromosomal disorder.
- Phenotypical markers for r(20) are not well-defined.
- This study investigates the electroclinical pattern in patients with r(20).
Observation:
- Three patients (one boy, his mother, and an unrelated man) were studied.
- Prolonged video-electroencephalography (EEG) and cytogenetic analyses were performed.
- Fluorescent in situ hybridization (FISH) with telomeric probes was utilized.
Findings:
- All patients exhibited a similar abnormal electroclinical pattern: long bursts of rhythmic theta waves and generalized spike waves (SW).
- Seizures of probable frontotemporal origin (SFT) were observed.
- Cytogenetic analysis revealed mosaicism with a normal cell line and a r(20) cell line in all patients.
Implications:
- The clinical presentation suggests haploinsufficiency due to instability of r(20)-generating cells.
- The specific electroclinical pattern, including theta waves and SW/SFT, may indicate r(20) syndrome, even with mild or no mental retardation and absence of dysmorphic features.