The Ring Chromosome 20 Syndrome is a rare disorder that can be difficult to diagnose without cytogenetic testing.
Basis: fusion of the chromosome ends (p13 and q13.3), resulting in a ring. These often show deletions in 20pter and/or 20qter.
Mosaicism may occur with the patient having both normal chromosome 20 and ring forms.
Clinical features:
(1) refractory epilepsy, typically partial with altered consciousness and originating in the frontal lobe
(2) seizures while sleeping
(3) behavioral problems
(4) cognitive impairment
Non-convulsive status epilepticus (prolonged confusional states lasting for minutes to hours) is characteristic.
Most patients appear phenotypically normal without facial dysmorphisms.
The condition is best diagnosed by chromosome analysis of the peripheral blood. Array-based techniques may not detect the condition if the patient has mosaicism or if there are not deletions or duplications.
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