Ring chromosome 20 syndrome: a differential diagnosis for autoimmune encephalitis

*Correspondence: [e-mail].

Abstract

Case Presentation: A 7-year-old boy with pharmacoresistant epilepsy was referred to our center for pre-surgical evaluation. Developmental was normal during infancy. His epilepsy began at the age of 4 years as daily nocturnal seizures characterized by waking up, staring and mild stiffening over face and of the extremities, with or without automatisms, followed by agitation and confusion. CSF examination was normal, but he was empirically treated for meningoencephalitis. Several anti-seizures medications were started with poor control. He also received methyl prednisolone, immunoglobulin and lastly rituximab, without success. Seizures began increasing in frequency despite treatment and he developed learning disabilities and behavior problems. Brain MRI was unremarkable. PET revealed bilateral fronto-temporal hypometabolism. The metabolic work up and the whole exoma sequencing test were normal. Paraneoplastic antibody panel was negative. The patient remained admitted in ICU for three months before being referred to presurgical assessment in a tertiary care epilepsy center. VEEG showed slow background and frontal epileptiform discharges. He presented nocturnal disperceptive seizures and electrographic seizures with frontal region onset. The predominant VEEG frontal region abnormalities made suspicions for r(20) syndrome. A Karyotype confirmed this diagnosis.

Discussion: The r(20) syndrome is a rare genetic disorder arising from a non-supernumerary ring chromosome 20 replacing a normal chromosome 20. It is commonly seen in a mosaic state and is diagnosed by means of karyotyping. The typical electro-clinical phenotype includes focal (frontal lobe) seizures and recurrent non-convulsive status epilepticus with typical EEG pattern, cognitive decline, behavioral changes, and absence of a consistent pattern of dysmorphic features. The seizures are mostly during sleep and is usually a combination of disperceptive and hyperkinetic seizures characterized by waking up, unresponsiveness, staring and motor activity (tonic, clonic or minimal motor activity) of the face and extremities, with or without automatisms, followed by agitation and confusion. Interictal EEG exhibits mild slowing or bursts of activity theta with clear contours, with a peak frequency of 5 Hz, in the fronto-temporal regions. Brain MRI is usually normal.

Final Comments: This case highlights the still lack of r(20) syndrome diagnosis despite the distinctive phenotype and simple genetic test as karyotype, especially in the exoma and genomic era.

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Artikel online veröffentlicht:
12. Mai 2025