A ring chromosome 20 mosaicism in an 11-year-old girl with complex partial seizures resistant to medication is reported from the Department of Paediatric Neurology, University Hospital of Turku, Finland. Early psychomotor development was normal, but speech was delayed. She attended special schools for dyslexia, writing difficulties, and a wide range of cognitive problems, which became progressively worse. She had no dysmorphic features. Her behavior was infantile and interrupted by uncontrolled bursts of laughter. Epilepsy began with absence attacks at 7 years of age. A prolonged partial status at 10 years was associated with fronto-temporal focal seizure activity and bilateral spikes on the EEG, compatible with partial, secondarily generalized epilepsy. MRI was normal. Control of absence attacks with valproate was incomplete, and trials of oxcarbazepine and clobazam for complex partial seizures were only partially effective. The karyotype was mosaic 46,XX/46,XX,r(20)(pl3ql3). 
COMMENT. Chromosome analysis may be indicated in a child with drug refractory idiopathic epilepsy and learning disabilities, despite the absence of dysmorphic features or other congenital anomalies.
Ring chromosome 20 syndrome is characterized by progressive cognitive impairments, behavior disorders and epilepsy resistant to conventional medications. Trials of newer antiepileptic medications with specificity against partial seizures (eg gabapentin) should provide more complete seizure control . Unlike many antiepileptic agents, gabapentin does not affect serum concentrations of AEDs and may be used as concurrent therapy. It had no hematologic, hepatic, pancreatic, or hypersensitivity adverse effects in this 12-week study of 306 patients.