Clonic seizures, continuous spikes-and-waves during slow sleep, choreoathetosis and response to sulthiame in a child with FRRS1L encephalopathy

BACKGROUND: Ferric chelate reductase 1 like (FRRS1L) encephalopathy is a rare cause of developmental and epileptic encephalopathy. Only a few cases have been reported thus far and seizures tend to be drug refractory. We report an additional case to highlight the good seizure response to sulthiame.

CASE REPORT: A boy from non-consanguineous parents presented with history of 'abnormal movements' from 7 months of age. At one year of age, video electroencephalogram (EEG) monitoring demonstrated the 'abnormal movements' to be clonic seizures. Valproate, lamotrigine and clobazam combination were only partially effective at reducing the seizures. Repeat EEG at 1 year 8 months old revealed a continuous spikes-and-waves during slow sleep (CSWS) pattern, prompting a trial of sulthiame. After 2 weeks of sulthiame, seizures ceased completely. The clonic seizures recurred at age 4 years when sulthiame supply was interrupted, but the seizures promptly remitted following sulthiame's resumption. Subtle choreiform movements appeared from age one year and later became more prominent. Whole exome sequencing (WES) identified a homozygous novel variant (nonsense) in the FRRS1L gene (NM_014334.3: c.670C>T:p.Gln224*). He has been seizure free since 4 years of age but remained profoundly delayed.

CONCLUSION: Sulthiame may have a role in the early treatment of seizures in children with refractory epilepsy due to FRRS1L mutation.