Ring chromosome 20 epilepsy syndrome: An overview

Abstract

The ring chromosome 20 [r(20)], epilepsy syndrome is a relatively under-diagnosed epilepsy syndrome that has a striking association with seizures, which is not seen with other morphological aberrations of chromosome 20. This syndrome is characterized by medically intractable complex partial epilepsy, subtle nocturnal frontal seizures, behavioral problems and mild mental impairment. In contrast to other epilepsy syndromes with chromosomal aberrations, dysmorphism (major or minor congenital malformations) and developmental delays are rarely reported. This lack of dysmorhism and relatively normal development in early life leads to delay in diagnosis. Additionally chromosomal testing is rarely considered in a patient with severe early onset epilepsy who does not have dysmorphic features, but this is the usual phenotype of r(20) epilepsy syndrome. More than 60 cases of r(20) have been reported in the literature. To date there is still no published data on the incidence and prevalence of this syndrome. This disorder appears to be pan-ethnic and non-gender specific. Cases of this syndrome have been identified in different parts of the world involving different ethnicities. Epilepsy in r(20) is often intractable with frontal lobe features. Non-convulsive status epilepticus and nocturnal seizures are frequently noted as are frontal lobe epileptiform electroencephalography abnormalities. Structural brain imaging is normal in most cases and is non-contributory. Definitive diagnosis can only be made by chromosomal analysis with mosaic screening. With more widespread cytogenetic chromosomal karyotyping in non-etiological cases of epilepsy, more cases of r(20) will undoubtedly be recognized.

Keywords

Medically intractable epilepsy - frontal lobe seizures - nocturnal seizures - non-convulsive status epilepticus - chromosomal testing - mosaic screening