• Cytogenetics
• epilepsy
• fish
• genetics

Herein, we report an unusual case of ring 20 mosaicism in a 15-year-old non-dysmorphic girl with epilepsy refractory to drug therapy.

Ring 20 syndrome is a rare condition still not well characterised both at the genetic and clinical levels. It was described for the first time by Borgaonkar and Bolling1 as a genetic syndrome. To date, about 60 mostly sporadic cases of patients have been reported with de novo ring formation. This syndrome is characterised by a large degree of phenotypic variability, in association with a characteristic form of epilepsy, refractory to any pharmacological therapy with non-convulsive status epilepticus and cognitive problems. The first seizures occur in the first years of life and represent the first clinical signs. Further clinical signs are mental retardation of varying degrees, and behavioural disorders. The case reported showed an unusual ring chromosome 20 mosaicism associated with epilepsy and generalised tonic clonic seizures refractory to drug therapy and behaviour disorders. Cytogenetic analysis, performed on cultured peripheral blood, revealed the presence of ring 20 mosaicism in 40% of the metaphases examined (20 out of 50).

The patient, the firstborn of non-consanguineous healthy parents, was born after a normal pregnancy. The neonatal period followed a normal course, with increases in weight–height and psychomotor development. The parents reported …